Oleg Sapozhnikov, Sergey Tsysar, Vera Khokhlova, and Wayne Kreider

March 1 (Tuesday), 2016Room: 4F, Conference RoomLaboratory for Nanoelectronics and Spintronics13:35~14:20

Center for Industrial and Medical Ultrasound, Applied Physics Laboratory,

University of Washington, Seattle, WA

Department of Acoustics, Physics Faculty,Moscow State University, Moscow, Russia

ACOUSTIC HOLOGRAPHY BY TWO-DIMENSIONAL ULTRASOUND ARRAY SYNTHESIS

The Joint Symposium of 10th International Symposium on Medical, Bio- and Nano-Electronics, and 7th International Workshop on Nanostructures & NanoelectronicsResearch Institute of Electrical Communication, Tohoku University, Sendai, Japan, March 1-3, 2016

CIMU-APL

INSERM

MSU

YDME

Examples of therapeutic ultrasound sources

PHILIPS

• Simplified assumptions (e.g. uniformity)

• Laser vibrometry

• Acoustic holography

How to know the source vibration?

Know your source

Optical holography -invented by Dennis Gabor

in 1947 (Nobel Prize in Physics, 1971)

HOLOGRAPHY Recording

Reconstructing

Such a hologram is an interferogram

Huygens-Fresnel Principle and Holography

Huygens – 1678Fresnel – 1815Kirchhoff – 1882Gabor – 1947

Acoustic holography as a way to predict in situ fields

2D 3D

Hologram =“whole record”

ARRAY SYNTHESIS: Scanning of 2D lateral distribution of magnitude and

phase by a single sensor

Amplitude

Phase

Measurement

Magnitude

HOLOGRAM RECORDERSynthesized “Ultrasound digital camera,” resolution 10 kilopixel (100x100)

PROGRAMS

Scanning, collecting hydrophone data (LabVIEW)

HOLOGRAPHIC RECONSTRUCTIONContinuous wave regime

Transient regime

Example: Characterization of 256-element Philips HIFU array

Array configuration Reconstructed amplitude Reconstructed phase

FOCUSING IN PHOTOGRAPHY

FOCUSING IN ACOUSTIC HOLOGRAPHY

FOCUSING IN PHOTOGRAPHY

FOCUSING IN ACOUSTIC HOLOGRAPHY

Validation in water

Focal waveforms modeled and measured with the FOPH hydrophone

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Linear projections of holographymeasurements match direct hydrophone

measurements (dots)

Linear pressure amplitude distribution on the axis of the array

Nonlinear waveforms with shock amplitudes of up to 100 MPa

modeled and measured at the focuswith good agreement

QUALITY OF THE HOLOGRAM

Prediction of the radiated acoustic field structure

Schlieren imageXZ-plane pressure amplitude distribution predicted by holography

Acoustic holography for transient fields

Transient Acoustic Holography

Reconstruction of the transient field along the

transducer surface (2D) and in space (3D)

Example: a single-element diagnostic probe

Single element Olympus probe

Freq: 1 MHzShape: FlatAperture: 38 mmExcitation: 2 cycles

3.5 MHz ultrasound probe: 19 elements are excited

0.44 mm 0.18 mm

12 mm

Peak velocity1 mm

3.5 MHz ultrasound probe: 19 elements are excited

0.44 mm 0.18 mm

12 mm

Peak velocity1 mm

Nonlinearacoustic holography

GENERALIZATION TO NONLINEAR CASE (Tsysar et al., ISTU, 2012)

One-way diffraction using angular spectrum

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Westervelt equation

pcz

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Linear wave equation

NUMERICAL APPROACH – operator splitting algorithm:

pcppcz

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Procedure of nonlinear holography

source

scansurface

nonlinear medium

Originalsource

2D scan

Physical forward propagation through nonlinear medium

Numerical back-propagation (nonlinear modeling)

Reconstructedsource

Numerical model test - forward projection

1st harmonic

2nd harmonic

3rd harmonic

Source Propagation Hologram

Experimental results

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Acoustic holography of a shock wave source

Dornier Compact S electromagnetic lithotripter

The lithotripter head embedded in a water tank wall

Pressure measurements with a fiber-optic hydrophone

Scanning region

Transient acoustic hologram of the Dornier Compact S electromagnetic lithotripter

Z

Back-propagated pressure pattern (peak-to-peak) at different distances

Peak-peak pressure reconstructed distribution

along the source face

Lithotripter head without cover

Revealing the hidden structures in the lithotripter head

Prediction of the radiated pressure field (linear model)

Measured pressure waveform at the focus (need to be

predicted in the future work)

ACOUSTIC HOLOGRAPHY FOR METROLOGY

Holography and numerical projection - IEC

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Consider linear CW case here

Rayleigh integral vs. angular spectrum

IEC/TS 62556, ed. 1.0 (2014)

Ultrasonics – field characterization –specification and measurement of field parameters for high intensity therapeutic ultrasound (HITU) transducers and systems

Errors associated with holography and field projections

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Error metrics:

scan aperture scan step size axial position of scan plane temperature errors hydrophone directivity axis skew in the scan plane axial misalignment

Sources of errors:

Reconstruction errors (simulations) – axial scan position

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Curved source, CW 1 MHz100 mm aperture100 mm radius of curvature

scan aperture 2ah = 50 mm (solid)2ah =150 mm (dashed)

zh

hologram

Reconstruction errors (simulations)

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Scan aperture Hydrophone directivity

Approach – physical experimentsHolographic reconstructions vs. independent measurements on axis

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single element @ 2.2 MHz45 mm aperture, ROC 45 mm10,201 scan points

7 elements @ 1 MHz147 mm aperture, ROC 140 mm25,921 scan points

C5-2 imaging probe @ 2.3 MHz49.9 × 13.5 mm aperturefocal distance 53 mm from apex66,807 scan points

Summary of results

Simulated experimentsmaximum errors around 1% or less if …

scan plane extends beyond the geometrical beam][scan position ~ halfway to the focus is useful] hydrophone diameter < λ/4temperature uncertainty ∆T < 1°Cskew angle between scan axes < 0.4°axial misalignment < 0.5°

Physical experimentssimulated errors for measurement parameters ~ 1–3% (largest on-axis)on-axis errors: 3–5% (even with temperature not recorded)higher in-plane errors: 7–20% (positioning errors, "dropped" steps?)

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correctable in reconstructions