The implications of decreased performance of new generation gamma-cameras on the interpretation of¹³¹i-hippuran renal images

Several patients with renal failure in whom the kidneys were more clearly imaged with⁹⁹Tc^m-DTPA than 1:111-Hippuran were recently observed. We have postulated that our newer generation gamma-cameras have a reduced capacity to image 1:111 in comparison to older generation cameras. This hypothesis was tested by comparing representative older and newer imaging systems. Full-width tenth-maximum⁹⁹Tc^mlinespread functions were 1.20 and 1.55 cm for the older and newer cameras, respectively. The⁹⁹Tc^mcount rate on the newer camera was 111% that of the older camera, and the observed kidney to background count ratios in a phantom model were virtually identical for the two cameras imaging a number of simulated⁹⁹Tc^m111 count distributions. Full-width tenth-maximum¹³¹Ilinespreads werel.55and4.78cm, respectively, on the older and newer cameras and the¹³¹I count rate on the newer camera was 27% of the count rate on the older system. The phantom model demonstrated a consistently lower¹³¹I perceived kidney to background count ratio on the newer gamma-camera compared to the older system. These findings should be considered in the interpretation of¹³¹I-Hippuran studies on newer-generation equipment until revised criteria of interpretation have been established. Non-visualization of the kidney may not have the same prognostic implication using modem cameras as has been reported from studies with older generation detector systems.