Ultrasound detection of the skull-brain interface: A phantom study

Transcranial Sonography is a clinical procedure for monitoring cerebral blood flow in patients suspected of suffering from severe blood flow disruption in the brain. The Transcranial Doppler (TCD) clinicians are currently only guided by their experience and the temporal bone surface to position the Doppler probe on a suitable site for TCD. This site is known as an acoustic window. Neither experience nor the bone surface can sufficiently improve TCD procedure time for new patients. A suitable acoustic window for transcranial Doppler ultrasound can be difficult to find, and in some patients, no such acoustic window is possible. It is hypothesized that the visibility of the temporal bone in an acousto-spectroscopic image suggests an appropriate transcranial Doppler ultrasound acoustic window. The aim of this research is to investigate the ultrasonic detection of such a pathological acoustic window. It was anticipated that an acoustic window would best be detected by its Acousto-spectroscopic properties in an attenuation-velocity image. These images contrast hard tissue from soft tissue based on their acousto-spectroscopic properties. Identifying where the temporal bone is the thinnest could potentially indicate the best location for performing a Transcranial Doppler procedure. Experimental investigations on a specially designed layered transcranial phantom were carried out to detect the region where the temporal bone is the thinnest and hence suggest an adequate acoustic window. It was shown that a plausible transcranial acoustic window is visible in an ultrasound image, a previously unreported and very promising result. Attenuation-velocity images showed greater boundary contrast between hard and soft tissue. However, hard and soft tissue regions appear similar in comparison to B-Mode images. It was determined that nonuniform scattering from inhomogeneous life-like tissues causes attenuation-velocity images to display less media contrast such as bone versus soft tissue contrast. This research is the first to report that B-Mode images are currently the best method for visually detecting a plausible potential acoustic window for Transcranial Doppler.