Objective: To apply amide proton transfer magnetic resonance imaging (APT-MRI) technique to acute ischemic stroke, and to discuss clinical values of the APT-MRI main parameter - MTRasym(3.5 ppm).
Methods: A total of 18 emergency admitted patients, with acute ischemic stroke from Beijing Hospital, were recruited from March to November 2015. Eventually, 18 patients (male 14, female 4, average age 72 years old, age ranged from 52 to 92 years, symptom onset ≤24 hours, 2 patients≤ 6 hours) were included in this study. All patients underwent MR scanning on the brain at 3.0 Tesla. Besides the conventional scans for stroke, the APT sequence (saturation time 0.8 s, saturation power 2 μT) was performed. APT weighted (APTW) images were calculated using magnetization transfer ratio asymmetry at 3.5 ppm with respect to water. MRI signals in APTW, diffusion weighted images (DWI) and fluid attenuated iversion recovery (FLAIR) were visually evaluated. Shapiro-Wilk tests were performed to find out the distribution of MTRasym(3.5 ppm) in the whole sample, infarction regions, and normal appearing white matter (NAWMs), respectively. Detrended normal P-P plots were also used to evaluate its normality. Paired-t test and two-sample t test were applied to compare the mean MTRasym(3.5 ppm) of infarction regions with that of contra lateral NAWMs.
Results: (1) High signal intensity was observed in DWI and FLAIR in all 18 patients. However, signal intensity was somewhat different in APTW. 13 patients were found decreased APT effect, and 5 patients were with equal APT effect in infarction regions. In NAWMs, 14 patients were found equal APT effect, and 4 patients were with decreased APT effect. (2) MTRasym(3.5 ppm)s were proven, with Shapiro-Wilk test, to distribute normally within the whole sample (W=0.964, P=0.288), infarction regions (W=0.962, P=0.645), and NAWMs(W=0.929, P=0.187). However, its normality was not so satisfactory due to greater deviations (absolute value>0.06) of some cases in detrended normal P-P plots. (3) Paired-t test analysis showed that MTRasym(3.5 ppm) in infarction regions (-0.035%±1.020%) was significantly lower than that in NAWMs (0.386%±0.790%) (t=-2.273, P=0.036). However, there was no statistically significant difference between infarction regions and NAWMs when two sample t-test was performed (t=-1.386, P=0.175).
Conclusion: MTRasym(3.5 ppm) can be used to evaluate acute ischemic stroke with a broad future scope in clinical.