PET/MR is gaining popularity now that it’s commercially available, but it’s not clear what clinical indications it should be used for. Detecting and characterizing pulmonary lesions is not one of those indications, according to a study from the University Duisburg-Essen.

The researchers had 121 oncology patients, with 241 lung lesions in total, undergo an FDG PET/MR exam after an FDG PET/CT. The detection rates were calculated for MR, the PET component of PET/CT and the PET component of PET/MR in relation to the CT component of PET/CT.

The researchers found that the detection rates were 66.8 percent, 42.7 percent and 42.3 percent, respectively. They also found that image quality was better for PET/CT than PET/MR.
For detecting and characterizing lung lesions that are 10 millimeters or larger, PET/MR and PET/CT perform comparably. But the overall detection rate of PET/MR is inferior to PET/CT because it’s not able to accurately detect lesions smaller than 10 millimeters. For example, staging thoracic cancer with PET/MR wouldn’t be a good idea because there is a risk that small lung metastases would be missed.

Dr. Hossein Jadvar, president of the Society of Nuclear Medicine and Molecular Imaging (SNMMI), wrote in a viewpoint that separate chest CT exams should be performed in conjunction with PET/MR if it doesn’t show lesions and there is a clinical suspicion of lesions.

He believes that PET/MR would be most useful for indications in which MR excels compared to CT, including prostate pathology and imaging the female pelvis. It would also be beneficial in clinical situations where repeated imaging exams may be needed, especially in younger patients or in female patients of childbearing age.

Even though PET/MR is not a right fit for lung cancer, it is showing promise for other cancers. A study published in late June in the journal PLOS ONE found that fast PET/MR may be a powerful alternative to PET/CT for a diagnostic workup of lymphoma patients.

According to SNMMI, PET and PET/CT are the most accurate tools for determining if treatment is working, whether the cancer is spreading to other parts of the body, and if there is reoccurrence.

However, not everyone agrees — the American Cancer Society stated that PET/CT’s role in checking whether treatment is working isn’t proven. Furthermore, most physicians don’t recommend PET/CT exams for routine follow up after treatment for patients with lung cancer.

In the field of molecular imaging, exciting advancements are on the horizon for better understanding lung cancer. Researchers have developed reporter-gene imaging systems, which involve engineering genes that can adhere to specific cells so they can be tracked with molecular imaging technologies.

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