A newly reported Journal of Nuclear Medicine study explores fibroblast activation protein inhibitor (FAPI) PET/MRI as a potential advanced imaging tool for endometriosis. The preliminary findings suggest that combining molecular FAPI imaging with the anatomical detail of MRI may identify disease sites that are difficult to recognize using conventional MRI alone.
Endometriosis frequently produces fibrosis and fibroblast activation, providing a biological rationale for FAPI-based imaging. By combining this molecular signal with high-resolution MRI, investigators aimed to improve visualization of both pelvic and extra-pelvic endometriotic lesions.
In a small retrospective cohort of premenopausal women, FAPI PET/MRI identified more endometriosis-suspicious anatomical segments than MRI alone, with additional findings particularly involving peritoneal, ovarian, and tubal locations.
Where operative findings were available for comparison, imaging demonstrated substantial agreement with laparoscopic disease mapping. Particularly interesting was the ability to demonstrate lesions in challenging locations, including suspected diaphragmatic endometriosis, where conventional pelvic imaging may provide incomplete assessment.
Why Better Mapping Matters Before Laparoscopy
The surgical challenge in endometriosis is not simply confirming the presence of disease. The extent and anatomical distribution of endometriosis determine the complexity of surgery.
Preoperative underestimation can result in unexpected involvement of the:
- Rectum or sigmoid colon
- Ureter and pelvic sidewall
- Bladder
- Ovaries and tubes
- Deep retroperitoneal spaces
- Upper abdomen
- Diaphragm
Identifying such disease before surgery may substantially change informed consent, operating time allocation, port positioning, patient positioning, multidisciplinary involvement, bowel preparation, ureteric strategy, and operative sequencing.
Potential Surgical Value
For advanced gynecologic laparoscopic surgeons, FAPI PET/MRI could eventually provide a more comprehensive preoperative endometriosis map. Rather than discovering the full extent of disease only after laparoscopic entry, surgeons may be able to anticipate complex multi-compartment involvement and assemble the appropriate gynecologic, colorectal, urological, or thoracic expertise beforehand.
The technology could be particularly relevant when symptoms suggest extensive disease but conventional MRI findings appear limited or when deep or extra-pelvic endometriosis is suspected.
Important Limitations
These findings remain preliminary. Only 18 women were included across the test and reference cohorts, menstrual-cycle timing was not standardized, and not every imaging finding had operative confirmation.
The study therefore does not establish FAPI PET/MRI as a replacement for conventional ultrasound, MRI, or laparoscopy. Larger prospective studies are required to determine diagnostic accuracy, false-positive rates, optimal imaging protocols, cost-effectiveness, and whether improved lesion detection actually changes surgical outcomes.
Clinical Takeaway
FAPI PET/MRI is a promising molecular-anatomical imaging approach that may improve mapping of deep, peritoneal, and extra-pelvic endometriosis before surgery. Its greatest potential surgical value may be in anticipating complex disease, improving multidisciplinary planning, and reducing unexpected findings during laparoscopy. For now, it should be regarded as an emerging investigational tool requiring prospective validation.
Source: Medical Xpress – PET/MRI Approach May Reveal Endometriosis in Difficult-to-Image Areas
Key Message
The 4 September 2026 update highlights the movement of minimally invasive gynecologic surgery toward more precise preoperative disease mapping. If validated, FAPI PET/MRI could help surgeons understand not merely whether endometriosis is present, but where it is located and how extensively it has altered anatomy before the first trocar is inserted—supporting better counselling, multidisciplinary preparation, operative planning, and safer laparoscopic excision.