Semi-automated segmentation to assess the lateral meniscus in normal and osteoarthritic knees.
OBJECTIVE
The goal of this study was to develop an algorithm to semi-automatically segment the meniscus in a series of magnetic resonance (MR) images to use for normal knees and those with moderate osteoarthritis (OA).


METHODS
The segmentation method was developed then evaluated on 10 baseline MR images obtained from subjects with no evidence, symptoms, or risk factors of knee (OA), and 14 from subjects with established knee OA enrolled in the Osteoarthritis Initiative (OAI). After manually choosing a seed point within the meniscus, a threshold level was calculated through a Gaussian fit model. Under anatomical, intensity, and range constraints, a threshold operation was completed followed by conditional dilation and post-processing. The post-processing operation reevaluates the pixels included and excluded in the area surrounding the meniscus to improve accuracy. The developed method was evaluated for both normal and degenerative menisci by comparing the segmentation algorithm results with manual segmentations from five human readers.


RESULTS
The semi-automated segmentation method produces results similar to those of trained observers, with an average similarity index over 0.80 for normal participants and 0.75, 0.67, and 0.64 for participants with established knee OA with Osteoarthritis Research Society International (OARSI) joint space narrowing (JSN) scores of 0, one, and two respectively.


CONCLUSIONS
The semi-automatic segmentation method produced accurate and consistent segmentations of the meniscus when compared to manual segmentations in the assessment of normal menisci in mild to moderate OA. Future studies will examine the change in volume, thickness, and intensity characteristics at different stages of OA.
Swanson
M S
MS
College of Medicine, The Ohio State University, Columbus, OH 43210, USA.
Prescott
J W
JW
Best
T M
TM
Powell
K
K
Jackson
R D
RD
Haq
F
F
Gurcan
M N
MN
D000465:Algorithms; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology*; D016022:Case-Control Studies; D006801:Humans; D007717:Knee / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008592:Menisci, Tibial / Q000000981:diagnostic imaging / Q000473:pathology*; D015233:Models, Statistical; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012720:Severity of Illness Index