Synthetic Aperture Focusing for Multi-Covariate Imaging of Sub-Resolution Targets

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 67; no. 6; pp. 1166 - 1177
• Main Authors: Morgan, Matthew R., Bottenus, Nick, Trahey, Gregg E., Walker, William F.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01-06-2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustics; Aperture imaging; Apertures; Beamforming; Coherence; Computer Simulation; Depth of field; estimation; Female; Focusing; Fossils; Frequency control; Geometry; Humans; Image contrast; Image Processing, Computer-Assisted - methods; Image quality; Image transmission; Liver - diagnostic imaging; Middle Aged; Phantoms, Imaging; Signal-To-Noise Ratio; spatial covariance; synthetic aperture; Synthetic apertures; Target recognition; Ultrasonic testing; Ultrasonography - methods; ultrasound
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2020.2966116

Coherence-based imaging methods suffer from reduced image quality outside the depth of field for focused ultrasound transmissions. Synthetic aperture methods can extend the depth of field by coherently compounding time-delayed echo data from multiple transmit events. Recently, our group has presented the Multi-covariate Imaging of Sub-resolution Targets (MIST), an estimation-based method to image the statistical properties of diffuse targets. MIST has demonstrated improved image quality over conventional delay-and-sum, but like many coherence-based imaging methods, suffers from limited depth of field artifacts. This article applies synthetic aperture focusing to MIST, which is evaluated using focused, plane-wave, and diverging-wave transmit geometries. Synthetic aperture MIST is evaluated in simulation, phantom, and in vivo applications, demonstrating consistent improvements in contrast-to-noise ratio (CNR) over conventional dynamic receive MIST outside the transmit depth of field, with approximately equivalent results between synthetic transmit geometries. In vivo synthetic aperture MIST images demonstrated 16.8 dB and 16.6% improvements in contrast and CNR, respectively, over dynamic receive MIST images, as well as 17.4 dB and 32.3% improvements over synthetic aperture B-Mode. MIST performance is characterized in the space of plane-wave imaging, where the total plane-wave count is reduced through coarse angular sampling or total angular span. Simulation and experimental results indicate wide applicability of MIST to synthetic aperture imaging methods.