Quantitative MR imaging using "LiveWire" to measure tibiofemoral articular cartilage thickness

To assess the reliability and accuracy of manual and semi-automated segmentation methods for quantifying knee cartilage thickness. This study employed both manual and LiveWire-based semi-automated segmentation methods, ex vivo and in vivo, to measure tibiofemoral (TF) cartilage thickness.

The articular cartilage of a cadaver knee and a healthy volunteer's knee were segmented manually and with LiveWire from multiple 3T MR images. The cadaver specimen's cartilage thickness was also evaluated with a 3D laser scanner, which was assumed to be the gold standard. Thickness measurements were made within specific cartilage regions. The reliability of each segmentation method was assessed both ex vivo and in vivo, and accuracy was assessed ex vivo by comparing segmentation results to those obtained with laser scanning.

The cadaver specimen thickness measurements showed mean coefficients of variation (CVs) of 4.16%, 3.02%, and 1.59%, when evaluated with manual segmentation, LiveWire segmentation, and laser scanning, respectively. The cadaver specimen showed mean absolute errors versus laser scanning of 4.07% and 7.46% for manual and LiveWire segmentation, respectively. In vivo thickness measurements showed mean CVs of 2.71% and 3.65% when segmented manually and with LiveWire, respectively.

Manual segmentation, LiveWire segmentation, and laser scanning are repeatable methods for quantifying knee cartilage thickness; however, the measurements are technique-dependent. Ex vivo, the manual segmentation error was distributed around the laser scanning mean, while LiveWire consistently underestimated laser scanning by 8.9%. Although LiveWire offers repeatability and decreased segmentation time, manual segmentation more closely approximates true cartilage thickness, particularly in cartilage contact regions.