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1 5/19/2011, Reid McCargar Photo-acoustic phase conjugation for biomedical imaging Reid McCargar, Research Assistant
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Photo-acoustic phase conjugation for biomedical imaging

Feb 11, 2022

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Page 1: Photo-acoustic phase conjugation for biomedical imaging

15/19/2011, Reid McCargar

Photo-acoustic phase conjugation for biomedical imaging

Reid McCargar, Research Assistant

Page 2: Photo-acoustic phase conjugation for biomedical imaging

25/19/2011, Reid McCargar

Outline

• Brief overview – current diagnostic imaging technologies and the motivation for new technologies

• Wavefront aberration by scattering

• Dynamic holography and phase conjugation

• The acousto-optic effect

• Synthetic guide star acousto-optic tomography

Page 3: Photo-acoustic phase conjugation for biomedical imaging

35/19/2011, Reid McCargar

Project relevance

Near-IR illumination used to image vasculature Visible light is of limited use in

modern diagnostic imaging mostly due to high scattering

Page 4: Photo-acoustic phase conjugation for biomedical imaging

45/19/2011, Reid McCargar

Current imaging technologies

Page 5: Photo-acoustic phase conjugation for biomedical imaging

55/19/2011, Reid McCargar

Why change anything?

• Not all features of medical interest have adequate contrast when viewed with currently-available technologies.

• Many of the imaging technologies involve ionizing radiation, require chemical contrast agents, or have prohibitive cost.

Page 6: Photo-acoustic phase conjugation for biomedical imaging

65/19/2011, Reid McCargar

Why not use optical wavelengths?

With 2-way propagation, imaging may be possible down to a centimeter or so.

Page 7: Photo-acoustic phase conjugation for biomedical imaging

75/19/2011, Reid McCargar

Wavefront aberration by scattering

On passing through a turbulent, or highly-scattering medium, a coherent wavefront becomes tattered.

If the shape of the wavefront can be duplicated by an appropriately-shaped mirror, the wavefront can be refocused in backward travel.

Page 8: Photo-acoustic phase conjugation for biomedical imaging

85/19/2011, Reid McCargar

Wavefront sensing

• Problem with recreating the shape of a tattered wave: optical detectors are phase-insensitive.

Locally regarded as plane-waves, a wavefront shape can be detected by focal position shifts

Page 9: Photo-acoustic phase conjugation for biomedical imaging

95/19/2011, Reid McCargar

Implementation

GS

CCDWS

CPU

Historically used for sharpening astronomical images, but can you imagine the implementation in diagnostic imaging?

Page 10: Photo-acoustic phase conjugation for biomedical imaging

105/19/2011, Reid McCargar

Not good – lasers inside people

GS

CC

DW

S

CPU

Page 11: Photo-acoustic phase conjugation for biomedical imaging

115/19/2011, Reid McCargar

Dynamic holography

E1

E2 = k E1 *E4 = k E3 *

E3

Material with transmittance changes due to interference of E1 and E3

Page 12: Photo-acoustic phase conjugation for biomedical imaging

125/19/2011, Reid McCargar

Acousto-optic frequency shifting

Ultrasound transducer

Transmitted zero-order-beam

1st -order diffracted beam, up-shifted in frequency by facoustic

Acoustic wave propagation

Page 13: Photo-acoustic phase conjugation for biomedical imaging

135/19/2011, Reid McCargar

Synthetic guide star

Ultrasound transducer

LaserPhotodetector identifies frequency-shifted photons as having passed through ultrasound focus

Page 14: Photo-acoustic phase conjugation for biomedical imaging

145/19/2011, Reid McCargar

Putting the pieces together – Xu, et. al

Page 15: Photo-acoustic phase conjugation for biomedical imaging

155/19/2011, Reid McCargar

A less bewildering look

AO AO

US

CCD

R (f0) R* (f0 )

fs=f0-F

Page 16: Photo-acoustic phase conjugation for biomedical imaging

165/19/2011, Reid McCargar

Results

Tissue analog imaged to 5 mm with better resolution than ultrasound focus

Page 17: Photo-acoustic phase conjugation for biomedical imaging

175/19/2011, Reid McCargar

Conclusions

• It is possible to image tissue with visible light to perhaps several centimeters.

• Applications of this new technology are mostly untested.

Page 18: Photo-acoustic phase conjugation for biomedical imaging

185/19/2011, Reid McCargar

References

Page 19: Photo-acoustic phase conjugation for biomedical imaging

195/19/2011, Reid McCargar

Questions?

Thank you