A prospective study included 66 patients presented with acute ischemic stroke in the period between October 2017 and November 2018. Six patients were excluded due to motion artifact that degraded the quality of the DTI maps and the final cohort was 60 patients. Written informed consents were obtained from all patients. The study is IRB approved.
MRI with diffusion tensor imaging was done for all patients within the first 2 days after the clinical presentation. The clinical neurological deficits were assessed by a neurology specialist with a 10-year experience using the National Institutes of Health Stroke Scale (NIHSS) on patient’s admission. The NIHSS is a systematic assessment tool providing a quantitative measure of stroke-related neurologic deficit. The NIHSS is widely used to evaluate the acuity of stroke patients, determine appropriate treatment, and predict the patient outcome (Fig. 1) .
The patients were then clinically followed up after 3 months to detect any residual neurological deficits. Neurological improvement was defined as a decrease in the NIHSS score after 3 months compared to that on admission.
MRI technique was done using a standard 1.5 Tesla unit (Achiva, Philips) using a standard head coil. The obtained sequences were axial T1W, T2W, FLAIR, diffusion-weighted imaging, and diffusion tensor. The diffusion tensor imaging consisted of a single shot, spin-echo echoplanar sequence in 12 encoding directions, and a diffusion weighting factor of 800 s/mm2, TR 8000 ms, TE 67 ms, flip angle 90, matrix 112 × 110, FOV 210 × 236 mm, and number of excitations, 2 and slice thickness, 2.0/00.
Post processing was done on the MR workstation (Phillips Extended MR Workspace, 18.104.22.168 Netherlands).
The maps obtained were as follows:
Grey scale FA maps.
Directionally encoded color FA maps.
3D fiber tractography was performed using multi-ROI technique based on known anatomy. Regions of interest (ROIs) were drawn in the unaffected portion of the white matter tracts, and the software detects the white matter tracts that passed through the ROIs.
Freehand drawings of the regions of interest (ROIs) were made at the FA color map overlaid on T2 or FLAIR images. Measurements were performed at the site of infarction and the corresponding area at the contralateral hemisphere.
For classification of the patterns of white matter tract affection as detected by 3D fiber tractography, we followed the classification of Witwer et al. . The tracts were classified into preserved, displaced, or disrupted.
Disrupted tract: if the tract showed marked reduction of the anisotropy so that it could not be identified on the FA maps and could not be traced by fiber tracking algorithm.
Displaced tract: if the tract showed abnormal location or abnormal orientation, but it maintains its normal anisotropy when compared to the corresponding contralateral tract.
Preserved tract: if the tract maintains its normal location, orientation, and anisotropy compared to the corresponding contralateral normal tract.
In cases with more than one tract affection, it is considered disrupted if at least one tract is disrupted.
The patients were classified according to the following:
○ The clinical score (NIHSS): Mild (1,2,3,4), moderate (5,6,7,8,9,10), and severe (> 10).
○ The degree of FA reduction of the white matter tracts at the site of infarction: mild (0.4), moderate (0.2–0.3), and severe (0.1).
○ The pattern of WM tract affection whether disrupted or non-disrupted (either preserved or displaced). Disrupted (if at least one tract is disrupted).