Earlier OA Detection With PET-MRI

Researchers from Stanford University have presented the first technique that simultaneously assesses a variety of early metabolic and cellular markers of joint tissue health in patients at risk for early knee osteoarthritis (OA).

Their work, “Quantitative imaging of bone–cartilage interactions in ACL-injured patients with PET–MRI,” appears in the April 12, 2018 edition of Osteoarthritis and Cartilage.

Feliks Kogan, Ph.D., with the Department of Radiology at Stanford University and study co-author told OTW, “Magnetic resonance imaging (MRI) has been a great tool for studying OA, providing excellent high-resolution morphologic information as well as quantitative metrics of early biochemical changes in soft tissues. However, tissues are often studied in isolation and MRI assessment of subchondral bone is limited to structural changes that occur late in the disease process.”

“Changes in bone metabolism have been linked to OA pathogenesis, particularly in the subchondral region. However, the role of bone injury or remodeling is often neglected or studied in the context of qualitative assessment of late stage disease processes such as osteophytes and marrow signal changes.”

“Given the importance of detecting early stage OA disease in all joint tissues, there is great interest in evaluating bone remodeling as a marker of early bone degeneration and its potential as a target for disease modifying therapies.”

“As a result, there is an urgent need to develop diagnostic technologies able to quantitatively evaluate early changes in bone remodeling and its role in degenerative changes observed in adjacent tissues.”

The Stanford researchers then took a hard look at early metabolic and cellular changes in bone and cartilage by using, simultaneously, positron emission tomography (PET) and magnetic resonance imaging (MRI). Knowing that PET imaging with ¹⁸F-Sodium fluoride (¹⁸F-NaF), can interrogate bone osteoblast activity, Kogan and the team were able to assess regional bone remodeling. But then, using quantitative MRI, the team was also able to take a non-invasive look at early OA changes in cartilage!

“In this work we studied patients with unilateral ACL-injured [anterior cruciate ligament] knees, which are at known risk for development of OA. We utilize ¹⁸F-NaF PET to evaluate early differences in subchondral bone metabolism between ACL-injured knees and unaffected contralateral knees.”

“We simultaneously collected T2 relaxation times to study early cartilage changes, which are known to occur in the OA susceptible population.”

“Lastly, our novel approach allows for simultaneous, and quantitative assessment of spatial relationships between multiple early markers of disease in subchondral bone and articular cartilage. We used this strength to study spatial relationships between increased subchondral bone metabolism and adjacent MRI markers of cartilage matrix changes.”

“We found that ACL-injured knee joints demonstrated significantly increased ¹⁸F-NaF PET uptake in the subchondral bone compared to their unaffected contralateral knees.”

“Increased metabolic bone activity detected with ¹⁸F-NaF PET can serve as an important marker of early OA and progression of disease. Significantly increased cartilage T2 relaxation times, indicative of early cartilage degradation, were observed in the ACL injured knees compared with their contralateral control knees (in agreement with prior results).”

“There is a spatial correlation between increased ¹⁸F-NaF PET uptake in subchondral bone and increased T2 relaxation times in adjacent cartilage, particularly in the deep layers of cartilage, which are adjacent to the subchondral bone.”