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 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 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 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, without 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.
Combining PET and MR imaging could be more effective in evaluating abdominalmalignancies than conventional body CT, according to a presenter at RSNA 2013.
Researchers in South Korea observed added value from PET/MR in more than 30 percent of the patients used in their study.
“Because of low soft-tissue contrast of CT examination, there are some limitations in the evaluation of abdominal oncologic diseases,” said presenter Beomsik Kang, a resident in the radiology department at Seoul National University Hospital where the study was conducted. “In fact, in our study, a relatively large proportion of additional findings of PET/MR compared to CT were characterization of hepatic lesions, which was not determined at CT scan.”
Researchers conducted a retrospective study of 122 patients (80 men, 42 women) who underwent 18-FDG PET/MR and contrast-enhanced CT for initial staging or follow-up of abdominal malignancy. Oncological diagnoses for the patients included anal cancer, colorectal cancer, cholangiocarcinoma, heptocellular carcinoma, gallbladder cancer, lymphoma, renal cell carcinoma and pancreatic cancer.
Using PET/MR, additional findings beyond the CT results were discovered in 38 patients. Lesion characterization was improved in 26 patients, while additional malignancies were identified in 12 patients. PET/MR also resulted in a change of treatment strategy for 22 patients.
Further analysis of the results shows dedicated MR improved lesion characterization in five patients. Whole-body PET/MR improved lesion characterization in six patients, and helped identify an additional malignancy in seven patients. Lesion characterization was improved in 15 patients when PET/MR was combined with MR. The combination also resulted in detection of additional malignancies in five patients.
No statistical improvement was shown in T and N staging of CT and PET/MR when compared with histopathologic findings in 24 patients who underwent surgery after the PET/MR scan. PET/MR produced correctly staged results for 18 of the 24, compared with 15 using CT. Overstaging with PET/MR occurred in three (compared to five), and understaging also occurred in three (compared with four).
But in the N stage, CT correctly staged 16 of the patients, while PET/MR had 15. Both methods overstaged four patients, while CT understaged four and PET/MR had five.
Despite the positive results that suggest PET/MR does add clinical value, Kang cautioned against using it as a replacement for CT. He added the convenience and relative short time needed for CT scans should be emphasized. It is also more cost effective than the PET/MR combined.
“It is too early for use to make a conclusion regarding whether PET/MR can replace a conventional CT based on our study results with a small number of patients,” Kang said. “As of now, it should be regarded as being in addition to CT.”
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