PET-MRI for the Study of Metabolic Bone Disease

Abstract

Purpose of review: This review article attempts to summarize the current state and applications of the hybrid imaging modality of PET-MRI to metabolic bone diseases. The advances of PET and MRI are also discussed for metabolic bone diseases as potentially applied via PET-MRI.

Recent findings: Etiologies and mechanisms of metabolic bone disease can be complex where molecular changes precede structural changes. Although PET-MRI has yet to be applied directly to metabolic bone disease, possible applications exist since PET, specifically ¹⁸F-NaF PET, can quantitatively track changes in bone metabolism and is useful for assessing treatment, while MRI can give detailed information on bone water concentration, porosity, and architecture through novel techniques such as UTE and ZTE MRI. Earlier detection and further understanding of metabolic bone disease via PET and MRI could lead to better treatment and prevention. More research using this modality is needed to further understand how it can be implemented in this realm.

Keywords: Imaging; Metabolic bone disease; Musculoskeletal diseases; Positron emission tomography-magnetic resonance imaging (PET-MRI).

Figure 1.

18F-NaF PET images showing (A) a sagittal image of the lumbar spine (L1– L4) and (B) a coronal image of the proximal femur. Both images are 2-dimensional projection views of the complete 3-dimensional PET scan data, and both are limited by the 15-cm field of view of the PET scanner. In the femur image, 18F-NaF activity collecting in the urinary bladder during the 1 hour dynamic scan has been removed to give a clearer view of the uptake in bone. [Blake GM, Frost ML, Moore AE, et al. The assessment of regional skeletal metabolism: studies of osteoporosis treatments using quantitative radionuclide imaging. J Clin Densitom 2011;14:263–71. with permission].

Figure 2.

18F-Fluoride PET (SUV) and MRI images of a male patient with posttraumatic osteoarthritis showing concordance between a BML (blue arrowhead) and osteophytes (red diamond arrows) on MRI with high 18F-fluoride uptake on PET. Additionally, a focal region of high uptake on PET (magenta line arrow) did not exhibit bone abnormalities on MRI but was adjacent to a grade 2 cartilage defect (light blue solid arrow). [Kogan F, Fan AP, McWalter EJ, et al. PET/MRI of metabolic activity in osteoarthritis: A feasibility study. J Magn Reson Imaging 2017;45(6):1736–45. (24) with permission]. Used with permission from John Wiley and Sons.

Figure 3.

(A) Midsagittal 18F-fluoride PET image through lumbar vertebrae showing region of interest within vertebral bodies (at right is magnification of L1–L5 vertebral bodies, with squares indicating regions of interest). (B) Coronal image of pelvis and both proximal femurs (at bottom is magnification of left femoral neck, with square indicating region of interest). [Uchida K, Nakajima H, Miyazaki T, et al. Effects of alendronate on bone metabolism in glucocorticoid-induced osteoporosis measured by 18F-fluoride PET: a prospective study. J Nucl Med 2009;50:1808–14. (16)

Figure 4.

MRI of a cadaveric forearm. While cortical bone produces a signal void on a conventional fast-spin echo (FSE) sequence (A), signal is detected from cortical bone with the use of an inversion recovery ultrashort echo time (IR UTE, TR/TI 300/120 ms) pulse sequence (B). Du J, Carl M, Bydder M, et al. Qualitative and quantitative ultrashort echo time (UTE) imaging of cortical bone. J Magn Reson 2010;207(2):304–11. With permission.

Figure 5:

Comparable images from (A) isotropic 3D PD-ZTE and (B) nearisotropic CT for grading of CNF stenosis. Images courtesy of Hospital for Special Surgery MRI Laboratory.

Figure 6:

Comparable 3D reconstructed surface models of gleno-humeral joint from ZTE and CT, following manually-supplemented region-growing segmentation. (A) Posterior aspect of joint where Hill-Sachs defect is clearly visible. Cortical thinness and spatial resolution of ZTE result in surface porosity (superior aspect of glenoid in ZTE). (B) Anterior aspect of joint. ‘Furrowing’ artifact due to coarser spatial resolution is visible in ZTE. (C) En face glenoid surface. Note 3 holes (anchors, labrum repair). There is a discrepancy in the segmentation of the superior hole in ZTE, owing to coarser spatial resolution/partial volume effects. Images courtesy of Hospital for Special Surgery MRI Laboratory.

Figure 7:

ZTE vs CT imaging of the hip. Axial images were acquired and multiplanar reformatting was performed for coronal and sagittal image reconstruction. Clinically relevant measurements for groin pain were taken from the images. Images courtesy of Hospital for Special Surgery MRI Laboratory.