Transcranial ultrasound tracking of brain shift

Abstract

Transcranial ultrasound provides a portable, inexpensive, rapid, and nonionizing technique to measure brain shift and structural changes. This technique may have important implications in neurosurgery, emergency room diagnosis, and long‐term or frequent patient monitoring. The ability of transcranial ultrasound to measure motion inside the skull was investigated in ex vivo human skulls. The skulls were submerged in degassed water and a 2‐D velmax positioning system was used to position a small needle within the skull. An array of low‐frequency transducers (0.5–2 MHz) was positioned in a frame around the skull. Ultrasound pulses were sent in longitudinal and shear wave modes through the skull. The digitized receive signals of all transducers were then analyzed with Matlab. Using geometric and time‐of‐flight analysis the magnitude and direction of the needle shifts were determined. The transcranial ultrasound tracking system was able to accurately (within 0.2 mm) detect the needle motion in the skull. Overall, transcranial ultrasound using both shear and longitudinal waves was shown to be an effective method to track motion in the skull and may be a useful real time method to correct for misregistration of presurgical images. [Work supported by NIH Grants R21EB004353 and U41RR019703.]