Urinary bladder blood flow. I. Comparison of clearance of locally injected 99mtechnetium pertechnate and radioactive microsphere technique in dogs.

The blood flow of the dog urinary bladder measured by radioactive microsphere technique was compared to the clearance of locally injected 99mTechnetium pertechnate (99mTc) in the bladder wall. In semilogarithmic plots the 99mTc washout curves showed a multiexponential course. From the initial slopes (median 5.7 min) the bladder blood flow was calculated to be only 30-62% of the results obtained from the radioactive microsphere technique (blood flow in the muscular layer 21.7-44.8 ml/100 g/min). These lower values imply that the rate of removal of the hydrophilic tracer 99mTc at these flow rates is limited by the capillary diffusion capacity. The multiexponential curves reflect recirculation and excretion of 99mTc by the kidneys with accumulation of 99mTc in the bladder. It is concluded, that clearance studies of locally injected 99mTc in the bladder wall are unable to evaluate bladder blood flow.