The new PET/MRI approach targets fibroblast activation protein (FAP) overexpressed in endometriosis. In a retrospective study, it identified more lesions than conventional imaging. The approach was particularly effective in difficult-to-assess areas of the pelvis and abdomen.
The study assessed the feasibility of FAP-targeted PET/MRI for endometriosis detection. It included 18 premenopausal women. Nine patients had suspected or confirmed endometriosis and underwent FAP-targeted PET/MRI or PET/CT. A reference cohort included nine patients who underwent FAP-targeted PET/MRI or PET/CT for initial breast cancer staging. The researchers assessed lesions by segment and evaluated focal radiopharmaceutical uptake. Clinical assessments and laparoscopic findings served as reference standards when available.
PET/MRI Identifies More Findings
The study reported the following findings:
- Test cohort: MRI alone identified endometriosis-suspicious findings in 19% of segments. Combined PET/MRI identified findings in 49% of segments.
- Reference cohort: Focal uptake of the FAP inhibitor radiopharmaceutical outside the uterus was found in 14 of 108 segments (13%).
- Test cohort: The same finding occurred in 44 of 108 segments (41%). Where available, PET/MRI findings showed substantial concordance with laparoscopic results.
According to Philipp Schindler, a radiologist and nuclear medicine diagnostic specialist at University Hospital Münster in Germany, MRI shows anatomical changes. FAP-targeted PET/MRI, he said, highlights tissue remodeling and fibrosis. These 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.”
Findings in Difficult-to-assess Regions
The combined examination identified findings suggestive of endometriosis in several difficult-to-assess areas. These included the peritoneum, ovaries and fallopian tubes. Findings were also reported in locations outside the pelvis.
Schindler explained furthermore: “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.”
Endometriosis affects 6% to 10% of women of childbearing age. The condition involves endometrial tissue growing outside the uterus. Diagnosis can be difficult and may be delayed by four to 12 years.
Schindler said further confirmation could establish a new application for FAP-targeted molecular imaging in endometriosis. He also cited potential use in other diseases involving tissue remodeling and fibrosis.
Overall, the study found more endometriosis-suspicious findings with FAP-targeted PET/MRI than with MRI alone. The additional findings included areas that are often difficult to assess.
