The myocardial washout rate of thallium-201 was studied in 85 subjects with a less than 5% likelihood of coronary artery disease undergoing rest (group I, n = 12), dipyridamole (group II, n = 24) and exercise (group III, n = 49) stress thallium-201 scintigraphy. Subjects receiving dipyridamole were subdivided into group IIA (n = 11), who received an aminophylline injection 10 minutes after dipyridamole infusion, and group IIB (n = 13), who did not. The mean and highest washout rate values in each of 3 segments in the anterior, 45 degrees and 85 degrees left anterior oblique views were calculated. In group II the mean washout rate of thallium-201 was similar in all segments of each view and the overall mean washout rate did not differ between the 3 views studied. There was a good correlation between the mean and highest washout rate values in individual subjects (r = 0.98, p less than 0.001). The mean +/- standard deviation myocardial 4-hour washout rate of thallium-201 (anterior view) was 10 +/- 6% in group I compared with 40 +/- 14% in group IIA (p less than 0.05 vs group I), 31 +/- 13% in group IIB (p less than 0.05 vs group I) and 54 +/- 11% in group III (p less than 0.05 each vs group IIA and group IIB, respectively). There was a wide variation in mean washout rate values in group II (range 12 to 58%), and this variation was not altered by aminophylline administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Radionuclide activity within the pericardial (P) space, either localized or surrounding the cardiac chambers, indicates active (P) bleeding when gated equilibrium radionuclide ventriculography (RNV) is performed with Tc-99m-labeled RBCs. To evaluate the ability of RNV to detect and to quantify the amount of accumulated P blood, the authors developed a simulated P bleeding model. By subxyphoid incision, a balloon (BAL) was inserted into the P space of 6 dogs. Images were reviewed to determine the presence and appearance of the P blood pool. Background-subtracted radioactive counts within each detected P blood pool were compared to known volume as a count rate (corrected for heart rate and acquisition duration) and as a fraction of left ventricular end-diastolic (LVED) peak counts. Using 3 views, an abnormal P blood pool was consistently visible at 10 ml when localized (BAL) and at 30 ml when freely distributed (BLD). Radioactive count rates and counts proportional to LVED counts increased (non-linearly) with volume. At 50 ml, the BAL dominated the RNV-BAL images, and a ''ring'' of BLD surrounded the heart in the RNV-BLD images. Thus, multiview RNV consistently detects small volumes of tagged pericardial blood. Measurement of radioactive counts from the pericardial blood pool and itsmore » appearance may allow a quantitative estimate of amount of pericardial bleeding.« less

Although useful for diagnosis of coronary disease, the ability of single photon emission computerized tomography (SPECT) to quantify infarct size (IS) is not well defined. Ten min after 2 mCi of intravenous Tl-201, 30 30-sec projections were obtained over 180° in 6 normal (nl) dogs and 10 other dogs 8 hours after closed-chest coronary occlusion (LAD in 7 and LCX in 3). After sacrifice, hearts were sliced and stained by triphenyl tetrazolium chloride (TTC). Pathologic IS was calculated on each slice and for the entire left ventricular myocardium (LV) as % weight. 0.4 cm-thick reconstructed oblique tomograms were quantified by automatic 60-point maximum count circumferential profile analysis, and computerized comparison of each point's activity to nl limit values derived from the 6 nl dogs. SPECT IS on each individual tomogram was defined as the % of circumferential points over the myocardial periphery falling below nl. SPECT and TTC IS on 62 corresponding slices with infarct correlated highly (mean±SD: 33±30 vs. 34±28, respectively, r=.87, p < .001). In order to obtain SPECT IS as % total LV, IS on each individual slice was multiplied by a different weighing factor depending on the depth of the SPECT slice along the long axis of the LV and values were subsequently added for the entire LV. SPECT and TTC IS for the entire LV also correlated highly (mean±SD: 20±8 vs. 22±7, respectively, r=0.87, p<0.01). Thus, computerized automatic analysis of SPECT T1–201 myocardial images is a valid method for the noninvasive assessment of the extent of myocardial infarction and thus may become a powerful prognostic indicator in ischemic heart disease.