An Ultrasonic Adaptive Beamforming Method and Its Application for Trans-Skull Imaging of Certain Types of Head Injuries; Part II: Reception Mode and Adaptive Imaging

Refraction-Corrected Transcranial Ultrasound Imaging Through the Human Temporal Window Using a Single Probe

“…As a result, optimal focusing with the imaging transducer was limited to a region, at rather large depth (for the imaging transducer) close to the part of the skull in contact with the calibration transducer, and at lateral positions where the skull was sufficiently flat to enable close contact with the calibration transducer. Prior knowledge on the compressional sound speed or thickness of skull [53], [58], [76], [88], [89] and correction based on CT scans [53]- [55] are also impractical on-site as these parameters vary in person [23], [25], [29], [51], [52], [90], [93] and EMS are not always equipped with CT scanners.…”

“…In a numerical study, Wang and Jing [50] estimated the sound speed of the aberrator by the method introduced by Wydra et al [77] and used the FMT to calculate the arrival times. Shapoori et al [52] also estimated the sound speed of the aberrator by the method introduced by Wydra et al [77] and used Fermat's principle for arrival time calculation, but no transcranial image through a human skull was reported. Wang and Jing [50] and Shapoori et al [52] used focused transmit beams, which necessitates calculating and applying transmit delays for each image line; this imposes complexity to the imaging strategy.…”

“…Shapoori et al [52] also estimated the sound speed of the aberrator by the method introduced by Wydra et al [77] and used Fermat's principle for arrival time calculation, but no transcranial image through a human skull was reported. Wang and Jing [50] and Shapoori et al [52] used focused transmit beams, which necessitates calculating and applying transmit delays for each image line; this imposes complexity to the imaging strategy. White and Venkatesh [6] reported on phase-corrected transcranial super resolution ultrasound imaging through the temporal region of human skull with a commercial probe, but the correction was achieved with a ground truth measurement, which is not feasible in vivo.…”

“…1) Beamforming: Several approaches (for instance, Wang and Jing [50] and Shapoori et al [52]) used focused transmit beams. Like [16], [56], our approach uses unfocused transmit beams and relies on a SAI sequence with single-element transmission.…”

“…This strategy was used for two dimensional (2-D) [24], [42] and 3-D TUI [46], [48], [49]. More recently, approaches that model refraction through the true geometry and thickness of the skull have been proposed; however, the method requires estimates of the thickness and wave speed in the skull at multiple positions with dedicated ultrasound measurements prior to image reconstruction [50]- [52]. Another family of methods relies on a CT or MRI scan of the skull to determine its geometry and knowledge or assumption of wave speed in bone, prior to TUI [53]- [56].…”