V.A. Fokin, G.E. Trufanov, I.V. Pyanov
Chair of Rentgenology and Radiology Medicomilitary Academy, Saint Petersburg, Russia
The goal of the present study was determining efficacy of diffusion-weighted and perfusion-weighted MRI in the acutest stage of disorders of cerebral circulation. The study was carried out with use of a MR-tomograph with magnetic intensity of 1.5 T.
We examined 23 cases in the acutest stage of disorders of cerebral circulation (up to 12 hours since the onset of clinical signs). Their age varied from 39 up to 73 years.
A superficial matrix radio-frequency coil was used for brain examination. Standard examination with the help of a high-field MR-tomograph started with use of a program of rapid scanning (Localizer or Scout). Anatomic images of the brain in axial, coronal and sagittal planes were obtained with (TSE) pd+Ò2-(TR/ÒÅ=2500/14), Ò2-(TR/ÒÅ=4000/96) quick spin-echoes and (SE) Ò1-(TR/ÒÅ=550/14) spin-echo weighted tomograms respectively.
Diffusion-weighted images (DWI) were received on the basis of single shot echo-planar tomography (DWI-EPI) without suppression of a signal from free water. DWI parameters were as follows: TR=3200 ms, TE=94 ms, a section thickness of 5 mm, FOV - 230 mm, matrix of 128´128, a repetition number - 3, a diffusion factor value - b=0.500 and 1000 s/mm2 for all directions. Each diffusion-weighted examination resulted in getting three series of sections with similar localization, the so-called combined images, for evaluation of a measured diffusion coefficient (MDC) of cerebral tissues. A usual period of data collection for one value of b was 26 sec; a maximum number of sections in diffusion study reached 19. The images were processed automatically with construction of MDC maps. We measured MDS on diffusion maps in an area of interest (ROI), equal to 100 mm; it was done with the purpose of quantitative analysis.
Perfusion tomography was used after obtaining DWI. Perfusion-weighted images were received on the basis of single shot echo-planar tomography (DWI-EPI) with the following parameters: TR=1440 ms, ÒÅ=47 ms, a section thickness of 5 mm, FOV - 230 mm, matrix of 128´128, a repetition number - 1. Examination started after bolus administration of a contrast substance with the help of an automatic syringe and an interval of 10 sec. There were 50 series with 12 images in each of them. Built-in post-processor programs (Perfusion MR) were used for data processing; perfusion maps were constructed and quantitative estimation of results was carried out.
As for DWI, an ischemic zone was represented by MR-signal with low intensity; there was a marked reduction of MDC. Native MR-tomograms did not reveal a zone of ischemia (it was characterized by isointensive signal). PWI demonstrated delay in mean time of transit (MTT) of a contrast substance through an ischemic zone (not less than 7 sec).
The study results allow to come to the following conclusion: efficacy of DWI and PWI in early diagnosis of disorders cerebral circulation is extremely high. Native images show no change of MR-signal intensity.