Promise of PET/MR in Gynecologic Imaging Explored
While PET/MR shows promise in detecting and staging women's pelvic cancers, more research is required to take full advantage of its capabilities, said presenters of scientific papers on Wednesday at RSNA 2013.
Patrick Veit-Haibach, M.D., of the Department of Medical Imaging at University Hospital Zurich, assessed and compared the diagnostic accuracy of PET/CT and PET/MR imaging for primary gynecological malignancies. "PET/MR imaging for advanced tumors works," he said. "It provided several pieces of useful information concerning the local tumor status. However, the overall detection rate for local and distant metastases was not different from PET/CT."
PET/MR imaging provided localized information, while PET/CT was obtained on the whole body to provide information on the distant metastases, Dr. Veit-Haibach said.
The study involved included 26 patients with 18 suspected primary cancers and eight with suspected recurrence. The two imaging procedures were performed within a single session, with a "shuttle" table facilitating the transition from the MR table to the PET/CT table. Following F18-fluorodeoxyglucose ([18F]FDG) contrast administration, the patients underwent MR imaging of the abdomen and pelvis and then standard unenhanced PET/CT with a field of view from the mid-thigh to the vertex of the skull.
"For primary tumor detection, PET/MR was superior in 14 cases and equal in 10," Dr. Veit-Haibach said. "But PET/CT provided advantages concerning distant metastases." PET/CT overall showed additional relevant additional information in nine cases, mainly concerning distant metastases, while PET/MR showed relevant additional information in three cases concerning the primary tumor, he added.
PET/MR imaging might be one of the future clinical routine indications for evaluating gynecologic tumors, Dr. Veit-Haibach said. "However, in advanced stages, whole-body imaging is needed. We have to figure out efficient whole body protocols which adequately cover the pelvis but also the rest of the body for evaluation of distant metastases, but not having the patient too long in the scanner. Otherwise it will be a very expensive staging tool."
Future research will also go into multiparametric PET/MR imaging with advanced MR techniques to better characterize the tumor itself, Dr. Veit-Haibach said.
Presenting the results of separate study, Karsten Beiderwellen, M.D., of the Department of Diagnostic and Interventional Radiology at University Hospital Essen in Germany, said PET/MR imaging as a whole-body technique allowed a higher detection rate of female pelvic metastatic lesions than MR imaging alone. "Integrated PET/MRI is a high-potential modality for whole body staging of patients with pelvic malignancies," Dr. Beiderwellen said.
"This very young technique combines two powerful modalities," Dr. Beiderwellen continued. "First, MR imaging, offering an excellent soft tissue contrast, allows for visualization of the local tumor extent and possible tumor infiltration. Second, FDG-PET allows for detection of small distant metastases as well as information on metabolic activity of suspect lesions."
Study results indicated that PET/MR imaging when compared to MR imaging alone leads to a higher detection rate of metastatic lesions, a higher lesion conspicuity and a higher diagnostic confidence in the assessment of metastatic lesions. The study included 20 patients with ovarian or cervical cancer who underwent a whole-body MR protocol using an integrated scanner. The researchers detected metastatic lesions in 17 patients.
"Based on PET/MR, there was correct identification of all 17 disease-positive patients, and based on MR alone there was correct identification of 15 patients," Dr. Beiderwellen said. He noted that PET/MR provided significantly higher lesion conspicuity and significantly higher diagnostic confidence.
"Today, pelvic MR imaging as well as whole-body PET—or, rather, PET/CT—are already part of the restaging procedure in patients with recurrent pelvic malignancies," Dr. Beiderwellen said. "However, these examinations are usually performed independently, on different days.
Administering independent exams means that, due to different patient positioning and differences in the state of bladder fullness, lesions characterized in one modality might not be comparable or present in the other modality, Dr. Beiderwellen said. "There is also the matter of radiation exposure. Nowadays, PET is usually performed as combined PET/CT. The added CT leads to an additional radiation exposure that can be avoided in PET/MR imaging."
While the study included a small patient cohort and lacked histopathological correlation for all lesions, the results are still promising, Dr. Beiderwellen said. "PET/MRI might be a valuable alternative to MR and PET/CT in re-staging of patients with recurrent pelvic malignancies," he concluded.