The impact of acquisition time of planar cardiac ¹²³I-MIBG imaging on the late heart to mediastinum ratio

The aim of this study was to investigate whether performing the late cardiac ¹²³I-metaiodobenzylguanidine (MIBG) scan earlier than 4 h post-injection (p.i.) has relevant impact on the late heart to mediastinum ratio (H/M ratio) in patients with heart failure (HF). Forty-nine patients with HF (median left ventricular ejection fraction of 31 %, 51 % ischaemic HF) referred for cardiac ¹²³I-MIBG scintigraphy were scanned at 15 min (early) p.i. and at 1, 2, 3 and 4 h (late) p.i. of ¹²³I-MIBG. Late H/M ratios were calculated and evaluated using a linear mixed model with the mean late H/M ratio at 4 h p.i. as a reference. A difference in late H/M ratios of more than 0.10 between the different acquisition times in comparison with the late H/M ratio at 4 h p.i. was considered as clinically relevant. Statistically significant mean differences were observed between the late H/M ratios at 1, 2 and 3 h p.i. compared with the late H/M ratio at 4 h p.i. (0.09, 0.05 and 0.02, respectively). However, the mean differences did not exceed the cut-off value of 0.10. On an individual patient level, compared to the late H/M ratio at 4 h p.i., the late H/M ratios at 1, 2 and 3 h p.i. differed more than 0.10 in 24 (50 %), 9 (19 %) and 2 (4 %) patients, respectively. Variation in acquisition time of ¹²³I-MIBG between 2 and 4 h p.i. does not lead to a clinically significant change in the late H/M ratio. An earlier acquisition time seems to be justified and may warrant a more time-efficient cardiac ¹²³I-MIBG imaging protocol. (orig.)