The design of a pentavalent 99mTc-dimercaptosuccinate complex as a tumor imaging agent

In our search for a technetium-tumor seeking agent, the chemical characteristic of polynuclear Ga-citrate attracted our attention. On this basis, we selected the ligand dimercaptosuccinic acid (DMS) and appropriate labeling conditions in the design of 99mTc(V)-DMS. Chemical characterization was performed by thin layer chromatography, electrophoresis, Sephadex column chromatography and spectrophotometric studies at the chemical concentration (99Tc). Biodistribution in mice bearing Ehrlich ascites tumor and scintigraphic images in VX-2 tumor-bearing rabbit, indicated the great applicability of 99mTc(V)-DMS as a new tumor imaging agent. Its distinctive characteristic, different from the kidney imaging agent (99mTc-DMSA) is demonstrated and the biological implication of hydrolytic polynucleation of pentavalent technetium, through an anionic specie Tc(V)O3-(4), in the tumor cell is discussed.     

Oxidative metabolism in the myocardium in normal subjects during dobutamine infusion

To assess the biventricular response of the clearance rate of carbon-11 acetate as an index of myocardial oxidative metabolism to increase in work-load, dynamic positron emission tomography was performed at rest and during dobutamine infusion in 14 normal subjects. The clearance rate constant (K_mono) of the left ventricular (LV) myocardium increased during dobutamine infusion (0.112±0.020 min^–1 vs 0.065±0.015 min^–1 at rest) (P<0.001) in proportion to the increase in the pressure-rate product. K_mono in the right ventricular (RV) myocardium also increased (0.080±0.018 min^–1 vs 0.034±0.013 min^–1 at rest) (P<0.001), with an excellent correlation with the LV K_mono (r=0.920). The fact that the increase in RV Kmono during dobutamine infusion was greater (158%±81%) than that in LV Kmono (79%±39%) (P < 0.005) indicates a greater increase in oxidative metabolism in the RV in response to inotropic stimulation in normal subjects. Correspondence to: N. Tamaki     

Myocardial positron computed tomography with 13N-ammonia at rest and during exercise

To assess the value of myocardial-perfusion positron computed tomography (PCT) for the evaluation of coronary artery disease (CAD), ¹³N-ammonia PCT using a whole-body multislice PCT device was performed at rest and during exercise in 6 normal subjects and 19 patients with angiographically documented CAD. The ¹³N-ammonia distribution in the myocardium was assessed both qualitatively and quantitatively. At rest and during exercise, the tracer distribution was homogeneous in the 6 normal cases. In the 19 patients with CAD, regional hypoperfusion was observed in 14 cases (74%) at rest and in 18 cases (95%) during exercise. Additional perfusion abnormalities were detecting during exercise in 12 cases. Segmental analysis of the myocardial perfusion identified 30 out of 34 stenosed vessels (88%) during exercise, with only one false-positive finding of diseased vessels (specificity, 98%). For the quantitative analysis of myocardial perfusion by PCT, the percentage of change in the tracer concentration in the same region between the rest and stress images was calculated. The concentration was slightly increased in normal myocardial segments (14.4%±5.8%; P<0.001), whereas in CAD, it was significantly decreased in segments with stenosed vesels (-18.0%±18.3%; P<0.02). We conclude that ¹³N-ammonia PCT at rest and during exercise provides highquality images, and is a sensitive and effective technique for detecting CAD and identifying individual stenosed vessels. Furthermore, this technique makes possible quantitative assessment of the coronary reserve function.     

Quantitative evaluation of tricuspid regurgitation by digital simulation of cardiac time-activity curves

To estimate tricuspid regurgitation (TR) quantitatively, a curve fitting method by computer has been employed. Transport in the right cardiac chambers after intravenous bolus injection of macro-aggregated albumin labeled with technetium 99m (^99mTc-MAA) was recorded in anterior view by a gammacamera system. Disturbance of the dilution curves from the left heart can be avoided by using ^99mTc-MAA injection. To know the radioisotope activity during the transport, time-activity curves are recorded for the superior vena cava, right atrium, and right ventricle. Parametric differential equations, obtained from compartmental analysis, interpret these curves mathematically.The rate of regurgitation is determined by comparison, using an iterative process, between the original and simulated curves. The whole process is performed automatically by computer. The calculated regurgitation value correlated well with the value from the analog simulation. The method clearly separated those with TR from those without TR.This digital simulation for estimating parameters using a compartmental model is a feasible tool in detecting and quantifying TR.     

Clinical evaluation of 99mTc-pyrophosphate myocardial emission computed tomography: Comparison with planar imaging

To depict the three-dimensional distribution of ^99mTc-pyrophosphate in the heart, emission computed tomography (ECT) was performed, following the conventional planar imaging, in 32 cases with suspected acute myocardial infarction (AMI). There were 23 cases with evidence of AMI, 7 with unstable angina (UA), and 2 with dilated cardiomyopathy (DCM). While the planar images showed discrete cardiac activity in only 11 of the 23 cases (48%) with AMI, the ECT images delineated focal myocardial uptake clearly in 20 of them (87%). On the other hand, the ECT images revealed cardiac blood-pool activity without significant myocardial uptake in all cases with UA and DCM in which the planar images showed diffuse activity. Thus, the ECT imaging of ^99mTc-pyrophosphate seems to be a valuable technique for assessing the presence and localization of myocardial necrosis, especially in cases showing diffuse cardiac activity in the planar imaging.