New MRI Approach Helps Assess Knee Osteoarthritis Progression

Patients with knee arthritis have abnormally high bone metabolism, according to images captured with new functional bone imaging tactic.

In a presentation at the Society for Nuclear Medicine and Molecular Imaging 2020 virtual annual meeting, investigators from Stanford University discussed their use of PET/MRI with 18F NaF to assess the degeneration of the knee joint in patients, and marker for osteoarthritis.

“Osteoarthritis is not very well understood, in part because we lack the tools to objectively evaluate early and reversible changes in key tissues,” said Lauren Watkins, MS, a researcher in the Stanford University Imaging of Musculoskeletal Function Group. “While many MRI methods have been developed for assessment of early degenerative changes in cartilage, functional imaging of bone in the joint remains a major challenge.”

Figure 2. ​Representative structural MRI image (PD-weighted IDEAL image, A and D), [18F]NaF PET SUV images (B and E), and PET/MR fusion images (C and F) of a healthy knee and a knee with osteoarthritis. MOAKS scoring of MR images was used to identify the size of osteophytes, bone marrow lesions and cartilage loss within various bone regions in the patella, tibia and femur. Arrows highlight bone regions with osteophytes in blue, bone marrow lesions in yellow, and cartilage loss in green. Credit: LE Watkins, et al., Stanford University, CA.

To assess the interplay between structural and physiological changes in knee osteoarthritis, the team used PET/MRI 18F NaF to image 12 subjects’ knees. They also tested the repeatability of the technique by imaging five patients twice, five days apart.

A musculoskeletal radiologist provided additional evaluation with an MRI Osteoarthritis Knee Score (MOAKS) for each knee. In addition, data collected from dynamic PET was used to determine the rates of bone perfusion, tissue clearance, and mineralization. That information was also used for tracer extraction fraction and total bone uptake rate. Additionally, the investigators performed kinetic modeling for regions representing the subchondral bone of the patella, medial and lateral tibia, and anterior, central, and posterior regions of the medial and lateral femur. 

Based on their MOAKS findings, the team divided knees into regions of cartilage loss, bone marrow lesions, and osteophytes and analyzed them along with the PET-data derived kinetic parameters. They determined there is a strong association between abnormal bone metabolism in regions with bone marrow lesions, osteophytes, and adjacent cartilage lesions and greater bone perfusion rates when compared to bone that appears normal on MRI.

These results highlight the usefulness and potential of PET imaging in studying the role bone physiology plays in degenerative bone disease, Wakins said.

“This knowledge may help us understand the order of events leading to structural and functional degeneration of the knee,” she said. “Further, this will help us to develop and quickly evaluate new interventions that target specific metabolic pathways to give us the best chance to slow or arrest the onset and progression of osteoarthritis.”