Journal of neuroimaging : official journal of the American Society of Neuroimaging
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Previous studies of transcranial Doppler (TCD) sonography in acute stroke have used the relative difference between the symptomatic and asymptomatic arteries to assess arterial occlusion. However, a simple measure of absolute mean flow velocity might provide a direct assessment of "perfusion reserve" in acute ischemic stroke. ⋯ The findings suggest that in the normal hemisphere (with intact autoregulation on the horizontal portion of the autoregulation curve), flow velocity and transit time are not closely related to each other, but in the symptomatic hemisphere (on the downward slope of the autoregulation curve), flow velocity is directly proportional to the transit time and, therefore, to its inverse, perfusion reserve. The use of absolute mean flow velocity values on TCD should be further explored as a simple way of assessing "perfusion" in acute ischemic stroke.
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Duplex scanning is an accepted method for noninvasive evaluation of carotid stenosis. However, the ultrasound criteria used for the detection of threshold stenoses vary widely between laboratories, and quality assurance measures to allow adjustment of criteria are often lacking. This study was completed using receiver operating characteristic (ROC) analysis to determine Doppler velocity criteria for threshold carotid stenoses, compared to an accepted standard, and to demonstrate methods to allow adjustment of criteria. ⋯ This study showed that duplex scanning is able to detect threshold carotid stenoses. For the best performance, each laboratory should have its own criteria; however, the criteria provided here could be a helpful reference to those laboratories that have not yet established their own criteria. Most important, this study provides an example of how to evaluate the performance criteria, how to modify them, how such changes can affect performance, and how performance can be modified depending on the goals of the laboratory.
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Several functional imaging studies have shown that the extent of activation and percentage change in cerebral blood flow in the supplementary motor area (SMA) during a bimanual mirror performance of a simple repetitive movement are almost identical to those during a unimanual movement. The aim of this study was to investigate whether this finding was also applicable to a more complex movement. Eight right-handed, healthy volunteers performed unimanually (with their right and left hands) and bimanually (in a mirror fashion) thumb-finger opposition in a nonconsecutive order (index-middle-index-ring-index-little-index-middle ... fingers). ⋯ This is in accordance with the hypothesis that bimanual movement, even in a mirror fashion, is more difficult than unimanual movement when the task is complex but not when the task is simple. Pre-SMA was inconsistently activated. The results suggest that the SMA proper plays an active role in executive processing during bimanual mirror performance of complex movements.
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Patients with objective evidence of memory impairment have been considered to be at risk for developing Alzheimer's disease (AD). However, little is known about patterns of regional cerebral blood flow abnormalities and their prognostic significance in these patients. ⋯ These results demonstrate that (1) subjects with an earlier onset of memory loss have an increased risk for developing AD, (2) SPECT can be useful for distinguishing subjects with memory loss who will rapidly progress to AD from those who will not, and (3) perfusion impairment typical of AD was evident even in subjects with memory impairment who remained nondemented.
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A persistent trigeminal artery (PTA) has been found in a number of cerebrovascular diseases. A 73-year-old asymptomatic woman was noted to have a left PTA and left subclavian steal by catheter angiography. Carotid duplex revealed a peak systolic flow velocity of 294 cm/s in the internal carotid artery (ICA) and an ICA to common carotid artery ratio > 4, suggestive of a high-grade stenosis. ⋯ Transcranial Doppler found an alternating flow pattern in the basilar artery (mean flow velocity [MFV] = 18 cm/s) and left vertebral artery (MFV = 43 cm/s). During brachial hyperemia, the MFV increased by 178% in the basilar artery and 102% in the left vertebral artery. The data suggest that a PTA may compensate for subclavian steal and may have a protective hemodynamic role in this setting.