Simultaneous PET–MRI in oncology: a solution looking for a problem?

Abstract

With the recent development of integrated positron emission tomography-magnetic resonance imaging (PET-MRI) scanners, new possibilities for quantitative molecular imaging of cancer are realized. However, the practical advantages and potential clinical benefits of the ability to record PET and MRI data simultaneously must be balanced against the substantial costs and other requirements of such devices. In this review we highlight several of the key areas where integrated PET-MRI measurements, obtained simultaneously, are anticipated to have a significant impact on clinical and/or research studies. These areas include the use of MR-based motion corrections and/or a priori anatomical information for improved reconstruction of PET data; improved arterial input function characterization for PET kinetic modeling; the use of dual-modality contrast agents; and patient comfort and practical convenience. For widespread acceptance, a compelling case could be made if the combination of quantitative MRI and specific PET biomarkers significantly improves our ability to assess tumor status and response to therapy, and some likely candidates are now emerging. We consider the relative advantages and disadvantages afforded by PET-MRI and summarize current opinions and evidence as to the likely value of PET-MRI in the management of cancer.

Improved Differentiation of Benign and Malignant Breast Tumors with Multiparametric 18Fluorodeoxyglucose Positron Emission Tomography Magnetic Resonance Imaging: A Feasibility Study

“…Another limitation is that all patients underwent fused but not simultaneous MP 18 FDG PET-MRI. Simultaneous PET-MRI scanners are now becoming clinically available (48), and it can be expected that the proposed reading scheme for MP 18 FDG PET-MRI in breast tumors will be equally applicable to simultaneous MP 18 FDG PET-MRI. All MR examinations were performed at 3T rather than 1.5T, which is the most commonly used field strength in breast MRI.…”

Potential Pediatric Applications of PET/MR

“…The aim of contemporary medical imaging is to integrate complementary imaging to increase information earned by a single modality (13). Tumor imaging not only is used for tumor detection and evaluation of tumor characteristics and tumor extension but also has a role in the assessment of a treatment response and surveillance for residual or recurrent tumor (10,14).…”

Workflow in Simultaneous PET/MRI

“…MRI offers a better soft tissue contrast than CT does and potentially a range of relevant, partly quantitative information on tumor biology related to, for example, blood flow, vascular and tissue spaces, pH and hypoxia, cellularity, and (via magnetic resonance spectroscopy) metabolite concentrations-all without exposing the patient to ionizing radiation. 18 Thus, combining MRI with PET information might give a more complete overview of the patient's disease state than PET/CT does.…”