This communication presents a new method of detecting the behaviour pattern in Sprague-Dawley (SD) rats based on the measurement of the dielectric properties of blood plasma at microwave frequencies at different periods of time. The microwave measurements were performed by rectangular cavity perturbation method in the S-band of microwave frequency with the blood plasma collected from normal rats (Controls) as well as chemically induced rats (A β). A change is observed in the dielectric properties of the A β samples but not the controls samples at the extended period of time. This measurement technique is simple and the collection of blood from the rats is nonsurgical in nature. These results prove a new method of diagnosing Alzheimer’s Disease (AD) using microwave techniques.
Alzheimer’s Disease, (AD) is the most common form of dementia with no cure at the moment. It worsens as it progresses, and eventually leads to death. The concept of senile dementia has evolved from a rather vague notion that mental decline occurred inevitably in old age, to become defined today by a distinct set of clinical and pathological features with the potential for treatment and prevention within grasp [
The microwave technology is often used in various diagnostic and therapeutic applications in medicine [
The study was conducted on Sprague-Dawley (SD) rats, weighing between 300 - 350 g (8/9 weeks of age). The animals were randomly divided into 4 groups upon arrival and housed with two animals/cage under standard lighting conditions of 12 hour light/dark cycles of protocol [
Pre-lesion behavioral trials were conducted using Morris Water Maze (MWM) in the temperature range 23˚C - 30˚C and in order to assess the learning capacities of the animals from day 1 to 3. On day 5, each animal was given atropine (0.1 mg/kg, i.p.) and subsequently anaesthetized using sodium pentobarbital (60 mg/kg, i.p.). After full anaesthesia (the absence of hind paw reflex), the animals stereotaxically received an intra-cerebral injection of 10 µl (5 µl/per site bilateral lesions) of Amyloid β-protein (Aβ42 dissolved in Tris buffer solution of 0.15 M to reach a concentration of 10 µg) directly into the CA1 region of the left and right dorsal hippocampi. The animals were given a 2 days recovery period following intra-cerebral injections. The animals then repeated the behavioral in the same MWM to assess any impairment in the recall ability caused by the neurotoxin. The animals were sacrificed 3, 7, 10 and 14 days following intra-cerebral injections by Halothane overdose. Blood was collected by cardiac puncture into heparin blood tubes, centrifuged at 3500 rpm for 10 minutes, and plasma was collected in eppendorfs, snap frozen by liquid nitrogen and stored at −80˚C. The blood plasma was then filled into capillary bulb for microwave measurements.
The experimental set-up consists of a transmission type S-band rectangular cavity resonator, Rohde & Schwarz ZVL network analyser. The cavity resonator is a transmission line with one or both ends closed. The numbers of resonant frequencies are determined by the length of the resonator. The resonator in this set-up is excited in the TE10ρ mode. The sample holder which is made of glass in the form of a capillary tube flared to a disk shaped bulb at the bottom is placed into the cavity through the non-radiating cavity slot, at broader side of the cavity which can facilitate the easy movement of the holder. The resonant frequency fo and the corresponding quality factor Qo of the cavity at each resonant peak with the empty sample holder placed at the maximum electric field are noted. The same holder filled with known amount of sample under study is again introduced into the cavity resonator through the non-radiating slot. The resonant frequencies of the sample loaded cavity is selected and the position of the sample is adjusted for maximum perturbation (i.e. maximum shift of resonant frequency with minimum amplitude for the peak). The new resonant frequency fs and the quality factor Qs are noted. The same procedure is repeated for other resonant frequencies. The measurement are made from 2 GHz to 4 GHz of S-band in microwave region [
When a material is introduced into a resonant cavity, the cavity field distribution and resonant frequency are changed which depend on shape, electromagnetic properties and its position in the fields of the cavity. Dielectric material interacts only with electric field in the cavity.
According to the theory of cavity perturbation, the complex frequency shift is related as [
− d Ω Ω ≈ ( ε r ¯ − 1 ) ∫ V s E ⋅ E 0 * d V 2 ∫ V c | E 0 | 2 d V (1)
But
d Ω Ω ≈ d ω ω + j 2 [ 1 Q s − 1 Q 0 ] (2)
Equating (1) and (2) and separating real and imaginary parts results
ε ′ r − 1 = f o − f s 2 f s ( V c V s ) (3)
ε ″ r = V c 4 V s ( Q o − Q s Q o Q s ) (4)
Here, ε r ¯ = ε ′ r − j ε ″ r , ε r ¯ is the relative complex permittivity of the sample, ε ′ r is the real part of the relative complex permittivity, which is known as dielectric constant. ε ″ r is the imaginary part of the relative complex permittivity associated with the dielectric loss of the material. Vs and Vc are corresponding volumes of the sample and the cavity resonator. The conductivity can be related to the imaginary part of the complex dielectric constant as
σ e = ω ε ″ = 2 π f ε 0 ε ″ r (5)
The microwave experiment in blood plasma was done using cavity perturbation technique collected from normal rats (Controls) as well as chemically induced rats (Aβ samples) and the results are shown in Figures 1-16. The Figures 1-4 shows the dielectric values and the corresponding Figures 9-12 shows the average values of the dielectric constant. From Figures 1-3 it is noticed that the controls as well as Aβ samples exhibit similar ranges of dielectric constant. This shows that dielectric constant of controls and Aβ samples from day 3, day 7 and day 10 have almost same values. This is quite evident from the average value
results dielectric constants shown in the Figures 9-11. From
microwave (ISM band), controls and Aβ samples of blood plasma of Sprague-Dawley rats were studied and exhibit distinct variation of dielectric constant and conductivity after 14 days.
The microwave characterization has been performed in the blood plasma obtained from normal rats (Controls) as well as chemically induced rats (Aβ samples) using the cavity perturbation technique. The cavity perturbation technique is quick, simple, and accurate and it requires very low volume of sample for measuring the dielectric properties of samples like blood plasma. It is observed that a substantial change in the dielectric properties of Aβ samples occurs on day 14. This measurement technique as well as the extraction of blood samples from Sprague-Dawley rats is simple. These results prove a new method of diagnosing Alzheimer’s Disease using microwave techniques.
This work done by Anil Lonappan is the part of his Doctoral studies in Electronic Engineering at the School of Electrical Electronic and Computer Engineering, University of KwaZulu Natal. The work done by Ernest Remy Hervé Ebell’a Dallé is the part of his Honours degree in human physiology at the School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal.
Lonappan, A., Dallé, E.R.H.E., Afullo, T.J.O. and Daniels, W.M.U. (2017) Analysis of Behaviour Pattern in Sprague-Dawley Rats Using Microwave Techniques. Journal of Electromagnetic Analysis and Applications, 9, 155-166. https://doi.org/10.4236/jemaa.2017.911014