PET/MRI applications in lung cancer

1157 Objectives: 1. Comparison between PET/CT and PET/MRI in detecting distant metastases of lung cancer 2. Review of the potential advantages of PET/MRI compared with PET/CT in assessment of patients with lung cancer 3. Highlight the limitations of PET/MRI in lung cancer assessment Abstract: Lung cancer is one of the most common cancers in the world, causing high morbidity and mortality, and is under active study through use of positron emission tomography/magnetic resonance imaging (PET/MRI). Lung cancers are divided into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) subtypes. The treatment and prognosis is greatly influenced by tumor type and stage at diagnosis. MRI has been investigated as a technique for whole-body cancer staging, providing high soft tissue contrast and the potential for multiparametric tissue characterization through diffusion-weighted and dynamic contrast-enhanced sequences. The primary tumor detection rate of PET/MRI is of interest to clinicians managing patients with lung cancer. It is hypothesized that small lung nodules may be harder to visualize on PET/MRI compared to positron emission tomography/computed tomography (PET/CT) based on the known differences between CT and MRI. Conversely, lung cancer has tendency to metastasize to the brain, adrenal glands, and bone marrow, which are all organs/tissues where MRI may perform better than CT. Therefore, MRI can detect metabolically inactive or minimally active metastases that are missed on PET/CT. Previous studies have assessed the feasibility of a whole-body MRI protocol for lung cancer staging and have demonstrated accuracy similar to that of PET/CT for NSCLC staging with better sensitivity than PET/CT for metastatic disease. PET/MRI is a new technique that has shown similar performance to PET/CT in several small retrospective studies. The potential advantages of the technique include the acquisition of multiparametric metabolic, functional, and morphological information provided by combining use of various radiotracers with different MRI sequences. Moreover, the lack of ionizing radiation exposure from MRI is a major advantage over CT, particularly when repeat studies are required for purposes of patient management. MRI has also evolved with newer and faster sequences that allow for whole-body imaging, as well as functional imaging sequences, including magnetic resonance spectroscopy (MRS), perfusion-weighted imaging (PWI), and diffusion-weighted imaging (DWI), which have broadened the applications of MRI for characterizing disease. Given the potential additional benefits of combined PET and MRI, the imaging algorithm currently used for lung cancers can be further optimized, potentially allowing for optimal clinical information to be obtained from a single imaging session. Ongoing research studies have reported on the utility of PET/MRI for biological characterization of tumors and for guiding future promising treatment strategies. PET/MRI may be useful to contribute to the future design of individually adapted treatment approaches based on multiparametric functional imaging. Combined PET/MRI may be particularly useful for radiotherapy treatment planning in terms of tumor description and characterization. Use of diffusion-weighted imaging during PET/MRI may increase diagnostic confidence to differentiate recurrent disease from post-treatment changes such as in the setting of prior radiation therapy.