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

• Published in: European journal of nuclear medicine and molecular imaging 2016-02, Vol.43 (2), p.319-325
• Main Authors: Okuda, Koichi, Nakajima, Kenichi, Sugino, Shuichi, Kirihara, Yumiko, Matsuo, Shinro, Taki, Junichi, Hashimoto, Mitsumasa, Kinuya, Seigo
• Format: Article
• Language: English
• Subjects: Cardiology; Imaging; Medicine; Medicine & Public Health; Nuclear Medicine; Oncology; Original Article; Orthopedics; Radiology
• ISSN: 1619-7070; 1619-7089
• DOI: 10.1007/s00259-015-3173-8

Purpose The washout rate (WR) has been used in 123 I-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 123 I-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 .