Myocsrdial uptake of technetium-99m stannous pyrophosphate following direct current transthoracic countershock.
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Abstract:
The effect of direct current (DC) countershock upon myocardial technetium-99m stannous pyrophosphate (PYP) uptake was studied in 22 dogs. All eight dogs imaged had positive abnormal PYP scintigrams that were usually indistinguishable from experimental infarction. In three animals, additional areas of radionuclide uptake were seen in overlying noncardiac tissue. Left and right ventricular myocardial PYP uptake averaged (+/- SEM) 23 +/- 5 times control and 24 +/- 6 times control, respectively. These activity ratios occurred without reduction in regional myocardial blood flow (RMBF), and were associated with histologic evidence of necrosis. The necrosis was usually epicardial, corresponding to the transmural site of greatest PYP uptake. The magnitude of PYP accumulation and the weight of damaged tissue increased with increasing applied energy. Thus, PYP uptake following DC countershock could result in false-positive interpretation of acute ischemic myocardial infarction. Since RMBF is normal in regions of PYP uptake, the major determinant of radionuclide accumulation is the extent of cellular damage.Keywords:
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Canine leukocytes were labeled with a γ-ray emitting isotope by permitting them to phagocytize technetium Tc 99m sulfur colloid particles in vitro and removing the unphagocytized particles by washing the cells. The labeled cells were reinfused intravenously into the donor dogs. Scintigraphic scans were performed 4 and 24 hours following the leukocyte infusion. In animals with sterile and infected intramuscular abscesses and pulmonary infections, it was possible to localize the lesions by scintigraphic scanning four hours following administration of labeled leukocytes. In one experiment, a positive scan was observed 24 hours after the leukocyte infusion. It was also shown that labeled leukocytes tend to concentrate in abscess fluid. These results suggest that technetium Tc 99m sulfur colloid-labeled leukocytes may be a useful diagnostic tool in localizing abscesses and inflammatory lesions in humans.
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The binding of technetium-99m sulfur colloid to in vivo thrombi was studied in a rat model of deep vein thrombosis. After thrombosis was induced by mechanical traumatization of a right femoral vein segment, technetium-99m sulfur colloid was injected into the peripheral veins of different experimental groups at intervals of 30 min and 1-7 days. Ratios of mean activity in traumatized right femoral vein segment to activity in control segments of left femoral vein (R/L ratios) ranged form 2.97-11.0 for all in situ venous thrombi studied. There was no relation between clot size and R/L ratios. The significant uptake ratios observed by us for venous thrombi up to 1 wk in age suggest that in vivo thrombus detection may be feasible by imaging with a gamma camera after technetium-99m sulfur colloid injection in a peripheral vein.
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Hepatobiliary imaging in a patient with an amebic abscess showed an early cold defect that later showed rim enhancement. A Tc-99m SC scan did not show prominent flow (making hepatoma unlikely) and showed the previously noted defect to appear larger and without rim enhancement. The differential damage to Kupffer cells and hepatocytes or edema may account for these findings. Amebic abscess should be included in the differential diagnosis of lesions that give increased Tc-99m IDA but cold Tc-99m SC images.
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Twenty-seven paired Tc-99m sulfur colloid (SC) and Tc- 99m RBC studies were evaluated for the detection of Gl bleeding. The only two positive Tc-99m SC studies had positive early Tc-99m RBC studies as well. There were 15 other positive Tc-99m RBC studies (three during the first hour) and these were associated with normal Tc- 99m SC scans. Approximately 70% of the positive Tc- 99m RBC studies occurred after 1 hour. Tc-99m RBCs should be the initial test in patients with Gl bleeding.
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Technetium-99m-labeled pyrophosphate and radiolabeled antimyosin antibodies are two infarct localizing agents with apparently different kinetics of localization. To determine whether these agents localize in a similar fashion in early acute myocardial necrosis, we studied the simultaneous distribution of 111In-labeled antimyosin and 99mTc-labeled pyrophosphate in dogs after intracoronary (i.c.) (n = 9) or intravenous (i.v.) (n = 9) administration of a mixture of these two agents in a reperfused infarct model. The mean infarct size (+/- s.d.) delineated by pyrophosphate [20.2 +/- 14.1 (i.v.), 29.8 +/- 12.3 (i.c.)] was larger than that by antimyosin [14.2 +/- 11.3 (i.v.) (p = 0.05), 20.0 +/- 11.8 (i.c.) (p = 0.05)] which was larger than that by triphenyl tetrazolium chloride [13.9 +/- 8.0 (i.v.) (p = 0.05), 15.3 +/- 6.5 (i.c.) (p = 0.05)]. This overestimation persisted whether the radiopharmaceuticals were administered by intracoronary or intravenous injections, although the latter with antimyosin was only slightly larger (TTC:AM = 13.9:14.2) (p = n.s.). There was a good correlation, however, between antimyosin and pyrophosphate delineated infarct sizes in dogs with intracoronary injection (y = 0.82x + 13.33, r = 0.79) or i.v. injection (y = 1.208x + 3.01, r = 0.97) of the mixture of the two agents. Since the images of the 111In and 99mTc activities were obtained consecutively by identical methods, the overestimation of infarct size by pyrophosphate cannot be due to differences in spatial resolution of the techniques used. The differences in the areas of myocardial damage delineated by pyrophosphate and antimyosin in our study most probably denote the area of viable but compromised myocardium.
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To study the scintigraphic detectability of cardiac rejection, we performed 135 planar myocardial scans ([99mTc]pyrophosphate, 85; 201Tl, 36; 67Ga, 14) together with endomyocardial biopsies in ten patients for a (mean) 17-mo postoperative period. Specificity of each agent exceeded 89%. Technetium-99m pyrophosphate showed results that significantly correlated with the severity of rejection (p = 0.03), as shown by biopsy, but neither 201Tl nor 67Ga did so (p = 0.63 and 0.81, respectively). Technetium-99m pyrophosphate showed better diagnostic accuracy (85%) than 201Tl (69%) and 67Ga (64%). Technetium-99m pyrophosphate also showed higher negative predictive value (91%) than thallium (76%) and gallium (69%). Thus, a normal 99mTc pyrophosphate scan was usually associated with absence of cardiac rejection. However, all three agents showed unacceptably poor sensitivity (0% to 30%) and thus were not useful as a screening test for cardiac rejection, even when the same agent was used serially in imaging a given patient.
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New chromatographic procedures are needed to accurately determine the radiochemical purity of technetium-99m labeled radiopharmaceuticals. A chromatography system has been developed for technetium-99m diethylenetriaminepentacetic acid, technetium-99m diphosphonate, and technetium-99m pyrophosphate. The technique involves spotting the radiopharmaceuticals on instant thin layer chromatography-silica gel and developing with acetone (solvent from migrates approximately 12 cm from the origin), air drying, and redeveloping the strip in normal saline (solvent front migrates approximately 6 cm from the origin). The procedure is simple to perform, rapid, accurate, and clearly separates technetium-99m pertechnetate, the technetium-99m radiopharmaceutical, and hydrolyzed reduced technetium-99m. It can be applied in most nuclear medicine laboratories and has the potential to predict the quality of radionuclide images obtained.
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A simple and rapid technique of preparing technetium-99m-labeled erythrocytes using commercial stannous pyrophosphate as the reducing agent was developed. The technique involves incubating red cells with stannous pyrophosphate, centrifugation, and addition of Tc-99m pertechnetate to the red cell fraction. A mean red cell labeling efficiency of 94% was achieved in 10 patient samples and less than 5% in vitro dissolution of Tc-99m red blood cells occurred up to two hours after preparation.
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