Richard A. Ponto

Early redistribution of thallium-201 after temporary ischemia.

To define the time course of redistribution of thallium-201 (251TI), ischemia was induced in seven pigs by temporary occlusion of the circumflex coronary artery. After 1½ min of occlusion 201T1 and labeled microspheres were injected into the left atrium. Flow was re-established 4 min after occlusion. Prior to reflow, the relative activities of 201TI and microspheres in the ischemic area were similar, but as early as 5 min after reflow the relative 201fT activity was considerably higher than the relative microsphere activity and from 15 to 105 min after reflow, relative 201TI activity (average 69% of that in normal myocardium) continued to be higher than relative microsphere activity (average 6% of normal). Myocardial arteriovenous differences for 201TI were followed sequentially after 201Tl injection in normal dogs and in dogs with temporary coronary occlusions. The results suggested both loss of 201TI from normal myocardium beginning 10 min after 205TI injection and increased extraction of 201TI from the blood pool immedately after release of a transient occlusion. Redistribution of 201TI therefore begins very soon after relief of myocardial ischemia and even a short delay in initiating myocardial imaging may decrease the sensitivity of the technique for detecting transient ischemia.

Regional Ventilation in the Differential Diagnosis of Pulmonary Embolism

In the diagnosis of pulmonary embolism by lung scanning, clinical errors of interpretation may arise. Diseases that affect the distribution of pulmonary blood flow, such as pulmonary emphysema and bronchial asthma, may be confused with pulmonary embolism.With the addition of ventilation studies with 133xenon to the perfusion scans, distinct differences appear between patients with emboli and those with obstructive lung disease. In patients with pulmonary emboli, ventilation is preserved in the areas of decreased perfusion, whereas patients with obstructive lung disease show both decreased ventilation and perfusion in the affected areas.

The Effect of Aging on Lung Perfusion

Abstract The effect of age on the uniformity of lung perfusion was studied, using intravenous injections of99mTc-labeled albumin microspheres, in a group of 30 normal men with a mean age of 69.6 ye...

Comparison and Performance of Anger Cameras

Measurements of sensitivity, spatial resolution, dead time, and field uniformity, as well as imaging of phantoms, provide a satisfactory means of evaluating and comparing Anger camera systems. The authors recommend that these parameters be measured periodically to detect deterioration of performance. A clinical evaluation of images depends upon the type of cathode-ray tube display and associated film response. Thus, given an optimized camera system, an appropriate display format is also required for best results.

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.

Quantification of image studies obtained with a scintillation (Anger) camera.

Abstract Quantitative data including graphic analysis and contour plots from image studies of various body organs were obtained with a scintillation camera, digitalized, stored, and later processed by a CDC-3300 computer. Contours included serial studies of the passage of rapidly changing radioactive elements through an organ. Mathematical procedures utilized in developing contours appear to emphasize diagnostic information. Improvements in displaying radionuclide distributions, together with the relative simplicity and low cost of the technique make contour plots a valuable tool in nuclear medicine.

Regional Evaluation of Pulmonary Function in Chronic Obstructive Pulmonary Disease

Abstract Use of xenon 133, a scintillation camera, and computer-analyzed data in the evaluation of regional pulmonary function is reviewed. Data from 17 normal subjects and 12 patients with chronic obstructive pulmonary disease are presented. One case report is given in detail to fully illustrate the applications of the technique.

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.

Limitations of Available Gamma Camera Oscilloscopes for Whole-Body Bone Image or Minified Multi-Image Display1

The limits of image minification on conventional cathode-ray tubes were determined for two commercially available Anger cameras. For medium intensity settings, it was found that minification of more than 8 to 1 (Pho/Gamma HP) and 6 to 1 (Nuclear Data 60), respectively, would result in degradation of system resolution.

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 Sobels 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.