PET/MRI

Both PET and MRI are imaging techniques that have been used separately for numerous applications, including the detection and diagnosis of brain tumors. Taken together, PET/MRI offers a more comprehensive diagnosis, while reducing the patient’s exposure to radiation.

PET (or positron emission tomography) is an imaging technology that detects the presence of a specific type of radiation (i.e. positrons). PET involves the injection, and subsequent tracking, of special compounds called radiotracers. Radiotracers are small, biologically active molecules labeled with positron emitters. For example, radiolabeled sugars, like fluorodeoxyglucose (FDG), are often used as a radiotracer to identify tumors. As a radiolabeled sugar, FDG is taken up by tissue with high metabolic activity, including tumors. Because of this application, PET is often used as a functional imaging tool to identify tumor sites. 

MRI (or magnetic resonance imaging) is a noninvasive imaging technology used for many applications, including neuroimaging. It is a standard neuroimaging technique for detection of tumors and the surrounding anatomical structures in the brain. 

After treatment, especially with radiation therapy, it may difficult to detect residual tumor with MRI alone. This is because treatment itself can cause changes in the brain tissue (often called treatment-related effects) that look similar to residual tumor, at least by MRI. For these patients, PET/MRI is particularly helpful for detecting any remaining or recurrent tumor. In general, PET/MRI offers a powerful combination of molecular, functional, and anatomical information in the convenience of a single scanning session, and often provides essential data for critical treatment decisions. 

In 2014, UCSF participated in the first PET/MRI clinical trial, which resulted in FDA approval.  Since the installation of the machine, researchers at UCSF have been working on numerous applications to leverage the capabilities of the new technology. For example, radiotracers that bind to tumor-specific proteins can help target other metabolic pathways that are unique to tumors. Ongoing research on the development of new radiotracers will allow for more precise imaging capabilities in the future. 

This content was reviewed by UCSF Professor of Radiology, Sabrina Ronen, PhD.