Knowledge and Practices of Dentists, Oral and Maxillofacial Surgeons of Cone Beam Computed Tomography (CBCT) and the Dentascanner in a Low Income Country: Case of Togo

Background: In dental-maxillofacial imaging, 3D sectional imaging progressively replaces conventional 2D imaging in developed countries. They are based specially on Computed tomography (CT-Scan), with the Dentascan application and cone beam computed tomography (CBCT). In developing countries those technics are newly introduced. Aim: This study aimed at studying the knowledge and practices of dentist and oral and maxillofacial surgeons on sectional imaging such as Dentascan and Cone Beam Computed Tomography (CBCT). Materials and Methods: We conducted an anonymous survey among dentists and oral maxillofacial surgeons in Togo over one month. Results: The response rate was 78.79% (27/33). They were mainly male sex (sex ratio of 2.25 men for one woman). They were aged between 27 and 71 years old with an average of 49.69 years old. The majority (61.54%) had a professional experience over 20 years. The majority of respondents (65.38%) believed their level of knowledge about dental x-Ray was poor. Half of them (50%) confirmed that they had never asked for a Dentascan, and 15.38% asked from time to time for it and only two (7.69%) asked often for this test. 96.15% confirm they have no knowledge of the Dentascan. Regarding the CBCT, 84.62% didn’t ask for it because this technique did not exist in Togo before. 69.20% of respondents confessed to be interested in continuing training on sectional imaging. Conclusion: This study shows that sectional imaging is very little used by oral and dental practitioners in Togo because of the ignorance of the new techniques How to cite this paper: Tchaou, M., Bissa, H., Pegbessou, P.E., Amadou, A., N’timon, B., Dansou, M., Adam, A.-R., Sonhaye, L., Agoda-Koussema, L.-K. and Adjenou, K. (2017) Knowledge and Practices of Dentists, Oral and Maxillofacial Surgeons of Cone Beam Computed Tomography (CBCT) and the Dentascanner in a Low Income Country: Case of Togo. Open Journal of Radiology, 7, 1-8. https://doi.org/10.4236/ojrad.2017.71001 Received: December 16, 2016 Accepted: January 22, 2017 Published: January 25, 2017 Copyright © 2017 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
In dental-maxillofacial imaging, 3D sectional imaging progressively replaces conventional 2D imaging in developed countries with the recommendations of professionals after consensus conferences [1]. It is more often used for diagnosis in dental care, reconstructive dentistry, and pediatric dentistry [1] [2]. This preference is due to the solution of shot confusing problem awkward situation in 2D imaging. There are various techniques to generate three-dimensional images in dentistry. Conventional tomography depicts a defined layer of the body; structures outside of this layer appear out of focus [3]. Computed tomography (CT-Scan) represents layers in the axial, coronal or sagittal plane and can provide information about the topographical location of various structures to one another. The CT scanner works using a rotating radiation source and high tube voltages. X-rays are emitted in a fan-shaped beam to stationary detectors placed 360˚ around the patient. Each rotation of the tube records an axial slice of the volume being examined. The 3-D domain is axially moved and each new section is recorded. The coronal and sagittal slices are computed from the axial data [4].
Arai Y. et al. 1999 [5] first described the application of cone beam computed tomography (CBCT). In contrast to computer tomography the Arai group introduced an Ortho-CT using a conical beam of radiation. The radiation source and the detector rotate around the patient. From a single 360˚ rotation, the complete volume under investigation is recorded. The cone beam computed tomography can capture a cylindrical volume of variable size.
In Togo, the CT-Scan was introduced in 2000 with a sequential cutting device which lacked of dental imaging software. Since then, new faster devices, including helical scanners, multi cuts (4 to 16 cuts) equipped with Dentascan software were installed. This study comes as a result of the scarcity of the use of the Dentascan by dental surgeons in Togo. The objective of this study was to review the knowledge and practices of dentists, maxillofacial surgeons and stomatologists in Togo on sectional imaging namely the Dentascan and the CBCT.

Materials and Methods
It is an anonymous cross-sectional study conducted with dentists, and oral and maxillofacial surgeons, of Togo over a period of a month from August 31st, 2015 to September 30th, 2015, during a meeting organized by the Dentists, Oral and Maxillofacial Surgeons Association. The survey was conducted on the basis of anonymous survey form, previously established and tested and distributed to practitioners. All the dentists, oral and maxillofacial Surgeons who agreed to respond to the survey had been included in the study. Only the correctly completed survey forms had been retained.
The collected information dealt with the following items: 1) the participant (age, sex, place of basic training or specialization, number of years of practice, mode of practice); 2) the practice of medical imaging (knowledge, use of x-ray device at the dental surgery, frequency of using Dentascan and CBCT, the indications of the Dentascan and the CBCT); and 3) the need for continuing training in 3D Imaging.

Out of 33 practitioners in Togo according to the Dentist, Oral and Maxillofacial
Surgeons Association, 27 forms had been returned to us and one had been rejected for incomplete information accounting for 26 forms selected. The response rate was 78.79%. Oral and maxillofacial surgeons were 02 (7.69%) while dentists were 24 (92.31%). There were 18 men (69.23%) and 8 women (30.77%) accounting for a sex ratio of 2.25 and aged between 27 and 71 years old with an average of 49.69 ± 9.93 years old. 23 practitioners were over 38 years old (88.46%). They were trained in Senegal (69.23%), Côte d'Ivoire (3.85%) and France (7.69%). Among them, five (19.23%) were trained outside of Africa and France, (Ukraine, Yugoslavia, Russia, Cuba). 61.54% of dentists and oral surgeons had more than20 years of professional experience ( Figure 1). 42.31% of the respondents practiced their profession only in private health center against 38.46% who practiced only in public. Those who practiced both in public and privateer presented 19.23%. 25 out of 26 practitioners accounting for 96.30% had admitted that they had at least one x-ray device in their office. Table 1 displays the x-ray devices practitioners have at their disposal. No Dental clinic had CT-Scan or the CBCT in Togo.
The Assessment by themselves of their own level of knowledge about dental radiology had enabled to notice that 18 practitioners (65.38%) had poor knowledge, 3 (11.54%) had good knowledge and 04 (15.38%) had average knowledge.
Only one (3.85%) had a very good knowledge.  About the quality of radiologic images they have been receiving from various imaging centers in Togo, 7.69% said they were very satisfied; 38.50% were satisfied; 23.10% were fairly satisfied; 7.69% were not satisfied and 23.10% were neutral.
As far as the quality of radiological reports received from imaging departments are concerned, 3.85% said to be very satisfied; 38.50% were satisfied; 23.10% were fairly satisfied; 7.69% were not satisfied and 23.10% were neutral.
Half of the respondents (50%) confirm they had never asked for Dentascan; 15.38% asked from time to time for it and only two (7.69%)asked often for it (Table 2). This is also noticeable in the assessment of their knowledge about Dentascan; a practitioner (3.85%) considered he had a good/sufficient knowledge, against 25 (96.15%) who considered their knowledge poor.
Regarding the CBCT, only 4 (15.38%) had exceptionally asked for it; the rest had (84.62%) never. None of the participants had good knowledge about the CBCT during our study, 38.50% had insufficient/poor knowledge of this technique while 42.30% had poor knowledge, and 15.38% did not know about it.
According to practitioners, the indications of the Dentas can were maxillofacial traumas (34.62%), followed by the exploration of the temporomandibular joint (15.38%), dental trauma (15.38%), orthodontic assessment (15.38%) and preimplantation assessment (7.69%). 69.20% of the respondents said to be very interested in continuing training on sectional imaging (Dentascan and CBCT); 26.90% were fairly interested and 3.85% were not interested at all.

Discussion
The response rates in our study was 78.79%, close to that usually obtained in similar surveys especially 72.73% in Iran in 2015 by Mehdizadeh M. et al. [6] and 74% in Norway in 2014 by Hol C. et al. [7]. Our sample is small, 26 participants in all. This could be explained by a very low number of practitioners of oral and dental survey in Togo. As a matter of fact, only 33 people practice this profession in Togo for a population estimated at 7.5 million [8] accounting for an average density of 1 dentist for more than 227,000 people, whereas in France, the average density was 63.1 dentists for 100,000 inhabitants in metropolitan France in 2013 [9].
The practitioners' population of oral and dental surgery in Togo is older than that of Switzerland, Turkey, despite the fact that life expectancy is shorter in zerland [10] and 37.14 years old, with extremes of 20 and 63 in Turkey [11]. The main reason for this difference is to be searched in the non-renewal of the specialists. For lack of training in Togo, and the scarcity of scholarships few people are interested in that field which cost a lot abroad. This is also noticeable through the analysis of the years of professional experience. In fact, more than half of dental surgeons (61.54%) had more than 20 years of professional experience. The predominance of male recorded in our study is also found in almost all of the studies [2] [10] [12].
Practitioners in Togo use very few cut imaging in their daily practice compared to those of European countries. This can be explained on the one hand by the absence or low availability of these imaging techniques in Togo; In fact the CBCT does not exist in Togo yet, however the Dentascan is available but it is only 5 CT-Scan devices across all the country and on the other hand by the ignorance of the Dentascan existence, the lack of information and sensitization on the part of dentists whose practice is much more private. They did not even talk to patients about CBCT because this technique did not exist yet. However in Switzerland, 19.2% of dentists were able to use CBCT on the spot, 40.8% of respondents asked for CBCT examination in second position, 4.9% asked for the conventional scanner, 34.2% would ask for a CBCT or a scanner depending on the situation, 11.1% said that they did not resort to any of the two options [10].
The Dentascan was the only technique in 3D cut imaging in oral and dental surgery available in Togo, and yet, its use is rare. Indeed, it was asked only twice in trimester by 15.38% of practitioners while two respondents (7.69%) said having asked for it more than once a month. Half of practitioners never used this technique in Togo whereas in Turkey, only 33.7% of them never used it [11].
The CBCT which is a rare technique in Togo is the most preferred one in other countries. It is the case in India where 72.7% of dentists preferred CBCT to scanner according to Sudhakara [13]. The fact that cut imaging is less used could be explained by the lack of sensitization and the poor knowledge in dental radiology in general, with those 65.38% who considered their knowledge poor. As for the CBCT, none of them did not assert having knowledge in that domain. As to the Dentascan, only one (3.85%) said to have good knowledge of this technique. This poor knowledge of cut imaging can be explained not only by the advanced age of practitioners who during their period of studies did not have access to these techniques because they are not developed yet, but also by the lack of continuing training. These two channels are the appropriate ways to acquire basic know-how and to update one's skills. For instance the observations made in Turkey show that 55.9% of dentists had knowledge about CBCT [11]; that knowledge was acquired by 59.9% of respondents during basic training at the faculty, 31% in seminars and 20.9% on the internet [14]. It is the same in Switzerland where half of dentists who took part in the study had confessed having received a good training in the field of medical imaging and 44.2% have acquired their knowledge during their basic training [10].
According to practitioners in Togo, trauma represents 34.62% of indications for 3D sectional imaging, 7.79% for implantology, whereas implantology alone accounted for 63.40% in Switzerland [10] and 62.5% in Iran [6]. According to directives in Switzerland in 2015, the CBCT is mainly used for implant treatment [2]. This evidence still confirms the ignorance of indications of the different techniques of sectional imaging of practitioners in Togo.
In view of knowledge deficiency recorded, 69.20% of practitioners expressed their interest in receiving a continuing training on the Dentascan/CBCT. This rate is higher than that of Switzerland (42%) [10]. One of the solutions would be to introduce in the teaching curriculum of the basic training, the new imaging techniques and to update those lecturers knowledge in accordance with the new techniques evolution. That is the wish of dentistry's students (91%) in Turkey who wanted that learning unit of the CBCT to be accessible at the dentistry Faculty [14] and in India where 49.1% of students wanted that training on the CBCT should be incorporated in the basic clinical training in dentistry [13].

