Targeted PET/MRI Improves Detection and Preoperative Mapping of Endometriosis

Endometriosis is a chronic inflammatory condition in which endometrial-like tissue grows outside the uterus, causing pelvic pain, infertility, and reduced quality of life. Conventional imaging can underestimate deep or extra-pelvic disease, limiting diagnosis and surgical planning. More accurate preoperative mapping is needed to guide individualized therapy and reduce repeat interventions. A new study shows that fibroblast activation protein-targeted PET/MRI may improve detection of hard-to-assess lesions.

Researchers at University Hospital Münster and the University of Münster, Germany, evaluated fibroblast activation protein–targeted PET/MRI (FAPI PET/MRI), an approach designed to visualize tissue remodeling and fibrosis associated with endometriosis. The technique uses a fibroblast activation protein inhibitor radiopharmaceutical to detect focal uptake while MRI delineates anatomic structures. The research was published in the August issue of The Journal of Nuclear Medicine.

In a retrospective study, investigators analyzed 18 premenopausal women. The test cohort included nine patients with suspected or confirmed endometriosis who underwent FAP‑targeted PET/MRI or PET/CT. A reference cohort of nine patients undergoing FAP‑targeted PET/MRI or PET/CT for initial staging of breast cancer was used to contextualize uptake patterns outside the uterus. Lesions were evaluated by segment‑based analysis, and clinical assessments with laparoscopic findings, when available, served as reference standards.

In the test cohort with PET/MRI data, MRI alone identified endometriosis‑suspicious findings in 19% of segments. Combined PET/MRI increased detection to 49% of segments. In the reference group, lesions with focal uptake outside the uterus appeared in 14 of 108 segments (13%), compared with 44 of 108 segments (41%) in the test group. Where available, PET/MRI findings showed substantial concordance with laparoscopy. The approach was notably informative for sites that are challenging to image, including the peritoneum, ovaries, fallopian tubes, and extra‑pelvic locations.

According to the report, more complete mapping before treatment could enable surgeons to plan procedures more carefully and support more personalized management. Collaborating institutions included University Hospital Münster’s Departments of Radiology, Nuclear Medicine, and Gynecology and Obstetrics, the Gerhard‑Domagk‑Institute of Pathology, and the European Institute for Molecular Imaging at the University of Münster.

“While MRI shows anatomical changes, FAP‑targeted PET/MRI highlights tissue remodeling and fibrosis, which are important features of endometriosis. In light of the established value of diagnostic MRI, combined FAP‑targeted PET/MRI may represent a valuable diagnostic tool for the evaluation of endometriosis by improving diagnostic performance,” said Philipp Schindler, MD, radiologist and nuclear medicine diagnostic specialist at the University Hospital Münster in Germany.

“Not only did the combined examination showed substantially more findings suggestive of endometriosis than MRI alone, but these included findings in areas that are often difficult to assess, such as the peritoneum, ovaries, fallopian tubes and locations outside the pelvis. If our findings are confirmed, FAP‑targeted imaging could establish a new application for molecular imaging in endometriosis, and potentially in other diseases involving tissue remodeling and fibrosis,” added Schindler.

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