High-resolution, selective water-excitation MRI-based cartilage thickness and volume measurements in upper extremity joints.

The objective if this study was to obtain quantitative data about cartilage thickness and volume in joints of the upper extremity by applying a high resolution MR imaging technique, and to validate these data by A-module ultrasound and CT arthrography.
10 elbow and 7 shoulder joints (age 20 to 69 yrs) were investigated with a 3D gradient echo sequence with selective water excitation (TR 18 ms; TE 9 ms; FA 250, resolution 1 x 0,25 x 0,25 mm2, imaging time 19 min.). After trilinear interpolation to a 0,125 x 0,125 mm2 in-plane resolution, snake-based segmentation, and 3D reconstruction, cartilage volume and thickness were determined with a 3D Euclidean distance transformation algorithm. For validation the cartilage volume and thickness values were compared with CT arthrography and A-mode ultrasound.
The mean cartilage thickness of the elbow joint ranged between 0,99 and 1,35 mm and that of the shoulder between 1,18 and 1,79 mm. The mean systematic difference between the elbow cartilage volume obtained from MR imaging and CT arthrography was -0,11% (-6,0 mm3) and the mean random difference 5,7% (314 mm3). Only in the distal humerus, the mean cartilage thickness (average = 1,35 mm) was overestimated relative to CT arthrography (+20,7%, 0,23 mm). In comparison to A-mode ultrasound a slight underestimation was found in the distal humerus (-6,0%, -0,05 mm) and in the shoulder joint surfaces (humeral head: -22%; -0,26 mm; glenoid cavity: -13%; -0,25 mm). With few exception, there were no significant differences between MRI, CT arthrography and ultrasound in the other joint surfaces of the upper extremity joints (random deviations between 0,08 and 0,39 mm).
This specific MR imaging and postprocessing technique can be used for non-invasive determination of cartilage volume and thickness in joints with thin cartilage layers such as the shoulder with a high degree of accuracy.