Conclusion
Dental imaging is an essential tool for diagnostic and therapeutic orientation in the oral and dental surgery field. In Togo, sectional imaging is less used by practitioners of oral and dental medicine because of the ignorance of the new techniques existence and the absence of the CBCT. This ignorance stems from the lack of sectional imaging course in the training syllabus at the time when most of those practitioners whose experience is more than 20 years were being trained and the lack of continuing medical education that would allow them to update their knowledge and to learn about the interests of new techniques. Therefore, it is necessary to promote the teaching of the new cut imaging technique in the training syllabus of oral and dental diseases specialists, and to initiate continuing medical training on that subject.

Keywords
Computed Tomography, Ischemia, Myocardial Area at Risk

Introduction
Coronary computed tomography angiography (CTA) is widely used in clinical practice for assessing obstructive coronary artery disease (CAD), because of its high sensitivity and negative predictive value [1] [2] [3]. However, because of the limited spatial resolution, further evaluation, such as invasive coronary angiography (ICA) or stress myocardial perfusion imaging (MPI), is often required in the diagnostic workflow of coronary artery disease (CAD) [4]. Stress MPI, using single-photon-emission computed tomography (SPECT) and magnetic resonance imaging (MR), can non-invasively detect and quantify ischemic myocardium as a standard reference [5] [6], and is useful as the ischemic ratio of the left ventricular (LV) myocardium provides important information for diagnostic and therapeutic purposes in patients with CAD [7].
Furthermore, the Voronoi diagram is a type of centerline method that divides space (i.e., volume) by seeded points or lines [8], and is utilized in industry and geography. In diagnostic imaging, a previous study has shown the usefulness of this algorithm for liver segmentation, based on CT portal venography [9], and a recent study has reported that ICA-based stenosis-related CT myocardial territory correlates with the SPECT-based myocardial area at risk (MAAR) [10]. Coronary CTA stenosis-related CT myocardial territory is an assumption of the maximum MAAR that is obtained from a resting coronary CTA dataset. Stress MR-MPI has a high spatial resolution and yields better diagnostic performance in assessing multi-vessel disease in comparison with SPECT-MPI [11] [12]. Thus, this study aimed to assess the clinical feasibility of applying automated segmentation of MAAR using coronary CTA, as compared to stress MR-MPI. All patient information was protected in compliance with the guidelines pro-vided by the institutional review board. The flow chart for patient selection is shown in Figure 1. Patients with myocardial ischemia diagnosed by stress MR-MPI were excluded if they fulfilled the following criteria: 1) no invasive coronary angiography (ICA) available; 2) previous history of revascularization therapy, such as coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI); 3) heart valve disease; 4) cardiomyopathy; 5) total coronary artery occlusion confirmed byICA and 6) poor image quality of coronary CTA.

Coronary CTA
We and a medium-smooth cardiac kernel.

Stress Cardiac MR-MPI
We used a 3-T MR system (Achieva 3.0 T Quasar Dual; Philips Healthcare, Cleveland, OH, USA) equipped with a 32-element cardiac phased-array coil.
Using an established comprehensive cardiac MR protocol [13]

Invasive Coronary Angiography
ICA was performed following the standard institutional catheterization approach. Quantitative coronary analysis was performed by an independent cardiologist (T.U., 15 years of experience), who was blinded to other results, using commercially available software (CAAS5.9; Pie Medical Imaging, Maastricht, the Netherlands). Coronary artery stenosis ≥50% and ≥70% were considered as significant and obstructive CAD, respectively. When multiple stenoses were seen in two or more segments, the proximal stenosis was defined as the culprit stenosis.
All coronary artery segments and stenotic lesions (≥50% stenosis) were classified by the main coronary vessels: the left anterior descend-ing artery (LAD), including diagonal branches, the left circumflex artery (LCX), including the high lateral branch and ramus intermedius, and the right coronary artery (RCA), based on the American Heart Association guidelines [14].

MR-Based Ischemic Burden
The 16-segment model, excluding the apex, was applied [15]. The perfusion images were visually analyzed by two observers (T.K. and R.O., with 3 years and 8 years of experience in cardiac MR, respectively). These observers were blinded to all other data. If a perfusion defect in the LV myocardium was present in four or more cardiac cycles in the stress image, but not present in the resting image, it was considered to be a stress-induced perfusion defect [16]. When a segment with ≥50% of stress-induced perfusion defect was seen along the circumferential direction of the LV short axial image, corresponding to significant ICA stenosis by vessel-based analysis, it was defined as the ischemic segment in this study.
Discrepancies between the opinions of the first two observers were solved by a third senior observer (T. K., with 15 years' experience).In the late image, a segment with any late gadolinium enhancement was defined as a segment with myocardial infarction, irrespective of the presence or absence of myocardial ischemia. Patients with any segments showing late gadolinium enhancement were excluded from the study. The ratio of the number of segments with myocardial ischemia to the total of 16 segments was defined as the standard reference in this study (range: 0% -100% with a 6.3%-interval scale). The vesselbased analysis of the 16-segment model was based on a standardized myocardial segmentation [15].

Assessment of Coronary CTA
All CTA images were evaluated by two observers (Y.T. and T.Y., who had 4 years and 2 years of experience in cardiac CT, respectively) using a commercially available workstation (Aquarius intuition; TERARECON, Inc., Tokyo, Japan).
First, an overall assessment of image quality was performed at the subject level to assess misalignment of the coronary arteries between the slabs and discontinuity of coronary vessels due to motion artifacts and arrhythmia. If any of the aforementioned requirements were unsuitable, the patient was excluded from the study. Using a single dataset of coronary CTA with sufficient image quality, stenosis severity per segment was semiquantitatively assessed using the standard guidelines for reporting coronary CTA [17]: "non-CAD", 0% -49%; "moderate", 50% -69%; "severe", 70% -99%; and "occluded", 100%. The unassessable calcified segments were assumed to indicate severe stenosis. When multiple stenoses were found in the same coronary segment and vessel, the proximal stenosis was considered to be the culprit stenosis. Discrepancies were solved by consensus.
Coronary artery segmentation was applied, in addition to ICA.

CTA-Based MAAR
The same two observers evaluated the coronary CTA-based myocardial territory using dedicated software (TVA; TERARECON Inc. Tokyo, Japan). Post-processing of Voronoi diagram-based myocardial segmentation using coronary CTA was shown in Figure 2. In a series of Voronoi diagram-based myocardial segmentations based on a single CT dataset, the LV myocardium was automatically extracted using basic cardiac function analysis, and the coronary arteries were extracted in a semiautomatic manner. The software three-dimensionally integrated the two datasets and quantified the LV territories distal to any point on coronary CTA irrespective of coronary stenosis severity.
For this study, the stenosis-related CT myocardial territory was quantified at both levels of stenosis (≥50% and ≥70% on coronary CTA). The discrepancies of the stenosis-related CT myocardial territories were individually reviewed and solved by consensus. The two sums of all stenosis-related CT myocardial territories (i.e., the ratio of the LV volume at risk to the whole LV volume) were calculated using the two standards of the CTA stenosis (≥50% and ≥70%) as significant and obstructive CTA stenosis-based CT-MAAR, respectively.

Statistical Analysis
Categorical variables were expressed as proportions and continuous variables were Altman plotting expressed as the mean ± the standard deviation or as the median (interquartile range), as appropriate. With regard to coronary CTA stenosis severity and the stenosis-related CT myocardial territory for stenotic lesions ≥50%, the intra-and inter-observer reproducibility of the two operators were assessed using Spearman's test and Bland-Altman plotting.

Stenosis-Related CT Myocardial Territory
Seventy-seven coronary CTA lesions with a stenosis of ≥50% were assessed. Voronoi-based segmentation was successfully performed for all lesions. The respesentati ve for Compute cases are shown in Figure 3 and Figure 4. The intra-and   burden as assessed with MR to within ±6.3% in 40% (12/30) of patients, but overestimated the area at risk by 6.3% in 60% (18/30) patients.

