Passive mapping of acoustic sources within the human skull cavity with a hemispherical sparse array using computed tomography-based aberration corrections

Abstract

Traditionally, the use of ultrasound (US) in the brain has been limited by the skull bone, which presents unique challenges for both transcranial therapy and imaging due to its attenuating and aberrating effects, which become more prevalent at higher US frequencies. On transmit, these skull-induced aberrations can be overcome through the use of large-aperture phased array transducers with appropriate driving frequencies, combined with computed tomography (CT)-based bone morphology and numerical models to derive element driving signals which minimize the distortions. Recently, we have demonstrated in silico that an analogous approach can be performed during beamforming on receive, to allow for passive acoustic imaging over a large region within the skull cavity [Jones et al., Phys. Med. Biol. 58, 4981–5005 (2013)]. We will present preliminary results obtained from applying this technique experimentally with a hemispherical (30 cm diam.) sparse receiver array (128 piezo-ceramic elements, 2.5 mm diam., and 612 kHz center frequency) to image acoustic sources through an ex vivo human skullcap. Images produced using non-invasive CT-based skull corrections will be compared with those obtained through an invasive hydrophone-based correction approach, and with images formed without skull-specific corrections. This technique has promising applications in both cavitation-mediated transcranial focused ultrasound therapies, by providing a method for treatment monitoring and control, as well as in ultrasound angiographic imaging of the brain.