Precision of MRI-based joint-surface and cartilage-thickness analyses using a fast water-excitation sequence and a semiautomated segmentation algorithm

The aim of this study was to analyse the precision of three-dimensional joi nt surface and cartilage thickness measurements in the knee, using a fast, high-resolution water-excitation sequence and a semiautomated segmentation algorithm. The knee joint of 8 healthy volunteers, aged 22 to 29 years, wer e examined at a resolution of 1.5 mm x 0.31 mm x 0.31 mm, with four sagitta l data sets being acquired after repositioning the joint. After semiautomat ed segmentation with a B-spline Snake algorithm and 3D reconstruction of th e patellar, femoral and tibial cartilages, the joint surface areas (triangu lation), cartilage volume, and mean and maximum thickness (Euclidean distan ce transformation) were analysed, independently of the orientation of the s ections. The precision (CV%) for the surface areas was 2.1 to 6.6%. The mea n cartilage thickness and cartilage volume showed coefficients of 1.9 to 3. 5% (except for the femoral condyles), the value for the medial femoral cond yle being 9.1%, and for the lateral condyle 6.5%. For maximum thickness, co efficients of between 2.6 and 5.9% were found. In the present study we inve stigate for the first time the precision of MRI-based joint surface area me asurements in the knee, and of cartilage thickness analyses in the femur. U sing a selective water-excitation sequence, the acquisition time can be red uced by more than 50%. The poorer precision in the femoral condyles can be attributed to partial Volume effects that occur at the edges of the joint s urfaces with a sagittal image protocol. Since MRI is non-invasive, it is hi ghly suitable for examination of healthy subjects (generation of individual finite element models, analysis of functional adaptation to mechanical sti mulation, measurement of cartilage deformation in vivo) and as a diagnostic tool for follow-up, indication for therapy, and objective evaluation of ne w therapeutic agents in osteoarthritis.