Discussion
In this study, we showed that: 1) the reproducibility of the procedural steps for assessment of the CTA-based MAAR was good, and that 2) severe coronary CTA stenosis-based MAAR more accurately estimated the MR-based myocardial ischemic burden than did moderate stenosis.
Stress MR-MPI has been established as a useful diagnostic tool for detecting obstructive CAD [11]. The high spatial resolution of MR-MPI enables the delineation of subendocardial ischemia and myocardial infarction in patients with CAD [18]. Therefore, a comprehensive cardiac protocol involving the use of stress MR-MPI is helpful for diagnosing and managing CAD, even in patients with multivessel disease [19]. Stress MPI is essential for assessing the MAAR; therefore, many researchers have investigated stress-induced myocardial perfusion abnormalities using SPECT, MR, and CT [20] [21] [22].
By using a Voronoi diagram, CTA-based myocardial segmentation can indicate the theoretical maximum potential myocardial territory to a seeded point on the coronary CT angiogram. A recent study has demonstrated the high reprodu-cibility of CTA-based LV myocardial territory and the good correlation of CTbased MAAR with SPECT-based MAAR [10]. SPECT has been established as a clinical standard because of the substantial evidence supporting its use in the diagnosis and management of CAD [5] [20] [23]. However, some studies [11] [12] have discussed the potential disadvantages of SPECT as compared to MR-MPI, such as its lower spatial resolution and visualization of relative myocardial perfusion abnormalities.
Some researchers have reported clinical application of Voronoi diagrams in cardiovascular imaging [24] [25] [26]. Termeer et al. [25] utilized the Voronoi algorithm for estimating the MAAR on a 2D bull's eye map of the 17-segment model. Kang et al. [26] agreements of recently reported that the impact of coronary stenosis severity as assessed by intravascular ultrasound on the dependent myocardial territory is related to the severity of the invasive fractional flow reserve.
We considered that the CTA stenosis-based CT MAAR might contain some The present study has several limitations. First, the study population was relatively small. Second, stress MR-MPI as a reference was obtained with three cardiac short axial images, assessed using a conventional 16-segment model (excluding the apex), with a step-formed ordinal scale per 6.3%, independent from the morphological volume-based or the transmural extent-based evaluation. It is to be noted that these differences between CT-MAAR and stress MR-MPI might potential place a limitation on the evaluation of CT-MAAR in the study. Third, this study excluded patients with myocardial infarction because a myocardial scar may influence the quantification of CT-MAAR, by affecting the volumetric estimation of CT-MAAR, and the true extent of myocardial ischemia. Fourth, the CT-MAAR was estimated based on the anatomical location of coronary stenosis, independent of whether the lesion was diagnosed as hemodynamically significant. Fifth, the precision of the ischemic burden in stress MR-MPI was not objectively validated on anatomical territory that corresponded to coronary artery stenosis. Further studies with a large number of patients will be required to clarify the significance of these findings in clinical practice.

Conclusion
Voronoi diagram-based myocardial segmentation has the potential for predict- Submit or recommend next manuscript to SCIRP and we will provide best service for you: Accepting pre-submission inquiries through Email, Facebook, LinkedIn, Twitter, etc. A wide selection of journals (inclusive of 9 subjects, more than 200 journals) Providing 24-hour high-quality service User-friendly online submission system Fair and swift peer-review system Efficient typesetting and proofreading procedure Display of the result of downloads and visits, as well as the number of cited articles Maximum dissemination of your research work Submit your manuscript at: http://papersubmission.scirp.org/ Or contact ojrad@scirp.org

Abstract
Objective: The aim of this study was to evaluate intra-and inter-observer reproducibility of sinus x-rays in comparison to sinus computed tomography (CT) in chronic rhinosinusitis (CRS) patients. Methods: This was a prospective controlled study for which 14 adult CRS patients were recruited. Patients underwent a sinus multi-detector CT scan as well as additional sinus x-rays at the same time. Symptom interview and skin prick tests were performed. Lund-Mackay (LM) scores and 43 other findings in paranasal sinuses were analyzed by three blinded observers from CT-scans and x-rays. We compared agreement between sinus CT and x-rays (intra-observer reproducibility) and between three observers (inter-observer reproducibility) by Cohen's kappa.
Results: In at least 90% of the cases, the status of 47/49 structures was detectable in CT scans, whereas the status of only 8/49 structures was detectable in x-rays. The majority of the 25 visualized structures had poor intra-observer and inter-observer reproducibility. Conclusion: Only a few structures can be visualized in paranasal sinus x-rays and compared to paranasal sinus CTscans, their reproducibility is poor. Our results strongly support the current consensus of radiation dose reduction by limiting the number of x-rays.

Introduction
Chronic rhinosinusitis (CRS) is a multifactorial and variable disease with a prevalence of 10.9% [1]. Computed tomography (CT) scans and/or nasal endoscopy are the recommended imaging modality for CRS [1]. Correlation between sinonasal symptoms and endoscopic or radiologic signs is poor [2]. The main findings of CRS are mucosal changes within the ostiomeatal complex and/or sinuses [1]. Paranasal sinus anatomical variants are very common and several critical anatomical structures (such as big vessels, orbit and central nervous system) are closely located to the sinonasal surgical area [3] [4].
CRS surgery has improved many patients' quality of life with hard to treat CRS [1]. Imaging of the nose and paranasal sinuses has progressed rapidly during the past decade. CT can demonstrate sinus anatomy specifically as well as anatomical variants and other important structures, when preparing for surgery or evaluating the cause of long lasting sinus symptoms. X-rays are not recommended for CRS imaging [2]. A simple radiogram of the nose and paranasal sinuses carries a radiation dose of 0.03 mSv (four days of natural background radiation). Although x-rays are inferior to CT in detecting bony structures and mucosal changes, little comparative data exists on the agreement between sinus CT and x-rays [2].
Despite the novel low dose sinus CT scan modalities, the number of performed sinus x-rays is high in Finland (13.1 per 1000 inhabitants in 2011, according to the statistics of the Radiation and Nuclear Safety Authority) [5]. The aim of this prospective controlled study was to evaluate intra-and inter-observer reproducibility of sinus x-rays in comparison to sinus CT, in order to contribute to the need for reduction of unnecessary radiation.

Ethical Consideration
The study was approved by the ethics committee of the Pirkanmaa Hospital District (no 96032) and was conducted in accordance with the Helsinki Declaration of 1975, as revised in 1983. Written informed consent was obtained from each participant. Volunteer patients were exposed to an extra radiation dose of 0.02 years (6 days of natural background radiation in Finland).

Patients
This study was carried out in the Department of Otorhinolaryngology, at Tam

CT Scans
Patients

X-Rays
X-rays were performed at the same time as sinus CT scans. Two X-ray projec-   (Table 3).

Evaluation of CT Scans and X-Rays
Each structure listed in the form could be scored by 2 -5 different listed choices.
Before evaluation of the CT scans, all choices were discussed between observers.
Before this study, the observers had participated a pilot study with 15 CT scans [6]. The radiologist did not respond to the question: "Need for septoplasty".

Data Analysis
Statistical analysis was carried out by SPSS Base 15.0 Statistical Software Package (SPSS Inc., Chicago, IL, USA). Cohen's kappa was used to compare the degree of agreement between CT scans and x-rays (e.g. intra-observer agreement); and the inter-observer agreement of x-rays. The calculation is based on the difference between how much agreement is actually present compared to how much agreement would be expected to be present by chance alone. The established interpretation of Kappa-value is classified into 6 subgroups: Poor < 0. A value under zero means that the agreement is worse than that by chance [7]. Two-tailed P-values of <0.05 were considered statistically significant.

Patient Characteristics
Patient characteristics are shown in Table 1. The median (min-max) age was 36.9 (20.0 -54.3) years. 57.1% of patients underwent sinonasal operation within a year after the CT scans (Table 1). 2 (14.3%) of the patients reported suffering from diseases besides CRS ± AR ± asthma with regular need for medication. One of the patient reported having melanoma and the other patient cardiac arrhythmia.

Visualized Structures in X-Rays
The number of visualized structures in x-rays was 25, e.g. the structures that were visualized in at least one patient´s paranasal sinus x-rays, whereas the number of visualized structures in at least one patient's CT scan was 49 ( Table  2). The visualized 25/49 structures in x-rays were Lund-Mackay (LM)-scores (except ostiomeatal unit), mucosa and size of paranasal sinuses, mucosa of inferior and middle turbinates, nasal mucosal oedema and septal abnormalities (Table 2). Yet, reliability to even detect these structures in most cases of x-rays was poor (Table 2). In at least 90% of the cases, the status of 47/49 structures was detectable in CT scans, whereas for x-rays it was only 8/49 (Table 2). Several diagnostically and surgically important structures were not visible in x-rays, such as ostiomeatal complex, insertion of the uncinate process, lamina papyrachea and anterior ethmoid artery (Table 2).

Intra-Observer Agreement
We compared the degree of agreement between x-rays and CT scans of the 25 structures that were visualized in x-rays. In general, the intra-observer agree- Abbreviations: SPT = skin prick test; AERD = patient-reported aspirin exacerbated respiratory disease; CT = computed tomography; VAS= visual analogue scale (0 -10). 1 At least one peroral corticosteroid treatment during the last 12 months. 2 Self-reported and patient-record information.  The CT scans and x-rays were taken from 14 patients with chronic rhinosinusitis symptoms. Each patient underwent CT scans and x-rays at the same time.
The columns show in alphabetical order the evaluated 49 structures from paranasal sinus CT-scans and x-rays. Visualized in x-rays = the 25 structures that were visualized in at least one patient's paranasal sinus x-rays (left column); Non-visualized in x-rays = the 24 structures that were non-visualized in paranasal sinus x-rays of all cases (right column); OMC = Ostiomeatal complex; Not detectable = the percentage of the observer´s responses "The status of the structure is not detectable" of both sides. 1 Evaluated by the ENT surgeon. Other structures evaluated by the radiologist. ment was poor (kappa < 0.2) in the majority of structures, such as LM scores.
Moderate and good agreement was only achieved for gross anatomical structures on the right hand-side only, concerning respectively, nasal septum deviation and size of the frontal sinus (Table 3). Fair or poor agreement was observed for the rest of the structures.

