PET/MRI: Applications in Clinical Imaging

PET/MRI: Where might it replace PET/CT?

Simultaneous positron emission tomography and MRI (PET/MRI) is a technology that combines the anatomic and quantitative strengths of MR imaging with physiologic information obtained from PET. PET and computed tomography (PET/CT) performed in a single scanning session is an established technology already in widespread and accepted use worldwide. Given the higher cost and complexity of operating and interpreting the studies obtained on a PET/MRI system, there has been question as to which patients would benefit most from imaging with PET/MRI versus PET/CT. In this article, we compare PET/MRI with PET/CT, detail the applications for which PET/MRI has shown promise and discuss impediments to future adoption. It is our hope that future work will prove the benefit of PET/MRI to specific groups of patients, initially those in which PET/CT and MRI are already performed, leveraging simultaneity and allowing for greater degrees of multiparametric evaluation.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:1247-1262.

Comparison of retrospective PET and MRI-DWI (PET/MRI-DWI) image fusion with PET/CT and MRI-DWI in detection of cervical and endometrial cancer lymph node metastases

OBJECTIVES

The aim of this study was to compare the accuracy of retrospective image fusion of PET/MRI-DWI with that of PET/CT and MRI-DWI alone in detecting metastatic lymph nodes in patients with cervical and endometrial carcinoma.

MATERIALS AND METHODS

Twenty-seven patients with endometrial (n = 14) and cervical (n = 13) cancer who had undergone preoperative MRI-DWI and PET/CT for staging were retrospectively evaluated. The accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of PET/CT, MRI-DWI, and PET/MRI-DWI image fusion were calculated on a per-patient basis and on a per-node basis. Histopathological and follow-up imaging results were used as the gold standard.

RESULTS

On a per-patient basis PET/MRI-DWI had the same sensitivity (87.5 %), specificity (84.2 %), diagnostic accuracy (85.1 %), PPV (70 %), and NPV (94.1 %) as PET-CT, but on a per-node basis PET/MRI-DWI showed better sensitivity (89 vs 70.2 %), specificity (91.6 vs 90.5 %), diagnostic accuracy (91.2 vs 87 %), PPV (68.7 vs 60.4 %), and NPV (97.6 vs 93.6 %) than PET-CT. Comparison of the areas under the ROC curves for the detection of metastatic lymph nodes demonstrated a non-significant difference (p = 0.055) between PET/CT and fused PET/MRI-DWI.

CONCLUSION

PET/MRI-DWI may be a valuable technique for N-staging patients with endometrial and cervical cancer, but more studies are needed to investigate its potential clinical utility.

MR-PET of the body: Early experience and insights

MR-PET is a novel imaging modality that combines anatomic and metabolic data acquisition, allowing for simultaneous depiction of morphological and functional abnormalities with an excellent soft tissue contrast and good spatial resolution; as well as accurate temporal and spatial image fusion; while substantially reducing radiation dose when compared with PET-CT.

In this review, we will discuss MR-PET basic principles and technical challenges and limitations, explore some practical considerations, and cover the main clinical applications, while shedding some light on some of the future trends regarding this new imaging technique.