Rocio - PowerPoint Presentation

Slide1

Rocio Cabrera Guillaume LemaitreMojdeh Rastgoo

CT and MR

Imaging

of

Abdominal

Aortic

AneurysmSlide2

Presentation OutlineIntroduction

to

Abdominal Aortic AneruysmsComputed Tomography of AAAImaging TechniqueImage ProcessingLevel Set MethodsActive Shape ModelsMagnetic Resonance of AAAImaging TechniquesGalodinium-enhancementDiffusion weightedImage ProcessingMarkovian Method Graph-Theoretic ApproachConclusions

1/13/2011

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Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic AneurysmsSlide3

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Aneurysm

Vascular pathology consisting of an irreversible dilation of a segment of a blood vesselAbdominal aortaContinuation of the thoracic aorta and begins at the level of the diaphragmLargest artery in the abdominal cavityAbdominal Aortic AneurysmAccepted criterion: 50% increase in vessel diameter

Introduction

What

is

an

Abdominal

Aortic

Aneurysm

?Slide4

CT ImagingCT has been used widely in AAA CT Imaging speed

CT provides detailed quality for better analysis of aneurysm and adjacent arteries

Detailed information of aorta and its branches for 3D reconstruction

Flexible to different post processing methods Appreciated in surgical planning 1/13/20114Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic AneurysmsSlide5

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Level Set Method (LSM) is a numerical method for tracking interface a shapes .

More specifically for shape varying objects

Level set function

plane

CT

Image

Processing

AAA

Segmentation

through

level

set

method

Slide6

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image Processing

AAA

Segmentation

through

level

set

method

Defining the mesh on the object (Level Set function )

Updating the mesh values using the Speed function

Multi resolution Analysis –

LR( half) volume

Top – Down , Narrow band update restricted to the zero level set

Scaling up the result

Repeating the algorithm on full data set

2 - 3D reconstruction – Using Marching cubes

1 - Segmentation the volumes

Force at mesh point (

x,y

)

Advection term = 1

Curvature force (x’ ,y’)

Image force based on the Gaussian derivative filter Slide7

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Advantage:

Level set method has the advantage to provide more accurate results specially in segmenting the small detailsDisadvantage It has a very high computational cost Suggestions Combination of the methods , while level set can be used to improve the initial segmentation results

CT

Image

Processing

AAA

Segmentation

through

level

set

method

Slide8

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image ProcessingAAA

Segmentation

using

Active

S

hape

M

odel

Active shape model (Smart Snake) was developed by

Cootes

et al. in order to over come the problems with snake segmentation

Active counter model (Snake) segmentation depends on the initial snake

Active counter model is not capable to deal with the occluded objects

In Medical Imaging ASM is applied on the combination of shapes and gray level sets Slide9

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image ProcessingAAA

Segmentation

using

Active

S

hape

M

odel

Shape Modeling

Shape alignment

Statistical Computations PCA

Aligning the images in the same reference axes , using

Procrustes

Analysis

Procrustes

Analysis minimize the distance between reference shape and each shape in the dataset

Modeling the shape variations

Computation of the mean shape

Computation of the scatter matrix

Sorting the eigenvectors and keeping the first k eigenvectors , based on the largest

eigenvalues

Eigen decomposition of the shapes where ,

Value of

k

is based on Slide10

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image ProcessingAAA

Segmentation

using

Active

S

hape

M

odel

Shape Modeling

M.

Bruijne

,B. van

Ginneken

, M. A.

Viergever

, W. J.

Nieesen

, « 

Interactive Segmentation of Abdominal Aortic Aneurysms in CTA Images

 », 2004Slide11

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image ProcessingAAA

Segmentation

using

Active

S

hape

M

odel

Grey level Appearance Modeling

Sum of absolute difference between the reference and sample image over several resolutions

The sum is performed for each landmarks for a defined window size

M.

Bruijne

,B. van

Ginneken

, M. A.

Viergever

, W. J.

Nieesen

, « 

Interactive Segmentation of Abdominal Aortic Aneurysms in CTA Images

 », 2004Slide12

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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CT

Image ProcessingAAA

Segmentation

using

Active

S

hape

M

odel

Model Fitting

First slice manually Initialized while for the others previous counter was considered as initialization

Performing the

multiresolution

analysis for higher accuracy

M.

