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The biodistribution, kinetics, imaging characteristics and blood flow correlations of 99mTc labeled DiArs and DMPE were studied. The mice biodistribution were compared to 201Tl in mice and dogs, respectively. The myocardial kinetics of these agents were evaluated in normal and ischemic myocardium using miniaturized endocardial detectors. DiArs had a lower myocardial concentration (9.4 +/- 0.8% dose/g at 1 min), than DMPE (11.7 +/- 1.1% dose/g at 1 min) but both were considerably less than 201Tl (23-26% dose/g at 1 min). The kinetic characteristic of both technetium labeled agents suggested that redistribution into ischemic myocardium would not take place, since the clearance rate from normal and ischemic myocardium was similar for both the DiArs and DMPE . The clear visualization of the canine myocardium after i.v. injection demonstrated the superiority of DMPE over DiArs and the potential use of these agents, if proven, to behave the same in human trials.

A simple technique for measuring 24-h whole-body retention (24-h WBR) of 99mTc-labeled methylene diphosphonate (MDP) is described. We chose a standard thyroid probe-scaler system (Picker-Magna Scanner) as our counting instrument and characterized it relative to: photon saturability; optimum counting time post administration; patient positioning; and results with prostate cancer patients with positive/negative scintigram diagnoses for bone metastases. Whole body retention values of 99mTc at 24 h were easily measured with our instrumentation. Initially whole body count rates were determined at 5-min post injection and, again at 24 h. Data accumulated prior to the 5-min time period were inaccurate due to a higher sensitivity for the activity in the early circulation. Also, initial count rates obtained from patients injected with (740 MBq) (20 mCi) 99mTc-MDP usually required a correction due to detector saturation. The data observed at 24 h, representing skeletal tracer uptake, required no such correction. Patient positioning was rigorously controlled for the two time intervals to insure constant geometry. The 24 h-WBR values measured for prostate cancer patients with positive bone scintigrams was significantly different from those patients with negative scintigrams (58.8 +/- 8.7% and 29.2 +/- 9.6% respectively). Measurement of the 24 h-WBR has great potential for following various pathologies in the clinical setting.