Magnetic resonance and clinical cerebrovascular disease. An update.

Abstract

-8 of living systems were reported in the literature. Since that time the clinical application of NMR has experienced exponential growth. Because of this rapid pace of development and the concurrent increase in hospitalbased NMR facilities, it is timely to review the application of NMR to the diagnosis and investigation of cerebrovascular disease.Nuclear Magnetic Resonance Detailed physics of the NMR experiment are beyond the scope of this review. However, the parameters used to determine contrast in magnetic resonance imaging and the basics of NMR spectroscopy are briefly described. Magnetic Resonance Imaging (MRI)There are three parameters that determine contrast in NMR imaging: nuclear density, p, and two intrinsic NMR parameters called T, and T 2 . T, and T 2 are relaxation time constants that can have characteristic values for various tissues. By exploiting certain timing aspects of the pulse sequence (a collection of radio frequency [RF] pulses delivered in a specifically timed sequence) used in obtaining an image, one can enhance the relative contribution of p, T l5 and T 2 contrast. The time delays in the RF pulse sequence, which are adjusted to produce variable contrast, are called TR (time-to-repetition) and TE (time-to-echo). TR is related to the speed with which the entire pulse sequence is delivered, usually on the order of seconds, and TE is related to the time between the individual RF pulses within the RF pulse sequence, usually on the order of

Hemorrhagic transformation in cardioembolic cerebral infarction.

“…MRI has a high sensitivity to detect even small amounts of blood, and blood degradation products are visible for a long time, which makes repeated examinations unnecessary. 5 We performed MRI 3 weeks after the stroke because most hemorrhages occur during this time, as former CT studies have shown. To avoid a selection bias, the patients were consecutive victims of acute TIA or ischemic stroke who underwent a standardized diagnostic routine.…”

Clinical, radiological, and functional evaluation following acute stroke.

“…Magnetic resonance imaging (MRI) (previously nuclear magnetic resonance or NMR) detects the changes of cerebral ischaemia earlier (at less than 4 h) and with greater sensitivity than CT scanning, and smaller infarcts including lacunar strokes are more frequently visualised (Brown et al, 1988;Ramadan et al, 1989) (Table 1, Figure 3). An additional area of superiority of MRI over CT is the differentiation of infarct from oedema, which is important in assessing the effects of drugs such as thrombolytics which may encourage oedema formation while improving cerebral perfusion.…”

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“…Magnetic resonance imaging, spectroscopy, and angiography Magnetic resonance imaging (MRI) (previously nuclear magnetic resonance or NMR) detects the changes of cerebral ischaemia earlier (at less than 4 h) and with greater sensitivity than CT scanning, and smaller infarcts including lacunar strokes are more frequently visualised (Brown et al, 1988;Ramadan et al, 1989) (Table 1, Figure 3). An additional area of superiority of MRI over CT is the differentiation of infarct from oedema, which is important in assessing the effects of drugs such as thrombolytics which may encourage oedema formation while improving cerebral perfusion.…”

“…An additional area of superiority of MRI over CT is the differentiation of infarct from oedema, which is important in assessing the effects of drugs such as thrombolytics which may encourage oedema formation while improving cerebral perfusion. MRI may also distinguish the ischaemic penumbra from the infarct core, as an area of peripheral hyperintensity (Ramadan et al, 1989). MRI frequently identifies brainstem infarcts which are either too small to be seen, or are 'hidden' because of bony artefact on CT (Weisberg et al, 1984).…”