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Controlled Spatio-Temporal Heating Patterns Using a Commercial, Diagnostic Ultrasound System

Controlled Spatio-Temporal Heating Patterns Using a Commercial, Diagnostic Ultrasound System. Kristin D. Frinkley, Mark L. Palmeri, Kathryn R. Nightingale Biomedical Engineering Department Duke University, Durham, NC. Potential Applications. Spot ablations Shallow and small volumes

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Controlled Spatio-Temporal Heating Patterns Using a Commercial, Diagnostic Ultrasound System

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  1. Controlled Spatio-Temporal Heating Patterns Using a Commercial, Diagnostic Ultrasound System Kristin D. Frinkley, Mark L. Palmeri, Kathryn R. Nightingale Biomedical Engineering Department Duke University, Durham, NC.

  2. Potential Applications • Spot ablations • Shallow and small volumes • Thyroid • Combined ablation, B-mode, and ARFI • Hemostasis • High temperature rise for 8-13 seconds • Femoral artery punctures Martin et al. UMB, 1999. • Drug Delivery • Low temperature rise for 1-5 minutes • Thermal activation of liposomes Kao et al. Acad. Radiol., 2003.

  3. Challenges for Diagnostic System • Transducer / Surface Heating • Thermal efficiency of broadband transducers • Power supply output and hardware tolerances • Programming of a diagnostic system • Size limitations for heated volume • Maximum of a few mm3 • Limited to short durations or lower temperatures

  4. Aims • Investigate the use of Acoustic Radiation Force Impulse (ARFI) imaging of ultrasonically ablated lesions • Image quality of B-mode versus ARFI • Evaluate the most efficient methods of heat delivery • Exposure Time • Power • Pulse Repetition Frequency • Maximize temperature rise based on methods explored • Spot ablations • Hemostasis • Maintain a constant temperature for extended durations • Drug delivery

  5. Normalized Intensity Distributions a = 1.0 dB/cm/MHz a = 0.3 dB/cm/MHz Axial Elevation Lateral

  6. ARFI • ARFI Imaging impulsively excites tissue • Induces displacement and shear waves • Characterizes tissue using mechanical properties • Potential applications: • breast lesions • atherosclerotic plaques • colonic tumors • RF ablation lesions

  7. Ex Vivo Bovine Liver HIFU Lesion HIFU ablation: 1.1 MHz Sonic Concepts Transducer Bmode/ARFI: 75L40 Transducer on Elegra

  8. Experimental Setup • Modified Siemens SONOLINE Antares TM • CH62 Transducer • Water path to porcine muscle and sound absorbing material • Type T thermocouple on transducer face or at focal depth • 5 cm focal depth • F/1.5 Transducer Water Tank Porcine Muscle Sound absorber Thermocouples

  9. Methods • Thermocouple Peaking • Visually with B-mode • Thermally in lateral, elevation, and axial dimensions with translation stage • Temperature Data Processing • Running average of 100 samples of temperature versus time data (5 kHz sampling rate) • Baseline mean subtracted from maximum temperature achieved • Temperature rise mean and standard deviations determined from 4 trials • Evaluation of Transducer Damage • Visually with B-mode • Single channel RF images

  10. Temperature Relative to Focus CH62 1.8% Duty Cycle 0.13 seconds 55% power

  11. Bio-heat Transfer Equation • Adapt a Green function to find solution: • Neglect perfusion so L and  go to : Nyborg, WL. “Solutions of the Bio-Heat Transfer Equation.” Phys. Med Biol. 33(7): 785-792, 1988.

  12. Increased Exposure Time Analytic • dv = (4/3)(F/2)3 cm3 • q = 2I J/cm3 •  =1.25x10-7 m2s-1 • c=4.2x106 Jm-3C-1 Thermocouple • CH62, F/1.5 • 4.44 MHz • 1.8% Duty Cycle • 55% Power

  13. Power – Focus and Lens CH62 4.44 MHz 1.8% Duty Cycle 0.13 seconds

  14. PRF – Focus and Lens CH62 4.44 MHz 0.2 – 3% Duty Cycle 55% Power 0.36 seconds

  15. Maximum T with Diagnostic System CH62 4.44 MHz 7% duty cycle 0.38 sec duration 55% Power 30.3°C maximum rise

  16. Drug Delivery CH62 4.44 MHz 4-6.8% duty cycle 13.9 sec duration 55% power ~4°C maintained rise

  17. Conclusions • Temperatures Achieved • ~30 °C maintained for 0.2 sec • ~4 °C for 14 sec • Size of Heated Volume • 0.52 mm laterally • 6.24 mm axially • large F/# in elevation • Transducer Damage • Occurred with repeated use of highest temperature sequences

  18. Future Work • Experiment with passively cooled transducers • Experiment with BSA phantoms • Quantify lesion size and shape • Compare denaturation temperature with thermocouple measurements for same sequences • Study methods for sustained application of lower temperatures for drug therapy applications • Continue to pursue spot ablations by achieving increased temperatures

  19. Acknowledgements • NDSEG Fellowship • NIH grant 8 R01 EB002132 • Dr. Gregg Trahey • Dr. Pei Zhong • Liang Zhai • Katherine Oldenburg

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