Detection of Regional Wall Motion Abnormalities in Compressed Sensing Cardiac Cine Imaging

Background: Recently faster cardiac magnetic resonance (CMR) cine sequences basing on k-t compressed sensing have been developed. Purpose: To compare two compressed sensing CMR sequences-one in breath-hold technique and one during free breathing—with the standard SSFP sequence with respect to regional left ventricular function assessment. Material and Methods: Left ventricular short-axis stacks of two compressed sensing sequences in breath-hold technique (sparse_HB) and during free breathing (sparse_FB; both spatial resolution, 1.8 × 1.8 × 8 mm) and a standard SSFP cine sequence (spatial resolution, 1.9 × 1.9 × 8 mm) were acquired in 50 patients on a 1.5 T MR system. Regional wall motion abnormalities (RWMA) were rated qualitatively (normal/hypo-/a-/dyskinesia) by two experienced readers in consensus for all cardiac segments (American Heart Association’s segment model) and sequences. RWMA detection rates were compared between sequences by kappa statistic. Results: In 13 patients, RWMA were detected in at least one cardiac segment. The RWMA detection rates were similar between CMR sequences (hypokinesia, 7.2% to 7.9%; akinesia, 0.8% to 1.3%; dyskinesia 0.3% to 0.4%) and kappa statistics revealed an almost perfect agreement in RWMA detection between both sparse and the standard SSFP sequence (standard versus sparse_HB: kappa, 0.918, p value, <0.001; standard versus sparse_FB: kappa, 0.868, p value, <0.001). Conclusion: Compressed sensing cine CMR acquired during breath-hold or free-breathing allows reliable RWMA detection, thus, might alternatively be used in cine CMR for regional left ventricular function assessment. How to cite this paper: Goebel, J., Nensa, F., Schemuth, H., Maderwald, S., Quick, H.H., Schlosser, T. and Nassenstein, K. (2018) Detection of Regional Wall Motion Abnormalities in Compressed Sensing Cardiac Cine Imaging. World Journal of Cardiovascular Diseases, 8, 277-287. https://doi.org/10.4236/wjcd.2018.86027 Received: April 20, 2018 Accepted: June 9, 2018 Published: June 12, 2018 Copyright © 2018 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
Cardiac magnetic resonance imaging (CMR) is an established imaging tool in the diagnostic workup of patients with suspected heart disease and plays an important role in risk stratification (e.g. in coronary artery disease or myocarditis) and non-invasive therapy monitoring [1] [2] [3].Due to continuous technical progress in CMR sequence design, hopefully the time consuming acquisition of standard breath-hold steady-state free precession (SSFP) cine sequences might be replaced by faster alternatives, which allow either a significant reduction in breath-hold times or even image acquisition during free breathing, which would be extremely helpful in patients with limited breath-hold capability.In this context, the recently developed k-t compressed sensing sequence technique with parallel imaging and iterative reconstruction seems very promising [4] [5] [6] [7].Provided that special conditions regarding image properties, aliasing artifacts, and image reconstruction are fulfilled, this technique allows a considerable acceleration of CMR data acquisition due to noticeable k-space under sampling [4] [5].Until now, several slightly different SSFP sequences basing on this new technical approach have been evaluated by different groups with the main focus on global left ventricular (LV) function [8]- [13].Regarding global LV function, the overall consensus of these studies was that compressed sensing cine SSFP sequences are as reliable as conventional cine SSFP imaging.Despite the fact that regional wall motion abnormality (RWMA) detection is also of high clinical relevance in many settings (e.g.assessment of ischemic heart disease, high-dose dobutamine stress CMR, where an ischemia is defined as a stress-induced new or aggravated RWMA [14] [15] [16] [17] [18]), only limited data exists concerning regional wall motion assessment by compressed sensing cine imaging.
Thus, the aim of the present study was to compare two different compressed sensing CMR sequences-one acquired in breath-hold technique, with reduced breath-hold times and one during free breathing-with the current standard SSFP sequence with the focus on regional left ventricular function assessment.

Material and Methods
Prospective analysis and use of data was approved by the local ethic committee.
All included patients gave written informed consent for CMR examination and study participation.

Assessment of Regional Wall Motion Abnormalities and Left Ventricular Volumetry
Analysis for RWMA was performed in consensus by two experienced readers (CMR experience > 12 years and >6 years).Presence and severity of RWMA were evaluated visually and graded as "normal", "hypokinesia", "akinesia", or "dyskinesia" in all CMR sequences and in all cardiac segments, except for segment 17 (in accordance to the American Heart Association's segmental model) [14] [19].Thus, a total of 800 cardiac segments in each CMR sequence were analyzed (50 patients with 16 analyzed cardiac segments each).
Left ventricular volumetry was performed in all patients and CMR sequences by one reader (CMR experience > 6 years) using the Argus software (Siemens Healthcare, Erlangen, Germany; employed standard values based upon [20]).
Because excellent inter-rater agreement for left ventricular volumes has been repeatedly reported for segmented compressed sensing cine SSFP sequences in breath-hold technique and during free breathing, we waived this subanalysis [10] [11] [13].The papillary muscles and trabecullae were attributed to the ventricular cavity, and the most basal short-axis slice to be included into volumetry was defined by having at least 270˚ of the chamber circumference surrounded by visible myocardium [21] [22].ferences in RWMA detection between the three employed CMR sequences kappa statistic was performed and interpreted as proposed by Landis and Koch [23].

