Phase aberration in Shear Wave Dispersion Ultrasound Vibrometry

Shearwave Dispersion Ultrasound Vibrometry (SDUV) is an acoustic radiation force based technique that measures tissue shear viscoelasticity by characterizing shear wave speed dispersion. An application of this technique is liver fibrosis staging. We previously reported findings from an animal study where shear modulus and viscosity reconstruction displayed larger variances for in vivo versus ex vivo cases. This study investigates two major causes of such increased variance, namely attenuation and phase aberration. Two sets of experiments were conducted using a custom phantom. In the first experiment, the phantom was imaged directly with varying pushing power by setting system transmit attenuation at different levels from 0 dB to 6 dB. The second set of experiments utilized different pieces of pork bellies as aberrators between the probe and the phantom, while maintaining the pushing power at 0 dB. For each data set, SDUV reconstruction algorithms yielded shear moduli within a region of interest (ROI) of 10 mm × 4 mm close to the pushing focus. The attenuation experiment showed that the variance in SDUV reconstruction results did not start to increase until the peak displacement dropped to 2.2 µm. On the other hand, insertion of an aberrator caused elevated variances even at a much higher peak displacement of 3.9 µm. The variances also swung greatly among different data sets with similar peak displacements. Moreover, thinner aberrators produced consistently better results even with lower peak displacements. All these observations indicate that phase aberration induced waveform distortion is more detrimental to SDUV than pure attenuation. It is beneficial to investigate phase aberration correction methods and apply them to improve SDUV performance.