Assessing the effect of increasing injection activity for myocardial perfusion imaging in overweight patients

In our previous publication, we proposed to increase the injection activity for overweight patients. We have now implemented this for our patients, i.e. increasing the activity for patients above 99 kg. In the present study, we audited whether this increased activity for overweight patients improved the myocardial counts effectively and also whether it improved the image quality for these patients. 125 consecutive normal myocardial perfusion studies were included into the study. The total left ventricular myocardial count was calculated, as was the total left ventricular myocardial volume using the Cedar Sinai QPS program. The myocardial count per millilitre of the myocardium (c ml(-1)) was correlated with patient weight using regression analysis. There was no significant difference (p = 0.120) among the mean myocardial counts for patients over 99 kg (n = 40, 1548 c ml(-1)) compared with patients in the 70-79 kg range (n = 26, 1746 c ml(-1)). This indicates that the previously proposed algorithm for adjusting injection activity maintains the count density in the myocardium and should be used for all patients over 99 kg. There was, however, a significant steady decrease with increased weight in the myocardial counts for patients under 100 kg (p<0.001), a range in which injection activity was not adjusted for weight. To correct for this, we now propose that the injection activity should be adjusted for all patients over 80 kg, using the previously proposed algorithm.