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Biomedical subjects

J F Greenleaf

Publications and source records attributed to J F Greenleaf.

At least 91 records · Page 5Linked to original sources
PubMed1982

Computed transmission ultrasound tomography.

Beginning with the wave equation, we have derived the classic reconstruction equations, which assume the ultrasonic energy travels in a straight line. The straight line reconstruction methods result in images that are not absolutely quantitative, although they may be useful in delineating speed and attenuation within two-dimensional cross sections, especially in organs such as the breast. Aberrations associated with straight-line reconstruction images are results of the effects of refraction and of diffraction. In addition, these methods assume that the acoustic wave travels within a plane and not in three dimensions; thus the assumed dimensionality of the problem also gives aberrations in the final image. The effects of diffraction are very complex and, given the current methods of measuring arrival time and amplitude, cause aberrations in the image, which result in errors both in geometry and in magnitude of the reconstructed values. Correction of diffraction effects with techniques termed 'diffraction tomography' are being investigated and have resulted in some preliminary data.

Breast Neoplasms↗
PubMed1978

Effect of force environment on regional pulmonary displacements and volumes in dogs.

Regional displacements of lung parenchyma due to respiratory movements at 1 G and 7 Gy were studied in anesthetized dogs in the left decubitus position in a water-filled respirator that provided control of respiratory volumes and rate and minimized inertial shifts in position and shape of the thorax and abdominal contents and related effects on the lungs. Inspiratory movements at 1 G were relatively uniform, although regional volume increased more in the nondependent (right) lung than in the dependent (left) lung. Regional functional residual capacity (FRC) increased in the nondependent lung and decreased in the dependent lung during exposures to 7 Gy. The greatest inspiratory increase in volume occurred near the midlung, where regional FRC changed the least during acceleration. The decrease in dependent and increase in nondependent lung volumes during acceleration are attributed to the increased weight and consequent downward displacement of the higher specific gravity mediastinal contents concomitantly with upward displacement of pulmonary gas, producing an exaggeration of the dependent-to-nondependent gradient in alveolar size.

Adaptation, Physiological↗
PubMed1978

Spatial distribution of pulmonary blood flow in dogs in increased force environments.

Spatial distribution of pulmonary blood flow (SDPBF) during 2- to 3-min exposures to 6-8 Gy acceleration was studied, using radioactive microspheres in dogs, and compared to previously reported 1 Gy control distributions. Isotope distributions were measured by scintiscanning individual 1-cm-thick cross sections of excised, fixed lungs. Results indicate: 1) the fraction of cardiac output traversing left and right lungs did not change systematically with the duration and magnitude of acceleration; but 2) the fraction is strongly affected by the occurrence or absence of fast deep breaths, which cause an increase or decrease, respectively, in blood flow through the dependent lung; and 3) Gy acceleration caused a significant increase in relative pulmonary vascular resistance (PVR) in nondependent and dependent regions of the lung concurrent with a decrease in PVR in the midsagittal region of the thorax. Result 3 may be mediated primarily by changes in regional alveolar volume and geometry in the nondependent hemithorax conbined with hydrostatic effects of extravascular fluid and active hypoxic response in the dependent region and is superimposed on, and may override, hydrostatic effects of perfusion pressures on SDPBF during acceleration.

Adaptation, Physiological↗
PubMed1978

Quantitative imaging of the structure and function of the heart, lungs, and circulation.

A 28-x-ray-source, cylindrical-scanning, transaxial tomographic x-ray-imaging system is in the process of being fabricated. This system will scan synchronously up to 250 parallel transverse cross sections of the human body over an axial range of 25 cm within 0.01 second at a maximum rate of 60 scans per second. The system will provide numerous variations of scanning configurations to permit quantitative assessment of the relative importance of transverse section thickness, image contrast, spatial and temporal resolution, and related computerized algorithms and display techniques. Synchronous imaging at high temporal resolution of a three-dimensional volume--for example, the heart--eliminates the need for successive periods of breath-holding and gated imaging techniques and is essential for quantitation of cardiovascular and pulmonary function and structure in intact animals or humans. Initial clinical applications are expected to be in the early detection of lung cancer and the diagnosis of the nature and degree of congenital and acquired cardiovascular disabilities.

Animals↗
PubMed1976

Biplane videoroentgenographic analysis of dynamic regional lung strains in dogs.

A method is described for determining the spatial distribution of pulmonary parenchymal strains in the intact canine thorax, using measurements of displacement of metallic (1-mm-diam)) markers percutaneously implanted throughout the parenchyma of the right lung. Dogs are supported head up or head down in a water-immersion respirator with the animal's airway connected to ambient air. Tracking of the parenchymal markers is accomplished by stereo biplane videoroentgenographic recordings, which allow high temporal (60/S) and spatial (+/- 1.5 mm) resolution measurements of the "tagged" lungs during various respiratory maneuvers. After transferring the video information to a stop-action video disc, an operator-interactive computer program is used to input the geometric coordinates of the markers into the computer. The true spatial coordinates are then determined after correction for pincushion and magnification distortions. Spatial and temporal distributions of regional parenchymal strains are obtained by determining the distance between markers on a frame-by-frame basis over the extent of the respiratory cycle. Data indicate nonuniformity in regional lung parenchymal strains.

Animals↗