PET/MRI Improves Management of Children with Cancer

Abstract

Integrated PET/MRI has shown significant clinical value for staging and restaging of children with cancer by providing functional and anatomic tumor evaluation with a 1-stop imaging test and with up to 80% reduced radiation exposure compared with ¹⁸F-FDG PET/CT. This article reviews clinical applications of ¹⁸F-FDG PET/MRI that are relevant for pediatric oncology, with particular attention to the value of PET/MRI for patient management. Early adopters from 4 different institutions share their insights about specific advantages of PET/MRI technology for the assessment of young children with cancer. We discuss how whole-body PET/MRI can be of value in the evaluation of certain anatomic regions, such as soft tissues and bone marrow, as well as specific PET/MRI interpretation hallmarks in pediatric patients. We highlight how whole-body PET/MRI can improve the clinical management of children with lymphoma, sarcoma, and neurofibromatosis, by reducing the number of radiologic examinations needed (and consequently the radiation exposure), without losing diagnostic accuracy. We examine how PET/MRI can help in differentiating malignant tumors versus infectious or inflammatory diseases. Future research directions toward the use of PET/MRI for treatment evaluation of patients undergoing immunotherapy and assessment of different theranostic agents are also briefly explored. Lessons learned from applications in children might also be extended to evaluations of adult patients.

Keywords: PET/MRI; cancer; oncology; pediatric oncology; pediatrics.

FIGURE 1.

¹⁸F-FDG PET/MRI helps to characterize activity in tonsils and stage patients with lymphoma. (A and B) Axial T2-weighted fat-saturated fast-spin-echo (FSE) image (A) and ¹⁸F-FDG PET image (B) of 15-y-old boy with follicular lymphoma show symmetric morphology and marked ¹⁸F-FDG uptake of both tonsils with reactive hyperplasia. (C and D) Axial T2-weighted FSE image (C) and ¹⁸F-FDG PET image (D) of 4-y-old girl with large B-cell lymphoma demonstrate asymmetric globular enlargement and relatively less intensive ¹⁸F-FDG uptake of left tonsil (arrows). Tonsillectomy revealed large B-cell lymphoma in left tonsil and reactive tissue in right tonsil. Intrinsic uptake in tonsil is more avid than lymphomatous involvement on second patient. Radiologists must be cognizant of this caveat and integrate metabolic and morphologic information to increase diagnostic accuracy.

FIGURE 2.

¹⁸F-FDG PET/MRI detects tumor invasion into spinal canal in 18-mo-old boy with metastasized germ cell tumor. (A) Sagittal short-inversion-time inversion recovery image, fused with simultaneously acquired ¹⁸F-FDG PET image, demonstrates presacral mass (red arrow), which extends into spinal canal. Also noted is ¹⁸F-FDG–avid lesion in S1 vertebra (yellow arrow) and extradural focus posterior to L4 vertebra (blue arrow). (B) Axial T2-weighted fast-recovery fast-spin-echo fat-saturated image shows soft-tissue mass entering spinal canal (red arrow). Also noted are metastatic lesions in S1 (yellow arrow) and right paraspinal muscle (orange arrow). (C) Fast-recovery fast-spin-echo fat-saturated image fused with ¹⁸F-FDG PET image shows hypermetabolism of all lesions. Information from PET/MRI helped in staging by showing metastatic disease and extent of disease in spinal canal, hence impacting patient management. Patient started chemotherapy right after PET/MRI.

FIGURE 3.

¹⁸F-FDG PET/MRI accurately stages rhabdomyosarcoma in 9-y-old girl. (A and B) Maximum-intensity projection of ¹⁸F-FDG PET scan (A) and ¹⁸F-FDG PET/MRI scan (B) show avid ¹⁸F-FDG uptake in lesion in thigh adductor muscles (blue arrow) and tiny additional ¹⁸F-FDG–avid lymph node in lateral thigh (yellow arrow). MRI helps to exclude any bone marrow disease or cortical invasion. (C and D) Axial contrast-enhanced fat-saturated T1-weighted MRI scan (C) and ¹⁸F-FDG PET/MRI scan (D) demonstrate relation between primary tumor (arrow) and superficial and deep femoral artery and vein. (E and F) Axial contrast-enhanced fat-saturated T1-weighted MRI scan (E) and ¹⁸F-FDG PET/MRI scan (F) demonstrate small lymph node (arrow) posterior to vastus lateralis muscle. Primary tumor and lymph node were resected and positive for sarcoma.

FIGURE 4.

¹⁸F-FDG PET/MRI enabled image-informed surgical planning in 21-y-old patient with neurofibromatosis type 1. From left to right: axial fat-saturated T2-weighted image through pelvis reveals heterogeneous lesion infiltrating sacrum (arrow); ¹⁸F-FDG PET fused with T2-weighted MRI scan shows increased glucose metabolism of sacral lesion (SUV_max = 6; arrow); axial contrast-enhanced fat-saturated T1-weighted MRI scan shows heterogeneous tumor enhancement (arrow); apparent diffusion coefficient map demonstrates restricted diffusion of lesion with mean apparent diffusion coefficient of 0.85·10⁻³ mm² s, which is suggestive of MPNST. Curative treatment of MPNST is critically dependent on early detection. Combined information from ¹⁸F-FDG PET and diffusion-weighted MRI led to tumor resection and histologic confirmation of MPNST.