A small study comparing two FAPI tracers found that [18F]AlF-FAPI-74 showed more activity in the blood pool, spleen and jejunum one hour after injection than [68Ga]Ga-FAPI-46. In the other normal organs and reactive tissue uptake foci examined, the tracers showed no significant differences.
The comparison involved the same five people. All had fibrotic lung disease, and each underwent PET/CT with both tracers as part of a substudy of a large prospective trial. That made it possible to compare the tracers within each patient.
The clearest differences
On visual review, the overall biodistribution, or broad pattern of where the tracers appeared in the body, looked similar. The clearest visual difference was more apparent activity in vascular and intestinal regions with [18F]AlF-FAPI-74.
Numbers sharpened that distinction in the blood pool. [18F]AlF-FAPI-74 had significantly higher SUVmean and SUVmax than [68Ga]Ga-FAPI-46. SUVmean and SUVmax were the study's measures of average and peak tracer uptake. The reported p-values were 0.01 for SUVmean and 0.03 for SUVmax.
The [18F] tracer also had significantly higher SUVmean in the spleen and jejunum, a section of the small bowel. The reported p-values were 0.01 for the spleen and 0.02 for the jejunum. No significant tracer differences were reported in the other normal organs or reactive tissue foci assessed.
A tightly matched comparison
The scans were performed 60 minutes after injection, using EARL2-compliant reconstructions. Researchers placed spherical volumes of interest in normal organs, background tissues and reactive tissue uptake foci. They calculated SUVmean and SUVmax and compared their means with paired t-tests.
The study's size sets a clear boundary around the result. It included only five patients with fibrotic lung disease, and the reported comparison describes the tracers at the one-hour scan. The evidence therefore supports a descriptive, within-patient picture for this group and time point. It does not establish a cause for the uptake differences or show that the same pattern applies to other diseases, patient populations or imaging times.
What the scan cannot settle
The authors' practical message is correspondingly specific. They say both tracers have low physiological background uptake, but their biodistribution differences should be considered when interpreting FAPI images and comparing quantitative metrics across studies that use different tracers. The conclusion concerns uptake patterns and measurement, not a demonstrated improvement in diagnosis, prognosis, treatment decisions or patient outcomes.
Questions remain about whether these differences persist or change at other post-injection times, whether they generalize beyond fibrotic lung disease, and whether tracer order or other acquisition factors influence paired estimates.
The study followed the Declaration of Helsinki, received approval from the Ethics Committee of Hôpital Erasme in Brussels, and obtained informed consent from all participants.
The parent project was funded by the Fonds Erasme pour la Recherche Médicale. SOFIE Biosciences and GE Healthcare provided the tracer precursors under a material transfer agreement. The authors disclosed travel or congress support, employment of one author by Telix Pharmaceuticals and institutional GE Healthcare advisory fees related to FAPI, while stating that the companies had no role in the study.
Paper data and sources
Original title: Intra-patient comparison of tracer uptake and biodistribution of [Ga]Ga-FAPI-46 and [F]AlF-FAPI-74.
Authors: Anne-Leen Deleu, Benjamin Bondue, Ayça Arçay Öztürk et al.
Journal/Repository: Annals of nuclear medicine
Status: Peer-reviewed
First online: 2026-08-21
DOI: 10.1007/s12149-026-02271-4
Original paper · Full text