Richard E. Snyder

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The authors report NMR measurements of the changes in water diffusion brought about by in vivo Wallerian degeneration due to either crush- or tie-injuries in the sciatic nerve of the frog. Using a pulsed-gradient spin-echo sequence with a diffusion measurement time of 28 ms, the degree of diffusion coefficient anisotropy ¿D(longitudinal)/D(transverse)¿ 4(More)
The contact process is used as a simple spatial model in many disciplines, yet because of the buildup of spatial correlations, its dynamics remain difficult to capture analytically. We introduce an empirically based, approximate method of characterizing the spatial correlations with only a single adjustable parameter. This approximation allows us to recast(More)
The multiexponential T2 relaxation spectrum of peripheral nerve undergoing Wallerian degeneration has been measured both in vivo and in vitro. Degeneration of the sciatic nerve of the amphibian Xenopus laevis was induced by crush injury, and T2 relaxation spectra of the nerve were measured at several times up to 35 days following injury. Histologic evidence(More)
We report here a study of longitudinal relaxation (T1) and magnetisation transfer (MT) in peripheral nerve. Amphibian sciatic nerve was maintained in vitro and studied at a magnetic field strength of 3 T. A CPMG pulse sequence was modified to include either a saturation pulse to measure T1 relaxation or an off-resonance RF irradiation pulse to measure MT.(More)
It is demonstrated that multi-exponential transverse (T2) relaxation components can be estimated from multi-echo images of peripheral nerve. Three T2-relaxation components with T2 values +/- standard deviations (populations +/- standard deviations) of 19 +/- 7 ms (26 +/- 9%), 63 +/- 31 ms (29 +/- 11%) and 241 +/- 24 ms (45 +/- 7%) have been identified in(More)
An electrocardiographic (ECG) unit suitable for cardiac-synchronized nuclear magnetic resonance imaging in high magnetic fields is presented. The unit includes lossy transmission lines as ECG leads in order to suppress radio frequency (RF) interference in the electrocardiogram. The unit's immunity to RF interference is demonstrated.
Although multiecho imaging may be used to measure transverse relaxation (T2), B1 and B0 inhomogeneity generally gives rise to unwanted coherence pathway signals which result in erroneous T2 measurements. One approach to suppressing this unwanted signal is to center each rf refocusing pulse between spoiler gradients which dephase the unwanted signal;(More)
The proton transverse-relaxation spectrum of peripheral nerve has been reported to consist of three components arising from microanatomical water compartments within the nerve. The component with the shortest decay time has been consistently seen to be a result of the myelin. In this study, experiments were performed to reveal the microanatomical sources of(More)
Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone “space”), were monitored continuously using gamma-ray computed tomography (γ-CT) prior to, during, and following intravenous infusion of strontium(More)