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Publications (5)10.1 Total impact

  • Ajay Anand, David Savéry, Christopher Hall
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    ABSTRACT: Thermal therapies such as radio frequency, heated saline, and high-intensity focused ultrasound ablations are often performed suboptimally due to the inability to monitor the spatial and temporal distribution of delivered heat and the extent of tissue necrosis. Ultrasound-based temperature imaging recently was proposed as a means to measure noninvasively the deposition of heat by tracking the echo arrival time shifts in the ultrasound backscatter caused by changes in speed of sound and tissue thermal expansion. However, the clinical applicability of these techniques has been hampered by the two-dimensional (2-D) nature of traditional ultrasound imaging, and the complexity of the temperature dependence of sound speed for biological tissues. In this paper, we present methodology, results, and validation of a 3-D spatial and temporal ultrasound temperature estimation technique in an alginate-based gel phantom to track the evolution of heat deposition over a treatment volume. The technique was experimentally validated for temperature rises up to approximately 10 degrees C by comparison with measurements from thermocouples that were embedded in the gel. Good agreement (rms difference = 0.12 degrees C, maximum difference = 0.24 degrees C) was observed between the noninvasive ultrasound temperature estimates and thermocouple measurements. Based on the results obtained for the temperature range studied in this paper, the technique demonstrates potential for applicability in image guidance of thermal therapy for determining the location of the therapeutic focal spot and assessing the extent of the heated region at subablative intensities.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/2007; 54(1):23-31. · 1.82 Impact Factor
  • A. Anand, D. Savery, C.S. Hall
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    ABSTRACT: Thermal therapies such as radio frequency, heated saline, and high-intensity focused ultrasound ablations are often performed sub-optimally due to the inability to monitor the spatial and temporal distribution of delivered heat and the extent of the necrotic tissue. Ultrasound imaging can be used to measure the deposition of heat through local thermally related changes in speed of sound; however the clinical applicability of these techniques have been hampered by the two-dimensional nature of traditional ultrasound imaging. In this paper, we present methodology, results, and validation of an imaging technique that uses a three-dimensional ultrasound imaging system to track the spatial and temporal evolution of heat deposition
    Acoustics, Speech and Signal Processing, 2006. ICASSP 2006 Proceedings. 2006 IEEE International Conference on; 06/2006 · 4.63 Impact Factor
  • Ajay Anand, David Savéry, Christopher Hall
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    ABSTRACT: Thermal therapies such as radio frequency, heated saline, and high-intensity focused ultrasound ablations are often performed sub-optimally due to the inability to monitor the spatial and temporal distribution of delivered heat and the extent of tissue necrosis. Ultrasound-based temperature imaging has been recently proposed as a means to measure non-invasively the deposition of heat by tracking the echo arrival time shifts in the ultrasound backscatter caused by changes in speed of sound and tissue thermal expansion. However, the clinical applicability of these techniques has been hampered by the two-dimensional nature of traditional ultrasound imaging. In this study, we present methodology, results, and validation of a three-dimensional spatial and temporal ultrasound temperature estimation technique to track the evolution of heat deposition over a treatment volume. Ultrasonic backscattered radio-frequency data were captured using a commercial clinical imaging system to monitor heat generated by a complex, three-dimensional geometrical construct of resistive wires in an ultrasonic phantom. Thermocouples were embedded at various locations in the phantom to independently measure the temperature evolution during 90 seconds of heating (peak temperature increase of 8.5 degC) and the subsequent cool-down. X-ray computed tomography was used to ensure accurate placement of thermocouples. Good agreement was observed between the ultrasound derived temperature estimates and the invasive thermocouple measurements throughout the heating and cool-down phase. The mean difference between the ultrasound and thermocouple data was calculated to be 0.06 degC, RMS difference: 0.12 degC, and maximum difference: 0.24 degC. Time varying, three-dimensional ultrasonic measurements of temperature yielded parametric maps of thermal deposition within the phantom, and illustrated the complex three-dimensional geometry of the heat source. The results demonstrate potential for the applicability - of the technique in monitoring and guidance of thermal therapy. To the best of the knowledge of the authors, this work represents the first demonstration of three-dimensional spatial and temporal ultrasound thermometry
    Proceedings of the IEEE Ultrasonics Symposium 01/2006;
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    ABSTRACT: We describe characterization of digital signals using analogs of thermodynamic quantities: the topological entropy, Shannon entropy, thermodynamic energy, partition function, specific heat at constant volume, and an idealized version of Shannon entropy in the limit of digitizing with infinite dynamic range and sampling rate. We show that analysis based on these quantities is capable of detecting differences between digital signals that are undetectable by conventional methods of characterization based on peak-to-peak amplitude or signal energy. We report the results of applying thermodynamic quantities to a problem from nondestructive materials evaluation: detection of foreign objects (FO) embedded near the surface of thin graphite/epoxy laminates using backscattered waveforms obtained by C-scanning the laminate. The characterization problem was to distinguish waveforms acquired from the region containing the FO from those acquired outside. In all cases the thermodynamic analogs exhibit significant increases (up to 20-fold) in contrast and for certain types of FO materials permit detection when energy or amplitude methods fail altogether.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2005; 52(9):1555-64. · 1.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We describe characterization of digital signals using analogs of thermodynamic quantities: the topological entropy, Shannon entropy, thermodynamic energy, partition function, specific heat at constant volume, and an idealized version of Shannon entropy in the limit of digitizing with infinite dynamic range and sampling rate. We show that analysis based on these quantities is capable of detecting differences between digital signals that are undetectable by conventional methods of characterization based on peak-to-peak amplitude or signal energy. We report the results of applying thermodynamic quantities to a problem from nondestructive materials evaluation: detection of foreign objects (FO) embedded near the surface of thin graphite/epoxy laminates using backscattered waveforms obtained by C-scanning the laminate. The characterization problem was to distinguish waveforms acquired from the region containing the FO from those acquired outside. In all cases the thermodynamic analogs exhibit significant increases (up to 20-fold) in contrast and for certain types of FO materials permit detection when energy or amplitude methods fail altogether.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2005; · 1.82 Impact Factor