Reliability of an efficient MRI-based method for estimation of knee cartilage volume using surface registration.

OBJECTIVE: To aid in detection of osteoarthritis (OA) progression in serial magnetic resonance (MR) scans, we assessed feasibility and accuracy of rapid 3D image registration of the tibial plateau in normal and arthritic subjects, and inter-scan reliability of semi-automated cartilage volume measurement from these images.
DESIGN: Two T1 fat-suppressed knee MR scans were obtained 2 weeks apart in healthy adults (n = 9, age 23-48 years). Four scans of each of three patients with established OA were obtained over 2 years. At baseline, the tibial surface was digitized by semi-automated edge detection and medial tibial plateau cartilage volume was calculated from high-intensity voxels within a manually drawn region of interest (ROI). In subsequent scans, the digitized tibial surface was registered to the baseline location by photogrammetric 3D coordinate transformation, and cartilage volume was automatically recalculated by reuse of the ROI. We measured registration accuracy by root mean square (RMS) distance between registered tibial surfaces.
RESULTS: In normals, RMS distance between tibial surfaces in baseline and subsequent scans was 1/3 voxel length (0.121 mm), and medial tibial plateau cartilage volumes varied by 1.4+/-3.2%. Despite change in cartilage volumes by up to 20% over 2 years in arthritic patients, surface registration accuracy was unaffected (0.122 mm). User-supervised processing time was 15 min at baseline and 7 min in subsequent scans.
CONCLUSION: Tibial surfaces on magnetic resonance imaging (MRI) can be rapidly and accurately co-registered, even in arthritic knees, allowing direct visualization of changes over time. Compared to most current methods, cartilage volume measurement in registered images is faster and has equivalent inter-scan reliability in initially normal subjects.