Biomedical subjects

W R Nitz

Publications and source records attributed to W R Nitz.

3 recordsLinked to original sources

PubMed1992

MP RAGE: a three-dimensional, T1-weighted, gradient-echo sequence--initial experience in the brain.

The authors evaluated a recently developed sequence for magnetic resonance imaging of the brain. The three-dimensional, Fourier-transformed acquisitions require magnetization-prepared 180 degrees radio-frequency pulses and rapid gradient-echo (MP RAGE) sampling. The resulting T1-weighted images were compared with T1-weighted spin-echo (SE) images; both were obtained after paramagnetic contrast material was administered to 33 patients with known or suspected focal brain lesions. Image quality and contrast between gray and white matter were superior with the MP RAGE sequence compared with the T1-weighted SE sequence. The time for obtaining contiguous thin-section (1.3-2.5-mm) images was also comparable, with readily acquired multiplanar reformations obviating additional images. MP RAGE imaging depicted more focal lesions than did T1-weighted SE imaging and matched the number seen with T2-weighted SE imaging. Demonstration of paramagnetic contrast enhancement of lesions was comparable in most cases; however, three lesions showed greater enhancement on T1-weighted SE images and two others were seen only on the T1-weighted SE images. Thus, the MP RAGE sequence may provide an alternative to T1-weighted SE imaging.

Adult↗

PubMed1992

Flow dynamics of cerebrospinal fluid: assessment with phase-contrast velocity MR imaging performed with retrospective cardiac gating.

To visualize the flow of cerebrospinal fluid (CSF) throughout the ventricles and subarachnoid space, measure mean and maximum CSF velocities, and quantitate CSF flow through the aqueduct of Sylvius, magnetic resonance (MR) imaging was performed with a sagittal technique that is flow-sensitive in the craniocaudal direction (along the readout axis) and a high-resolution axial technique sensitive to through-plane flow in three healthy subjects and 19 patients with known or suspected disorders of the CSF circulation. In both techniques, retrospective cardiac gating was used to cover the complete cardiac cycle. The sagittal technique was superior in overall assessment of CSF flow dynamics, including the motion of adjacent brain parenchyma. The high-resolution axial technique provided an accurate measurement of the rate of CSF flow through the aqueduct; only this technique provided sufficient accuracy to enable distinction between normal and hyperdynamic CSF flow. It is concluded that assessment of CSF flow dynamics is a useful adjunct to routine MR imaging in communicating and obstructive hydrocephalus.

Adult↗

PubMed1990

Nuclear magnetic resonance velocity spectra of steady flow.

Nuclear magnetic resonance (NMR) velocity spectra are a compact way to represent the flow information in a velocity-resolved image set. Fully developed steady flow in long tubes gives NMR velocity spectra with average velocities which correlate well with the values derived from the flow rate. The ratio of average velocity to peak velocity correlates well with the Reynolds number. Tubes with compressed cross sections have velocity spectra similar to those of circular tubes. Tubes with irregular walls have velocity spectra in the entrance region that are markedly different from those from smooth-walled tubes.

Arteriosclerosis↗