Phase correction of skull aberration with 1.75-D and 2-D arrays using speckle targets
Wavefront distortion induced by the skull severely impacts transcranial ultrasound. In particular, the skull reduces the ability to monitor flow in the cerebral vasculature. We present B-scan and color flow images, aberratred with polymer casts of skull bone, that have been improved with near-field phase correction techniques. These algorithms rely on speckle targets for estimation of the phase profile. Real-time adaptive imaging experiements in tissue-mimicking phantoms with 4 mm spherical voids were performed using multi-lag cross-correlation and multi-lag speckle brightness phase correction algorithms. The real-time adaptive imaging was constructed on a Siemens Antares™ scanner and used a custom 3.5 MHz, 1.75-D transducer (8 × 96 elements). Phase correction with the 1.75-D array was performed in a matter of a few seconds. The contrast-to-speckle (CSR) of the spherical voids improved from 1.16 ± 0.39 in the aberrated images to 1.52 ± 0.37 in the phase corrected images. Using a 2.5 MHz, 2-D array on a real time 3-D scanner similar experiments with spherical voids were performed. The CSR of the lesions on the 3-D scanner improved from 0.9 in the aberrated images to 1.6 in the phase corrected images. In addition, phase correction was shown to improve the estimation of 3-D color flow when the transducer was focused on a speckle target through the skull cast. © 2005 IEEE.
