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-mode
elastogram
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)
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Two CW beams at slightly different frequencies interfere in the focal zone
A modulated ultrasound field is generated at the “beat” frequency Df (low)
A highly-localized dynamic (oscillating) radiation force is produced
In response to the force (stress field), the object vibrates at the same Df
Vibration  acoustic emission  Detected by hydrophone/laser vibrometer
USVA
• Detection sensitivity: few nanometers
• Image resolution:
PSF~700μm
X-Ray
Photo
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
Fundamental
Second harmonic
Proposed Deconvolution Scheme (II)
 First and Second-harmonic image formation:
? ξ(r1) object function
Each PSF hi represents the response of a point target to the radiation force Fi (i=1,2)
Find F1, F2
Form h1, h2
Filter each χ1(r), χ2(r) with the inverse PSFs
Fuse the outputs based on the different
attenuations: ξ = α1 ξ1 + α2 ξ2
Obtain 2 deblurred images ξ1, ξ2