Inter-Observer Agreement
The 25 structures that were visualized in x-rays were evaluated by a radiologist, an ENT surgeon and an ENT resident. The inter-observer agreement between radiologist and ENT resident for x-rays was poor (kappa ≤ 0.02) in 88% of the structures and fair (kappa 0.21 -0.4) for the rest (12%) of the structures. The agreement between radiologist and ENT surgeon for x-rays was poor or fair in 80% of the structures and the agreement between ENT surgeon and ENT resident was poor or fair in 92% of the structures.

Discussion
This study was carried out to evaluate intra-and inter-observer reproducibility of sinus x-rays in comparison to sinus CT scans. When this study was started, multi-detector CT scans had a high radiation dose (in average 0.9 mSv) and x-rays were still relative widely used due to a clearly smaller radiation dose (in average 0.03 mSV per image). After this, low-dose CT scans (such as cone beam CT scans) have emerged (radiation dose between 0.08 -0.27 mSv) and hence have largely replaced both sinus x-rays and high-dose sinus CT scans [8]. The number of performed sinus x-rays is still high in Finland [5]. Consequently, this study could contribute to the reduction of unnecessary radiation.
Our main finding was that a small proportion of structures can be visualized in x-rays; and x-ray evaluations have poor reproducibility. CRS specific changes that should be observed in CT-scans including degree of opacification of the paranasal sinuses and/or obstruction of the ostiomeatal complex cannot be visualized or only poorly in simple x-rays, making CRS diagnosis unreliable [1]. Similarly, others found in a small study that engorged turbinates and opaque nasal fossa could be observed from paranasal sinus x-rays. In the x-rays of 19.7% of patients with nasal and/or paranasal symptoms during at least 8 weeks, no changes were observable [9].
Intra-observer agreement was fair to poor regarding most of the 25 structures that could be visualized in plain x-rays. Similarly to us, others report in a study with 47 patients with acute rhinosinusitis that plain sinus radiograms have a low sensitivity for detecting sinus inflammatory changes in other paranasal sinuses besides the maxillary sinus, in comparison to CT-scans [10].
Inter-observer agreement was poor for the majority of structures that could be visualized by the radiologist, ENT surgeon and ENT resident. Very good interobserver agreement was only achieved in regard to structures that could not be visualized, between ENT resident and surgeon. The CT scans and x-rays were taken from 14 patients with chronic rhinosinusitis symptoms. Each patient underwent CT scans and x-rays at the same time. Agreement is presented only of the 25 structures that were detected in x-rays ( Table 2). The 24 structures that were non-detectable in x-rays have been withdrawn from evaluation. The order of the structures is the same as they were in the evaluation form. Structures with substantial to almost perfect agreement level by Kappa-coefficient. 1 Evaluated by the ENT surgeon. Other structures evaluated by the radiologist.
Simple X-rays of sinuses are currently used to exclude acute sinusitis. Longterm smoking, decline in lung function and poor health-related quality of life are risk factors for exacerbation of asthma exacerbations and emergency room [11]. Prevalence of chronic rhinosinusitis is twice as common in asthmatics needing acute care compared to those without emergency room. However, CRS is not an independent risk factor for acute care. With progressing severe symptoms not responding to antibiotics and other forms of treatment, especially in this patient group, simple X-rays are in some cases used to evaluate the signs and extent of acute bacterial infection [12] [13].
The limitation of our study is the small sample size, which was due to ethical reasons and to difficulties in recruiting volunteer patients for additional x-ray images, carrying extra radiation. We acknowledge that small sample size hinders large scale extrapolation of results and selection bias may have occurred.

Conclusion
Only a very small number of structures can be visualized in paranasal sinus x-rays and their evaluation reproducibility is poor compared to paranasal sinus CT scans. Despite the small study sample size, our results strongly support the current European position paper on rhinosinusitis and nasal polyps consensus that sinus CT-scans are needed when estimating the need for surgical treatment of CRS (Figure 1).  neuronal integrity, energetic status and membrane turnover respectively [1].

Introduction
Recently, there has been significant interest in using edited MRS to reveal signals from less concentrated metabolites, such as GABA [2] [3], glutathione [4] and ascorbate [5]. Due to the fundamental insensitivity of MRS, larger measurement volumes are required for these edited experiments, typically on the order of (3 cm) 3 compared to (2 cm) 3 or less for traditional single-voxel MRS [6].
In cohort MRI studies, one common post-processing step is the co-registration of images either to each other, or to a standard-space template. Co-registration of images across a cohort allows comparisons between images to be drawn for anatomically equivalent regions, limited only by the quality of co-registration. In contrast, MRS is usually performed as a single-voxel measurement, and placement of voxels involves planning on the basis of predefined anatomical or functional landmarks. This is an irreversible anatomical judgment that cannot be mitigated by post-processing co-registration. For single-voxel acquisitions, the measurement acquired corresponds to the region prescribed without any further spatial resolution, or opportunity for spatial realignment. Conclusions drawn from MRS studies are usually based upon the functional role of a particular anatomical structure, and there is generally an implicit assumption that voxel placement is accurate and reproducible. To date, a landmark-based approach is the main method for edited MRS voxel placement. Given the reliance on anatomical landmarks, it is therefore particularly important to assess the reproducibility of voxel placement in MRS studies [7], especially for edited MRS experiments.
To our knowledge, no previous study has investigated the placement reliability of voxel for edited MRS, compared with traditional MRS. The increase in voxel size required for edited MRS of less concentrated metabolites may have several impacts on placement precision: displacement of the voxel by a fixed distance will have a relatively smaller impact on the voxel contents; larger voxels may suffer from additional anatomical restrictions; and operator care or judgment may be influenced by the size of the voxel to be planned. One further development that is relevant for studies of GABA is the increasing adoption of functionally motivated measurement regions, as opposed to anatomically defined studies.
Tolerance of placement variance might be greater for a fronto-parietal region than a primary sensorimotor region, both because of the greater specificity of the functional definition and the qualitative difference in the conclusions likely to be drawn from such a study.
In this current study, the reproducibility of voxel placement for two anatomically defined and functionally motivated, regions of interest (occipital and sensorimotor), commonly used in MRS studies of sensory and motor function [8] [9] [10] [11], was assessed. Using the Dice overlap coefficient (DOC), placement precision both within-subject within-session, and between-subject was investigated. Differences between within-and between-subject results are discussed in terms of the interpretation of individually different anatomy and the limitations of the DOC.

Participants
13 healthy male subjects (all right handed, age 30 ± 6.1 years old) participated in the study. Only male participants were included to mitigate gender effects on brain anatomy and voxel localization. Written informed consent was obtained for each participant under the approval of the local Institutional Review Board prior to testing.

Edited-MRS
Data were acquired on a Philips 3T "Achieva" MRI scanner (Best, the Netherlands) using a 32-channel head coil for receive and body coil for transmit. For each participant, sagittal 1 mm 3 isotropic T1-weighted (T1w) images (MP-RAGE) were acquired and resliced in axial and coronal views (TR = 7.99 ms, TE = 3.76 ms, Flip angle = 8˚). GABA-edited MRS voxels were manually placed in two regions (with the visualized voxel in Figure 1 correct for the 3 ppm GABA signal) viewing all 3 planes by a single experimenter. A (3 cm) 3 voxel was placed on the right sensorimotor cortex (SM1, Figure 1(b)) and was centered on the central sulcus posterior to the hand-knob [12] in the axial plane; the voxel was rotated to align with the cortical surface by rotating in the coronal plane and subsequently in the sagittal plane. A second (3 cm) 3 voxel was placed in the occipital cortex (OCC, Figure 1(c)), centered on the midline and rotated in the sagittal slice to align along the cerebellar tentorium and placed as posterior as possible without including the sagittal sinus or skull. Each voxel was placed twice in all participants. The first placement was part of a standard GABA-edited MEGA-PRESS scan with the following scan parameters: TE/TR = 68/2000 ms, 320 transients acquired with editing pulses placed at 1.9 (edit-ON) and 7.5 (edit-OFF) ppm, 2 k bandwidth and VAPOR water suppression(as described in [8]). The second placement was only performed to log voxel location parameters, although minimal MRS data were acquired (a 12-second water acquisition). Prior to the second placement, voxel location and angulations were zeroed so that the voxel was centered approximately in the center of the brain without rotation, and independent placement was again performed on the basis of the landmarks described above. All voxel placements were performed by a single experimenter and participants were not removed from the scanner in between the first and second voxel placement. No additional information (e.g. screen shots of the first placement) was used for the second placement. A total of 51 MRS voxels' data, from 13 participants were included in this study (1 subject's second SM1 voxel was unavailable).

Analysis
The following image analysis pipeline was used ( Figure 2): 1) Generation of the MRS voxel mask (Figure 2(a)). Each MRS acquisition volume was reconstructed as a binary mask in the image matrix of the T1w image of the same subject using the SVMask tool (in house software), which ex-tracts the required geometric information from MRS and MRI file headers. 2) Brain extraction (Figure 2(b)). Skull-stripping of 3D T1w images was performed using the Brain Extraction Tool (BET, v2.1) [13], from the FSL suite.
3) Image co-registration (Figure 2(b)). T1w images were co-registered to (2 mm) 3 MNI standard-space brain using FMRIB's Linear Image Registration Tool (FLIRT, v6.0) [14]. 4) Voxel transformation to standard space (Figure 2(c)). For each subject, the transformation matrix determined in step 3 was applied to all the voxel masks generated in step 1 to give voxel masks in standard space (as shown in Figure 1).

Within-Subject Overlap
The quantification of voxel overlap within subjects between the two scans was performed using the Dice overlap coefficient (DOC [15]). The DOC is defined as the intersection volume, divided by the mean volume of the two voxels; it ranges between 0 and 1, where 1 represents perfect overlap. For example, A might refer to the first OCC voxel mask and B to the second OCC voxel mask: Within-subject voxel overlap DOC was calculated using FSL tools in subjectspace (rather than standard space), prior to step 2 above (as shown in Figure 2(a)).

Between-Subject Overlap in Standard Space
Between-subject voxel placement reliability was calculated using the firstplacement voxel masks for each region from the 13 participants, registered to standard space. For each of the thirteen subjects, another subject was selected randomly (without replacement and prohibiting double comparisons e.g. 1-8 and 8-1) to generate thirteen unique pair-wise comparisons. The DOC was calculated for OCC and SM for each of these pairs. This process was repeated five times, so that in all 65 between-subject overlap coefficients were calculated for each region.

