Novel PET/MRI approach improves detection of endometriosis in difficult-to-assess areas

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by Society of Nuclear Medicine and Molecular Imaging

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Images from patient T1, who had menstrual cycle–dependent right shoulder pain. (A) Maximum-intensity-projection images show abnormal findings for right diaphragm (arrowhead), bilateral round ligaments, peritoneum around bilateral ovaries, and left fallopian tube. Combined PET/MRI show hyperintense lesion with focal uptake inferior of right diaphragm, indicative of endometriosis (arrowhead, B). Confirmatory laparoscopy demonstrated extensive pelvic disease and implants of right diaphragm (C) that stained intensely positive for FAP (D). Credit: Society of Nuclear Medicine and Molecular Imaging

A new PET/MRI technique that targets fibroblast activation protein (FAP) overexpressed in endometriosis is more effective at identifying lesions than conventional imaging. According to new research published in The Journal of Nuclear Medicine, this approach was particularly effective in regions of the pelvis and abdomen that are typically difficult to image. By accurately mapping the extent of endometriosis, FAP-targeted PET/MRI has the potential to enable more personalized management and improve patient outcomes.

Endometriosis is a chronic inflammatory condition characterized by endometrial tissue growing outside the uterus, affecting 6% to 10% of women of childbearing age. It is a leading cause of chronic pelvic pain, infertility and decreased quality of life, posing significant public health and economic challenges. Diagnosis of endometriosis is difficult and often delayed by four to 12 years.

Until recently, laparoscopy with histologic confirmation was considered the diagnostic gold standard for endometriosis. However, diagnostic laparoscopy is increasingly being abandoned because of advancements in diagnostic imaging. Transvaginal ultrasound and MRI are commonly used in diagnosis; however, they may underestimate the extent of disease, particularly in deep infiltrating endometriosis.

"While MRI shows anatomical changes, FAP-targeted PET/MRI highlights tissue remodeling and fibrosis, which are important features of endometriosis," said Philipp Schindler, MD, a radiologist and nuclear medicine diagnostic specialist at the University Hospital Münster in Germany.

"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."

The retrospective study investigated the feasibility of using FAP-targeted PET/MRI to improve endometriosis detection.

Participants included 18 premenopausal women: a test cohort of nine patients with suspected or confirmed endometriosis who had undergone FAP-targeted PET/MRI or PET/CT and a reference cohort of nine patients who had undergone FAP-targeted PET/MRI or PET/CT for initial staging of breast cancer.

Lesions were assessed using a segment-based analysis, and focal radiopharmaceutical uptake was assessed. Clinical assessments and laparoscopic findings, when available, served as reference standards.

In the test cohort with available PET/MRI data, MRI alone identified endometriosis-suspicious findings in 19% of segments. In contrast, combined PET/MRI identified findings in 49% of segments.

In the reference group, lesions with focal uptake of the FAP inhibitor radiopharmaceutical outside the uterus were identified in 14 (13%) of 108 evaluated segments, compared with 44 (41%) of 108 segments in the test group. Where available, PET/MRI findings showed substantial concordance with laparoscopic results.

"Not only did the combined examination show 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," Schindler noted.

"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."

Publication details

Philipp Schindler et al, Initial Results of FAPI PET/MRI to Assess the Extent of Endometriosis, Journal of Nuclear Medicine (2026). DOI: 10.2967/jnumed.125.271376

Journal information: Journal of Nuclear Medicine

Key medical concepts

EndometriosisMagnetic Resonance Imaging

Clinical categories

Obstetrics & gynecologyWomen's healthDiagnostic radiology Provided by Society of Nuclear Medicine and Molecular Imaging Who's behind this story?

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Citation: Novel PET/MRI approach improves detection of endometriosis in difficult-to-assess areas (2026, September 3) retrieved 3 September 2026 from https://medicalxpress.com/news/2026-09-petmri-approach-endometriosis-difficult-areas.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.