Comparing the image quality of myocardial perfusion agents in the clinical laboratory: small test groups and large reference populations.

Myocardial perfusion studies have been performed for 6 years using technetium-99m (99Tcm)-sestamibi (MIBI). In this study we evaluated a newer agent, 99Tcm-tetrofosmin (TF), on a trial basis for 2 weeks, and compared the results from each week to those in an adjacent week of MIBI use. The routine protocol included weight-based dosing, frequent dipyridamole use, and separate-day rest and stress wherever possible. During the first week, TF was used with 'usual' image timing, i.e. stress tomography performed 30-60 min after stress, and ancillary immediate images performed 4 min after injection. For the second week, 'early' tomography was performed 15-30 min after stress. TF scans (n = 53) were compared with MIBI scans for the adjacent weeks (n = 54) and with a historical reference series (n = 1800). Blinded analysis was made of tomographic image quality, peak myocardial counts and background activity (lung and abdomen) on immediate and delayed acquisitions and on tomographic reconstructions. The TF and MIBI test groups were similar with respect to gender, weight, stress protocol, tracer doses, imaging times and scintigraphic findings. Using analysis of variance, the tomographic quality scores were similar for the two observers, with stress>rest (P<0.0001), 'usual'>'early' (P<0.001) and MIBI>TF (P<0.05). Myocardial counts were approximately 20% higher with the MIBI test group than with TF at all times after stress (P=0.001), and were similar to the reference population. MIBI with usual timing gave more favourable stress abdominal background ratios than the other three agent/timing combinations. Satisfactory images could be obtained with TF, but no apparent advantage over MIBI could be attained with earlier post-stress imaging. Subtle advantages for MIBI over TF were suggested by comparison of the small test groups. In our local imaging context, these conclusions were reinforced by a large control series.