Thesis Defense - Spatial Averaging Corrections from 1-100 MHz
Date: December 11, 2002
Time: 1:30 PM
Location: Commonwealth, Room: 610
Speaker(s):
Emil George Radulescu
Research Assistant
Drexel University,
Ultrasound Research Lab
School of Biomedical Engineering, Science and Health Systems
Adviser: Dr. Peter A. Lewin
Details:
The purpose of this work was to develop and experimentally verify a set of robust and readily applicable spatial averaging models to account for ultrasonic hydrophone probe's finite aperture in acoustic field measurements in the frequency range 1 - 100 MHz. Electronically and mechanically focused acoustic sources of different geometries were considered. The geometries included single element circular sources and rectangular shape transducers that were representative of ultrasound imaging arrays used in clinical diagnostic applications. The field distributions of the acoustic sources were predicted and used in the development of the spatial averaging models. The validity of the spatial averaging models developed was tested using commercially available hydrophone probes having active element diameters ranging from 50 to 1200 microns. The models yielded guidelines which were applicable to both linear and nonlinear wave propagation conditions. By accounting for hydrophones' finite aperture and correcting the recorded pressure-time waveforms, the spatial averaging models allowed the uncertainty associated with determining the key acoustic output parameters such as: Pulse Intensity Integral (PII) and the intensities derived from it to be minimized. In addition, the work offered an indication for a correction factor for the safety indicator Thermal Index (TI) that is required by AIUM/NEMA standards. The novelty of this research stems primarily from the fact that such comprehensive set of models and guidelines has not been developed so far. Although different spatial averaging models have already been suggested, they have been limited to circular geometries, linear propagation conditions and conventional medical imaging frequencies, only. Also, the spatial averaging models provided the necessary corrections to obtain the true sensitivity versus frequency response during calibration of hydrophone probes up to 100 MHz and allowed for a subsequent development of two novel calibration methods.
Biosketch:
Directions:
|