Voxel Density Images
In standard space, an image was calculated of the sum of the voxel masks of all subjects (separately for OCC and SM voxel). For each point in space, this image reflects how often that point is included in the different subjects' MRS voxels.

Within-Subject Voxel Overlap
The overlap between the first and second voxel prescriptions for each subject were 87% ± 5% in the occipital region and 86% ± 5% in the SM region ( Figure   3). The displacement between the centers of the two voxels was 2.6 ± 1.2 mm (mean ± standard deviation), with very similar average displacements for both the OCC and SM locations (2.66 mm for SM and 2.63 mm for OCC).

Between-Subject Voxel Overlap
Mean between-subject voxel overlap was 75% ± 10% in OCC and 78% ± 7% in SM (as shown in Figure 3 and Figure 4). Due to substantial variation in brain volume between subjects (from 1.05 liter to 1.50 liter for males [16]), the volume of the MRS voxels is scaled in standard space through the registration process.
Voxel volumes were scaled relative to the mean by −13% to +15% (standard deviation 9%). The mean pair-wise volume mismatch is 11%.

Discussion
It is a tacit assumption of the majority of single-voxel MRS studies that metabolite concentrations are measured from equivalent regions in each subject. It is therefore somewhat surprising that the fidelity of voxel placement has only occasionally been investigated in the literature [7] [17]. In order to evaluate the repeatability of voxel placement for MEGA-PRESS GABA scans, this study calculated the DOC both within-subject and, after image co-registration, betweensubject. The primary results suggest the within-subject DOC is 85% in both occipital and sensorimotor measurement regions, and that the between subject DOC is 75% for a 3 × 3 × 3 cm 3 voxel.
At first glance, these overlap numbers are surprisingly low; however, 85% overlap is equivalent to 5% (or 1.5 mm of one direction of a (3 cm) 3 voxel) displacements along each of the three spatial directions, without any variability in rotations. The mean displacement between voxel centers is 2.6 mm, equal to the diagonal of a 1.5 mm cube, suggesting that displacement accounts for the majority of the overlap loss, with only minor losses due to rotation. Given that voxels are placed using T1w images with 1-mm-isotropic resolution, precision better than 1 mm in each direction would not be expected. Similarly, the 75% overlap between subjects corresponds to a 9% (or 2.7 mm) displacement along all three axes-again not substantially greater than the (2 mm) 3 matrix on which co-registration was performed.
Some limitations arise from the choice of the Dice coefficient (DOC). Firstly, the DOC only reports on the overlap between the tissues contained in different voxels, and cannot address the impact that any change in voxel contents has on measured GABA concentration. Secondly, it is difficult to interpret the difference in DOC from within-to between-subjects comparisons (85% vs. 75%).
Some of this reduction in overlap is "real", reflecting the operator's variable interpretation of individual anatomy, while some of it is artifactual reflecting imperfections in co-registration on a (2 mm) 3 matrix.
A further limitation of using the Dice coefficient in standard space is that two voxels with identical position and orientation that originate from different-sized brains will not give overlap of 100% due to a volume mismatch in standard space. In this special case, the Dice coefficient is less than 1 by half the fractional difference in volume between the brains. This suggests that the mean volume mismatch in our cohort (11%) therefore accounts for about half of the additional between-subject overlap loss compared to within-subject. Thus, while the DOC reflects the mathematical overlap between voxels, in standard space it does not report simply on operator reliability. One might even suggest that voxel volume should be scaled relative to total brain volume when MRS scans are prescribed (which would likely result in increased DOC), but this has signal-to-noise (SNR) and data quality implications also. Additional limitations are the consideration of only two voxel positions, the lack of within-subject between-session data, and the single operator prescribing voxels. Although the strong agreement between the two regions studied suggests that the findings may be generalizable, these results are likely to be affected to some degree by several factors including the complexity of the prescription protocol including the number of rotations, reproducibility of subject placement in the scanner (i.e. brain orientation in the anatomical images), and ease of identification of landmarks used (which may differ due to lesions, atrophy or normal/abnormal anatomical variation). Additional advances in co-registration, as well as an in-depth investigation of the effect of small changes in voxel tissue composition on GABA levels, would allow for a better understanding of the effect of small changes in voxel placement within and between subjects. Furthermore, we restricted our investigation to single-prescriber, single-scanner and single-session. For longitudinal or mul-ti-center studies, the effects of multi-prescriber, multi-scanner, and multi-session on voxel localization and overlap would need to be investigated as well.
In practical terms, this study shows that voxel placement to a precision of 2 -3 mm in three directions is possible, with care. Although these results give surprisingly low Dice coefficients of ~75%, this level of precision is approximately equal to the ability of subjects to remain motionless during the 10-minute scan.
This agreement is only possible due to the rigorous specification of voxel placement protocol, including three-dimensional position and rotation information.
Of particular note is the need to specify the order of multiple voxel rotations (which do not commute) for voxels. A range of voxel overlaps have been shown previously, from 57% within-subject for a small (15 mm) 3 parietal voxel [7] to 86% for a slightly larger (20 mm) 3 posterior cingulate voxel [17]. There is some evidence that automated voxel placement protocols, which typically calculate voxel location parameters from parameters co-registering images to standard space within-session, can perform as well as human operators and remove some variance [17], and prospective voxel placement correction has been demonstrated with a navigator-based acquisition [18]. Another methodological improvement is the use of voxel density maps (as used in Gaetz et al. [19]) to simultaneously display the position of MRS voxels and the placement precision across subjects.

Conclusion
In conclusion, the percentage of equivalent tissue included by 3 × 3 × 3 cm 3 MRS voxels in different subjects is surprisingly low at 75%. However, this corresponds to displacements of less than 3 mm along three axes, which seems to be relatively good agreement, and some fraction of this overlap loss is caused by brain volume mismatches. Within-subject agreement is ~85%, again low at first glance, but equivalent to acceptable 3D displacements of 1.5 mm in all three directions.

Introduction
Spinal stenosis is a major predisposing factor for cervical myelopathy and spinal cord injury [1] [2]. The spinal canal can be tightened congenitally or take the tight form by arthritic injuries resulting in its strong biomechanical implication [3].

Material and Method
It was prospective study carried out over a twelve-month (12) period at the university hospital center of the campus. It concerns CT Scans of adults people of more than 18 years, who did not present any clinical sign of neck pain or cervicobrachial neuralgia. We excluded from our study the cervical spinal which presented malformation, degenerative, infectious, rheumatic, traumatic lesions or spinal surgery backgrounds. The studies have been carried out on General Electric's CT Scan. The volume acquisition has been realized on the cervical spinal. The stocked images have been processed on the image processing console with the measurement tools that facilitate the enlargement and rotation.
The measurement of the dimensions of the cervical spinal canal and spinal cord was realized on pedicular axial CT Scan cuts.
APD1 has been measured between the posterior edge of the vertebral body and the fore junction of the blades (Figure 1). IPD represents the longest distance between two pedicles (Figure 1). APD2 has been measured between the anterior and the posterior edges of the spinal cord (Figure 2), at the same level as the APD1, in order to assess their ratio (R1).
TD has been measured between the right and the left edges of the spinal cord (Figure 2), at the same level as the IPD, in order to assess their report (R2).
The data have been processed and analyzed with Epi info 7 and Microsoft Excel software.

Results
Our study involved 350 CT Scans of the cervical spinal. The mean age stood at 35 ± 10.55 years old. Both genders were involved, with 217 men (62%) and 133 women (38%).
The average of the APD1 stood at 14 ± 2.1 mm, with a minimal average of 12.7 ± 1.5 mm and a maximal average of 18.3 ± 1.9 mm. The highest average was at C1 and the lowest at C3, C4 and C5 (Table 1).
The IPD average was 24 ± 1.3 mm, with a minimal average of 22.2 ± 1.8 mm, and a maximal average of 26 ± 1.9 mm. We found the highest average at C1 and the lowest at C2 and C3 ( Table 2).
The APD2 average was 11.66 ± 0.66 mm, with a minimal average of 9.1 ± 0.67 mm and a maximal average of 10.5 ± 1.5 mm. The highest average was found at C1 then at C2. From C3 to C7, the averages were slightly lower, but substantially equal (Table 1).  The TD average stood at 12.64 ± 1.77 mm. The Minimal TD average was 9 ± 0.6 mm and the maximal average was 14.63 ± 2.5 mm. The highest average was at C1 and the lowest at C5 ( Table 2).
While comparing the measurements of the cervical spinal canal (APD1 and IPD) and the spinal cord (APD2 and TD), as well as R1 and R2 between the two genders, we found that there is no significant difference (Table 3).

