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UBO: unidentified bright objects, bright spots in the brain on T2-weighted images; mostly small regions of état criblé and état lacunaire; small infarctions, scars, or high- intensity regions in demyelinizating diseases.
ultra-high field: fields strength beyond 2.5 Tesla, e.g. 3-Tesla or 7-Tesla systems.
USPIO: ultrasmall superparamagnetic iron oxide particles.
Vector: a quantity having both magnitude and direction, frequently represented by an arrow whose length is proportional to the magnitude.
Velocity: (blood) flow per area: cm3 × s-1 × cm-2.
Volume imaging: imaging techniques in which NMR signals are gathered from the whole object volume to be imaged at once, with appropriate encoding sequences. Many sequential plane imaging techniques can be generalized to volume imaging, at least in principle. Advantages include potential improvement in signal-to-noise ratio by including signal from the whole volume at once; disadvantages include a bigger computational task for image reconstruction and longer image acquisition times (although the entire volume can be imaged from the one set of data) (→ Simultaneous volume imaging).
VOSY: volume spectroscopy (→ Localized spectroscopy).
Voxel: volume element; the element of 3-D space corresponding to a pixel, for a given slice thickness.
Water suppression: in proton spectroscopy the water signal is usually several orders of magnitude greater than the next strongest signal. To avoid the resulting dynamic range problem the water signal is suppressed, typically with presaturation or by using binomial pulses. Similar techniques can be applied to imaging so as to remove the water component from images.
Window: relationship between signal intensity and shade of the display gray scale. Window width: number of digital levels between pure black and pure white; window center: digital level on which the window is centered.
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