Automatic MRI-based 3D Models of Hip Cartilage Using a 3D U-net-like Fully Convolutional Network for Improved Morphologic and Biochemical Analysis

Purpose: The time-consuming and user-dependent postprocessing of biochemical cartilage magnetic resonance imaging (MRI) has prevented its widespread use. A time-efficient, fully automated analysis of biochemical three-dimensional (3D) images could provide more straightforward and comprehensive information on cartilage thickness, surface area, and volume.

Methods and Materials: This study, approved by the institutional review board, reports on 25 symptomatic hips undergoing a contrast-enhanced MRI at 3T including a 3D delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) sequence (0.8 mm³). Development of a fully automated deep learning–based approach for 3D segmentation of hip cartilage models was based on two steps: (1) 3D training data of hip cartilage were provided by one reader (manual 3D analysis); and (2) a deep neural network for fully automated cartilage segmentation (automated 3D analysis) and software for 3D analysis was developed. The dGEMRIC index, cartilage thickness, surface area, and volume were measured in the four joint quadrants and compared. Mean average surface distance and mean Dice coefficient were calculated.

Results: Regional patterns were comparable for manual/automated 3D methods. Highest dGEMRIC indices were found posterosuperiorly (602.1 ± 158.4 ms; 601.8 ± 158.4 ms). Thickest cartilage was found anteroinferiorly (5.3 ± 0.8 mm; 4.3 ± 0.6 mm). Smallest surface area was found anteroinferiorly (134 ± 60 mm²; 155 ± 60 mm²). Largest volume was found anterosuperiorly (2343 ± 492 mm³; 2294 ± 467 mm³). Mean average surface distance was 0.26 ± 0.13 mm; mean Dice coefficient was 85.7 ± 2.7%.

Conclusion: This validation paves the way to large-scale use of this method for fully automatic 3D cartilage segmentation for an improved morphological and biochemical analysis of hip cartilage. In the future this may be helpful to identify those patients who would benefit from joint-preserving hip surgery.