13 T RANSDUCER O UTPUT C HARACTERIZATION Acoustic Holography + - - PowerPoint PPT Presentation

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13 T RANSDUCER O UTPUT C HARACTERIZATION Acoustic Holography + - - PowerPoint PPT Presentation

Dec 31, 2023 693 likes •876 views

A B OILING H ISTOTRIPSY S YSTEM FOR D EEP T ISSUE A BLATION Adam Maxwell 1,2 , Wayne Kreider 1 , Petr Yuldashev 3 , Tanya Khokhlova 1 , Oleg Sapozhnikov 1,3 , Michael Bailey 1 , and Vera Khokhlova 1,3 1 CIMU, Applied Physics Laboratory, University

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SLIDE 1

A BOILING HISTOTRIPSY SYSTEM FOR DEEP TISSUE ABLATION

Adam Maxwell1,2, Wayne Kreider1, Petr Yuldashev3, Tanya Khokhlova1, Oleg Sapozhnikov1,3, Michael Bailey1, and Vera Khokhlova1,3

1CIMU, Applied Physics Laboratory, University of Washington

  • 2Dept. of Urology, University of Washington School of Medicine
  • 3Dept. of Acoustics, Physics Faculty, Moscow State University

ISTU 2013 May 15, 2013 Shanghai, China

1

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SLIDE 2

BOILING HISTOTRIPSY

Boiling histotripsy is a noninvasive method to generate mechanical lesions in tissue using millisecond-long focused ultrasound pulses with shock fronts.

Study Objectives:

1. Develop a system capable of producing boiling histotripsy lesions at clinically relevant depths (> 5-6 cm) 2. Characterize output of this system 3. Evaluate use of a derating procedure to determine exposure for boiling histotripsy at different tissue depths

5.5 6 6.5 7 7.5

  • 20

20 40 60 80 100 Time (µs) Pressre (MPa)

Shock-induced Heating Millisecond Boiling Tissue Emulsification

2

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SLIDE 3

BOILING HISTOTRIPSY SYSTEM

  • 7-element lens-focused design
  • Center Frequency: 1 MHz
  • Aperture:

14.7 cm

  • Focal Length:

14.0 cm

Elements

Transducer

FPGA Timing Board Amplifier Board HV Supply LV Supply Capacitor Array Matching Network Transducer MATLAB

  • Class D RF Amplifier1
  • Peak Power: >30 kW for ≤10 ms pulse
  • Frequency Range: 0.1 – 4.0 MHz

Amplifier

1Hall TL and Cain CA. AIP Conf Proc. 2005;829: 445-449

3

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SLIDE 4

TRANSDUCER OUTPUT CHARACTERIZATION

  • 5

5 10

  • 20

20 40 60 80 Time (µs) Pressre (MPa)

  • 1. Acquire low

amplitude waveforms with hydrophone in prefocal plane at z = -5.5 cm

  • 2. Create 2D pressure

field map from data

  • 3. Apply linear

backward propagation algorithm to obtain a source hologram in a plane z = 0

  • 4. Apply nonlinear forward propagation

at increased p0 amplitude to obtain focal waveforms and beam profiles

4

Acoustic Holography + Nonlinear Simulation1:

Compare simulated results with direct measurement

  • f focal waveforms using

fiber optic probe hydrophone (FOPH 2000)

1 Kreider W et al., IEEE Trans. Ultrason.

  • Ferroelectr. Freq. Control 2013; in press.

4Yuldashev P.V., Khokhlova V.A.

  • Acoust. Phys. 2011, 57(3): 334-343.
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SLIDE 5

5

NONLINEAR PROPAGATION MODEL

3 3 3 2 2 2 3 2 2 2 2 2 2 2

2 2 2 t d t r b t ¶ ¶ + ¶ ¶ + ÷ ÷ ø ö ç ç è æ ¶ ¶ + ¶ ¶ + ¶ ¶ = ¶ ¶ ¶ p c p c z p y p x p c z p

3D Westervelt equation in the retarded temporal coordinates

Boundary condition:

back propagated hologram

0.5 1

p/pmax x, mm y, mm

  • 80 -60 -40-20

0 20 40 60 80

  • 80
  • 60
  • 40
  • 20

20 40 60 80

Linear field distribution:

axial plane, dB scale

Yuldashev P.V., Khokhlova V.A. Simulation of three-dimensional nonlinear fields of ultrasound therapeutic

  • arrays. Acoust. Phys. 2011, 57(3), p.334-343.
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SLIDE 6

RESULTS FROM CHARACTERIZATION

6

Focal Pressure Waveforms:

FOPH measurements versus simulations

Focal Peak Pressures

versus Transducer Voltage

10 15 20 20 40 time, radians Pressure (MPa) b) 10 20 Pressure (MPa) a) experiment hologram

45 V 35 V

Simulations for higher input voltages are in progress

20 40 60 80 100 120

  • 20
  • 15
  • 10
  • 5

Source voltage, V p-, MPa 20 40 60 80 100 p+, MPa

p+ p-

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SLIDE 7

RESULTS FROM CHARACTERIZATION

7

50 100 Pressure (MPa) 100 Pa)

