Harmonic Deconvolution in Ultrasound Vibro-Acoustic images Alexia Giannoula Communications group, Dept of Electrical & Computer Engineering, University of Toronto

Elastography  Changes in elastic properties of soft tissue have been often attributed to the presence of disease or abnormal structures  Most techniques in elasticity imaging or elastography involve: » tissue excitation by an external or internal force » detection of the tissue motion or displacement Using Ultrasound, magnetic resonance (MR), acoustic/optical methods Hard inclusion/tumor: smaller displacement B-modeelastogram

Acoustic Radiation Force  A way to excite directly a target inside the body is through the use of the radiation force of ultrasound  Advantages: » Non-invasive (external) excitation » Highly-localized radiation stress field (leads to increased precision)  The radiation force mainly depends on: » The type of propagating medium (lossless/lossy, viscoelastic fluid etc.) » Mechanical properties of the target object » Geometry of the target object

Ultrasound Vibro-Acoustography (USVA) 1.Two CW beams at slightly different frequencies interfere in the focal zone 2.A modulated ultrasound field is generated at the “beat” frequency Df (low) 3.A highly-localized dynamic (oscillating) radiation force is produced 4.In response to the force (stress field), the object vibrates at the same Df 5.Vibration  acoustic emission  Detected by hydrophone/laser vibrometer Detection sensitivity: few nanometers Image resolution: PSF~700μm USVAX-RayPhoto

Proposed Deconvolution Scheme (I)  Usually a blur is observed around the object » Due to the sidelobe effects of the system PSF  Apply separate deconvolution to the fundamental and second harmonic signals recorded by the hydrophone  Higher-harmonics arise due to tissue nonlinearities » Harmonic imaging  better resolution and less noise/blur Second harmonic Fundamental

Proposed Deconvolution Scheme (II)  First and Second-harmonic image formation: ? ξ(r 1 ) object function Each PSF h i represents the response of a point target to the radiation force F i (i=1,2) Obtain 2 deblurred images ξ 1, ξ 2 Fuse the outputs based on the different attenuations: ξ = α 1 ξ 1 + α 2 ξ 2 Form h 1, h 2 Filter each χ 1 (r), χ 2 (r) with the inverse PSFsFind F 1, F 2