Korean J Radiol.  2015 Feb;16(1):32-49. 10.3348/kjr.2015.16.1.32.

Integrated Whole Body MR/PET: Where Are We?

• Yoo HJ
• Lee JS
• Lee JM

• KMID: 2069983
• DOI: http://doi.org/10.3348/kjr.2015.16.1.32

Abstract

Whole body integrated magnetic resonance imaging (MR)/positron emission tomography (PET) imaging systems have recently become available for clinical use and are currently being used to explore whether the combined anatomic and functional capabilities of MR imaging and the metabolic information of PET provide new insight into disease phenotypes and biology, and provide a better assessment of oncologic diseases at a lower radiation dose than a CT. This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions. Various early clinical applications of integrated MR/PET are also addressed. Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

Keyword

MR/PET; Hybrid imaging; Positron emission tomography; Magnetic resonance imaging

MeSH Terms

Coordination Complexes/chemistry/diagnostic use
Heart/radiography
Humans
*Magnetic Resonance Imaging
Neoplasm Metastasis
Neoplasm Staging
Neoplasms/pathology/radiography
*Positron-Emission Tomography
Radiopharmaceuticals/diagnostic use
Tomography, X-Ray Computed
Whole Body Imaging/*standards/*trends
Coordination Complexes
Radiopharmaceuticals

Figure

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  Fig. 1 Dixon MRI-based attenuation correction. Dixon water (A) and fat (B) images. C. MRI-based attenuation map generated by combining water and fat images. D. CT of same patient.

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  Fig. 2 Ultrashort echo time (UTE) MRI-based attenuation correction. MR images acquired at first (A) and second (B) echo times (echo time = 0.07 ms and 2.46 ms, respectively). C. Differential image of A and B. D. UTE-based attenuation map. E. CT of same patient.

• 

  Fig. 3 Whole-body acquisition protocol of MR/PET in oncology patients, which consists of whole-body and dedicated MR/PET. Diagnostic MR pulse sequences in whole-body MR/PET include half-Fourier acquisition single shot turbo spin echo, short-tau inversion recovery T2-weighted sequences, three-dimensional volumetric interpolated breath-held examination or turbo spin echo T1-weighted images. On dedicated MR imaging, variable pulse sequences were used according to diagnostic purpose and specific body part. AC = attenuation correction, MR/PET = magnetic resonance imaging/positron emission tomography

• 

  Fig. 4 63-year-old male had pancreatic mass. A. Axial CT image showed 2.5-cm, low-attenuated mass with heterogeneous enhancement (arrow) in pancreas tail, which was indeterminate finding. B. Axial, post-contrast, T1-weighted image demonstrated conglomerated cystic mass (arrow) with septal enhancement. C. MR cholangiopancreaticography also showed conglomerated cystic mass (arrow) in pancreas tail. D. ADC map showed no diffusion restriction in mass (arrow). E. Fused FDG-MR/PET image showed no FDG uptake in mass (arrow). Anatomical MR images (B, C) were helpful for characterizing mass, and functional images (D, E) suggested that mass was benign lesion. Mass was resected and confirmed as serous cystadenoma. ADC = apparent diffusion coefficient, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography

• 

  Fig. 5 66-year-old man with 3.7-cm lung mass (not shown) in right lower lobe. A. Axial, post-contrast, three-dimensional volumetric interpolated breath-hold examination image showed two small right interlobar lymph nodes (arrows). B. Axial fused FDG-MR/PET image showed increased FDG uptake in interlobar nodes (SUVmax: 4.4 and 3.8). Axial, DWI (b = 400) (C) and ADC map showed diffusion restriction in two lymph nodes (D). Concordant findings of right interlobar lymph nodes on ADC map and on fused MR/PET image increased our confidence in reporting right interlobar lymph-node metastasis, and pathology results confirmed right interlobar lymph-node metastasis. ADC = apparent diffusion coefficient, DWI = diffusion-weighted image, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value

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  Fig. 6 63-year-old male had colon cancer with brain, lung, and mediastinal lymph node (LN) metastasis. A. Coronal fused FDG-MR/PET image showed mediastinal LNs (arrows) with increased FDG uptake. B. Axial fused FDG-MR/PET image showed metastatic retroperitoneal LN (arrow) and metastatic bone lesion at L5 vertebral body (arrowhead). C. FLAIR image demonstrates brain metastasis in left temporal lobe (arrow). D. Reconstructed sagittal fused FDG-MR/PET image showed bone metastasis in cervical and lumbar spine (arrows). FDG = fluorodeoxyglucose, FLAIR = fluid attenuated inversion recovery, MR/PET = magnetic resonance imaging/positron emission tomography

• 

  Fig. 7 53-year-old male with radiation-induced osteosarcoma in right ilium before (A-C) and after (D-F) chemotherapy. A. Axial, T2-weighted MR image showed heterogeneous, T2 hyperintense soft-tissue mass in right ilium. B. Axial, post-contrast, T1-weighted MR image showed soft-tissue enhancement (arrow) with central non-enhancement before chemotherapy. C. Axial PET-CT image demonstrated increased FDG uptake (SUVmax = 21.84) in corresponding lesion. D. Axial, T2-weighted MR image obtained after chemotherapy shows decrease in tumor size. E. Axial, post-contrast, T1-weighted MR image obtained after chemotherapy shows decrease in area of soft-tissue enhancement (arrow). F. Corresponding to fused FDG-MR/PET image obtained after chemotherapy and which showed no pathological FDG uptake (SUVmax = 2.23). FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value

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  Fig. 8 One-year-old male with neuroblastoma. Coronal, T1-weighted image (A) and coronal STIR T2-weighted sequences image (B) showed multiple, metastatic tumors in right adrenal gland (white arrow), left ilium (black arrow), and proximal metaphysis of both femora (arrowheads). C. Coronal FDG-MR/PET image demonstrated strong FDG uptake in lesions. Thin arrow shows multiple spine metastases. FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, STIR = short-tau inversion recovery

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