The effect of low scatterer number density on ultrasound attenuation estimation

Nicholas Rubert*, Tomy Varghese

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations

Abstract

The ultrasound attenuation coefficient has been established as a marker of thermal ablation therapy. The reference phantom method (RPM) has been proposed as a practical technique for estimating the attenuation coefficient in patients. However, tissue is frequently modeled with a high scatterer number density (SND). In this work, attenuation slope estimation was performed in simulations, modeling a linear attenuation coefficient and both high and low SND. For the numerical phantom studies, tissue was simulated having an SND ranging from 0.2 to 128 scatterers/mm3. Using a fixed kernel size of 9.6 mm axially along with 10 independent A-lines and a center frequency of 5.5 MHz, it was found that the bias in the estimate of the attenuation coefficient was no more than 0.10 dB/cm MHz, while the standard deviation increased to over 1.0 dB/cm MHz for different SND values. Attenuation slope was also estimated using the reference phantom method in five ex vivo bovine livers and another five bovine livers following intense heating in a water bath. In normal ex vivo bovine liver and heated bovine liver it was found that the received ultrasound echo signal from a Siemens 9L4 linear array transducer, operating at a center frequency of 6 MHz, exhibited a low envelope SNR, 1.10 in normal liver and 1.28 in heated liver. These results deviate from the SNR value of 1.91 expected for Rayleigh distributed envelope values. The same transducer was used for the attenuation slope estimates with a variable kernel size. As the kernel size was varied from 6 to 16 mm axially the mean attenuation slope estimate varied between 0.4 and 0.5 dB/cm MHz in unheated liver and 1.1 and 0.9 dB/cm MHz in heated liver. Meanwhile, the standard deviation in the attenuation estimates varied from 1.8 to 0.5 dB/cm MHz in unheated liver and 1.6 to 0.5 dB/cm MHz in heated liver. From the simulation and ex vivo results, we conclude that the variance in attenuation slope estimation in ex vivo bovine liver is primarily due to the low SND. Future work in attenuation estimation should consider both high and low SND in tissue when RPM algorithms are utilized.

Original languageEnglish (US)
Title of host publicationIEEE International Ultrasonics Symposium, IUS
PublisherIEEE Computer Society
Pages2418-2421
Number of pages4
ISBN (Electronic)9781479970490
DOIs
StatePublished - Jan 1 2014
Event2014 IEEE International Ultrasonics Symposium, IUS 2014 - Chicago, United States
Duration: Sep 3 2014Sep 6 2014

Other

Other2014 IEEE International Ultrasonics Symposium, IUS 2014
CountryUnited States
CityChicago
Period9/3/149/6/14

Keywords

  • attenuation
  • quantitative ultrasound
  • thermal ablation

ASJC Scopus subject areas

  • Acoustics and Ultrasonics

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