Detection of cardiac sarcoidosis using F-18 FLT PET/CT: Comparison with F-18 FDG PET/CT

Objectives F-18 FDG (FDG) PET has been proposed to play a role in the diagnosis of sarcoidosis including cardiac involvement. However, assessing inflammatory lesions in cardiac sarcoidosis using FDG can be challenging because the FDG accumulates in normal myocardium, a phenomenon known as physiological uptake. 3'-deoxy-3'-F-18 fluorothymidine (FLT) has been investigated as a promising PET tracer for evaluating tumor proliferative activity. In contrast to FDG, FLT uptake in normal myocardium is low. The purpose of this study was to investigate the feasibility of FLT PET/CT, compared with FDG PET/CT, for the detection of cardiac sarcoidosis.

Methods Twenty-one FLT and FDG PET/CT studies were performed in 15 patients with cardiac sarcoidosis. Eleven PET/CT studies were performed before therapy and 10 studies were performed after immunosuppressive therapy. The patients fasted for at least 18 hrs before FDG PET studies, although no special dietary instructions were given to the patients before FLT PET studies. PET emission scanning of the cardiac region with a 10-min acquisition was performed 60 min after each radiotracer injection. CT data for attenuation correction was obtained. A focal or focal on diffuse FDG uptake pattern was defined as positive. In positive case, the maximal standardized uptake value (SUV) of lesion was measured. In negative case, the mean SUV of myocardium was measured.

Results Of the 11 studies before therapy, 9 (82%) were positive on both PET studies, one (9%) was positive on FDG PET but negative on FLT PET, and one (9%) was negative on both PET studies. Of the 10 studies after therapy, 3 (30%) were positive on both PET studies and 7 (70%) were negative on both PET studies. Linear regression analysis between FLT and FDG indicated a significant correlation for SUV (p=0.007). The mean (±SD) FLT SUV after therapy (1.46±0.51) was significantly lower than that before therapy (2.78±0.91; p=0.002). The mean (±SD) FDG SUV after therapy (2.89±1.46) was also significantly lower than that before therapy (8.28±4.98; p=0.003).

Conclusions FLT PET/CT is feasible for detection and therapy monitoring of cardiac sarcoidosis, as well as FDG PET/CT.