Discussion
Knowing the normal values of the spinal canal is important, because it enables to detect central canal stenosis by reduction of the canal caliber [4].
The antero-posterior diameter of the cervical spinal canal (APD1) is important in traumatic, degenerative and inflammatory situations, and a small diameter of APD1 is associated to the increase of lesions occurrence [5]. Generally, it is admitted that a cervical canal stenosis exists when the APD1 of the cervical canal is under the threshold of 12 mm [5] [6]. The global average of the APD1 cervical spinal canal in our study stood at 14 ± 2.1 mm, with a larger APD1 at C1 and the lowest at C3, C4 and C5. We noticed a decrease of APD1 from C1 to C5. Singh et al. [7], as well as Gupta et al. [8] in India found an average higher (17.05 ± 1.61 mm) than ours. The average of our study is close to that of Lee et al. [9] in Korea, to Taitz [10] in South Africa and Gepstein [11] in Israel. Few studies [4] [10] found the smallest APD1 at C3. Some studies [7] [9] [12] found a smallest Table 3. Comparison of the APD1 and the IPD of the cervical spinal canal, the APD2 and the TD of the cervical spinal cord, the ratio R1 and the ratio R2 between male and female patients (division of P values).  [7] found a decrease of the APD1 from C1 to C5. UlbriCH [14] noted a lowering from C1 to C6. Other studies [13] [15] noticed a fall from C1 to C4 with an increase to C5 and a decrease to C6. Our study as well as Singh et al. [7] has not found any statistical significant difference between the APD1 of the cervical spinal canal of men and those of women. However, Evangepolos et al. [13] noticed a significant difference between the genders at C1. The comparison of the APD1 of our study with those of Singh et al. [7] on the one hand and with those of Evangepolos et al. [13] on the other hand, revealed that the differences are not statistically important. As for Taitz [10], the APD1 would be larger  [16], many studies found out the lowest IPD at C3 and the highest at C5. Like our study, Chazono et al. [16], have not found any significant statistical difference of IPD between ethnic groups.
Few studies concerning the measurement of the cervical spinal cord exist [14].
Studies [17] revealed that the average of antero-posterior diameter of the cervical spinal cord (APD2) varies between 5 mm and 6 mm. Our study found out an average of APD2 higher than 11.66 mm ± 0.66 with a variation from 9.1 mm ± 0.67 à 10.5 mm ± 1.5. Yet, the diameters measurement of the cervical spinal cord only would not enable to determine a cervical spinal cord compression. But when the measurement of the cervical spinal cord is coupled with that of the cervical spinal canal, it is possible to calculate the gap or to establish the relationship between the two. Tierney et al. [2], in their study, measure the gap between the spinal cord and the spinal canal by calculating the difference between the two. Our study considered the relationship between the cord and the canal, then it decreases to reach C7 (0.65 ± 0.04 mm). There is no study concerning the relationship between the cord and the medullar canal regardless of in the antero-posterior plan or in the transverse plan. It is acknowledged that the spinal cord compression is due to an inadequacy between the cord and the medullar canal [18]. The gap around the spinal cord would diminish at the level of the cervical low segment [2], increasing the risk of medullar compression at this level [19] [20]. In our study, the smallest antero-posterior ratio stands in C4 and C5, and the largest ratio stands in C2. With regard to transverse plan report, our study found out an increase of the ratio from C1 to C5, then a decrease from C5 to C7. The assessment of the gap around the cord would be more contributing than the diameters of the canal and the spinal cord and the medullar canal in the determination of the spinal cord compression [21]. derive their blood supply from the pial vessels. These often produce symptoms by compressing the neighboring structures [1]. Haemangioblastomas are twice common in men than women and majority of these falls in 20 -40 years age group. These have been labeled as WHO grade I benign tumors originating from the blood vessels. Sometimes the inferences of the imaging modalities can confuse the diagnosis which leads to the mismanagement as was in our case.

Case Report
24-years female reported to the outpatient department with complaints of headache of one year duration. She had occasional difficulty of balancing herself while walking. There was history of off and on low grade fever with slight evening rise in nature. She was diagnosed as posterior fossa giant tuberculomas on the basis of imaging studies and biomedical investigations. Pre-operative non contrast computerized tomography (NCCT) of head had shown posterior fossa mass which was compressing upon fourth ventricle leading to hydrocephalus (Figure 1(a) and Figure 1(b)).
Post contrast study had shown enhancement of the solid part with cystic component as hypo dense region ( Figure 2).
MRI studies have shown a mixed intensity structure with avid enhancement of the mural nodule. Spectroscopy of the tumor had shown lipid and lactate peaks without any significant choline rise. NAA peak was decreased with increased Choline/Creatinine ratio. Though the possibility of haemangioblastoma was kept, but as per the laboratory investigations, spectroscopy and presentation she was labeled as a case of giant tuberculomas (Figures 3(a)-(c), Figure 4(a) and Figure 4(b) and Figures 5(a)-(c)).
She was put on ATT for six months after these findings. However the condition deteriorated and the patient had to undergo surgical excision of the mass. Histopathological findings confirmed the diagnosis of Hemangioblastoma. The  (b) MR spectroscopy shows increased lipid and lactate peaks. N-acetyla sparate peak is decreased with increased Ch/Cr peak. specimen was predominantly constituted abundant vacuolated stromal cells with capillary network (slides not available). Post operation CT scan was done after one month had shown encouraging result without any residual tumor. Post surgical recovery was uneventful and the patient had been kept on six monthly follow up.

Discussion
Haemangioblastomas are slow growing tumors with tendency to rupture. These remain undiagnosed for a long time because of their asymptomatic nature. This has got a close association to the tune of 25% with von Hipple Lindau disease and rest 75% are of sporadic in nature [2]. Common complaints are headache in 70% of the cases and 50% report with hydrocephalus. These tumors cause disturbances in movements, equilibrium and muscle tone because of cerebellar involvement. The coordination of movements is always affected. There can be sudden bleeding inside the cranial cavity because of the rupture which is a medical emergency. These can cause hydrocephalus because of compression over the CSF pathway.
Magnetic resonance imaging and computerized tomography imaging are the modalities of choice for their evaluation. On CEMRI and CECT of the brain these are well demarcated cystic masse with mural nodule and non enhancing wall [3]. Mural nodule within this cystic mass enhances vividly [4]. MR spectroscopy of haemangioblastoma shows high lipid peak without any lactate peak. Coline peak is raised with low creatinine/phosphocreatinine ratio. N-acetylaspartate (NAA) is absent which indicates of non neurogenic origin of these tumors.MR spectroscopy in our present case had shown increased lipid peak, decreased NAA peak and increased Choline/Creatinine ratio and this was the reason for labeling her as a case of giant tuberculomas [5] [6] [7].
Management is always by surgical intervention and Gamma knife radio surgery has become the fashion of the day. The tumors can partially be drained before surgery as these constitute mixed pattern of solid and cystic. Pre surgical embolisation is done to minimize the blood loss and neat surgical excision [8].
Recurrence is seen in 25% of the cases associated with von Hipple-Lindau syndromes.

Conclusion
Hemangioblastomas can be best diagnosed by the modalities like CECT and MR contrast studies. But sometimes spectroscopy can mislead the issue of final diagnosis as happened in this case.

Introduction
Schwannomas are rare nerve tumors, accounting for 2% of neurogenic mediastinal tumors [1]. This tumor, usually poly-lobulated, rounded and well encapsulated, is generally located in the para vertebral groove around the intercostal nerve [2]. It is often discovered fortuitously as it is usually asymptomatic, or even more rarely in the event of compression of adjoining organs [1].
We deem highly interesting to report the case of a large cystic mediastinal schwannoma ruptured in the pleura, whose diagnosis was suspected on CT and confirmed on magnetic resonance imaging. for diagnostic imaging. Extensive diagnostic imaging was required for a gradual worsening of a sub-acute chest pain with pleural effusion on plain chest X-ray dating few weeks prior to her referral.
Physical examination found a conscious patient, having a febrile with dyspnea and good general condition. Plain chest X-ray showed a right side opacity occupying almost the entire right lung space consistent with abundant pleural effusion.

Discussion
Schwannoma, also called neuroma is a rare tumor representing only 2% of all neurogenic mediastinal tumors [1] [3] [4]. This tumor, made up of cells forming the Schwann sheath, usually affects young adults between 20 and 50 years, with a female predominance, as was the case in our patient. [5] The circumstances of discovery are in most cases fortuitous with symptoms in relation to compression of adjoining structures. It could present as dyspnea or most often as cough associated with chest pain [3] [5].
In the case of our patient notwithstanding, the discovery of a schwannoma after rupture into the pleural cavity constitutes a rare clinical phenomenon. Thus representing to the best of our knowledge of recent literature, the first case of mediastinal cystic schwannoma ruptured in the pleura whose clinical setting was dominated by gradual onset of dyspnea.
In the presence of a mediastinal schwannoma, thoracic CT should be considered as an essential first-line imaging tool. It allows characterization of the lesion by determining its size, its outline, but above all, it confirms the presence of a cystic component or otherwise. Contrast medium injection improves its sensi-tivity as it shows a significant enhancement of the solid component vis-a-vis the cystic component as was the case in our patient [3] [4] [6] [7]. MRI allows the study of its links with adjacent mediastinal structures as well as foraminal and endocanal extension as evidenced in our patient where foraminal extension was detected on MRI [8].
Given all the above clinical and radiological arguments we concluded the diagnosis of cystic mediastinal schwannoma ruptured in pleura. The patient was referred for surgical management

Conclusion
This case relates a particular mode of revelation of cystic mediastinal schwannoma whose rupture constitutes its main peculiarity. In the presence of a cystic lesion of the posterior mediastinum, the diagnosis of a nerve tumor in the mediastinum such as schwannoma should be considered. Diagnostic workup should include not only a CT scan but also an especially MRI as its enhanced resolution, facilitating the positive diagnosis while eliminating other differential diagnosis such a hydatid cyst especially in endemic areas.

Introduction
Iodinated contrast media (CM) have been administered safely in millions of people worldwide [1], and constituted a crucial tool that is frequently used for imaging procedures carried out during diagnostic clinical practice. The first iodinated CM to be used for the purpose of diagnostic imaging was sodium iodide (1920), subsequent to which Sodium and Meglumine salts of tri-iodinated benzoic acid derivatives were developed in the 1950s. These CM were hyperosmolar (>1400 mOsm/kg), with an osmolality five to eight times that of blood [2]. Since then, low osmolality (600 -850 mOsm/kg), non-ionic CM agents have been developed and Iopromide is one such example. The safety and tolerability of this agent has already been evaluated in previous post-marketing surveillance studies carried out on Western as well as Asian populations [3]. Currently, several different CM are available and while the use of iodinated CM has proved relatively safe [4] [11]. While their safety profiles have already been established as part of routine clinical trials that preceded their marketing and commercialization; extensive post marketing surveillance on a large number of patients is required in order to identify and determine the frequency of all extremely rare adverse drug reactions that may occur. To our knowledge, such a non-interventional study that seeks to quantify the rate of ADR and AE occurrence due to Iopromide use in an unselected Chinese population has not been conducted so far. The patient population analysed in this manuscript was recruited during the execution of a large, international, multi-centre, post marketing surveillance carried out in order to assess the safety and tolerability of Iopromide in various populations. The majority (44.6%) of patients who enrolled were from centres in China, and this study focuses on the detailed analysis of data from these Chinese patients in order to determine the safety and tolerability of Iopromide based on patient parameters such as pre-existing risk factors and use of pre-medication.
Additionally, a subjective analysis of diagnostic image quality based on the investigators' evaluation has also been included in our analyses.

