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Plaque Characterization with LogVoA

Background

LogVoA (logarithm of the Variance of Acceleration) is an Acoustic Radiation Force Impulse (ARFI)-derived parameter designed to quantify pixel-wise, local differences in tissue mechanics and acoustic scattering properties. It is computed as the temporal variance of the second time derivative of displacement profiles derived from ARFI Imaging.

This technique originates from the principle that displacement estimation variance, or “jitter,” increases in regions of low signal correlation and low signal-to-noise ratio (SNR). According to the Cramér–Rao lower bound, displacement variance (σ²) depends on the parameters of the correlation coefficient between tracking A-lines and SNR reflects local echogenicity.

Application

The primary application of LogVoA Imaging has been in studying atherosclerotic plaques in the carotid artery, for stroke risk assessment. In in vivo human studies with histological validation, LogVoA demonstrated the ability to discriminate between plaque components of calcium (CAL), collagen (COL), lipid-rich necrotic core (LRNC), and intraplaque hemorrhage (IPH).

The following figure shows an example of LogVoA imaging used to delineate components of plaque, alongside a B-mode image of the plaque and histology-based plaque characterization:

Recent work has extended LogVoA to plane-wave tracking, maintaining equivalent plaque characterization performance while enabling higher frame rate than focused tracking, as well as making improvements to the filter used to isolate “jitter” and better delineate plaque components.

Select Publications

  • G. Torres et al., “Delineation of Human Carotid Plaque Features In Vivo by Exploiting Displacement Variance,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 66, no. 3, pp. 481–492, Mar. 2019, doi: 10.1109/TUFFC.2019.2898628.
  • G. Torres, T. J. Czernuszewicz, J. W. Homeister, M. A. Farber, M. C. Caughey, and C. M. Gallippi, “Carotid Plaque Fibrous Cap Thickness Measurement by ARFI Variance of Acceleration: In Vivo Human Results,” IEEE Trans. Med. Imaging, vol. 39, no. 12, pp. 4383–4390, Dec. 2020, doi: 10.1109/TMI.2020.3019184.
  • K. S. Anand, G. Torres, J. W. Homeister, M. C. Caughey, and C. M. Gallippi, “Comparing Focused-Tracked and Plane Wave-Tracked ARFI Log(VoA) In Silico and in Application to Human Carotid Atherosclerotic Plaque, Ex Vivo,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 70, no. 7, pp. 636–652, July 2023, doi: 10.1109/TUFFC.2023.3278495.
  • S. Qazi, K. Anand, J. W. Homeister, M. A. Farber, and C. Gallippi, “Comparison of Filtering Methods for Calculating ARFI log(VoA) to Delineate Carotid Plaque Features, In Vivo,” IEEE Open J. Ultrason., Ferroelect., Freq. Contr., pp. 1–1, 2025, doi: 10.1109/OJUFFC.2025.3609675.