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

• Kristin D. Frinkley, Mark L. Palmeri, Kathryn R.
  Nightingale
• Biomedical Engineering Department
• Duke University, Durham, NC.

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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.

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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

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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
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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
• c4.2x106 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

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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
• 30.3C maximum rise

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Drug Delivery

• CH62
• 4.44 MHz
• 4-6.8 duty cycle
• 13.9 sec duration
• 55 power
• 4C 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