T. Lindenmaier D. Buchanan, S. McKay, I. Gyacskov, Semi-Automated Segmentation of Three-dimensional Ultrasound Carotid Artery Plaque Volume T. Lindenmaier D. Buchanan, S. McKay, I. Gyacskov, A. Fenster and G. Parraga Imaging Research Laboratories, Robarts Research Institute, Department of Medical Biophysics, Biomedical Engineering Graduate Program, The University of Western Ontario, London, CANADA April 4, 2012

Overview Atherosclerosis and the carotid artery Image acquisition using ultrasound Imaging phenotypes of carotid atherosclerosis Limitations of current methods Development of semi-automated measurement Application and Reproducibility

Motivation: Carotid Atherosclerosis Libby, Peter. Inflammation in Atherosclerosis. Nature. December 2002.

ICA ECA CCA BF

Motivation: Atherosclerosis in Carotid Artery Cerebrovascular disease accounts for 10% of all deaths worldwide1 1WHO, 2004

Ultrasound of Carotid Atherosclerosis Intima-Media Thickness Courtesy of Christiane Mallet

Manual Planimetry Measurements lumen-intima media-adventitia Longitudinal View Axial View

Intima-Media Thickness Carotid Atherosclerosis: US Measurements Vessel Wall Volume Egger et al. J Ultrasound Med. (2008) Intima-Media Thickness Buchanan et al. Accepted to Ultrasound Med Biol. (2012) Total Plaque Volume Al-Shali et al. Atherosclerosis. (2005) Egger et al. Ultrasound Med Biol. (2007) Total Plaque Area Riccio et al. Cardiovascular Ultrasound. (2006)

Manual Segmentation of 3DUS TPV User sets axis of segmentation Measurements made in an axial view at 1mm inter-slice distance Inter-slice distance multiplied by segmentation area to calculate volume 100 500 400 300 200 600 V (mm3) CV (%) 5 10 15 20 Total Plaque Volume Adapted from Landry et al. Stroke. (2004)

Limitations of Current Measurements Intima-Media Thickness (IMT) Narrow dynamic range (0.5mm to 1.0mm) 1-dimensional measurement No plaque Total Plaque Area (TPA) High inter-observer variability 2-dimensional measurement Not adequate to estimate 3D change with 2D measurement Total Plaque Volume (TPV) Long measurement time (slice-by-slice) Laborious

Semi-automated TPV Measurement Longitudinal View Axial View

Schematic of Longitudinal View Semi-Automated TPV Measurement Contour 1 (longitudinal view) Contour 2 (axial view) Contour 3 (axial view) Contour 4 (axial view) Measurement View Schematic of Longitudinal View C1 C2 C3 C4 Min Z Max Z

Semi-Automated TPV Measurement C1 Min Z C2 C3 C4 Max Z x z y c b a P V = volume PFj = representative vertex Aj = area of triangle 1Van Gelder. Graphic Gems 5. (1995)

Methodology echogenic plaques from 17 subjects Selection of 23 2x5 rounds of semi - automated segmentation Images measured 5x with 5 Minutes between measurements Images measured 5x with 20 hours between measurements 1 round manual segmentation

Manual vs. SA Measurements

Results Landry et al. Stroke. (2004)

Conclusion Intra-observer variability similar to manual measurement variability reported by Landry et al. (2004) High correlation between manual and SA for both time durations between measurements The manual TPV measurement can be replaced by the novel segmentation method. If adopted for clinical use, measurements could be generated right away (faster diagnosis).

Acknowledgements Research Team Sandra Halko CRCC RPT Shayna McKay BSc Andrew Wheatley BSc Miranda Kirby BSc Stephen Costella MESc Amir Owrangi MSc Trevor Szekeres MRT Sarah Svenningsen Lauren Villemaire Supervisory Committee Grace Parraga PhD Daniel Buchanan BSc Collaborators Aaron Fenster PhD FCCPM Igor Gyacskov 20

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