- Poster presentation
- Open Access
Background-oriented schlieren imaging and tomography for rapid measurement of FUS pressure fields: initial results
© Kremer et al; licensee BioMed Central Ltd. 2015
Published: 30 June 2015
FUS pressure field mapping is important for dosimetry, quality assurance, and other uses. Hydrophone measurements are the current standard, and are accurate but costly and slow. As a simple low-cost alternative, background-oriented schlieren (BOS) imaging of ultrasound fields has been proposed. In that technique, a predetermined image (usually a grid of lines or a random dot pattern) is placed on one side of a water tank and viewed from the other side, through the water and FUS pressure field. When the FUS is on, spatial variations in the water’s index of refraction are created that blur the image. Subtracting images with and without the FUS field provides a rapid visualization of it. The method has also been used to tomographically reconstruct air flow density. The overall goal of the present work is to develop a low-cost BOS hardware system and BOS tomography acquisitions and reconstructions to enable rapid and cheap volumetric measurements of continuous-wave FUS fields. Here we present our current progress towards that goal.
During acquisitions, the transducer was continuously pulsed at 1.1 MHz to generate a sound field with a peak negative pressure of 5.7 MPa at the focus. BOS acquisitions used background images comprising alternating white and black lines with varying positions, thicknesses and orientation angles.
BOS Tomography Simulation
A 2D simulation was performed in MATLAB to validate the principles underlying BOS tomography, by implementing the forward model relating a spatially-varying index of refraction pattern to acquired BOS projection images, and a conjugate gradient reconstruction to invert that model. A parallel beam geometry was assumed.
Results and conclusions
This work was supported by the Focused Ultrasound Foundation Global Internship Program and DoD W81XWH-12-BCRP-IDEA.
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