1. Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved. Characterization of 3D Echo-Morphology of Carotid Atherosclerotic Plaques by use of B-Mode 2D Ultrasound José C. Seabra*, Luís M. Pedro, José Fernandes and João Sanches Technical Superior Institute, Lisbon Portugal University of Lisbon Medical School, Lisbon Portugal (jseabra@isr.ist.utl.pt)

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

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

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

5. Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved. Potential clinical applications Morphology 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)

6. Copyright © 2008 Society for Heart Attack Prevention and Eradication. All Rights Reserved. Potential clinical applications Echo-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)

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

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