Noninvasive acoustical image reconstruction of a static object through a simulated human skull bone

A new method for image reconstruction of a foreign object, i.e. any reflector which somehow could be inserted into the brain tissue, such as a bullet or a piece of shrapnel, is investigated. The method is based on noninvasive transcranial ultrasound propagation through skull bone and brain tissue. A simulation has been developed during the study to process the experimental results and reconstruct an image showing the position of the foreign object. The algorithm is designed for use with a linear array of 128 receivers and a source of ultrasound as the reflector (all at the optimized frequency of 1.7MHz). A simplified simulated skull bone (scattering medium) was also added to the program to distinguish how it affects passing through ultrasonic fields in different circumstances. From an experimental point of view, to check the effectiveness of the algorithm, a simplified skull bone phantom was made and used in data acquisition at the array of receivers. When passed through phantom layer, the ultrasound field (initially generated at the reflector) reaches the array of receivers, and after being saved, the distribution on the array is processed to compensate for the distortion and reconstruct an image which contains data about the reflector\u27s position. Due to high attenuation in scattering medium (which represents skull bone\u27s acoustical properties) and brain tissue, it has been determined that the method can reconstruct the reflector\u27s position roughly at a maximum distance of 15cm from the array of receivers in presence of the phantom which is far enough to cover all inside of a typical skull

Transcranial Adaptive Beamforming via Ultrasonic Phased Arrays and its Application to 3D Imaging of Certain Types of Head Injuries

A new adaptive beamforming method for ultrasonic imaging via small-aperture phased arrays through composite layered structures, such as human skull, is developed. If there is a scattering layer between the phased array and the imaged volume, acoustic phase aberration and wave refraction at undulating interfaces between the barrier and the rest of the propagation media can cause significant distortion of an ultrasonic image pattern produced by conventional beamforming techniques. This distortion takes the form of defocusing the ultrasonic field transmitted through the skull and causes loss of resolution, overall degradation of image quality and generation of non-informative final sonograms. To compensate for the phase aberration and refractional effects, an adaptive beamforming algorithm is developed and examined. After accurately assessing the skull's local geometry and sound speed, the method calculates a new timing scheme to refocus the distorted beam at its original location. The procedure is in fact a construction of a matched filter that automatically adapts the transmission and reception patterns of the phased array to the local geometry and acoustical properties of the skull and cancels its distorting effects. Results of numerical simulations, developed to accommodate and verify the proposed theory, are provided and discussed. The simulation results are verified experimentally by applying the method on realistic human skull phantoms in water immersion setups. The developed adaptive beamforming algorithms were implemented on an open-platform phased array controller and a lab prototype of the imaging system was delivered. Results of 2D and 3D adaptive imaging through skull phantoms via 2MHz linear and matrix phased arrays are presented.Ph.D.2016-11-30 00:00:0

Acoustic Field Simulation and Initial Safety Measurements of a Novel Ultrasound Probe for the Diagnosis of Intracranial Hemorrhages

Ultrasound imaging of brain tissue features and abnormalities is notoriously difficult through the skull because of the high attenuation and skull-induced phase aberration. A custom-designed transcranial matrix probe with a novel adaptive beamforming method has been developed at Tessonics Inc., Windsor, Ontario. The technology corrects for skull-induced distortions in the reconstructed sonograms. The current goal is to diagnose intracranial hemorrhages with the motivation of reducing the time between an injury and appropriate aid. In emergency situations, a portable point-of-care device may save vital time and reduce fatalities. Conventional screening methods, like computed tomography, do not offer the portability, low-cost, and non-ionizing radiation benefits that ultrasound imaging provides. Ultrasonography is also non-invasive and allows for real-time imaging.  The analysis of the acoustic field for the ultrasound probe is an integral part of device development. Standards for ultrasound machine intensity output must be met to eliminate the risk of damage to body tissues. Simulations of the acoustic field are created through the Fast Object-oriented C++ Ultrasound Simulation (FOCUS) software based on desired focal points. The measurements and simulations presented in this work will ensure patient safety for future testing.&nbsp