PET and MR imaging: the odd couple or a match made in heaven?

Abstract

PET and MR imaging are modalities routinely used for clinical and research applications. Integrated scanners capable of acquiring PET and MR imaging data in the same session, sequentially or simultaneously, have recently become available for human use. In this article, we describe some of the technical advances that allowed the development of human PET/MR scanners; briefly discuss methodologic challenges and opportunities provided by this novel technology; and present potential oncologic, cardiac, and neuropsychiatric applications. These examples range from studies that might immediately benefit from PET/MR to more advanced applications on which future development might have an even broader impact.

Keywords: PET/MR imaging; applications; cardiology; multimodality imaging; neurology; oncology.

Fig. 1

Integrated PET/MR scanners currently available for human use: (A) Siemens MR-BrainPET prototype, (B) Philips sequential PET/MR whole-body scanner and (C) Siemens Biograph mMR whole-body scanner.

Fig. 2

Simultaneous PET/MR exam in a colorectal cancer patient. T1-weighted post-contrast MR image demonstrates an enhancing mass within the rectum (white arrow). The PET image shows FDG-avidity of the mass without anatomic correlate. The DWI image at the same level demonstrates a hyperintense lesion. Low signal intensity compatible with restricted diffusion is observed in the ADC map. Data acquired on the Biograph mMR scanner, A.A. Martinos Center, MGH.

Fig. 3

Sequential PET/MR for staging in a patient with an epidermoidal carcinoma of the cervix after conization and sigmoidectomy. (A) Whole-body PET shows hypermetabolic uptake in lower pelvis. (B–D) MR shows thickening of the colon wall with involvement of the outer fatty tissue corresponding to a hypermetabolic tracer uptake. Follow-up biopsy revealed granulomatosis without residual tumor. Data acquired on the Philips Ingenuity PET/MR scanner, University Hospital of Geneva. Images courtesy of Osman Ratib.

Fig. 4

Multiparametric imaging using [¹¹C]choline PET and DCE-MRI increases diagnostic confidence/accuracy in a patient with prostate-specific antigen recurrence after radical prostatectomy. Only faint anatomical correlate is observed in the contrast-enhanced CT. Similarly, the T2-weighted MR image shows superb anatomical detail but also only small tumor correlate. However, very clear enhancement is observed in the early arterial phase of the DCE-MRI and the parametric map, correlating with the PET signal. The cumulative evidence suggesting local recurrence as opposed to scar tissue/unspecific enhancement increases the diagnostic certainty. Data acquired on the Biograph mMR scanner, TUM/LMU, Munich, Germany. Images courtesy of Ambros Beer.

Fig. 5

Simultaneous PET/MR in a myeloma patient. (A) Plain film of the left knee demonstrating lytic lesions in the medial femoral condyle and proximal tibia (black arrows). (B) Coronal FDG-PET, (C) fat-saturated T2-weighted MR and (D) fused images at the same level demonstrating concordant foci in the right tibia, right femoral condyle, and left medial femoral condyle. Data acquired on the Biograph mMR scanner, A.A. Martinos Center, MGH.

Fig. 6

Multi-parametric PET/MR imaging in glioblastoma: FDG-PET and morphological MR image after administration of MR contrast agent (middle column). Parameters derived from the MR data (K^trans, cerebral blood volume (CBV) and ADC) and the PET data (metabolic rate of glucose (CMRglu), K1, k3) in the region of interest (red contour) defined on the enhancing part of the tumor are shown in the left and right column, respectively. Data acquired on the MR-BrainPET prototype, A.A. Martinos Center, MGH. Images courtesy of Dan Chonde and Dominique Jennings.

Fig. 7

Simultaneous cardiac PET/MR study: (A) EKG-gated PET and (B) delayed contrast enhanced cardiac MR images. PET data acquired in list mode and binned. (C) The MR images acquired in diastole are fused with diastolic PET data. Patient has a normal heart. Data acquired on the Biograph mMR scanner, Washington University in St. Loius. Images courtesy of Pamela Woodard and Richard Laforest.

Fig. 8

Simultaneous PET/MR study in an AD patient. Left column: axial FDG-PET, morphological MR and fused images. Upper right column: Surface projections of cerebral metabolism showing the areas with reduced metabolism as compared to controls. Lower right column: Diffusion tensor imaging showing the white matter tracts in the same patient. Data acquired on the MR-BrainPET prototype, A.A. Martinos Center, MGH.