Study Design and Conduct
The rationale, design and conduct of the study from which data were collected and analyzed has previously been reported in detail [12]. Briefly, Data analysed in this manuscript were obtained during the conduct of a prospective, phase IV post-marketing surveillance study [IoproMide (UltrAvist ® )-to Gain further information on tolerability and safety in X-ray Examination (IMAGE) study] (ClinicalTrials.gov identifier: NCT00876083) conducted in 21 countries in Europe and Asia and sponsored by Bayer HealthCare Pharmaceuticals, Berlin, Germany. Patients undergoing an X-ray or computed tomography (CT) examination, for which the investigator had elected to use Iopromide, were eligible. The 44,835 patients who comprised the overall patient population, a majority, i.e., 20,000 (44.6%) were from China, with 56 centres in China participating in the study. Iopromide was administered in a routine manner, based on investigator discretion and procedure requirements and in accordance with recommendations in the local package insert.

Ethical Approval
This study was non-interventional and was conducted in a routine clinical setting in accordance with local and international legal and ethical requirements, which did not necessitate the provision of written informed consent from Chinese subjects.

Observational Plan
Investigators used case report forms (CRF) to capture demographic data, patient clinical history (including risk factors), drug administration, type of examination, contrast quality and tolerability, as previously described [12]. Briefly, CRFs recorded patient parameters such as demographics, concomitant diseases, pre-and concomitant medications, examination region, indication, contrast medium volume, type of application and examination, contrast quality, and adverse events. Paper CRFs were converted to electronic CRFs using a double data entry process and validated electronic edit checks were performed on all CRFs. In case any queries arose regarding the information recorder in the CRFs, they were redirected to the investigator wherever necessary. Investigators assessed image quality according to five qualitative categories: excellent, good, adequate, nondiagnostic and not specified.

Iopromide Administration
Patients requiring administration of iopromide for an imaging procedure were considered eligible for inclusion. The administration of Iopromide and any premedication was at the discretion of the investigator, providing it was in ac-cordance with the local package insert. Two formulations of iopromide were compared in this study, Ultravist ® -300 [1 mL contains 623 mg of iopromide (equivalent to 300 mg iodine)] and Ultravist ® -370 [1 mL contains 769 mg of iopromide (equivalent to 370 mg iodine)].

Adverse Events and Adverse Drug Reactions
Investigator-observed adverse events (AEs) and pre-specified ADRs of interest that occurred within the observation period (30 -60 min according to the local packaging information) were recorded in a separate questionnaire, and as free text, in terms of symptoms, onset, duration, intensity, and causal relationship (see [12] for further details). The intensity of each event was classified by investigators as mild, moderate, or severe (In line with the recommendations of the ACR Manual on Contrast media [20]). Mild symptoms included scattered urticaria, pruritus, rhinorrhea, nausea, brief retching, and/or vomiting, diaphoresis, coughing and dizziness. Moderate symptoms included persistent vomiting, diffused urticaria, headache, facial edema, laryngeal edema, mild bronchospasms or dyspnea, palpitations, tachycardia or bradycardia, hypertension and abdominal cramps. Severe symptoms included life-threatening arrhythmias (i.e., ventricular tachycardia), hypotension, overt bronchospasm, laryngeal oedema, pulmonary oedema, seizures and syncope. In addition, events were designated as serious if they met one of the following criteria: resulted in death; were life-threatening; required inpatient hospitalization/prolongation of current hospitalization; resulted in persistent or significant disability/incapacity; or resulted in a congenital anomaly/birth defect. ADRs of special interest included injection site warmth and/or feeling hot, nausea and/or vomiting, urticaria, erythema, rash and/or papular rash, cough and/or sneezing, dyspnea and/or bronchospasm, and changes in blood pressure (increase and/or decrease). ADRs were compared between all patients and at-risk patients (those with history of bronchial asthma, allergies, and/or contrast media reaction). Injection site warmth, feeling hot or injection site pain of mild intensity were defined (post-hoc) as tolerance indicators. No laboratory tests were required.
Patients were also asked to complete questionnaires to record AEs. Special attention was paid to ADRs among patients with risk factors for idiosyncratic CM reactions, specifically asthma, allergy and/or prior history of the occurrence of such reactions (at-risk group).

Statistical Analysis
Results are reported for all evaluable patients in the Chinese population, i.e. eligible patients with documented evidence of receiving iopromide. Qualitative descriptive statistical analyses were conducted.

Results
Patient demographics and clinical characteristics of the Chinese subpopulation included in this study are presented in Table 1. The majority of patients were male (61.3%) and the mean age was 54 years. Approximately half the patient population (n = 9042, 45.2%) had at least one concomitant disease, most commonly a reduced general condition (17.4%), hypertension (7.9%) and coronary heart disease (7.1%). Risk factors for idiosyncratic CM reactions were reported for 153 patients (0.77% of the total; constituting the at-risk group). Premedication was recorded in 5658 patients overall (28.3%), including over half (n = 86, 56.2%) of the at-risk group ( Figure 1). As premedication, corticosteroids were the most frequently prescribed drugs (84.4% and 89.5% of all patients and the at-risk group received premedication, respectively).

Radiological Examinations and Iopromide Administration
There were a total of 20,000 radiological examinations in which Iopromide was used as a CM agent in the Chinese population included in this study. Iopromide was administered via intravenous injection in 19,935 patients (99.7%) and via intra-arterial injection in the remainder (n = 65, 0.33%). The most frequent examination was multi-slice computerized tomography (99.5%). The most frequent means of administration was automatic injection (99.7%). The mean [± standard deviation (SD)] dose of iodine administered was 29 ± 5.5 g and the median flow rate was 3 mL/s. Ultravist ® -300 was the most commonly used formulation of iopromide (Table 2).

Adverse Drug Reactions
ADR findings were similar to the overall AE profile, since only 14 of the 672 reported events were found to be unrelated to the administration of Iopromide. The overall incidence of ADRs was 2.9% (571 patients), the most frequent reac- tions being nausea, dysgeusia and feeling hot. More patients receiving Ultravist ® -300 experienced ADRs compared with those receiving Ultravist ® -370 (3.4% and 1.9%, respectively). The majority of ADRs were of mild (n = 525) or moderate (n = 43) intensity and resolved without sequelae, and there were no clinically relevant sex or age-related trends (data not shown). Three ADRs were of severe intensity. Excluding tolerance indicators such as any occurrence of injection site warmth, feeling hot or injection site pain, (of mild intensity only), the overall incidence of ADRs was 2.4% (469 patients) and the corresponding value in the at-risk sub-group was 8.5% (13 patients; Figure 2). Two serious ADRs were reported following the administration of Ultravist ® -300 [oedema (n = 1) and decreased blood pressure and dyspnea (n = 1)]. Findings for ADRs of special interest are summarised in Table 4. 119 patients (0.60%) reported injection site warmth/and or feeling hot, including one patient in the at-risk group (0.65%). Nausea and/or vomiting were reported in 200 patients from the overall population and in 4 at-risk patients (1.0% and 2.6%, respectively), and urticaria, erythema, rash and/or papular rash were reported in 94 and 4 patients, respectively (0.47% and 2.6%). Further analysis showed that at-risk patients who received premedication had a lower incidence of ADRs versus at-risk patients who received Iopromide alone (Table 5).

Secondary Outcome Measures: Contrast Quality
Overall, contrast quality was considered by investigators to be "good" (64.7%) or "excellent" (29.3%) in the majority of patients. Contrast quality was comparable for the two Ultravist ® formulations used, with 27.9% and 32.0% as "excellent" for Ultravist ® -300 and Ultravist ® -370 66.4% and 61.5% of investigators rating it as "good" respectively. Approximately 5% of examinations were reported as "adequate". Images were non-diagnostic for only one patient (of 20,000).

Discussion
To our knowledge, this is the first analysis of the safety and diagnostic image quality of the non-ionic, iodinated CM-Iopromide-in a routine clinical setting in a large group of Chinese patients. Indeed, we found that the safety profile of Iopromide was excellent in this population, with only very few patients experiencing ADRs that were typically transient and of mild intensity. The incidence of injection site pain and/or warmth was also low, indicating a good tolerability profile as well. Overall, our findings are consistent with earlier reports of favourable safety and tolerability profile of Iopromide in Western populations [3] [13] [14]. Our results are also in agreement with the results from a previous large-scale post-marketing surveillance study that included Asian patients and which concluded that the safety of Iopromide in routine clinical practice was comparable with the published safety profiles of other non-ionic, iodinated contrast agents [3]. In addition, a large-scale comparative study concluded that the use of non-ionic CM significantly reduced the incidence of ADRs when compared to ionic CM, including those categorised as severe and potentially lifethreatening [4]. Moreover, in the present study, the contrast quality of Iopromide was considered to be "excellent" or "good" by investigators in the majority of patients, and this was comparable for the two Ultravist ® formulations investigated. Allergy, asthma and a history of CM reactions are risk factors for idiosyncratic reactions to Iopromide, and 153 of the 20,000 Chinese patients (0.77%) were considered to be at risk of such reactions. The incidence of ADRs (excluding tolerance indicators) in this sub-group was higher compared with the total patient population, but such results were not entirely unexpected. Indeed, patients with asthma, previous reactions to CM, a history of allergy, pre-existing illness (diabetes mellitus, renal or cardiac impairment, myelomatosis and sickle-cell anemia), and children are generally at increased risk of developing ADRs [ [16]. These differences may be attributed to a higher proportion of at-risk patients experiencing allergy-like gastrointestinal (nausea/vomiting), cutaneous (erythema, urticaria, rash) or respiratory (coughing, sneezing) reactions. Moreover, nausea and vomiting could also be anxiety-related [17]. Additionally, there may be a genetic component, given that Asian patients (mainly of Japanese heritage) are more likely to experience delayed skin reactions after administration of non-ionic iodinated CM [18] [19].
The American College of Radiology's Manual of Contrast media recommends that corticosteroids should comprise an essential component of the premedication protocol in at-risk patients [20]. Notably, in our study, the incidence of ADRs of special interest showed a favourable reduction with premedication (most frequently corticosteroids) in at-risk patients. This finding is in contrast to what was previously reported for Western and Asian populations in the post marketing surveillance study conducted by Kopp et al., where the use of pre-medication did not have a favourable impact on the incidence of ADRs in the at-risk population. In our analyses, the benefits of premedication were most pronounced in terms of a reduction in the incidence of sneezing, pruritus, urticaria and rash. However, "breakthrough" ADRs still occurred in some patients, and this finding is consistent with previous studies [21]. While a controversy remains regarding the use of premedication for patients at high risk of an ADR [1] [9], the present study appears to support the recommendation to use appropriate premedication in Chinese patients at risk of such reactions.
Study strengths include the population size and the fact that the study conduct mirrored routine clinical practice, with the inclusion of patients at risk of idiosyncratic CM reactions. However, the non-interventional design is a possible limitation; as such studies tend to detect a lower incidence of ADRs compared with randomized controlled trials. There could also be other sources of bias along with a lack of cardiac and renal monitoring that have not been accounted for during the analysis.

Conclusion
Iopromide, when given according to the prescribing information, is well tolerated among Chinese patients undergoing computed tomography and other diagnostic imaging procedures that require the use of contrast agents. Data from this study supports its efficiency in 20,000 Chinese patients and confirms the very low risk of ADR occurrence associated with the use of Iopromide.
tion, the quality control tests for image quality parameters carried out at the two centers were performed by using the Chat Phan phantom and all the tests were within the acceptable limits, according to Sudan Atomic Energy Commission (SAEC) Standardizations. The study concludes with a number of recommendations, such as; the necessity for an extensive collaboration among manufacturers, radiologists, technologists and physicists to find a plan to decrease patient radiation dose (ALARA Principle) from computed tomography scanner.

Keywords
CT, Image Quality, Patient Dose

Introduction
X-ray-computed tomography (CT) has rapidly evolved in terms of both technical performance and clinical use. It has become one of the most important of all x-ray procedures worldwide [1]. The CT technique has been introduced into many medical applications and it is accepted as a useful method in diagnostic imaging owing to the fact that it provides three-dimensional image reconstructions with low contrast detectability, fast volume coverage, easy hardware implementation and considerable spatial resolution [2] [3] [4] [5].
The components of CT image quality are noise, slice thickness (Z-axis resolution), low contrast resolution and high contrast resolution. While image quality has always been a concern for the physics community, clinically-relevant image quality has become important to get clear diagnostic findings for early detection of serious diseases. Image quality can be defined in terms of image noise, which limits low contrast resolution, and spatial resolution.
To optimize image quality, patient dose and relevant issues such as CT dosimetry should not be ignored as obtaining high quality images is always associated with high patient doses.
In Sudan, as far as the authors' knowledge, few studies regarding CT image quality and patient doses have been published locally and worldwide. This study, therefore, would have a good contribution to the existing literature.
The main purpose of this study is to assess image quality parameters and patient dose parameters, in order to optimize imaging procedure.
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Materials and Methods
This prospective, analytical and experimental study deals with diagnostic parameters of the computed tomography scan to evaluate the image quality in CT images. The study was carried out in Sudan at Khrtoum State in the CT departments of Antalya medical center, Elnileen diagnostic center and Al Amal diagnostic center. The data was collected from June 2014 to Augest 2016. A special data collection sheet was designed by the authors after was approved by the research ethics committee at each center. The inclusion criteria of the study variables that were measured are, the diagnostic parameters (kVp, mAs, slice thickness and pitch), and the radiation dose [CT dose indices volume (CTDIvol) and dose length product (DLP) and image noise (SD)]. The authors concentrated on image noise as a image quality parameter because it is a key parameter in assessing CT image quality according to previous studies [ [20].
Before data collection, extensive quality control (QC) tests were performed in all the CT departments in our study. The QC tests used both Catphan 600 and-Catphan 500/600 (The Phantom Laboratory, Salem NY, USA) phantoms. Catphan 500/600 is a CT quality assurance phantom suitable to test low contrast detectability, spatial resolution, noise, slice thickness and homogeneity. It is specially designed to evaluate image quality for CT. Different tests can be performed, evaluating the homogeneity, the noise level, the modulation transfer function and the visibility of low contrast details (Laboratory 2006). The evaluation method of interest in this study was measuring the noise level along with routine quality control tests performed by local quality control (QC) committee, the QC tests for this study was carried out by Sudan Atomic Energy Commission (SAEC) and all departments have successfully passed the extensive tests.
The CTDI vol and DLP based on the manufacturer's data were used for estimation the radiation dose in axial images of the rando-phantom.
The corresponding CTDI vol and DLP of each acquisition condition indicated on the monitor screen were recorded. The CTDI vol and DLP obtained by the standard protocol were compared with that obtained by other protocols.
In order to perform the experiments with doses and noise levels representative of routine phantom values, thirteen clinical data of normal liver examinations performed by the same CT department and scanning parameters were recorded. The radiation dose and the level of the noise were chosen as they are the most important quality parameters and have a direct effect on the quality of the image.
Seven additional abnormal examinations including liver metastases (hyper vascular) were performed. For each patient, one region of interest (ROI) was chosen from one liver metastasis and another ROI from a homogeneous normal area adjacent to the liver. The mean CT number and SD then recorded to calculate contrast to noise ratio (CNR) as follows: CNR = (CTL − CTM)/SDM, where CTL is the mean CT number of the normal liver and CTM is the mean CT number of the metastasis and SDM is the SD of the metastasis liver.
So the contrast-to-noise ratio was defined as the difference between the mean CT attenuation values of the right lobe of the liver and the background references divided by image noise [9].
The statistical analysis was performed using the software statistical package for the social science (SPSS) version 18.0. The relationship between SD and tube current-time product settings and the relationship between CNR and CTDI vol were investigated using the linear regression analysis and Pearson correlation coefficient (r). To optimize the technical factors (kVp, mAs, ST and pitch) as a function of CTDI vol and SD, tagutchi setting was used.

Results
The results show in Table 1 and Table 2

Discussion
The low contrast detectability is dependent on how much noise is present in the image. One way of quantifying the contrast in an image is to determine the contrast-to-noise ratio, which provides a value describing the quality of an image. In this study, the noise was determined by measuring noise at Region of interest ROIs at the centers and peripheries, as shown in table one for slices less and more than 5 mm (Table 1). This is considered to be acceptable according to SAEC standardizations that were obtained from the international atomic energy agency IAEA.
Two diagnostic parameters were evaluated to obtain a minimum image noise or an optimal radiation dose. The best minimum image noise was obtained by having a slice thickness of 5 mm and kV p of 120 at Antalya center (GE scanner) ( Table 2). However, at Elnileen diagnostic center (Siemens scanner) the minimum image noise was obtained by having a slice thickness of 10 mm and kV p of 130 at Antalya center (GE scanner). The different values are due to differences in multi detector scanner types between the two centers. In addition, at Antalya center, the optimum CTDIvol (9.76 mGy) was obtained with 120 kV p and slice thicknesses of 5 mm. At Elnileen diagnostic center, however, the optimum CTDI vol (3.17 mGy) was obtained with 110 kV p and slice thicknesses of 8 mm. Finally (Figure 1 and Figure 2), at Antalya medical center, the optimum dose length product DLP (88 mGy•cm) was obtained when 120 kV p was used with 5 mm slice thickness. However, at Elnileen Diagnostic center, the optimum DLP (67 mGy•cm) was obtained with 110 kV p and 8 mm slice thickness.
Other adjustment factors were (pitch & kilo voltage). At Antalya Medical center, the minimum image noise was obtained by using the pitch of 1.3 with 120 kV p , However, at Elnileen diagnostic center, 130 kV p and pitch of 2 provided the minimum image noise.
Moreover, at Antalya medical center, the optimum CTDI vol (10.45 mGy) was obtained with 120 kV p and pitch of 1.3. However, at Elnileen diagnostic center, 110 kV p and pitch of 1.5 provided the optimal CTDI vol (3.66 mGy). Finally, the optimal DLP (88 mGy•cm) at Antalya medical center (Figure 8 and Figure 9), was obtained with 120 kV p and pitch of 1.3). At Elnileen diagnostic center, however, 110 kVp and pitch of 1.5 were used to obtain the optimal DLP (69 mGy•cm).
The relationship between tube current-time product (mAs), tube kilo voltage (kVp) and image noise (SD) were evaluated. It showed that a reduction in mAs and kV p increases the image noise. This is consistent with studies done by Seung-Wan 2010 and Reid et al 2010; they found that doses increased linearly with an increase in mAs and by the power function of kV p for increases in kV p . They also found that the image noise decreases as a function of kV p and mAs and increases as a function of the phantom diameter.
Also the relation between slice thickness (ST) (Figure 7 and Figure 8), pitch (P) and image noise showed that as pitch increases (Figures 3-5), the image noise decreases, and approximately inversely nonlinear relationship between slice thickness and image noise, i.e. increasing slice thickness decreases the image noise. For some manufacturers of multi detector scanners, the slice thickness is independent of the table speed based on the interpolation algorithm used. This is in line with a study done by Brochure. 2001 who showed that an increase in slice thickness leads to an improvement in the noise level and a reduction in the spatial resolution. He also found that decreasing the pitch decreases the duration of the patient exposure to radiation, and hence the patient dose per slice and image noise increase. This agrees with previous studies done by Yu

Recommendations
This study recommends the following: First of all, further studies are required to optimize protocols in different CT examination in multi-detector CT. Secondly, further studies are required to look at the effect of the patient age (pediatric and adult). Finally, developing a CT training program in quality assurance program, targeted for technologists, radiologist, physicists and CT scanner manufacturer. It is necessary for manufacturers, radiologists, technologists and physicists to work side by side to find a plan to decrease patient radiation dose (ALARA Principle) from CT scanner.