The effect of imaging time, radiopharmaceutical and milk on extra-cardiac activity in myocardial perfusion SPECT

Abstract

Background and aim: Extra-cardiac activity can interfere with the interpretation of myocardial perfusion SPECT images. Fatty meals to clear hepatobiliary uptake have been attempted. However, the simple solution of delayed imaging has not been studied. The aim was to quantify the effects of imaging time, oral administration of full fat milk and radiopharmaceutical on interfering activity. Method: Myocardial perfusion SPECT images were acquired using either 99mTc tetrofosmin or sestamibi. Patients were imaged at 30 min, 1 h or 2 h post-injection (tetrofosmin=72, sestamibi=59). A further set of patients was imaged either with or without milk (tetrofosmin=54, sestamibi=45). A myocardial region was drawn on the anterior projection and an extra-cardiac region automatically generated. The count density ratio was calculated and validated with a trial of 5 observers. A decreasing ratio correlated significantly with observer rank of increasing interference with SPECT image interpretation (r=0.95, P=0.001). Results: Results are shown in Table 1. The ratio improved significantly as the imaging time increased for both tetrofosmin and sestamibi groups (P<0.05). Milk made no significant improvement (P=0.2). There was no significant difference between tetrofosmin and sestamibi (P=0.4).Table 1: Results for myocardial perfusion SPECT images acquired by using either 99mTc tetrofosmin or sestamibiConclusion: Image interpretation may be improved by delayed imaging for tetrofosmin and sestamibi. However, in contrast to common practice administration of milk is of no clinical value.