Synopsis

Keywords: Cross-organ: Cancer, Image acquisition: Multiparametric

PET/MRI is a hybrid imaging modality that combines the benefits of PET and MRI, especially useful in the context of personalized medicine. PET/MRI offers functional information and excellent soft tissue contrast, making it a powerful tool in diagnostics and treatment of numerous conditions. Its simultaneous scanning capabilities save time and reduce radiation exposure compared to PET/CT. Though the number of PET/MRI scanners worldwide is still low, the development and implementation of novel PET tracers can contribute to shaping its future use.

Personalized medicine aims to deliver the right treatment to the right patient at the right time, and medical imaging is a key element within this concept (1). While positron emission tomography (PET) and magnetic resonance imaging (MRI) has been clinically available as separate modalities for around 40 years, the hybrid modality PET/MRI is much newer, with commercial scanners available for clinical use since 2011. The main advantage of PET/MRI has often been considered to be the excellent soft tissue contrast and structural information from MRI provided together with the functional information from PET. However, the capability of MRI to provide functional information through diffusion-weighted imaging, dynamic contrast-enhanced imaging, and other specialized sequences as well as MR spectroscopy together with the quantitative physiologic information provided by PET is also important (2). This makes up a powerful technology, with several advantages that can be exploited within the concept of personalized medicine. For conditions requiring double modality imaging, simultaneous PET/MRI examination saves time, and compared to PET/CT this is achieved at a significantly lower overall radiation dose. Both clear benefits for the patients. Moreover, simultaneous scanning improves the image registration, facilitating the health personnel interpreting the images, but also medical image analysis approaches in general. The number of PET/MRI scanners installed worldwide is still quite low (app. 320 PET/MRI scanners in 2023), and most centers with access to the technology use it for approaches with combined clinical and research purposes. The main fields of applications are currently found within oncology, neurology and cardiology. 18F-FDG has been a workhorse for PET examinations since its introduction. However, the number of available PET tracers are steadily increasing and a variety of novel PET radioligands as well as theranostic and therapeutic agents are evaluated for their potential clinical applications. There is a trend towards the development of more disease specific PET tracers, still, some of the more general tracers also have very interesting potential. This lecture will focus on applications of PET/MRI in personalized medicine exploiting other tracers than 18F-FDG, with emphasis on breast and prostate cancer, and how development and implementation of novel PET tracers together with the functional capabilities of MRI can shape clinical use of the technology in the years to come.

Acknowledgements

The Trond Mohn Foundation, the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology and the Norwegian Cancer Society are acknowledged for research funding to advance the use of PET/MRI.