Biological and imaging characteristics and radiation dose rates associated with the use of technetium-99m-labelled imidodiphosphate in the horse.

The biological and imaging characteristics of technetium-99m imidodiphosphate (Tc99m-IDP) were measured in 4 horses once and in 1 horse twice. All computational results are expressed with 95.5% (mean +/- 2 SD) confidence limits. The clearance half-time of the radiopharmaceutical from the blood was 29.6 +/- 2.3 min. The percentage of the administered dose circulating in the whole-blood volume at 4 h was 3.9 +/- 0.8%. The Tc99m-IDP radioactivity confined at the plasma fraction of the whole blood at 4 h was 85.3 +/- 1.6%. At 8 h, approximately 45 +/- 16% of the dose administered had been excreted via the urine. The mean effective half-time of the urine activity concentration was 1.1 +/- 0.3 h. The ratios of bone-to-soft tissue activities increased with time postinjection. Urinary radioactivity concentration measurements and radiation dose rate measurements immediately behind the elbows were analysed and it was determined that 24 h is an appropriate radioisolation time for mature horses administered 3.7 GBq (100 mCi) Tc99m-IDP.