Compensation for Aberrations of Focused Ultrasound Beams in Transcranial Sonications of Brain at Different Depths

The study analyzes the possibilities of compensating for aberrations when focusing an ultrasound beam through the skull bones using arrays with mosaic pattern of elements, curvature radius and aperture of F = D = 200 mm, frequency of 1 MHz, and fully populated randomized pattern of the elements. The effect of the number of elements (256, 512, and 1024) and focusing depth (25–65 mm from the inner surface of the skull) on the quality of aberration correction is considered, i.e., the sharpness of focusing, location of the focus, and the maximum pressure therein. An acoustic model of the human head is constructed from magnetic resonance imaging (MRI) data. The field and compensation for aberrations are calculated using the Rayleigh integral and wave equation in the Kelvin–Voigt model. The possibility of sharp focusing with the focal region width of about 2 mm at the level of 6 dB using the considered arrays is demonstrated within the indicated depth interval. The relative contribution of different wave effects to distortion of the ultrasound beam as it passes through the skull is analyzed. It is shown that the strongest contributions to beam attenuation come from aberrations (7.4 dB) and absorption (6.7 dB). Contributions from reflection (2.1 dB) and shear-wave generation in the skull (2 dB) are less significant.