Medical Physics Seminar – Monday, October 10, 2011
Quantitative Ultrasound for Breast Tumor Diagnosis
Kibo Nam (student of Drs. Tim Hall and James Zagzebski)
Research Assistant, Department of Medical Physics, UW-School of Medicine & Public Health, Madison, WI USA
Backscatter and attenuation variations are essential contrast mechanisms in ultrasound B-mode imaging, and these features are qualitatively assessed in clinical breast examinations. We are developing Quantitative Ultrasound methods that display absolute values of these tissue properties to aid in interpretation of ultrasound images. Attenuation and backscatter coefficients can be estimated from unprocessed, RF echo data acquired from a clinical scanner if use is made of a calibrated reference phantom to account for system dependencies of echo signals. However, backscatter and attenuation parameters sometimes are not easily measured because of tissue inhomogeneities within or above a region of interest (ROI). Work described in this seminar focuses on estimates of attenuation and backscatter coefficients for breast masses. To account for attenuation along paths proximal to the ROI, a least squares method was applied, fitting echo signal power spectra to model spectra derived assuming different values for the frequency dependence of scattering. The reference phantom method (RPM) is convenient for accounting for system factors on echo data. However the speeds of sound in the tissue and reference need to be the same for this method to be most effective. An assessment of accuracy of attenuation measurements by the RPM when the tissue sound speed differs from that of the reference will be presented, and methods to minimize errors will be discussed.