New PET/MRI Scan Spots More Endometriosis Lesions Than MRI Alone, Study Finds

Endometriosis, a chronic inflammatory condition in which tissue similar to the uterine lining grows outside the uterus, affects 6% to 10% of women of childbearing age and is a leading cause of chronic pelvic pain, infertility and reduced quality of life. Diagnosis is often delayed by four to 12 years, partly because standard imaging can underestimate how far the disease has spread, particularly in its more deeply invasive form. A new imaging technique combining positron emission tomography (PET) and MRI, targeting a protein called fibroblast activation protein (FAP) that is overexpressed in endometriosis tissue, identified significantly more lesions than conventional imaging, according to a study published in The Journal of Nuclear Medicine.

Laparoscopy with tissue confirmation was long considered the diagnostic gold standard for endometriosis, but it is increasingly being replaced by imaging methods such as transvaginal ultrasound and MRI. The new retrospective study, involving 18 premenopausal women, compared a test group of 9 patients with suspected or confirmed endometriosis against a reference group of 9 patients who had undergone the same scans for initial breast cancer staging. In the test group, MRI alone identified endometriosis-suspicious findings in 19% of body segments examined, compared with 49% of segments when PET and MRI were combined.

In the reference group, focal uptake of the FAP-targeting radioactive tracer outside the uterus was seen in 14 of 108 evaluated segments (13%), compared with 44 of 108 segments (41%) in the test group. Where laparoscopy results were available, the combined PET/MRI findings showed substantial agreement with them. "While MRI shows anatomical changes, FAP-targeted PET/MRI highlights tissue remodeling and fibrosis, which are important features of endometriosis," said Philipp Schindler, a radiologist and nuclear medicine specialist at University Hospital Münster in Germany.

Schindler said the combined scan found substantially more findings suggestive of endometriosis than MRI alone, including 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," he said.