Current Status of Hybrid PET/MRI in Oncologic Imaging

Abstract

Objective: This review article explores recent advancements in PET/MRI for clinical oncologic imaging.

Conclusion: Radiologists should understand the technical considerations that have made PET/MRI feasible within clinical workflows, the role of PET tracers for imaging various molecular targets in oncology, and advantages of hybrid PET/MRI compared with PET/CT. To facilitate this understanding, we discuss clinical examples (including gliomas, breast cancer, bone metastases, prostate cancer, bladder cancer, gynecologic malignancy, and lymphoma) as well as future directions, challenges, and areas for continued technical optimization for PET/MRI.

Keywords: MRI; PET; cancer; hybrid PET/MRI.

Fig. 1. 45-year-old woman with multifocal nonenhancing glioma

A and B, Axial FLAIR (A) and contrast-enhanced T1-weighted (B) MR images show glioma involves right periventricular white matter (arrow). C and D, FDG map (C) shows faint uptake, whereas regional cerebral blood volume (rCBV) parametric map (D) shows markedly increased rCBV in right periventricular white matter nonenhancing lesion (arrow), which was targeted with stereotactic biopsy and revealed grade III glioma.

Fig. 2. Recurrent enhancing lesions

A–C, 56-year-old man with previously treated lymphoma. Axial contrast-enhanced T1-weighted MR image (A), regional cerebral blood volume (rCBV) perfusion map (B), and corresponding FDG map (C) show increased rCBV as well as increased FDG uptake in small lesion (arrow) consistent with recurrent lymphoma. D–F, 46-year-old woman with previously treated grade III glioma. Axial contrast-enhanced T1-weighted MR image (D), rCBV perfusion map (E), and corresponding FDG map (F) show markedly low rCBV and markedly low FDG uptake in recurrent enhancing lesions (arrow) suggestive of radiation necrosis that was proven with biopsy.

Fig. 3. 42-year-old woman with invasive lobular carcinoma (ILC) of right breast

A, ILC (arrow) fails to exhibit marked enhancement on early contrast-enhanced T1-weighted MR image. B and C, ILC shows increased FDG activity (arrow) on FDG PET image fused with contrast-enhanced T1-weighted MR image (B) and FDG PET image (C). D, Apparent diffusion coefficient (ADC) map of right breast shows ILC has decreased ADC (arrow), typical of malignancy.

Fig. 4. 85-year-old man with prostate cancer who underwent initial staging workup that showed metastases to bone

A, Standard bone scan shows one metastatic lesion in left acetabulum (solid arrow) and small subtle lesion in upper thoracic spine (dashed arrow) which was attributed to degenerative spine disease. ANT = anterior view, POS = posterior view. B and C, NaF PET/MR image obtained 3 weeks later (B) reveals nine metastatic lesions (circles), showing higher sensitivity of PET/MRI. Lesion in T2 spinous process on PET/MRI (dashed arrows) corresponds to small subtle lesion on bone scan (dashed arrow, A). ANT = anterior view; LAT = lateral view. D and E, Lesion in T2 spinous process shows low mean apparent diffusion coefficient (ADC) of 0.57 × 10⁻³ mm²/s in ROI (circle) on ADC map (D) and high maximum standardized uptake value of 38.7 in ROI (circle) on fused PET/ADC image (E), consistent with metastatic lesion.

Fig. 5. 71-year-old man with prostate cancer imaged by hybrid ¹¹C-choline PET/MRI

A, Axial T2-weighted image shows T2-hypointense lesion involving both right anterior peripheral and transition zones (arrow). B, Apparent diffusion coefficient (ADC) map shows decreased ADC within lesion (arrow). C, Fusion image depicting PET image as color overlay on T2-weighted-image shows excellent registration of abnormality between two image sets (arrow). (Courtesy of Eiber M, TU Muenchen, Munich, Germany)

Fig. 6. 57-year-old man with bladder cancer imaged by hybrid FDG PET/MRI

A, Early contrast-enhanced T1-weighted image shows right anterolateral bladder thickening with early enhancement relative to remainder of bladder wall (arrow). B, Fusion image depicting PET image as color overlay on T2-weighted-image shows marked increased activity (standardized uptake value = 19.8) within lesion (arrow), with excellent registration of abnormality between two image sets.

Fig. 7. 8-year-old boy with neurofibromatosis type 1 imaged by whole-body hybrid FDG PET/MRI

A–C, Coronal STIR MR image (A), coregistered PET/MR image (B), and coronal PET image (C) show large infiltrative plexiform neurofibroma in right retroperitoneum extending into right thigh. Foci of hypermetabolism (arrows, B and C) with maximum standardized uptake value (SUV_max) of 2.5 are seen within superior aspect of mass adjacent to inferior vena cava, but remainder of mass was not FDG avid. Findings were suggestive of benign plexiform neurofibroma given low-grade metabolic activity and stability since PET/CT done 1 year earlier (not shown). (Courtesy of Raad R, New York University School of Medicine, New York, NY)