Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

Characterization of 3D Echo-Morphology of Characterization of 3D Echo-Morphology of Carotid Atherosclerotic Plaques by use of B-Carotid Atherosclerotic Plaques by use of B-

Mode 2D UltrasoundMode 2D Ultrasound

José C. Seabra*, Luís M. Pedro, José Fernandes and João Sanches

Technical Superior Institute, Lisbon PortugalUniversity of Lisbon Medical School, Lisbon Portugal

(jseabra@isr.ist.utl.pt)

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

Data Acquisition Protocol Based on Free-Hand UltrasoundData Acquisition Protocol Based on Free-Hand Ultrasound

• Ultrasound image acquisition requires a common ultrasound equipment, a location sensor and a frame grabber

• During each exam, a sequence of cross-sectional images of the carotid artery (near the bifurcation) is stored, jointly with its spatial location and time point in the cardiac cycle

Figure 1. a-b) Free-hand system apparatus; c) Example of cross-sectional image of the carotid artery

a) b) c)

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

3D Reconstruction/De-noising from 2D images 3D Reconstruction/De-noising from 2D images

Figure 2. a) Cross-sectional ultrasound image, showing clearly a plaque; b-c) normalized and de-noised images, respectively; d) intensity profiles along the main diagonal; e-f) two different views of the 3D recontructed plaque

• Particularly useful to build a 3D representation of the carotid structure from a set of ultrasound images with different orientations

• A reconstruction/de-noising method is implemented to: clearer 3D representations, minimally perturbed by

speckle noise a set of local statistical estimators derived from the

statistics of the signal, which can be further used for tissue (plaque) characterization

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

Segmentation of Carotids and Plaques Segmentation of Carotids and Plaques

Figure 3. a) Ex-vivo carotid bifurcation plaque; b) Surface rendering resulting from the extraction of contours (c)

• Region extraction is a crucial step for characterization of plaque echo-morphology

• Semi-automatic sequential segmentation method based on active contours employed under medical supervision

• A set of contours estimated per frame are interpolated to form the surfaces of both carotid and plaque

a) b) c)

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Potential clinical applicationsPotential clinical applicationsMorphologyMorphology

Figure 4. a) Virtual representation of the echogenicity contents of a 3D plaque; b) Surface rendering of normal and diseased carotids (top) and 4 distinct atherosclerotic plaques (bottom)

• Early assessment of the carotid and plaque anatomies• Quantification of the atherosclerotic lesion, in terms

of extension, volume and degree of stenosis• Evaluation of surface regularity• Less operator-sensitive because it uses 3D

information, thus quantification is independent on the selection of a representative 2D image of the lesion

a) b)

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

Potential clinical applicationsPotential clinical applicationsEcho-structureEcho-structure

Figure 5. a) identification of hypoechogenic sites by use of the local mean feature, grayscale mapping of plaque texture by use of variance feature, inspection and quantification of a representative vulnerable region detected inside the plaque; b) Labeling of vulnerable regions in 3 distinct plaques using a graph-cuts segmentation method with features of the median and percentile40

• Plaque echo-structure is related to echogenicity and texture• Statistical features (mean, variance, median, percentile40) are

extracted from inside the plaque and compared to reference clinical thresholds

• Characterization is employed globally – to obtain averaged values of plaque echo-morphology; and locally – to identify and quantify vulnerable sites inside the plaque

a) b)

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

SummarySummary

• A methodology for the characterization of 3D echo-morphology of carotid atherosclerotic plaques by use of B-mode 2D ultrasound was presented

• The methodology includes a rigorous data acquisition protocol, 3D reconstruction and segmentation methods, followed by characterization and labeling

• The proposed diagnostic pipeline improves current carotid plaque characterization methods based on 2D ultrasound by: Using a 3D reconstruction approach from conventional 2D images while keeping the operating

and technological simplicity

Extracting new risk indicators from the 3D echo-morphology contents from inside the plaque

Performing local identification and quantification of vulnerable regions throughout the 3D plaque

Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved.

Find out more at…Find out more at…

http://users.isr.ist.utl.pt/~jseabra/

http://users.isr.ist.utl.pt/~jmrs/

A 3D Ultrasound-Based Framework to Characterize the Echo Morphology of Carotid Plaques Seabra, J.; Pedro, L.; Fernandes e Fernandes, J; Sanches, J., IEEE Trans Biomed Eng. 2009 Feb 6. [Epub ahead of print]