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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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Controlled spatio temporal heating patterns using a commercial diagnostic ultrasound system l.jpg

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 l.jpg

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.


Challenges for diagnostic system l.jpg

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


Slide4 l.jpg

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


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Normalized Intensity Distributions

a = 1.0 dB/cm/MHz

a = 0.3 dB/cm/MHz

Axial

Elevation

Lateral


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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


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Ex Vivo Bovine Liver HIFU Lesion

HIFU ablation: 1.1 MHz Sonic Concepts Transducer

Bmode/ARFI: 75L40 Transducer on Elegra


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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


Methods l.jpg

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


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Temperature Relative to Focus

CH62

1.8% Duty Cycle

0.13 seconds

55% power


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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.


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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


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Power – Focus and Lens

CH62

4.44 MHz

1.8% Duty Cycle

0.13 seconds


Prf focus and lens l.jpg

PRF – Focus and Lens

CH62

4.44 MHz

0.2 – 3% Duty Cycle

55% Power

0.36 seconds


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Maximum T with Diagnostic System

CH62

4.44 MHz

7% duty cycle

0.38 sec duration

55% Power

30.3°C maximum rise


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Drug Delivery

CH62

4.44 MHz

4-6.8% duty cycle

13.9 sec duration

55% power

~4°C maintained rise


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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


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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


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Acknowledgements

  • NDSEG Fellowship

  • NIH grant 8 R01 EB002132

  • Dr. Gregg Trahey

  • Dr. Pei Zhong

  • Liang Zhai

  • Katherine Oldenburg


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