IMAGES THAT TEACH Proliferation imaging with 11 C-4DST PET/CT for the evaluation of cardiac sarcoidosis, compared with FDG-PET/CT given a long fasting preparation protocol Ryogo Minamimoto, MD, PhD, a Masatoshi Hotta, MD, a Michiaki Hiroe, MD, PhD, b Toru Awaya, MD, PhD, b,c Kazuhiko Nakajima, a Osamu Okazaki, MD, PhD, b Hiroyuki Yamashita, MD, PhD, d Hiroshi Kaneko, MD, PhD, d and Yukio Hiroi, MD, PhD b a Division of Nuclear Medicine, Department of Radiology, National Center for Global Health and Medicine, Tokyo, Japan b Department of Cardiovascular Medicine, National Center for Global Health and Medicine, Tokyo, Japan c Division of Cardiovascular Medicine, Toho University Ohashi Medical Center, Tokyo, Japan d Division of Rheumatic Diseases, National Center for Global Health and Medicine, Tokyo, Japan Received Jan 7, 2020; accepted Jan 7, 2020 doi:10.1007/s12350-020-02069-5 INTRODUCTION A thymidine analog, 11 C-labeled 4 0 -thiothymidine (4DST) can provide cell proliferation imaging based on the mechanism of incorporation into DNA. In our experience, sarcoidosis lesions show increased 4DST uptake. We therefore promote a prospective study of 4DST positron emission tomography (PET)/computed tomography (CT) for the evaluation of cardiac sarcoido- sis (CS). In the sarcoid region characterized by granuloma formation, the presence of replicating lym- phocytes correlated with disease activity which was concluded by numerous Ki67-positive cells in the lesion. 1 In a previous study, 4DST showed a high correlation with Ki67 expression as a marker of cell proliferation. 2 Advantages of 4DST PET/CT are low physiological uptake by myocardium without any neces- sity of dietary preparation, and low uptake in the blood pool providing good contrast for myocardial lesions. Another advantage of 4DST PET/CT is the short scan duration, with 10 minutes PET scan starting 20 minutes after 370 MBq of 4DST injection. We present several cases underlining the outstanding performance of 4DST in the management of patients with definitive or sus- pected CS, compared to 2-deoxy-2- 18 F-fluoro-D-glucose (FDG)-PET/CT with a long fasting preparation protocol. CASE SUMMARY Figure 1 shows a 36-year-old male patient with sarcoidosis in whom FDG-PET/CT image suggested cardiac sarcoidosis. The use of 4DST PET/CT showed potential for correcting false-positive FDG uptake in the myocardial wall. Figure 2 shows findings for a 47-year- old male patient with suspected recurrence of CS. Findings from 4DST PET/CT showed stable, low physiological uptake in the myocardial wall, which may prove helpful in cases with unstable suppression of physiological FDG uptake in the myocardium that may be mistaken as lesion recurrence. Figures 3 and 4 show findings for a 71-year-old female patient with CS. Use of 4DST PET/CT allowed detection of active CS with good contrast to background, and showed potential for assessing response to treatment of CS. A 36-year-old man was diagnosed with sarcoidosis based on findings of multiple lymph node swelling and pathologically confirmed sarcoidosis by hilar lymph node and skin biopsy. FDG-PET/CT after 18 hour of Funding Funding supported by National Center for Global Health and Medicine (29-2005). Reprint requests: Ryogo Minamimoto, MD, PhD, Division of Nuclear Medicine, Department of Radiology, National Center for Global Health and Medicine, 1-21-1, Toyama, Shinjyuku-ku, Tokyo162- 8655, Japan; ryogominamimoto@yahoo.co.jp J Nucl Cardiol 1071-3581/$34.00 Copyright Ó 2020 American Society of Nuclear Cardiology.