Clinical utility of diffusion‐weighted magnetic resonance imaging in the assessment of ischemic stroke

Abstract

Diffusion-weighted imaging (DWI) detects small changes in water diffusion that occur in ischemic brain. This study evaluated the clinical usefulness of a phase-navigated spin-echo DWI sequence compared with T2-weighted magnetic resonance imaging (T2W MRI) in patients with cerebral ischemia and assessed apparent diffusion coefficient (ADC) and T2-weighted imaging (T2WI) changes over time. ADC values and T2 ratios of image intensity were measured from the region of ischemia and from the corresponding contralateral brain region. The clinical histories of patients with DWI scans obtained over the course of 1 year were reviewed to ascertain whether DWI aided in clinical diagnosis or management. Of 103 scans obtained a mean of 10.4 days after symptom onset, DWI detected six lesions not seen on T2WI and discriminated two new infarcts from old lesions. DWI was most useful within 48 hours of the ictus. The evolution of ADC values and T2 ratios was evaluated in 26 cases with known symptom onset times. ADC values were low at less than 1 week after stroke onset and became elevated at chronic time points. T2 ratios were near normal acutely, increasing thereafter. DWI was superior to T2W MRI in detecting acute stroke, whereas both techniques assisted in determining lesion age.

Evolution of lesion volume in acute stroke treated by intravenous t‐PA

“…Both animal (1,12) and human studies (2,13,14) have highlighted its ability to detect early the ischemic lesion with better sensitivity than other conventional MRI techniques (15,16). Even without a complete understanding of the biophysical background, it is certain that an acute increase of DWI signal intensity during ischemia is due to a failure of ion pumps and anoxic cell membrane depolarization with a subsequent water shift from the extracellular to the intracellular space, which, in turn, causes cell swelling (17).…”

“…The decrease primarily consists of regression of the vasogenic component, but cell lysis, necrosis, and retraction of the late infarcted core may also play a role. Comparison between day 1 DWI and day 60 T2WI is a limitation, but T2WI is more appropriate than diffusion to evaluate late infarct size (16,21), although DWI is more pertinent than T2 for stroke imaging at day 0 and day 1 (16,37). Using T2WI could overestimate the late infarct size because of the hypersignal of sulcus enlargement next to the lesions; however, volumes decreased significantly in both groups between day 1 and day 60.…”

Local planar gradients with order‐of‐magnitude strength and speed advantage

“…For the x-gradient coil, the x-component J xc x [1] of the current density function can be represented as…”

“…[1] and [2] for the x-and y-gradient coils generate zero net force and zero net moment in a constant axial magnetic field. The current density function for the z-coil of Eq.…”

The Role of Diffusion Weighted MR for Differentiation Between Benign and Malign Pancreatic Masses

“…[3][4][5] EPI gibi hızlı MRG sekanslarının geliştirilmesi ile diğer vücut bölümlerinde de uygulama alanı bulunmuştur. İlk olarak 1994 yılında Müller ve ark.…”