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Biomedical subjects

A F Gmitro

Publications and source records attributed to A F Gmitro.

6 recordsLinked to original sources
PubMed1994

Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation.

The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Magnetic resonance imaging of lipid deposits in human atheroma via a stimulated-echo diffusion-weighted technique.

NMR images of subintimal lipid deposits within the vessel walls of atherosclerotic human aortas were obtained at 37 and 27 degrees C at 4.7 T. A combination of a stimulated-echo and pulsed-field gradients was used for suppressing the mobile tissue water relative to the less mobile tissue lipids. At 27 degrees C there was also a substantial reduction of the subintimal lipid signal intensity, which is consistent with the characteristic phase transition of cholesteryl esters in human atheroma. These results represent the first direct detection of lipid deposits in nonprotruding atherosclerotic lesions with NMR imaging.

Aorta↗
PubMed1989

Fluorescence spectroscopy guidance of laser ablation of atherosclerotic plague.

Laser-induced fluorescence (LIF) spectroscopy can only be used for laser angioplasty guidance if high-power laser ablation does not significantly alter the pattern of tissue fluorescence. Although the spectra of normal and atherosclerotic arteries differ, the change in fluorescence spectra following laser angioplasty has not been well studied. Therefore, the purpose of this study was to assess whether laser-induced fluorescence spectroscopy could guide selective laser ablation of atherosclerotic plaque and, if so, to develop a quantitative LIF score that could be used to control a "smart" laser angioplasty system. Baseline LIF spectroscopy of 50 normal and 50 atherosclerotic human aortic specimens was performed using an optical fiber coupled to a He-Cd laser and optical multichannel analyzer. LIF was then serially recorded during erbium:YAG laser ablation of 27 atherosclerotic specimens. Laser ablation was terminated when the arterial LIF spectrum visually appeared normal. Histologic analysis revealed a mean initial plaque thickness of 1,228 +/- 54 microns and mean residual plaque thickness of 198 +/- 27 microns. Ablation of the media occurred in only three specimens. A discriminant function was derived to discriminate atherosclerotic from normal tissue for computer guidance of laser angioplasty. The LIF score, derived from stepwise multivariate linear regression analysis of the LIF spectra, correctly classified 93% of aortic specimens. The spectra obtained from the atherosclerotic specimens subjected to fluorescence-guided laser revealed a change in score from "atherosclerotic" to "normal" following plaque ablation. Seven atherosclerotic specimens were subjected to laser angioplasty with on-line computer control using the LIF score. Mean initial plaque thickness was 1,014 +/- 86 microns, and mean residual plaque thickness was 78 +/- 29 microns. There was no evidence of ablation of the media. Therefore, LIF guidance of laser ablation resulted in minimal residual plaque without arterial perforation. These findings support the feasibility of an LIF-guided laser angioplasty system for selective atherosclerotic plaque ablation.

Arteriosclerosis↗
PubMed1989

Development and evaluation of spectral classification algorithms for fluorescence guided laser angioplasty.

Laser angioplasty, or the ablation of atherosclerotic plaque using laser energy, has tremendous potential to expand the scope of nonsurgical treatment of obstructive vascular disease. Clinical laser angioplasty, however, has been hindered by an unacceptable risk of vessel perforation. Laser-induced fluorescence spectroscopy can discriminate atherosclerotic from normal artery and may therefore be capable of guiding selective plaque ablation. To assess the feasibility of utilizing spectral information to discriminate arterial tissue type, several classification algorithms were developed and evaluated. Arterial fluorescence spectra from 350 to 700 nm were obtained from 100 human aortic specimens. Seven spectral classification algorithms were developed with the following techniques: multivariate linear regression, stepwise multivariate linear regression, principal components analysis, decision plane analysis, Bayes decision theory, principal peak ratio, and spectral width. The classification ability of each algorithm was evaluated by its application to the training set and to a validation set containing 82 additional spectra. All seven spectral classification algorithms prospectively classified atherosclerotic and normal aorta with an accuracy greater than 80 percent (range: 82-96 percent). Laser angioplasty systems incorporating spectral classification algorithms may therefore be capable of detection and selective ablation of atherosclerotic plaque.

Algorithms↗
PubMed1981

A low-cost computed tomographic scanner.

The authors describe a film-recorded computed tomographic (CT) scanner that uses optical processing methods for reconstruction of a sectional image. Results are comparable to commercial CT methods using the same patient dose. Consequently, clinically satisfactory CT imaging can be performed at a substantially reduced cost.

Animals↗