Assessment the Optimal Effect of Time of Repetition: Extrinsic Pulse Parameter on Gd-DTPA Enhanced, Spin-Echo T1-Weighted MR Images under Low Magnetic Field Strength

The contrast agent concentration, the time of repetition (TR) and magnetic field strength are significant parameters that influence for the accurate signal intensity (SI) in quantitative Magnetic Resonance Imaging (MRI). Therefore, this study was conducted to investigate and refine the dependence and the optimal effect of Time of Repetition (TR) on the relationship between signal intensity and Gd-DTPA (Gadolinium-diethylene-triaminepenta-acetic acid) concentration, after applying two-dimensional (2D) Spin Echo (SE) pulse sequence under low-field MRI. In addition to that, the optimal concentration of Gd-DTPA at given sequence parameters at low-field MRI was also evaluated. A water-filled phantom was constructed for a range of Gd-DTPA concentrations (0 - 6 mmol/L) and the mean signal intensities (SIs) were assessed in the defined region of interest on T1-weighted images with different TR values (40 - 2000 ms). The generated signal-concentration curves for Gd-DTPA revealed that increasing TR was associated with the increase of the overall SIs and the maximum relationship between SI to concentration. Moreover, the required Gd-DTPA concentration to produce the maximum SI was associated to decrease with the increase of TR. In addition to this, the application of beyond 100 ms TR values in this study with relatively higher concentrations (beyond 1 - 2 mmol/L) has resulted predominantly non-linear patterns in the signal-concentration curves and it appears the saturation or decay of the SIs due to T2 effect. From these results, it can be suggested that the selection of relatively lower Gd-DTPA concentration ( mmol/L) with less than 800 ms (<800 ms) TR values can produce a better linear relationship between the concertation and SIs in T1-weighted SE low field contrast-enhanced MRI. Furthermore, this study also outlined the significance and necessity of the optimization of TR in SE sequence in low field MRI prior to a particular examination.

Correlation between magnetic resonance T2 image signal intensity ratio and cell apoptosis in a rabbit spinal cord cervical myelopathy model

Background Cervical spondylotic myelopathy （CSM） is a common cause of disability in elderly patients.Previous studies have shown that spinal cord cell apoptosis due to spinal cord compression plays an important role in the pathology of myelopathy.Although changes in magnetic resonance imaging （MRI） T2 signal intensity ratio （SIR） are considered to be an indicator of CSM,little information is published supporting the correlation between changes in MRI signal and pathological changes.This study aims to testify the correlation between MRI T2 SIR changes and cell apoptosis using a CSM animal model.Methods Forty-eight rabbits were randomly assigned to four groups：one control group and three experimental chronic compression groups,with each group containing 12 animals.Chronic compression of the cervical spinal cord was implemented in the experimental groups by implanting a screw in the C3 vertebra.The control group underwent sham surgery.Experimental groups were observed for 3,6,or 9 months after surgery.MRI T2-weighted SIR Tarlov motor scores and cortical somatosensory-evoked potentials （CSEPs） were periodically monitored.At each time point,rabbits from one group were sacrificed to determine the level of apoptosis by histology （n=6） and Western blotting （n=6）.Results Tarlov motor scores in the compression groups were lower at all time points than the control group scores,with the lowest score at 9 months （P ＜0.001）.Electrophysiological testing showed a significantly prolonged latency in CSEP in the compression groups compared with the control group.All rabbits in the compression groups showed higher MRI T2 SIR in the injury epicenter compared with controls,and higher SIR was also found at 9 months compared with 3 or 6 months.Histological analysis showed significant apoptosis in the spinal cord tissue in the compression groups,but not in the control group.There were significant differences in apoptosis degree over time （P ＜0.001）,with the 9-month group displaying the most severe spinal cord apoptosis.Spearman＇s rank correlation test showed that there was close relation between MRI SIR and degree of caspase-3 expression in Western blotting （r=0.824.P ＜0.001）.Conclusions Clear apoptosis of spinal cord tissue was observed during chronic focal spinal compression.Changes in MRI T2 SIR mav be related to the severity of the apoptosis in cervical spinal cord.