Parametric imaging using a clinical scanner

Abstract

Ultrasonic scatterer size estimation and imaging has proven to be both feasible and useful for monitoring, diagnosis, and study of disease. We are implementing scatterer size imaging and attenuation coefficient imaging on a clinical scanner equipped with a research interface. The interface provides radio frequency echo data over the image of a sample, which are then analyzed offline. Echo data from a reference phantom, acquired using the same transducer and scanner settings used in acquisition from the sample, accounts for system dependencies on the data. Backscatter coefficient and attenuation coefficients are estimated for small regions. Scatterer size images are generated by performing a modified least squares fit of the backscatter estimate to a theoretical model, which relates backscatter to scatterer size. Tests in well-characterized phantoms have demonstrated the accuracy of the method have revealed limitations. Ultrasonic scatterer size estimates generally have large variances due to the inherent noise of the spectral estimates used to calculate size. Compounding partially correlated size estimates associated with the same tissue, but produced with data acquired from different angles of incidence, is an effective way to reduce the variance without making dramatic sacrifices in spatial resolution. Initial compound acquisitions on the clinical system have been done using manually generated scripts supported by the research interface. Results confirm theoretical expectations of the improvement in signal to noise ratio of scatterer size estimations with selected compounding parameters. Additional parameters, including the attenuation coefficient may also be derived.

Method for Estimating Total Attenuation from a Spatial Map of Attenuation Slope for Quantitative Ultrasound Imaging

“…First, a parametric image of attenuation can show contrast between regions that do not appear different in a conventional B-mode image and gives quantitative information about the regions. Zagzebski et al 9 implemented a QUS imaging capability on a clinical scanner that had an offline attenuation imaging ability. To mitigate errors caused by changes in backscatter at tissue boundaries, Kim and Varghese developed the hybrid spectral shift method, which uses the downshift in center frequency of the ultrasound pulse for estimating attenuation.…”

Stable and transient subharmonic emissions from isolated contrast agent microbubbles

“…Some kinds of echographic equipment able to provide RF output are described in the literature for various applications. They are based on ultrasound scanners modified to provide RF data output and user control of the acoustic field features [33]- [35].…”