Systematic Review: PET/MRI May be More Advantageous than PET/CT in Cancer Imaging

For cancer recurrence, lesion-level metastasis and patient-level regional nodal metastases, positron emission tomography/magnetic resonance imaging (PET/MRI) offers comparable pooled sensitivity to PET/computed tomography (PET/CT), according to findings from a new systematic review. However, the authors of the review also found that PET/MRI offered significant advantages in imaging for breast cancer, colorectal cancer, cervical cancer, and liver cancer.

For the systematic review, recently published in the American Journal of Roentgenology, researchers reviewed findings from 29 comparative studies (with a total of 1,656 patients) involving the use of fluorodeoxyglucose (FDG) PET/MRI and FDG PET/CT for diagnosing cancer.

The researchers found fairly similar overall pooled sensitivity and specificity for the imaging modalities for cancer recurrence and metastasis. In five studies assessing the detection of lesion-level recurrence and/or metastases, the review authors noted a 94 percent sensitivity rate and 83 percent specificity rate for PET/MRI in comparison to 91 percent and 81 percent, respectively for PET/CT.

In five other studies examining patient-level regional nodal metastases, PET/MRI had similar sensitivity to PET/CT (88 percent vs. 86 percent) and slightly higher specificity (92 percent vs. 86 percent), according to the review authors.

However, in other reviewed studies, PET/MRI provided sensitivity and staging accuracy rates that were significantly higher than PET/CT across different kinds of cancer.

Specifically, the review authors pointed out that PET/MRI had staging accuracy rates that were 23.5 percent higher for breast cancer (98 percent vs. 74.5 percent) and 27 percent higher for colorectal cancer (96.2 percent vs. 69.2 percent) than PET/CT. The researchers also noted a 27 percent higher sensitivity with PET/MRI in detecting primary cervical cancer (93.2 percent vs. 66.2 percent).

“PET/MRI generally demonstrated comparable or better performance with respect to PET/CT. For example, PET/MRI showed better performance than PET/CT in a pooled assessment for detection of regional lymph node metastases and showed better performance than PET/CT in individual studies relating to breast cancer and colorectal cancer staging, primary detection of breast cancer and cervical cancer, detection of liver metastases, and detection of endometrial cancer local invasion,” wrote lead meta-analysis author Amit Singnurkar, MDCM, MPH, MBA, FRCPC, who is affiliated with the Department of Medical Imaging at the University of Toronto in Canada, and colleagues.

While the systematic review didn’t specify the rationale behind PET/MRI’s stronger diagnostic performance in individual studies, the authors suggested key capabilities and emerging advances with MRI.

“ … The improvements likely related to the high soft tissue contrast and soft tissue differentiation of MRI, as well as the use of advanced sequences such as (diffusion-weighted imaging) DWI,” posited Singnurkar and colleagues. “The advantages of PET/MRI can aid lesion detection and characterization in anatomic regions including the liver and pelvis.”

For the diagnosis of lesion-level liver metastasis, the researchers noted PET/MRI sensitivity ranging between 91.1 to 98 percent in contrast to 42.3-71.1 percent for PET/CT.

However, the review authors noted a number of challenges with PET/MRI with access being particularly limited.

“PET/MRI systems are less widely available than PET/CT systems due to higher cost and operational complexity, with approximately 30 PET/MRI systems versus over 1,600 PET/CT systems installed in the United States. Additionally, PET/MRI has substantially longer examination times, impacting patient tolerability and throughput,” explained Singnurkar and colleagues.

(Editor’s note: For related content, see “Study: PSMA PET/CT More Advantageous than MRI for Locoregional Staging of Prostate Cancer,” “PET/CT or mPMRI: Which is Better for Detecting Biomechanical Recurrence of Prostate Cancer?” and “SNMMI: New Study Suggests Merits of FAPI PET/CT for Breast Cancer Staging.”)

In regard to limitation of the meta-analysis, the authors conceded a lack of clarity on bias risk in 26 of the reviewed studies and suggested publication bias with a possible emphasis on reporting studies on PET/MRI with favorable results. The researchers also noted variability with image acquisition protocols and that the FDG PET focus of the meta-analysis precluded any discussion of newer PET radiotracers.