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Biomedical subjects

R A Ponto

Publications and source records attributed to R A Ponto.

At least 19 recordsLinked to original sources
PubMed1983

Decrease in thallium-201 image defect size after permanent coronary occlusion.

In the 24 hours after coronary occlusion, some defects on thallium-201 images decrease in size. This study examined the mechanism of the decrease in defect size in dogs with experimental coronary occlusion. The left anterior descending coronary artery was permanently occluded in chronically instrumented awake dogs. Myocardial blood flow was measured with radioactive microspheres immediately before occlusion, 30 minutes, and 24 hours after occlusion. Thallium-201 was injected and imaging was performed 2 to 6 days before occlusion, 30 minutes, and 24 hours after occlusion. Two dogs, in which less than 1% of the left ventricle was infarcted, had no defects on the 30-minute postocclusion images. In four dogs the thallium-201 images did not change appreciably over 24 hours (group 1), while in three dogs the image defect size decreased (group 2). In groups 1 and 2 respectively the percent increase in blood flow to the hypoperfused area was: subendocardium 9 +/- 7% vs 31 +/- 15%; subepicardium 26 +/- 6% vs 47 +/- 2% (p less than 0.05). Therefore a decrease in the size of thallium-201 image defects occurred if a sufficient increase in collateral flow to the hypoperfused area took place in the first 24 hours after coronary occlusion. The defects appeared to decrease in size even in the absence of a detectable change in the lateral borders of the hypoperfused area.

Animals↗
PubMed1979

Evaluation of three imaging instruments in dogs with liver hemotomas: concise communication.

Single-gamma emission computerized tomography (ECT) was compared with transmission computerized tomography (TCT) and scintillation-camera imaging (SC) in eight dogs with acute, solitary hematomas in the left liver lobe. The superior performance of TCT was attributed to its inherently better spatial resolution than those of ECT or SC, and to the fact that studies with TCT could be performed during apnea. ECT was more sensitive than SC to small changes in the spatial distribution of radionuclides. In addition, the ECT, by virtue of its sectioning capability, was more sensitive than is SC to differences in radionuclide concentrations at same depth in an organ.

Animals↗
PubMed1978

Scintigraphic visualization of myocardial infarcts in baboons using thallium-201 and technetium-99m pyrophosphate.

4 baboons with myocardial infarcts were evaluated using thallium-201 for myocardial imaging and 99Tcm pyrophosphate for infarct visualization. Scintiphotographic findings were compared with the size of myocardial infarcts calculated from measurements of the activity of MB isoenzymes of creatine kinase (CK-MB) in serum and in the myocardium at autopsy, as described by Sobel's method. Lack of thallium-201 accumulation was noted in left ventricular infarcts of 3 of the 4 baboons. These same areas localized 99Tcm pyrophosphate administered 24--30 h after infarction.

Animals↗
PubMed1977

Evaluation of early myocardial ischemia with thallium-201 in the pig.

Thallium-201 was found to be a reliable agent for detecting decreased myocardial perfusion in domestic pigs 1-4 hours after acute coronary occlusion. Substantial variation in myocardial-to-liver count ratios and diagnostic quality was observed in serial images performed in 3 normal pigs, although areas of 1-4 hours-old myocardial ischemia produced by acute circumflex coronary artery ligation in 6 pigs could be reliably detected by in vivo 201Ti imaging. After intravenous 201Ti administration, the animals were sacrificed and sections of normal and ischemic myocardium were counted in a scintillation well counter. The activity in the ischemic area in pigs averaged 12% of the activity in the normal area, and varied over a narrow range; in dogs the activity averaged 62% of normal, and varied over a wide range. The pig was a more consistent model than the dog.

Animals↗
PubMed1976

Frequency dependence of regional lung clearance of 133Xe in normal men.

We measured the one-half time of 133Xe washout from the whole lung and from 9 horizontal lung regions in 6 normal men during normal breathing and at 50 breaths/min. The diaphragm was located with a contour map prior to the selection of the 9 horizontal regions. Artifacts caused by the tissue solubility of 133Xe were reduced by expressing regional clearance relative to whole lung clearance. During normal breathing there was a progressive increase in the relative clearance of 133Xe from the lung apex to the base when each region was compared to the lung as a whole. At 50 breaths/min, relative clearance increased from the lung apex only for about 18.5 to 20 cm. At that point, the relative clearance rate of the horizontal regions began to fall and at the lung base was slower than that of the whole lung. These results are consistent with the concept that dependent lung regions have longer time constants than regions at the top of the lung.

Adult↗
PubMed1974

Dual camera studies of pulmonary function with computer processing of data.

Xenon 133 and 2 scintillation cameras arranged to view both anterior and posterior lung fields are being used routinely for evaluation of pulmonary function. Scintiphotograms are obtained from both cameras throughout the course of both perfusion and ventilation portions of the study. In addition, data from both cameras are digitized and stored on line in a dedicated computer for further analysis. Computer processing of data permits quantitative information to be obtained on perfusion, ventilation and clearance of the radioactive gas from selected regions of the anterior and posterior lung fields. Ventilation-perfusion ratios and washout times are likewise calculated by computer.

Computers↗