Phase correction of skull aberration with 1.75-D and 2-D arrays using speckle targets

Abstract

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 TM 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.