Bruijne

,B. van

Ginneken

, M. A.

Viergever

, W. J.

Nieesen

, « 

Interactive Segmentation of Abdominal Aortic Aneurysms in CTA Images

 », 2004Slide13

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Gadolinium injection (paramagnetic CA)

Shortens the T1 relaxation time of blood, distinguishing it from its surroundingsNo known side effects nor nephrotoxicityPrince et al. [2] reported an agreement in measured AAA size in CT, MR and USOrta et al. [1] reported its use to diagnose inflammatory AAAHyper-intensity surrounding the aortaRegion ADC = 1.24 x 10-2 mm2/sADC consistent with a restricted diffusion due to inflammation

Gadolinium-enhanced MRI

Diffusion Weighted MRI

MR Imaging of AAA

Alternate MR Imaging ApproachesSlide14

X – 2D [MxN] random field that models the segmentation labels Y – 2D [MxN

] random field that models the input image

s – site (pixel) located at position (

i,j)MAP – Maximum A Posteriori Probability, through the Bayes RuleAssuming Gibbsian distributions A pixel s will switch classes if and only if at least one of its neighbors has already been assigned the new class label1/13/201114Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

MR

Image

Processing

Markovian

-Active

Contour

Segmentation

Likelihood Energy.

Natural Logarithm of a GaussianSlide15

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Direct extension to 3D and 4D

3D – Neighbouring sites in k+1 and k-1 images4D – Neighbouring sites in t+1 and t-1 time framesAAA reconstruction from MRIInitialization done by expert handSeed growth until convergence4D segmentation resultsMR Image Processing

Markovian

-Active Contour SegmentationSlide16

1/13/2011Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Aortic Surface Pre-segmentation

Fast marching level set method used to compute {appSt}tє[0,N-1]Centerline ExtractionCenterline determined from each approximate surface by skeletonizationAccurate Surface SegmentationWeighted graph G = (V; E)V – node set of image pixelsE – arc set of neighbourhood systemEvery arc ‹vi, vj› є E has a costGraph-cuts aim to partition a weighted graph into 2 disjoint subsets Minimize the cost function ε(f)

Appropriate design of a energy function, a minimum s-t cut can

segment a region of interest in an image.

MR Image Processing

Graph-Theoretic

SegmentationSlide17

ConclusionsStrong interest in exploiting the capabilities of the medical imaging modalities to diagnose AAA

Choice of the imaging modality

CT

Modality of choice in most institutionsAppropriate for emergency patientsUse of an iodinated contrast medium and ionizing radiationMR Appropriate to detect inflammatory AAADoes not employ ionizing radiationContrast agent is appropriate for patients with renal insufficiencyImage processing techniques 2 CT and 2 MR methods have been presentedMost methods rely on segmentation of the aorta and measurement of the vessel diameterEach methods could be extended to the other modality, but not much research has been done on itIt would be interesting to perform a study in which the several segmentation methods are used on CT and MR in order to evaluate the methods and the imaging modalities in a better way.1/13/201117

Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic AneurysmsSlide18

References[1] Orta, K. and

Kilickesmez

, O. Clear Depiction of Inflammatory Abdominal Aortic Aneurysm with Diffusion-Weighted Magnetic Resonance Imaging. Cardiovascular and Interventional Radiology. (2010) 33:379-382.

[2] Prince, M. et al. Gadolinium-enhanced Magnetic Resonance Angiography of Abdominal Aortic Aneurysms. Journal of Vascular Surgery. (1995) Volume 21. Number 4.[3] Jodoin, P. et al. Markovian Method for 2D, 3D and 4D segmentation of MRI. (2008) 15th IEEE International Conference on Image Processing. [4] Sonka, M. et al. Early Detection of Aortic Aneurysm Risk from 4D MR Image Data. (2006) Computers in Cardiology.[5] Kang Li et al. Optimal Surface Segmentation in Volumetric Images - A Graph-Theoretic Approach (2006) IEEE Transactions on Pattern Analysis and Machine Intelligence. Volume 28. Number 1.[6] Crawford, C. et al. Abdominal Aortic Aneurysm: An Illustrated Narrative Review. (2002) Journal of Manipulative and Physiological Therapeutics. Volume 26. Number 3. [7] Marleen de Bruijne and Bram van Ginneken and Max A. Viergever and Wiro J. Niessen. Interactive Segmentation of Abdominal Aortic Aneurysms in CTA Images. 2004.[8] TF. Cootes and A. Hill and C.J.Taylor and J.Haslam and Manchester M Pt. The Use of Active Shape Models For Locating Structures in Medical Images. 1994.[9]T.F.

