Clinical applications of PET/MRI in oncology: Opportunities and challenges

Learning Objectives 1. To review performance of PET/MRI for diagnosis, staging, prognostication, response assessment, and treatment planning of malignancies. 2. To discuss new and evolving horizons related to PET/MRI and their potential in the management of malignancies.

PET/MRI has been recently introduced for clinical use and has the potential for superior diagnostic performance compared to PET/CT for some applications in the oncological setting. Higher soft tissue contrast resolution, improved lesion detection and characterization, multiplanar image acquisition, and functional imaging capability are some of the factors, which provide additional capabilities over PET/CT. Structural and functional information provided by MRI about neoplasms is complementary to the molecular information provided by PET, where tumor volume and extent can be defined with high spatial resolution, specifically in organs where CT is suboptimal. In this review, we will discuss these topics: 1. Advantages of PET/MRI vs PET/CT i. Superior detection and characterization of tumors over CT in areas with suboptimal CT soft tissue contrast (e.g., brain, head & neck, spinal cord, peripheral nerves, liver, pelvic organs) ii. Optimization of treatment planning and response assessment iii. Reduction of radiation dose 2. Applications of PET/MRI for assessment of patients with cancer i. Local tumor assessment a. Tumor detection b. T staging and volume delineation ii. Lymph node assessment a. Nodal characterization as benign vs. malignant b. N staging iii. Distant metastasis assessment a. M staging in bone marrow, liver, and brain iv. Representative tumor examples a. Head and neck tumors b. Pancreatic tumors c. Gynecologic tumors v. Advanced MRI methods a. Diffusion-weighted imaging, perfusion-weighted imaging, magnetic resonance spectroscopy