1. Semi-automated segmentation to assess the lateral meniscus in normal and osteoarthritic knees 
M.S. Swanson, J.W. Prescott, T.M. Best, K. Powell, R.D. Jackson, F. Haq, M.N. Gurcan 
Osteoarthritis and Cartilage 
Volume 18, Issue 3, Pages (March 2010)
DOI: /j.joca
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

2. Fig. 1
An example of a Sagittal view of a (a) normal knee, (b) one with OA OARSI 1, (c) OARSI 2, and (d) OARSI 3. Notice that as the OARSI score increases, meniscus degeneration becomes apparent along with osteophytes and cartilage damage.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

3. Fig. 2 Flowchart of the segmentation process.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

4. Fig. 3
Here are three consecutive images showing the lateral meniscus horns arranged lateral to medial. In this case, the middle slice would be chosen as the end point because the meiscofemoral ligaments predominate in the next image.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

5. Fig. 4
Image (a) is the original image, and (b) is a mask of high and low intensity pixels. This mask was used to determine pixels restricted from being included in the segmentation.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

6. Fig. 5
Image (a) shows a mask of high intensity areas. Image (b) isolates the femur, which is dilated in image (c) to include cartilage in the mask as an indirect way to exclude it from meniscus segmentation. The same process is done for the tibia.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

7. Fig. 6
Image (a) shows the original image before filtering. Image (b) is the result of a range filter with a 3×3 neighborhood. Image (c) is a mask of pixels having an intensity value greater than 120 made from the range filtered image. The masked pixels on image (c) are excluded from segmentation.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

8. Fig. 7
(a) A dilation of a sample segmentation result, (b) with corresponding histogram and fitted Gaussian curves of the region used for threshold determination.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

9. Fig. 8
Image (a) shows a mask after thresholding and (b) is the mask after morphological operations. Note the high intensity areas within the meniscus (a) which were not included in the thresholding operation. OA participants tended to have a higher proportion of these areas than those of non-exposed participants.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

10. Fig. 9
The same mask shown in Fig. 7(b) after the growth phase was completed. The edges of the meniscus are now better defined.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

11. Fig. 10
The green outline is a segment completed by a human reader, and the yellow outline is the segmentation completed by the semi-automated algorithm. Note the high degree of similarity (0.91), even when the posterior horn of the meniscus has high intensity areas throughout.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

12. Fig. 11
This is an automatic segmentation (yellow) with a similarity index of .79 compared to a manual rater (green) showing the average level of agreement for normal knees (see Table III).
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

13. Fig. 12
This is a more extreme example of a segmentation error where incorrect areas were segmented due to a low intensity area in the cartilage. The yellow outline is the automatic segmentation, and the green outline is a segmentation performed manually. The error is limited due to area and intensity constraints, and has a similarity index of 0.66.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

14. Fig. 13
A series showing the manual segmentations (green) and automatic segmentations (yellow) of the lateral meniscus from a patient with OA progression.
Osteoarthritis and Cartilage  , DOI: ( /j.joca )
Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions