a fully automated method for segmentation and thickness determination of hip joint cartilage from 3d...

A fully automated method forA fully automated method forsegmentation and thickness determinationsegmentation and thickness determination

of hip joint cartilageof hip joint cartilagefrom 3D MR datafrom 3D MR data

Authors: Yoshinobu Sato,et al. Authors: Yoshinobu Sato,et al. Source: Proceedings of the 15th International Congress and Exhibition,Source: Proceedings of the 15th International Congress and Exhibition, Berlin, Germany, June 27-30, 2001 Berlin, Germany, June 27-30, 2001Presented by: Ku-Yaw ChangPresented by: Ku-Yaw Chang

222007/11/102007/11/10 Ku-Yaw ChangKu-Yaw Chang

OutlineOutline

IntroductionIntroduction

MethodMethod

ResultsResults

ConclusionConclusion



Distribution of articular cartilage thickness Distribution of articular cartilage thickness important in the diagnosis of joint diseasesimportant in the diagnosis of joint diseases

Magnetic Resonance (MR) imaging Magnetic Resonance (MR) imaging The most suitable modality for cartilage imagingThe most suitable modality for cartilage imaging



To develop a fully automated methodTo develop a fully automated method Segmentation of hip joint cartilageSegmentation of hip joint cartilage

Femoral headFemoral head

AcetabulumAcetabulum Determination of cartilage thicknessDetermination of cartilage thickness



MR imagesMR images Leg tractionLeg traction

Clearly depict the articular spaceClearly depict the articular space

Assume that Assume that Both femoral and acetabular cartilage is distributed on Both femoral and acetabular cartilage is distributed on

a spherical surface whose center corresponds to the a spherical surface whose center corresponds to the rotational center of the hip joint motionrotational center of the hip joint motion

The proposed method is evaluated by using 13 The proposed method is evaluated by using 13 sets of in vivo MR data of normal and diseased sets of in vivo MR data of normal and diseased hip jointship joints


MethodMethod

Overview – four stepsOverview – four steps Automated determination of the center of a Automated determination of the center of a

sphere that approximate the femoral headsphere that approximate the femoral headHough transformHough transform

Enhancement of cartilage regions and their Enhancement of cartilage regions and their inner edgesinner edges

First and second derivatives along radial directions First and second derivatives along radial directions originating from the sphere centeroriginating from the sphere center


MethodMethod

Overview – four steps (cont.)Overview – four steps (cont.) Automated segmentation of individual regions Automated segmentation of individual regions

of femoral head and acetabular cartilageof femoral head and acetabular cartilageRadial derivate images using adaptive thresholdingRadial derivate images using adaptive thresholding

Automated subvoxel localization of cartilage Automated subvoxel localization of cartilage boundaries for thickness determinationboundaries for thickness determination


Step One -Step One -

Determination of Center Point Determination of Center Point

Determination of center point of sphere Determination of center point of sphere approximating the femoral headapproximating the femoral head Femoral headFemoral head

A spherical shape with a radius of around 20 to 25 A spherical shape with a radius of around 20 to 25 mmmm

Center position is estimated from the 3D MR Center position is estimated from the 3D MR datadata

Hough transformHough transform



Determination of Center PointDetermination of Center Point

MR imaging protocolMR imaging protocol Cartilage is imaged much more brightly than Cartilage is imaged much more brightly than

bonebone



Determination of Center PointDetermination of Center Point

Voxels around the boundaries of the Voxels around the boundaries of the femoral head and cartilagefemoral head and cartilage The direction of the gradient vector is aligned The direction of the gradient vector is aligned

the direction from the femoral head center to the direction from the femoral head center to the voxel position.the voxel position.

The magnitude of the gradient vector is largeThe magnitude of the gradient vector is large

Hough transform with weighted votingHough transform with weighted voting Based on the gradient magnitude is Based on the gradient magnitude is

performedperformed


Step TwoStep Two --

Radial Directional DerivativesRadial Directional Derivatives

The directional first derivativeThe directional first derivative Enhance cartilage-bone boundariesEnhance cartilage-bone boundaries

The directional second derivativeThe directional second derivative Enhance cartilage and articular spaceEnhance cartilage and articular space Combined with Gaussian blurringCombined with Gaussian blurring

Different standard deviations Different standard deviations (Multiscale integration)(Multiscale integration)

The above directional derivatives are used forThe above directional derivatives are used for Automated and accurate segmentationAutomated and accurate segmentation Subvoxel localizationSubvoxel localization


Step ThreeStep Three --Segmentation of Segmentation of

Cartilage and Articular Space RegionsCartilage and Articular Space Regions

Edge regions are extractedEdge regions are extracted From the directional first derivative imagesFrom the directional first derivative images ByBy

Adaptive thresholdingAdaptive thresholding Minimize overlooking true edge regionsMinimize overlooking true edge regions Avoid any unwanted components being connected to the Avoid any unwanted components being connected to the

main componentmain component

Connectivity analysisConnectivity analysis



Cartilage and Articular Space RegionsCartilage and Articular Space RegionsThe adaptive thresholding procedure (between The adaptive thresholding procedure (between the pelvic bone and acetabular cartilage):the pelvic bone and acetabular cartilage):

1.1. Set the initial threshold value (which should be Set the initial threshold value (which should be sufficiently low such that no overlooking occurs).sufficiently low such that no overlooking occurs).

2.2. Threshold the radial directional first derivate images Threshold the radial directional first derivate images to obtain a binary image.to obtain a binary image.

3.3. Extract the largest connective component from the Extract the largest connective component from the binary image.binary image.

4.4. If the largest connective component satisfies the If the largest connective component satisfies the following condition, stop. Otherwise, increase the following condition, stop. Otherwise, increase the threshold value and go back to 1.threshold value and go back to 1.



Cartilage and Articular Space RegionsCartilage and Articular Space RegionsCondition:Condition:

Whether or not the extracted component is one-Whether or not the extracted component is one-layer is checkedlayer is checked

Cartilage edge region should be a one-layer surfaceCartilage edge region should be a one-layer surfaceRays along all radial directions originating from the femoral Rays along all radial directions originating from the femoral head centerhead center Pass only one or zero times through the cartilage regionPass only one or zero times through the cartilage region The number of rays passing through two or more layers The number of rays passing through two or more layers

should be sufficiently smallshould be sufficiently small

The edge region between the femur bone and The edge region between the femur bone and femoral head cartilage is extracted in a similar femoral head cartilage is extracted in a similar wayway



Cartilage and Articular Space RegionsCartilage and Articular Space RegionsThe approximated regions of cartilages are The approximated regions of cartilages are extracted from binarized versions of directional extracted from binarized versions of directional second derivative imags.second derivative imags.

The edge region are used as constrains to restrict The edge region are used as constrains to restrict the possible area for the cartilage and articular the possible area for the cartilage and articular space regionsspace regions


Step FourStep Four --

Subvoxel LocalizationSubvoxel Localizationand Thickness Determinationand Thickness Determination

A subvoxel zero-crossing searchingA subvoxel zero-crossing searching Along radial directionsAlong radial directions

The thickness is estimated from the The thickness is estimated from the distance betweendistance between Inner edgeInner edge

Bone attachedBone attached Outer edge Outer edge

Articular spaceArticular space

along radial directions.along radial directions.


ResultsResults

a fully automated method for segmentation and thickness determination of hip joint cartilage from 3d...

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