Statistical Analysis
Comparison of volumetric data between the CMR sequences was done by Wilcox on test, and inter-rater agreement was assessed by Bland-Altman analysis.A p value less than 0.05 was considered statistically significant.

Left Ventricular Volumetry
Left ventricular volumetric values of all three CMR sequences are presented in Table 2. Comparing standard SSFP and sparse_HB, small, but significant median Table 1.Detection rates of regional wall motion abnormalities given in absolute numbers and percent values (in brackets) for the three CMR sequences.Figure 1.Midventricular short-axis slices in end-diastole and -systole in a 14-year-old male with history of anthracycline-based chemotherapy for acute lymphatic leukemia reveal an unimpaired global and regional left ventricular function: in all three employed CMR sequences excellent imaging details and blood-myocardium contrast can be seen (standard SSFP sequence; compressed sensing sequence in breath-hold technique (sparse_HB); compressed sensing sequence during free breathing (sparse_FB)).
Figure 2. Short-axis slices of a 65-year-old woman with history of transmural myocardial infarction: in all three CMR sequences (standard SSFP; sparse in breath-hold (sparse_HB); sparse during free breathing (sparse_FB)) an anteroseptal and anterior akinesia is clearly detectable.
differences were found for EDV (difference of median, 8 ml; p value < 0.001), SV (difference of median, 8 ml; p value < 0.001), and EF (difference of median, 1%; p value, 0.016), but not for ESV (p value, 0.198).Comparing standard SSFP and sparse_FB, small, but significant median differences were found for ESV (difference of median, 4 ml; p value < 0.001), SV (difference of median, 4ml; p value, 0.004), and EF (difference of median, 2%; p value< 0.001), but not for EDV (p value, 0.817).These findings were confirmed by the Bland-Altman analysis (Table 3, Figure 3), where an overall good agreement in volumetric values between the standard SSFP sequence and both sparse sequences was found.

Discussion
In this study we could demonstrate for the first time that not only our compressed sensing CMR sequence acquired in breath-hold technique, but also our compressed sensing CMR sequence during free breathing allowed reliable regional left ventricular function assessment.This result is in line with the findings J. Regarding the global left ventricular function, only small, not relevant differences in left ventricular values were found between the standard SSFP sequence and both compressed sensing CMR sequences.For the sparse_HB sequence slightly lower EDV, SV, and EF values were found which might be caused by an insufficient capture of the end-diastole [10].For the sparse_FB sequences lightly higher ESV and consecutively lower EF values were found.But overall a sufficient agreement between the standard SSFP sequence and both sparse sequences was found which is in accordance to recently published studies where a sufficient to excellent agreement between the investigated sparse and reference se-World Journal of Cardiovascular Diseases quences were reported [10] [12] [13].
Our study is not without limitations.First, we analyzed the RWMA exclusively visually.Although this is common practice, accuracy might benefit from a quantitative RWMA analysis.Second, only a limited number of patients/cardiac segments with RWMA were included, which was due to our unselected patient cohort.

Conclusion
In conclusion, compressed sensing cine imaging of the left ventricle acquired either during breath-hold or during free breathing allows the reliable detection of regional wall motion abnormalities.Thus, these fast cine sequences can alternatively be used for the assessment of LV function.

Figure 3 .
Figure 3. Bland-Altman plots demonstrate a good agreement between the volumetric values derived from the standard SSFP sequence and both sparse sequences.

Table 2 .
Volumetric values (presented as median and interquartile range (in brackets)) of all 50 investigated patients comparing the three CMR sequences.

Table 3 .
Results of the Bland-Altman analysis comparing the volumetric values of the standard SSFP sequence with both sparse sequences.
[7]Allen et al. who compared an iteratively reconstructed k-t under sampled breath-hold SENSE cine sequence with a conventional breath-hold SSFP cine sequence based on GRAPPA (acceleration factor, 2) with respect to RWMA detection in 20 patients and in 9 healthy volunteers[7].They rated the RWMA qu-Based on our results, we totally agree with Lin et al. and believe that the faster compressed sensing CMR sequences, which were proven to reliable detect RWMA, have the potential to replace standard cine SSFP imaging in clinical routine for the assessment of regional and global LV function.Moreover, Goebel et al.DOI: 10.4236/wjcd.2018.86027283 World Journal of Cardiovascular Diseases