Quantitative Imaging of Bone-Cartilage Interactions in ACL-Injured Patients with PET-MRI

Osteoarthritis (OA) is a degenerative whole-joint disease that affects more than half of the population during their lives and is the leading cause of disability worldwide. Diagnostic imaging of osteoarthritis is often limited to x-ray, but more sensitive and specific imaging is a critical need for development of disease-modifying treatments. Advanced MRI methods have shown promise for assessment of tissue microstructure in OA, but are limited to soft tissues such as cartilage. In this work, we evaluate simultaneous ¹⁸F-NaF PET/MR Imaging to study early changes in bone and cartilage in ACL-injured knees, which are at known risk for development of OA. We found that ACL-injured knee joints demonstrated significantly increased ¹⁸F-NaF PET uptake, representative of increased metabolic bone activity, compared to their unaffected contralateral knees. This suggests that increased metabolic bone activity detected with ¹⁸F-NaF PET can serve as an important marker of early OA and progression of disease. Further we observed a spatial correlation between increased subchondral bone remodeling on ¹⁸F-NaF PET and adjacent changes in the cartilage microstructure on MRI T₂ relaxation time maps. This result supports the hypothesis of a spatial relationship between early degenerative OA changes across bone and cartilage. ¹⁸F-NaF PET-MRI thus holds tremendous potential to provide biomarkers that quantitatively assess early progression of OA, which are crucial to develop and evaluate disease-modifying treatments, and ultimately arrest or reverse the progression of OA.

Kogan F, Fan AP, Monu U, Iagaru A, Hargreaves BA, Gold GE. Quantitative imaging of bone-cartilage interactions in ACL-injured patients with PET-MRI. Osteoarthritis Cartilage. 2018 Jun;26(6):790-6.

Online Journal Article

¹⁸F-NaF PET (SUV), cartilage T₂ relaxation time (ms) and PET-MRI fusion maps of the ACL injured knee [top] and contralateral knee [bottom] of a subject with a unilateral reconstructed ACL tear.¹⁸F-NaF PET is able to detect an area of increased bone metabolism in the patellar subchondral bone (magenta line arrow). Further, an area of increased cartilage T₂ relaxation time (solid green arrow), indicative of early cartilage matrix degradation is seen in the adjacent cartilage. This technique is uniquely able to quantitatively study multiple markers of early OA in bone and cartilage as well as spatial relationships between the two tissues.