Parametric imaging using a clinical scanner

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.