Abstract Identifying risky atherosclerotic plaques has high clinical relevance.

1. Probe Velocity Tracking in Free-hand US without Spatial Locator David Afonso (dafonso@isr.ist.utl.pt), J. Miguel Sanches (jmrs@ist.utl.pt) Institute for Systems and Robotics, Department of Bioengineering InstitutoSuperior Técnico, Technical University of Lisbon • Abstract • Identifying risky atherosclerotic plaques has high clinical relevance. • 3D reconstruction allows a more complete plaque characterization. • Aim: Improve 3D reconstruction quality of 2D US data without additional costs. • Where: Freehand data acquisitions with no tracking system, where the probe travels in a straight-line. • How: Estimate probe speed profile. • Using: Dissimilarity criteria between tissue texture in consecutive frames. • Experimental Data • Synthetic • A tube-shaped [214×214×428] object, with realistic dynamic range and with Rayleigh noise was generated. • To induce spatial correlation, a normalized [2×2×10] mean filtering was applied. • To simulate the probe acquisition process, two sampling strategies of this object were performed: with constant speed (s) and constant acceleration (a). • Problem Formulation • In a straight line free-hand acquisition, the greater the speed, the lower the expected similarity between frames (s) (a) • Real • 160 frames of US data acquired at operator constant speed. • Selection of two separate regions with little tissue transitions. • Median and Gaussian filtering was performed to remove high frequency variability in ρ(k). (R2) (R1) • Results • Synthetic results show a slope in clear inverse relation with the sampling speed. • Real data results show a common trend between different image regions. Assumption: The interplane similarity of the Speckle field (tissue texture) will provide an estimate of probe position change (speed) (R1) (a) Similarity metric: (R2) (s) Normalized covariance between consecutive frames Texture extraction: Was achieved with the Convex Rayleigh Log-Euclidean Total Variation method in [1], by minimizing the following energy: • Conclusions • The proposed cross-variance proves a reasonable metric of similarity between consecutive frames. • Speckle of US data allows for tissue texture characterization. • The method show promising results in estimating the probe speed profile, but requires further validation: • Comparison with data from spatial tracking system. • 3D reconstruction of a phantom object 1 RecPad 2011, the 17th edition of the Portuguese Conference on Pattern Recognition, Casa da Música, Porto, in October 28, 2011