5 10 50 100 time, radians Pressure (MPa)

FOPH measurements simulations 60 V 60 V

Focal Pressure Waveforms Nonlinear peak pressure distributions: axial plane, dB scale

p- p+

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SLIDE 8

DERATING FOR LESION GENERATION

Hypothesis: a derating procedure enables us to determine the source output to provide a desired nonlinear focal waveforms when focusing at a depth L in tissue.

p0,Liver = p0,Water exp αL

( )

α = 0.5 dB/cm

1Bessonova et al. Acoustical Physics 2010;56(3):376–385. 2Canney et al. Ultrasound Med Biol 2010;36:250-267

98 99 100 101 102

  • 20

20 40 60 Time (µs) Pressre (MPa)

Axial Beam Pressure Profile

p+ p-

98 99 100 101 102

  • 20

20 40 60 Time (µs) Pressre (MPa)

Canney et al.

8

Bessonova et al.

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SLIDE 9

THRESHOLD FOR BOILING

Pulse duration: 10 ms Total on time: 500 ms PRF: 1 Hz Tissue Depth: 12 mm

20 40 60 80 0.2 0.4 0.6 0.8 1 Peak Positive Pressure (MPa) Proportion with Lesion

n ≥ 9

Khokhlova et al1

1TD Khokhlova et al. J Acoust Soc Am 2011; 130:3498-3510

Present Study – Lesion Probability vs. Pressure

Analytical Boiling Time

Δt = ΔT 6c0

4ρ2Cs

β f0As

3

5 mm p+ = 58 MPa 5 mm 5 mm Khokhlova et al1 Present Study p+ = 75 MPa

9

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SLIDE 10

BOILING VS. TISSUE DEPTH

  • Lesions generated at tissue depths up to 6 cm
  • Linear derating underestimated pressure at greater depths by ≤14%
  • Lesions at 6 cm depth required 26% maximum p0 of US transducer

18 mm 35 mm 50 mm 60 mm 70 VDC 90 VDC 100 VDC 105 VDC

Transducer Voltage for Lesions vs. Depth Lesion Photographs

10

1 2 3 4 5 6 7 20 40 60 80 100 120 Tissue Depth (cm) Transducer Driving Voltage (V) Maximum Pressure - No Lesion Minimum Pressure - Lesion Derated 0.5 dB/cm Derated 0.61 dB/cm (best fit)

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SLIDE 11

CONCLUSIONS

  • Boiling histotripsy can be applied to create lesions at

clinically relevant (6 - 16 cm) tissue depths

  • Acoustic holography + nonlinear modeling provides

characterization of transducer output in water and in tissue

  • Derating of focal waveforms obtained in water

estimates in situ pressures and output needed from the transducer to induce boiling histotripsy

11

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SLIDE 12

ACKNOWLEDGMENTS

  • Tim Hall and Yohan Kim at University of Michigan
  • Julianna Simon at APL - University of Washington
  • Work supported by:

– NIH 2R01 EB007643-05 – Multidisciplinary Training Program in Benign Urology at UW (NIH 2T32 DK00779-11A1)

12

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SLIDE 13

13

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SLIDE 14

TRANSDUCER OUTPUT CHARACTERIZATION

  • 5

5 10

  • 20

20 40 60 80 Time (µs) Pressre (MPa)

Acoustic Holography + Nonlinear Simulation1:

1. Acquire pressure waveforms at low amplitude in prefocal plane 2. Apply backward propagation algorithm to obtain transducer surface hologram 3. Apply nonlinear forward propagation simulation with Westervelt equation to

  • btain focal waveforms, beam profiles

(1) (2) (3)

Results compared with direct measurement of focal waveforms using fiber optic probe hydrophone (FOPH 2000)

1 Kreider W et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Control 2013; in press.

14

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SLIDE 15

POWER OUTPUT MEASUREMENTS

  • Electrical Power

– Voltage and current output from amplifier measured for 10 ms pulse duration – Average power calculated from V, I waveforms – Power measured to 250 VDC, extrapolated to 400 VDC

  • Acoustic Power

– Power calculated from hologram at 5 VDC – Scaled for other power outputs – Surface pressure output was measured to be linear with input voltage to 150 VDC, extrapolated to 400 VDC

15

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SLIDE 16

POWER OUTPUT

  • Amplifier (Electric Power)

– Maximum tested peak power: 36.1 kW @ 250 VDC – Maximum tested mean power over 10 ms: 10.1 kW @ 250 VDC – Maximum est. peak power: 92.4 kW @ 400 VDC – Maximum est. mean power over 10 ms: 25.9 kW @ 400 VDC

  • Transducer (Acoustic Power)

– Peak power @ 250 VDC: 8.9 kW – Mean power @ 250 VDC: 4.5 kW – Maximum est. peak power: 23.0 kW @ 400 VDC – Maximum est. mean power over 10 ms: 11.5 kW @ 400 VDC

  • Transducer Power Efficiency (from Avg. Power)

– 44-49%

16

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SLIDE 17

POWER OUTPUT MEASUREMENTS

17

Measurement error Maximum output we have tested Maximum rated

  • utput