[¹²⁴I]FIAU: Human dosimetry and infection imaging in patients with suspected prosthetic joint infection

Introduction: Fialuridine (FIAU) is a nucleoside analog that is a substrate for bacterial thymidine kinase (TK). Once phosphorylated by TK, [¹²⁴I]FIAU becomes trapped within bacteria and can be detected with positron emission tomography/computed tomography (PET/CT). [¹²⁴I]FIAU PET/CT has been shown to detect bacteria in patients with musculoskeletal bacterial infections. Accurate diagnosis of prosthetic joint infections (PJIs) has proven challenging because of the lack of a well-validated reference. In the current study, we assessed biodistribution and dosimetry of [¹²⁴I]FIAU, and investigated whether [¹²⁴I]FIAU PET/CT can diagnose PJIs with acceptable accuracy. Methods: To assess biodistribution and dosimetry, six subjects with suspected hip or knee PJI and six healthy subjects underwent serial PET/CT after being dosed with 74 MBq (2 mCi) [¹²⁴I]FIAU intravenously (IV). Estimated radiation doses were calculated with the OLINDA/EXM software. To determine accuracy of [¹²⁴I]FIAU, 22 subjects with suspected hip or knee PJI were scanned at 2-6 and 24-30 h post IV injection of 185 MBq (5 mCi) [¹²⁴I]FIAU. Images were interpreted by a single reader blinded to clinical information. Representative cases were reviewed by 3 additional readers. The utility of [¹²⁴I]FIAU to detect PJIs was assessed based on the correlation of the patient's infection status with imaging results as determined by an independent adjudication board (IAB). Results: The kidney, liver, spleen, and urinary bladder received the highest radiation doses of [¹²⁴I]FIAU. The effective dose was 0.16 to 0.20 mSv/MBq and doses to most organs ranged from 0.11 to 0.76 mGy/MBq. PET image quality obtained from PJI patients was confounded by metal artifacts from the prostheses and pronounced FIAU uptake in muscle. Consequently, a correlation with infection status and imaging results could not be established. Conclusions: [¹²⁴I]FIAU was well-tolerated in healthy volunteers and subjects with suspected PJI, and had acceptable dosimetry. However, the utility of [¹²⁴I]FIAU for the clinical detection of PJIs is limited by poor image quality and low specificity.