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Biomedical subjects

R K Crane

Publications and source records attributed to R K Crane.

At least 19 recordsLinked to original sources
PubMed1996

Microwave imaging for tissue assessment: initial evaluation in multitarget tissue-equivalent phantoms.

A prototype microwave imaging system is evaluated for its ability to recover two-dimensional (2-D) electrical property distributions under transverse magnetic (TM) illumination using multitarget tissue equivalent phantoms. Experiments conducted in a surrounding lossy saline tank demonstrate that simultaneous recovery of both the real and imaginary components of the electrical property distribution is possible using absolute imaging procedures over a frequency range of 300-700 MHz. Further, image reconstructions of embedded tissue-equivalent targets are found to be quantitative not only with respect to geometrical factors such as object size and location but also electrical composition. Quantitative assessments based on full-width half-height criteria reveal that errors in diameter estimates of reconstructed targets are less than 10 mm in all cases, whereas, positioning errors are less than 1 mm in single object experiments but degrade to 4-10 mm when multiple targets are present. Recovery of actual electrical properties is found to be frequency dependent for the real and imaginary components with background values being typically within 10-20% of their correct size and embedded object having similar accuracies as a percentage of the electrical contrast, although errors as high as 50% can occur. The quantitative evaluation of imaging performance has revealed potential advantages in a two-tiered receiver antenna configuration whose measured field values are more sensitive to target region changes than the typical tomographic type of approach which uses reception sites around the full target region perimeter. This measurement strategy has important implications for both the image reconstruction algorithm where there is a premium on minimizing problem size without sacrificing image quality and the hardware system design which seeks to economize on the amount of measured data required for quantitative image reconstruction while maximizing its sensitivity to target perturbations.

Algorithms↗
PubMed1995

An active microwave imaging system for reconstruction of 2-D electrical property distributions.

The goal of this work is to develop a microwave-based imaging system for hyperthermia treatment monitoring and assessment. Toward this end, a four transmit channel and four receive channel hardware device and concomitant image reconstruction algorithm have been realized. The hardware is designed to measure electric fields (i.e., amplitude and phase) at various locations in a phantom tank with and without the presence of various heterogeneities using standard heterodyning principles. Particular attention has been paid to designing a receiver with better than 115 dB of linear dynamic range which is necessary for imaging biological tissue which often has very high conductivity, especially for tissues with high water content. A calibration procedure has been developed to compensate for signal loss due to three-dimensional radiation in the measured data, since the reconstruction process is only two-dimensional at the present time. Results are shown which demonstrate the stability and accuracy of the measurement system, the extent to which the forward computational model agrees with the measured field distribution when the electrical properties are known, and image reconstructions of electrically unknown targets of varying diameter. In the latter case, images of both the reactive and resistive component of the electrical property distribution have been recoverable. Quantitative information on object location, size, and electrical properties results when the target is approximately one-half wavelength in size. Images of smaller objects lack the same level of quantitative information, but remain qualitatively correct.

Algorithms↗
PubMed1984

Studies of the kinetics of Na+ gradient-coupled glucose transport as found in brush-border membrane vesicles from rabbit jejunum.

The Na+-dependent D-glucose transport reaction in rabbit jejunal brush-border vesicles was studied. Initial rate data were obtained by fitting a polynomial equation to progress curves at different D-glucose concentrations and extracting the slope of the tangent at zero-time. Kinetic replots of the initial rate values produced biphasic Hofstee patterns indicative of two pathways for transport distinguished by their Km values for glucose. Neither was dependent on the presence of a membrane potential. Both were dependent on Na+ and both were inhibited by phlorizin. Increasing external sodium was found to elevate the apparent Vmax for both pathways. Internal sodium was inhibitory. Pulsed progress curve analysis indicated that the effect of internal sodium was best characterized as carrier sequestration by a sodium-carrier binary complex. Inhibition by internal sodium was completely reversed by the presence, internally, of D-glucose. The presence of two pathways and the kinetic constants for these pathways do not agree with the conclusions of Hopfer and Groseclose (1980) J. Biol. Chem. 255, 4453-4462). Experiments are presented which bear on the reason for the disagreement.

Animals↗
PubMed1979

A rapid method for the isolation of kidney brush border membranes.

A simple rapid method for the preparation of purified brush border membranes from rabbit kidney proximal tubules is described. The method is based on hypotonic lysis, Ca2+ aggregation of contaminants and differential centrifugation. In contrast to most other published methods, the brush border membranes are free of contamination by basolateral membranes.

Alanine↗
PubMed1979

Isolation of brush border membranes in vesicular form from the intestinal spiral valve of the small dogfish (Scyliorhinus canicula).

A simple, rapid method for the preparation of purified brush border membranes in vesicular form from rabbit kidney proximal tubules has been applied with closely similar results to the intestinal spiral valve of the small dogfish (Scyliorhinus conicula). Since the dogfish belongs to one of the most ancient species of fish, it may be suggested that the method is generally applicable to all species later evolved which possess a brush border membrane at the mucosal surface of the cells of the intestine or kidney.

Animals↗
PubMed1979

Reconstitution into liposomes of glucose active transport from the rabbit renal proximal tubule. Characteristics of the system.

This paper describes the characteristics of Na+ -dependent D-glucose transport into liposomes made from soybean phospholipids into which have been reconstituted detergent-solubilized components from the rabbit renal proximal tubular brush border membrane. Conditions for optimal and quantitative reconstitution of glucose carriers are defined. Na+ -dependent D-glucose uptake occurs via a saturable system with a Km of 0.125--0.135 mM, is responsive to the volume of the internal liposomal space, and shows 'overshoot' as seen in natural membranes. The rate of Na+-dependent D-glucose uptake and the magnitude of the 'overshoot" are proportional to the concentration of protein used in reconstitution.

Animals↗
PubMed1979

Intestinal structure and function related to toxicology.

The study of toxic effects on small intestinal function is complicated by the integration of the activity of the small intestine with the activities of other regions of the GI tract. Also, the barrier and portal functions of the intestine are not as clearly defined as sometimes assumed. The intestinal surface functions as a barrier to the ingress of large quantities of large water soluble molecules. Lipidic substances enter the body quite readily as do small water-soluble molecules. The small intestinal surface is more a portal than a barrier, with its portal functions divided between nonspecific diffusional entry, which depends on physical properties and electric charge, and entry by specific membrane transport, which depends upon chemical structure. The implications of these properties of the small intestine for toxicological studies are stressed.

Animals↗