Biomedical subjects

J Pekar

Publications and source records attributed to J Pekar.

24 records · Page 2Linked to original sources

PubMed1991

In vivo measurement of cerebral oxygen consumption and blood flow using 17O magnetic resonance imaging.

We used 17O NMR imaging techniques to measure the H2(17)O concentration in a 0.8-ml voxel in the cat brain following injection of an arterial bolus of enriched H2(17)O and during inhalation of enriched 17O2. We also measured the H2(17)O concentration in arterial blood during 17O2 inhalation. The data from the first measurement were used to calculate the blood flow in the voxel. The data from all three measurements were combined to calculate the oxygen consumption in the voxel. The values of cerebral blood flow and oxygen consumption calculated with 17O NMR techniques agree reasonably well with values calculated for a similar region of the cat brain using autoradiographic techniques.

Administration, Inhalation↗

PubMed1991

The Ocutech Vision Enhancing System (VES): utilization and preference study.

An NIH-sponsored user and prescriber preference trial was conducted comparing a new low vision telescope system, the Ocutech Vision Enhancing System (VES) to two conventional Keplarian spectacle telescope systems in a controlled cross-over clinical study performed at four independent low vision clinics. Fifty-five visually impaired individuals, 18-81 years of age, with both previous and no telescope experience, were followed for 8-16 weeks. The experimental and control devices were compared on a series of subject-selected visual tasks using a standardized clinical protocol. Subjects were trained in the use of the systems with standardized clinical methods. The data shows a statistically significant preference of the new design by both patient and clinician with the overriding factors relating to appearance, weight, adjustability and the fit of the frame.

Adolescent↗

PubMed1990

Echo-planar imaging of intravoxel incoherent motion.

The recently established single-shot technique of echo-planar imaging of intravoxel incoherent motion (IVIM) for determining and imaging the variations of microscopic motions of water has been applied to studies of water perfusion in phantoms and to in vivo studies of diffusion and perfusion in cat and human brains. The phantom results demonstrate that perfusion levels comparable with those found in vivo have easily observable and reproducible effects on signal amplitude that are consistent with previous IVIM theory. Reliable measurements of the diffusion coefficient in various types of brain tissue have been obtained. The results for white matter are consistent with the existence of anisotropic diffusion in oriented bundles of myelinated nerve fibers. The results for gray matter can be fitted to the IVIM theory and suggest a value of up to 14% for the fraction of the signal contributed by randomly perfusing fluid in normal cerebral cortex.

Animals↗

PubMedDate not supplied

Imaging of diffusion and microcirculation with gradient sensitization: design, strategy, and significance.

Recent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation ("perfusion") are summarized. After a brief description of the effects of diffusion and perfusion on the MR signal, the different methods (conventional spin-echo, stimulated-echo, gradient-echo, and echo-planar imaging) that have been proposed and used to image and measure diffusion and perfusion by gradient sensitization are presented, along with their advantages and limitations. The difficulties of diffusion/perfusion imaging related to both hardware and software are then discussed. Special attention is given to specific problems encountered with in vivo studies and data analysis. Finally, the potential biologic and clinical applications are outlined, and some examples are presented.

Brain↗

PubMedDate not supplied

Measuring random microscopic motion of water in tissues with MR imaging: a cat brain study.

Cat brain images sensitized to incoherent motion by additional gradient pulses were obtained on a 4.7 T magnetic resonance unit equipped with shielded gradient coils. The apparent diffusion coefficient of water in gray and white matter was accurately determined and imaged from the signal attenuation curve obtained as a function of gradient strength. Contrast in calculated diffusion images differed from typical T2-weighted contrast. Furthermore, in gray matter and in areas containing flowing CSF the attenuation curve was found to be biexponential. These results are interpreted in terms of a simple voxel model with microcirculation and diffusion contributions.

Animals↗

PubMedDate not supplied

MR color mapping of myelin fiber orientation.

Diffusion of water in brain white matter has been shown to be anisotropic: Water mobility is lower when measured perpendicular to the fiber direction rather than parallel to it. This feature was used to produce images of the myelin fiber orientation. Coronal and sagittal MR diffusion images were obtained in volunteers using an echo-planar imaging sequence sensitized to molecular diffusion in perpendicular directions. Color-coded images of myelin orientation were then generated by combining these images together. The orientation of the white matter tracts was found to be in excellent agreement with known anatomy. Myelin fiber orientation mapping may offer a new perspective to evaluate white matter disorders.

Algorithms↗