Cootes and C.J. Taylor and Manchester M Pt. Statistical Models of Appearance for Computer Vision. 2000.

[10] Cootes, T. F. and Taylor, C. J. and Cooper, D. H. and Graham, J. Active shape models - their training and application. Comput

. Vis. Image

Underst

. 1995. Volume 61. Issue 1. Pages 38-59.

[11] A. Hill and A.

Thornham

and C. J. Taylor. Model-Based Interpretation of 3D Medical Images. In British Machine Vision Conference. 1993. BMVA Press.

[12] Michael

Kass

and Andrew

Witkin

and

Demetri

Terzopoulos

. Snakes: Active contour models. International Journal of Computer Vision. 1988. Volume 1. Number 4.

[13] Derek Magee and Andrew

Bulpitt

and Elizabeth Berry. Level Set Methods for the 3D Segmentation of CT Images of Abdominal.

[14] Steven C. Mitchell and

Boudewijn

P. F.

Lelieveldt

and Rob J. van

der

Geest

and Hans G. Bosch and Johan H. C. Reiber and Milan and Milan Sonka. Multistage Hybrid Active Appearance Model Matching: Segmentation of Left and Right Ventricles in Cardiac MR Images. IEEE Transactions on Medical Imaging. 2001. Volume 20.

[15] Wikipedia. Level Set Method. December 2010. $http://en.wikipedia.org/wiki/Level\_set\_method$

[16] Wikipedia. Isosurface. December 2010. $http://en.wikipedia.org/wiki/Isosurface$[17] Wikipedia. Marching Cubes. December 2010. $http://en.wikipedia.org/wiki/Marching\_cubes$

[18] George G. Hartnell. FRCR, FACC. Imaging of Aortic Aneurysm and Dissection: CT and MRI. Journal of Theoretical Imaging. 2001.

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Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic AneurysmsSlide19

Appendix - AAA Segmentation through level set method1/13/2011

Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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Defining static and evenly spaced mesh in the image using Mesh values are updated using the speed functionSpeed function F depends on : Advection term (constant value)Curve term based on zero level set Image term (Based on the edges) Updating the curve and Image terms based on nearest neighbor in the zero level set !! Computationally expensiveReducing the computational cost by updating the mesh restricted to the zero level set area ; Narrow band with the level set method Slide20

1/13/2011

Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic Aneurysms

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ElastinResponsible for the elastic recoil of the arteries due to the pulsatile blood flow Degradation of elastin fibres will shift load to collagen fibresElasticity decreaseDiameter increaseAortic rupture Genetic

and environmental factors contribute to AAA development

Great clinical

importance

to

determine

aortic

diameter

Environment

Atherosclerosis

Smoking

Inflamation

Genetic

Factors

Elastase

activity

increase

vs.

Inhibition

decrease

Elastin

Destruction

Failure

of

E

lastin

Increased

load

on

collagen

Failure of

Collagen

Aneurysmal

Dilation

Rupture

Ageing

Hypertension

Collagen

remodelling

Alteration

in

vessel

geometry

Introduction

Pathogenesis

of

an

Abdominal

Aortic

AneurysmSlide21

Traditional MRI Widely used to retrieve anatomical and physiological information of patientsVascular imaging limitationsFlow artifacts generated in different pathologiesAneurysms – slow, swirling flow

Stenotic

vessels – turbulent flow

1/13/201121Biological Basis of Medical Imaging - CT and MR Imaging for Abdominal Aortic AneurysmsMR Imaging of AAATraditional MRI limitations on Vascular Imaging