Diverging beam with synthetic aperture technique for rotation elastography: preliminary experimental results

Rotation Elastogram (RE) is a 2D spatial distribution map of the estimated local rigid-body rotation undergone by a target when subjected to an external compression, which is one of the recent variants in elastographic imaging. A recent study has shown that inclusion-contrast in RE is independent of inclusion-background modulus contrast and thus may be helpful in distinguishing between barely-stiff benign and malignant lesions. However, estimation of quality RE requires not only precise axial displacement estimates but also lateral displacement estimates. The widely used conventional focused beamforming technique using linear array (CFB-LA) provides better lateral resolution only over the depth of focus, which still results in poorer quality lateral displacement estimates compared to the axial displacement estimates. As an alternative to overcome this depth-dependent lateral resolution and obtain an improved lateral resolution, synthetic aperture-based approaches have been proposed in literature. Recently, we developed a synthetic aperture-based method, diverging beam with synthetic aperture technique (DB-SAT) that was aimed to not only reduce the ultrasound system complexity, but also provide improved lateral resolution throughout the depth of imaging and at higher frame-rate than that is possible in CFB-LA. In this paper, we report the preliminary experimental findings on the use of DB-SAT on RE and compare the resultant image quality against that obtained using often-employed CFB-LA and the synthetic transmit aperture (STA) technique. The investigation was done on tissue-mimicking phantoms and using contrast-to-noise ratio (CNR) as the metric for performance evaluation. The estimated CNR values from the REs obtained using CFB-LA, STA, and DB-SAT were 2.69  ±  0.81, 1.35  ±  0.22, and 14.71  ±  9.83, respectively, for inclusion present at 55 mm depth. The obtained results clearly demonstrated that the quality of RE can be improved significantly, especially at larger depth, using DB-SAT compared to that obtained using CFB-LA and STA technique.