[Modern nuclear magnetic resonance techniques in stroke]

[Perfusion measurement using the T2* contrast media dynamics in neuro-oncology. Physical basics and clinical applications]

Perfusion imaging in the central nervous system (CNS) is mostly performed using the first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) MRI. The first-pass of a contrast bolus in brain tissue is monitored by a series of T2*-weighted MR images. The susceptibility effect of the paramagnetic contrast agent leads to a signal loss that can be converted, using the principles of the indicator dilution theory, into an increase of the contrast agent concentration. From these data, parameter maps of cerebral blood volume (CBV) and flow (CBF) can be derived. Regional CBF and CBV values can be obtained by region-of-interest analysis. This review article describes physical basics of DSC MRI and summarizes the literature of DSC MRI in neurooncological issues.Studies, all with relatively limited patient numbers, report that DSC MRI is useful in the preoperative diagnosis of gliomas, CNS-lymphomas, and solitary metastases, as well as in the differentiation of these neoplastic lesions from infections and tumor-like manifestations of demyelinating disease. Additionally, DSC MRI is suitable for determining glioma grade and regions of active tumor growth which should be the target of stereotactic biopsy. After therapy, DSC MRI helps better assessing the tumor response to therapy, residual tumor after therapy, and possible treatment failure and therapy-related complications, such as radiation necrosis. The preliminary results show that DSC MRI is a diagnostic tool depicting regional variations in microvasculature of normal and diseased brains.

Cerebral infarction: incidence and risk factors after diagnostic and interventional cardiac catheterization--prospective evaluation at diffusion-weighted MR imaging

PURPOSE

To prospectively evaluate incidence of clinically silent and clinically apparent embolic cerebral infarction following diagnostic and interventional coronary angiography and associated risk factors.

MATERIALS AND METHODS

Written informed consent was obtained from all patients, and the study was approved by the research ethics committee of University of Heidelberg, Germany. Fifty-two patients, including 37 men (mean age, 66.1 years +/- 11.9 [standard deviation]) and 15 women (mean age, 65.3 years +/- 10.3), undergoing elective cardiac catheterization were examined 3-26 hours (mean, 15.3 hours +/- 6) before and 12-48 hours (mean, 25.9 hours +/- 10.4) after cardiac catheterization. Magnetic resonance imaging protocol included isotropic and anisotropic diffusion-weighted single-shot echo-planar sequences. T2-weighted turbo spin-echo and T1-weighted spin-echo sequences also were performed. Apparent diffusion coefficient maps were calculated to exclude false-positive reading results on diffusion-weighted images because of T2 shine-through effect. Images were assessed by two experienced radiologists blinded to clinical data. Cardiac catheterization was performed by 11 experienced cardiologists to exclude operator-related risk. A neurologic examination according to the National Institutes of Health Stroke Scale and Barthel index was performed by a senior cardiologist before acquisition of each image. Sixteen clinical and angiographic variables were analyzed with univariate analysis for ability to predict occurrence of cerebral infarction.

RESULTS

No embolic cerebral lesions could be detected at diffusion-weighted imaging before catheterization. After coronary angiography, seven (15%) of 48 patients demonstrated nine focal cerebral infarcts affecting anterior and posterior circulation. Patients remained asymptomatic. Of all tested variables, only duration of the procedure was identified as an independent predictor of occurrence of cerebral infarction (P < .05).

CONCLUSION

In this prospective study, asymptomatic cerebral infarction following cardiac catheterization occurred in 15% of patients in whom duration of the procedure was significantly longer than in those without infarction (P = .017).

MRI-guided therapy in acute stroke

Stroke is the third leading cause of death after myocardial infarction and cancer and the leading cause of permanent disability and of disability-adjusted loss of independent life-years in Western countries. Thrombolysis is the treatment of choice for acute stroke within 3 h after onset of symptoms. Treatment beyond the 3-h time window has not been shown to be effective in any single trial, however, meta-analyses suggest a somewhat less but still significant effect within 3 to 6 h after stroke. It seems reasonable to apply improved selection criteria that allow the differentiation of patients with a relevant indication for thrombolytic therapy from those who have not. An overview of a diagnostic approach to acute stroke management that allows patient management individualization based on pathophysiological reasoning and not rigid time windows, established by randomized controlled trials is presented. Therefore, this review concentrates in the first part on giving the reader an integrated knowledge of the current status of thrombolytic therapy in stroke, and in the second part, develops a treatment algorithm based on pathophysiological information rendered by a multiparametric stroke magnetic resonance imaging protocol.