Abstract

Positron emission tomography/magnetic resonance imaging (PET/MRI), a hybrid imaging method, is increasingly used in colorectal cancers. In PET/MRI, the advantages of MRI, which is an anatomical method, and F-18 fluorodeoxyglucose PET imaging, which is a functional method, are used simultaneously. Rectal cancer PET/MR protocols generally include axial, coronal, and sagittal images taken from the pelvic region using T1- and T2-weighted imaging. For staging of the primary tumor, PET/MRI may help better define the size of the tumor as well as the extent of the tumor beyond the muscularis propria. PET imaging can help characterize small lymph nodes seen on MRI and may improve the detection of hepatic metastases not yet seen on computerized tomography with imaging from the liver. Another useful aspect of PET/MRI is evaluation of response to treatment. Limitations of PET/MRI include the inability to detect small lung nodules and problems with attenuation correction. As a result, PET/MRI can improve the staging of colorectal cancers and contribute to treatment management.