PET/MRI

The merger of 2 fundamentally different scanner technologies, PET and MRI, is forming a more accurate and dependable way to diagnose different cancers, researchers say in a report published in the September issue of Current Radiology Reports.

The relative strengths and weaknesses of the 2 modalities are both synergistic and complementary, which allows each component to compensate for the limitations of the other, according to the research team, led by Karin Anna Herrmann, MD, from the Department of Radiology at University Hospitals Case Medical Center and Case Western Reserve University in Cleveland.

The PET/MRI combination first appeared in the clinical setting in 2007 for brain applications, the researchers report.

Since then, it has undergone many alterations and "tweaks," and is no longer an experimental research device but has real use in the clinic, at least in Cleveland. The researchers note that their institution is the first cancer center hospital in the world to house this technology in a purely clinical setting.

"This hybrid scanner has the potential to improve patient care by increasing understanding of the causes, effects, and development of disease processes to better diagnose cancer and various other diseases," said coauthor Norbert Avril, MD, professor at the Case Western Reserve University School of Medicine.

"We are very excited to be among the first to be able to help establish guidelines of how best to use this technology to guide physicians on the value of the PET/MRI in diagnosing and staging various forms of cancer," he said in statement.

To date, the center has examined 145 cancer patients with the double-scanning protocol of PET/CT followed by PET/MRI, performed on the Philips Ingenuity TF PET/MRI system.

"Our preliminary experience with this new diagnostic imaging technology proves that it is promising for oncologic applications," Dr. Herrmann said in a statement. "We found the PET/MRI enhanced our ability to detect malignant areas and more accurately and confidently diagnose several types of cancers, potentially providing physicians with the ability to improve treatment planning and better monitor the disease."

In the current report, Dr. Herrmann and her colleagues focus on their initial experiences with PET/MRI in various oncology settings.

Head and Neck Cancers

"In our own experience, PET/MRI has a performance similar to that of PET/CT in the nodal staging of head and neck cancers," Dr. Herrmann said.

She and her team studied 14 patients with head and neck neoplasms who underwent both PET/CT and PET/MRI in 1 imaging session after a single injection of 2-deoxy-2(¹⁸F)fluoro-D-glucose (FDG). The average delay between the 2 scans was 56 minutes.

The analysis, by independent readers, showed that of the 105 FDG-avid lesions identified with PET/CT, 80% were correctly identified and exactly matched in PET/MRI.

Additionally, in 11 of the patients (79%), there was complete agreement in staging between the observers. In cases with discrepant findings, PET/MRI found 2 additional lymph nodes per patient.

"In the case of head and neck cancer, the expected potential benefit of PET/MRI rests in the exact superimposition and, as a result, precise anatomic correlation between FDG-avid tissue and the anatomic detail derived from MRI images," Dr. Herrmann explained.

Lung Cancer

Currently, lung cancer staging and follow-up is done with PET/CT, which provides very high accuracy for local T and N and distal M staging. So far, the researchers report that more evidence is needed to show that PET/MRI is better than the current diagnostic algorithms for patients with lung cancer.

In their use of PET/MRI for nodal staging only, the researchers found that standardized uptake values showed a strong positive correlation between the technique and PET/CT with regard to FDG-avid lesions.

Although the overall diagnostic performance of PET/MRI was slightly inferior to that of PET/CT, the difference was not statistically significant.

Pancreatic Cancer

Seven patients gave permission for the researchers to test the potential of PET/MRI compared with individual imaging with PET/CT and MRI.

"One of the most striking benefits of PET/MRI in pancreatic cancer in our opinion is its ability to provide comprehensive information about local T stage, resectability, and distant metastatic disease in a single examination," Dr. Herrmann said.

Their experience with these 7 patients showed that PET/MRI improved the diagnostic confidence in TNM staging over that of PET/CT in 4 of the patients, mainly in the T staging.

In 1 patient, MRI improved the confidence in the diagnosis of hepatic metastases, but with PET, the presence of metastases was questionable because of poor FDG uptake and the small size of the metastatic lesions.

Also, the information from PET, when added to information from CT and MRI, was "distinctly" helpful in 3 of 7 patients who had postoperative changes after a Whipple procedure.

Colorectal Cancer

The researchers write that the combination of PET and MRI for diagnosing and staging colon cancer is a winning one that "will only strengthen their already high performance in this disease category."

The hope is that the hybrid technology will allow comprehensive TNM staging in a single examination.

The researchers also suggest that the combined use of MRI and PET/CT to detect lymph node involvement in rectal cancer would be very beneficial. "The high soft tissue contrast and morphologic criteria established in MRI for assessment of metastatic nodal involvement may complement the lack of sensitivity of PET/CT alone in this application," they write.

Ovarian Cancer

PET and MRI "are distinctly complementary and synergistic" in the diagnosis and detection of recurrent ovarian cancer, the researchers write. "With both modalities superimposed, our experience shows that the subjective diagnostic confidence regarding the presence or absence of disease increases to a substantial degree," Dr. Herrmann said.

Lymphoma

The group has had experience with PET/MRI in 10 patients with malignant lymphoma. The patients underwent FDG-PET/CT followed by PET/MRI in a single imaging session, and results showed a high correlation in terms of localization and characterization between the 2 techniques.

Pediatric Neoplasms

"The value of combining PET and MRI has been demonstrated extensively in the world of pediatric oncology, not only for neuroradiologic applications but also in children with sarcoma, lymphoma, small cell cancers, and other cancers," the researchers write.

The obvious benefits of combining the 2 modalities in 1 examination include reduced radiation exposure when the CT component is substituted with MRI and the "expected improvement of the logistics and workflow of such complex examinations," the researchers write.

This research was supported by Philips Healthcare . Dr. Herrmann has disclosed no relevant financial relationships. Dr. Avril reports that his institution is funded by a grant from Philips Healthcare.

Curr Radiol Rep. 2013;1:161-176. Full text