| Description |
Transcranial High-Intensity Focused Ultrasound (HIFU) is a promising treatment method for a number of different diseases including essential tremors, Parkinson's, OCD, brain tumors, and other neurological disorders. The benefits of HIFU include being non-invasive, localized, and avoiding ionizing radiation. This dissertation will present work related to the rapid simulation of transcranial HIFU, which is necessary for efficacy, safety, and speed of HIFU treatments. One of the biggest obstacles in transcranial treatment is the acoustic parameters of bone. Besides attenuating the ultrasound, the very high speed of sound when compared to soft tissue creates aberrations which can hinder or prevent treatment. A novel method to correct these aberrations will presented. This method utilizes the Hybrid Angular Spectrum (HAS) technique to quickly calculate corrections for use with a phased array transducer. Experimental results show the method can recover 95% of the potential peak pressure in a 3D printed aberrating model and 70% of the peak pressure in an ex vivo human skull flap as well as correct for multiple focal points with negligible additional computational costs. Scattering of ultrasound in the skull can be difficult to predict as clinical resolution CT scans do not have high enough resolution to resolve scatters. This dissertation will investigate a method for determining acoustic scattering based on relating pores imaged via microCT scans to a registered clinical-resolution CT scan of the same skull. Artificial models were then created for various ranges of Hounsfield Units in the clinical-resolution scan by filling uniform models with pores from the microCT scan so that the density was matched. After simulating with no absorption, these models were used to create patient-specific acoustic scattering models. When high pressure is present in HIFU treatments, nonlinear ultrasonic effects may become prominent. These nonlinearities can create unexpected heating or cavitation, reducing the safety of treatments. The final portion of this dissertation will examine adding nonlinear effects into the HAS method of ultrasound prediction using the slowly varying envelope approximation (SVEA). Comparisons are made with other simulation techniques. |
