Thursday, April 10, 1997
In response to physical limits on invasive temperature measurements used during thermotherapy, non-invasive techniques to measure tissue temperatures are being explored. Several techniques have been proposed, including using MRI, impedance tomography, and pulse-echo ultrasound. In this talk we will describe a realtime noninvasive method for temperature estimation using pulse-echo ultrasound.
The principles used to detect temperature changes with pulse-echo ultrasound are the temperature-dependant variations in the echoes resulting from both thermal expansion of the medium and changes in the speed of sound with respect to temperature. The relationship between the local temperature and these variations can be formulated as a linear relationship between local temperatures and the apparent shifts in the location of scatterers in the medium. By tracking these apparent scatterer displacements over time within 2D ultrasound RF data, a 2D image of the temperatures within the medium can be generated.
Several tracking techniques have been used to accomplish this purpose, including various forms of cross-correlation. Here we present a new technique which allows real-time processing of the data. Data can be gathered from a commercial ultrasound machine, processed on a Sparc-10 workstation, and the results displayed at a rate of approximately a frame per second, limited primarily by the data transfer rates.
Using this thermal imaging technique, we propose a combined imaging
and therapy system. With such a system, one can monitor temperatures
during ultrasound thermotherapy to verify the location and quality of
the therapy beam prior to lesion formation. Examples will be given
using this technique in both tissue-mimicking phantoms and in beef
muscle, demonstrating the ability to visualize the temperature fields
induced by high-intensity ultrasound beams.
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