Development and validation of a direct-comparison method for cardiac 123I-metaiodobenzylguanidine washout rates derived from late 3-hour and 4-hour imaging

Purpose The washout rate (WR) has been used in 123I-metaiodobenzylguanidine (MIBG) imaging to evaluate cardiac sympathetic innervation. However, WR varies depending on the time between the early and late MIBG scans. Late scans are performed at either 3 or 4 hours after injection of MIBG. The aim of...
Ausführliche Beschreibung

Purpose The washout rate (WR) has been used in 123I-metaiodobenzylguanidine (MIBG) imaging to evaluate cardiac sympathetic innervation. However, WR varies depending on the time between the early and late MIBG scans. Late scans are performed at either 3 or 4 hours after injection of MIBG. The aim of this study was to directly compare the WR at 3 hours ($ WR_{3h} $) with the WR at 4 hours ($ WR_{4h} $). Methods We hypothesized that the cardiac count would reduce linearly between the 3-hour and 4-hour scans. A linear regression model for cardiac counts at two time-points was generated. We enrolled a total of 96 patients who underwent planar 123I-MIBG scintigraphy early (15 min) and during the late phase at both 3 and 4 hours. Patients were randomly divided into two groups: a model-creation group (group 1) and a clinical validation group (group 2). Cardiac counts at 15 minutes ($ count_{early} $), 3 hours ($ count_{3h} $) and 4 hours ($ count_{4h} $) were measured. Cardiac $ count_{4h} $ was mathematically estimated using the linear regression model from $ count_{early} $ and $ count_{3h} $. Results In group 1, the actual cardiac $ count_{4h} $/$ count_{early} $ was highly significantly correlated with $ count_{3h} $/$ count_{early} $ (r = 0.979). In group 2, the average estimated $ count_{4h} $ was 92.8 ± 31.9, and there was no significant difference between this value and the actual $ count_{4h} $ (91.9 ± 31.9). Bland-Altman analysis revealed a small bias of −0.9 with 95 % limits of agreement of −6.2 and +4.3. $ WR_{4h} $ calculated using the estimated cardiac $ count_{4h} $ was comparable to the actual $ WR_{4h} $ (24.3 ± 9.6 % vs. 25.1 ± 9.7 %, p = ns). Bland-Altman analysis and the intraclass correlation coefficient showed that there was excellent agreement between the estimated and actual $ WR_{4h} $. Conclusion The linear regression model that we used accurately estimated cardiac $ count_{4h} $ using $ count_{early} $ and $ count_{3h} $. Moreover, $ WR_{4h} $ that was mathematically calculated using the estimated $ count_{4h} $ was comparable to the actual $ WR_{4h} $. Ausführliche Beschreibung