Application of contrast agents in the evaluation of stroke: Conventional MR and echo‐planar MR imaging

Abstract

The availability of new therapeutic interventions, including neuroprotective agents and endovascular thrombolysis, has given new hope to patients suffering an acute stroke. Early intervention remains a key factor in the effectiveness of these new and traditional treatments. More importantly, the capability to assess the viability and reversibility of the ischemic tissue became essential for better delineation and differentiation of infarcted versus ischemic tissue and patient management. Abnormal MR imaging (MRI) findings during acute stroke usually reflect the underlying pathophysiologic changes, which can be classified into three sequential stages: (a) hypoperfusion, (b) cellular dysfunction and (c) breakdown of the blood-brain barrier. The first stage is a kinetic phenomenon (not biologic) and, therefore, can be detected immediately. Contrast agents accentuate the abnormal flow kinetics and facilitate the early diagnosis of ischemia using either conventional MRI or newly developed echo-planar perfusion imaging (EPPI). The demonstration of abnormal arterial or parenchymal enhancement on conventional MRI during acute stroke provides the earliest sign of vascular occlusion/stenosis. EPPI, in contrast, provides information related to microcirculation (< 100 microns) and tissue reserve (cerebral blood volume) that cannot be obtained by conventional angiography and is directly related to the target end-organ. Further information obtained from both contrast MRI and EPPI may have a predictive value in the clinical outcome of acute stroke patients.

Abnormal hyperintensity within the subarachnoid space evaluated by fluid-attenuated inversion-recovery MR imaging: a spectrum of central nervous system diseases

“…The AH observed in patients with acute stroke is thought to represent slow arterial flow associated with stenosis or occlusion of vessels in the presence of poor collateral circulation, a mechanism that is essentially the same as that of arterial enhancement on contrast-enhanced T1-weighted images (Fig. 7c) [35,36]. Thrombus in the artery is another possible mechanism for the high signal of vessels on FLAIR images.…”

Significance of hyperintense vessels on FLAIR MRI in acute stroke

“…The incidence of ischemic stroke in women of childbearing age is estimated between 3.5 and 18 per 100,000 per year in Western countries. [1][2][3][4][5][6][7] This risk may be slightly increased during pregnancy, particularly during the postpartum period. [8][9][10][11][12][13] To our knowledge, no data are available on the influence of pregnancy on the risk of recurrent stroke, [14][15][16] thereby making it difficult to counsel women with a history of ischemic stroke regarding future pregnancies.…”

“…1,2 Contrast agents have been used in conventional and echoplanar imaging to demonstrate abnormal blood flow kinetics in the early detection of ischemia. 3 Intravascular enhancement secondary to slow flow has been described as an early sign of ischemia. 4,5 Recently, the fluid-attenuated inversion recovery (FLAIR) sequence has shown promise in earlier and better detection of ischemic lesions compared to T1-weighted images (T1WI), proton density-weighted images, and T2WI, and is now a recommended part of regular stroke MRI evaluation.…”

Correlation of the apparent diffusion coefficient and the creatine level in early ischemic stroke: A comparison of different patterns by magnetic resonance

“…MAGNETIC RESONANCE CONSOLIDATES ADVANCES made in the understanding of the pathogenesis involved in both acute and subacute ischemic stroke (1–3). There are several approaches for evaluating stroke according to the different pathophysiological stages after stroke, commencing with perfusion deficit, followed by an imbalance of the cerebral energy metabolism and cellular dysfunction, and finally leading to edematous processes (4). Emphasis may be placed on 1) microcirculation, perfusion, and diffusion; 2) cellular energy metabolism; and 3) structural alterations.…”