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Material and technique development for ultrasound optical tomography using spectral hole burning filters

Bengtsson, Alexander LU (2022)
Abstract

The molecular sensitivity
provided by optical photons has potential advantages in medical diagnostics,
for example, in distinguishing healthy from cancerous tissue. However,
scattering resulting from inhomogeneities in the refractive index of tissues
prevents spatially resolved optical measurements in biological material, except
at very shallow depths. This thesis presents research on a medical imaging
technique called ultrasound optical tomography (UOT), which overcomes the limit
on resolution resulting from scattering by combining photons and ultrasound.
Photons are locally frequency shifted (tagged) by ultrasonic waves inside the
tissue. Optical contrast... (More)

The molecular sensitivity
provided by optical photons has potential advantages in medical diagnostics,
for example, in distinguishing healthy from cancerous tissue. However,
scattering resulting from inhomogeneities in the refractive index of tissues
prevents spatially resolved optical measurements in biological material, except
at very shallow depths. This thesis presents research on a medical imaging
technique called ultrasound optical tomography (UOT), which overcomes the limit
on resolution resulting from scattering by combining photons and ultrasound.
Photons are locally frequency shifted (tagged) by ultrasonic waves inside the
tissue. Optical contrast can be obtained with ultrasonic spatial resolution by
detecting these tagged photons. In this work, the tagged photons were detected
using narrowband optical passband filters created in rare-earth-ion-doped
crystals using spectral hole burning techniques.



The thesis presents UOT
measurements using Pr3+:Y2SiO5 filters
operating at 606 nm, which characterize the signal strength under various
well-controlled experimental conditions. Improved understanding of the performance
of an optimized UOT set-up based on spectral hole burning was obtained by
fitting experimental data with theoretical models, indicating that imaging
depths of several centimetres should be possible in biological tissues.



A theoretical comparison of the
many UOT methods described in the literature is presented. The findings
indicate that spectral hole burning filters may have better contrast-to-noise
scaling, and thus potentially greater imaging depths, than other UOT methods
such as digital off-axis holography, photorefractive holography, and speckle
contrast imaging.



A major challenge for
spectral-hole-burning filter-based UOT to become useful for in vivo applications, is to identify and
develop crystals capable of supporting the required high-contrast filters at
wavelengths within the optical window for tissue (~650-950 nm). Experimental
values of the filter contrast obtained in UOT measurements in this wavelength
range have so far been limited to 14 dB. Based on spectroscopic measurements,
Tm3+:LaF3 is proposed as a candidate for UOT filtering at
690 and 797 nm. Measurements show that a filter contrast above 50 dB is
possible at the 690 nm transition for a collimated laser beam. The high filter
contrast of Tm3+:LaF3 is expected to be important for the
future development of UOT using spectral hole burning filters.

(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Louchet-Chauvet, Anne, Institute Langevin, ESPCI, France.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Biomedical imaging, ultrasound optical tomography, acousto-optical tomography, rare-earth-ion doped crystals, spectral holeburning, slow light filters, Tm+3:LaF3, Fysicumarkivet A:2022:Bengtsson
pages
221 pages
publisher
Atomic Physics, Department of Physics, Lund University
defense location
Lecture Hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund. Zoom: Publiklänk: https://lu-se.zoom.us/j/69608233051?pwd=Z29YdHozSFh4OW1SaVJmcVQ4SEpjZz09
defense date
2022-05-20 09:15:00
ISBN
978-91-8039-224-2
978-91-8039-223-5
language
English
LU publication?
yes
id
a20293a1-0264-41e7-a77d-564a79b30770
date added to LUP
2022-04-25 10:12:58
date last changed
2022-08-18 11:19:42
@phdthesis{a20293a1-0264-41e7-a77d-564a79b30770,
  abstract     = {{<p class="MsoNormal" style="text-align:justify">The molecular sensitivity<br>
provided by optical photons has potential advantages in medical diagnostics,<br>
for example, in distinguishing healthy from cancerous tissue. However,<br>
scattering resulting from inhomogeneities in the refractive index of tissues<br>
prevents spatially resolved optical measurements in biological material, except<br>
at very shallow depths. This thesis presents research on a medical imaging<br>
technique called ultrasound optical tomography (UOT), which overcomes the limit<br>
on resolution resulting from scattering by combining photons and ultrasound.<br>
Photons are locally frequency shifted (tagged) by ultrasonic waves inside the<br>
tissue. Optical contrast can be obtained with ultrasonic spatial resolution by<br>
detecting these tagged photons. In this work, the tagged photons were detected<br>
using narrowband optical passband filters created in rare-earth-ion-doped<br>
crystals using spectral hole burning techniques.</p><br>
<br>
<p class="MsoNormal" style="text-align:justify">The thesis presents UOT<br>
measurements using Pr<sup>3+</sup>:Y<sub>2</sub>SiO<sub>5</sub> filters<br>
operating at 606 nm, which characterize the signal strength under various<br>
well-controlled experimental conditions. Improved understanding of the performance<br>
of an optimized UOT set-up based on spectral hole burning was obtained by<br>
fitting experimental data with theoretical models, indicating that imaging<br>
depths of several centimetres should be possible in biological tissues.</p><br>
<br>
<p class="MsoNormal" style="text-align:justify">A theoretical comparison of the<br>
many UOT methods described in the literature is presented. The findings<br>
indicate that spectral hole burning filters may have better contrast-to-noise<br>
scaling, and thus potentially greater imaging depths, than other UOT methods<br>
such as digital off-axis holography, photorefractive holography, and speckle<br>
contrast imaging.</p><br>
<br>
<p class="MsoNormal" style="text-align:justify">A major challenge for<br>
spectral-hole-burning filter-based UOT to become useful for <i>in vivo</i> applications, is to identify and<br>
develop crystals capable of supporting the required high-contrast filters at<br>
wavelengths within the optical window for tissue (~650-950 nm). Experimental<br>
values of the filter contrast obtained in UOT measurements in this wavelength<br>
range have so far been limited to 14 dB. Based on spectroscopic measurements,<br>
Tm<sup>3+</sup>:LaF<sub>3</sub> is proposed as a candidate for UOT filtering at<br>
690 and 797 nm. Measurements show that a filter contrast above 50 dB is<br>
possible at the 690 nm transition for a collimated laser beam. The high filter<br>
contrast of Tm<sup>3+</sup>:LaF<sub>3</sub> is expected to be important for the<br>
future development of UOT using spectral hole burning filters.</p>}},
  author       = {{Bengtsson, Alexander}},
  isbn         = {{978-91-8039-224-2}},
  keywords     = {{Biomedical imaging; ultrasound optical tomography; acousto-optical tomography; rare-earth-ion doped crystals; spectral holeburning; slow light filters; Tm+3:LaF3; Fysicumarkivet A:2022:Bengtsson}},
  language     = {{eng}},
  publisher    = {{Atomic Physics, Department of Physics, Lund University}},
  school       = {{Lund University}},
  title        = {{Material and technique development for ultrasound optical tomography using spectral hole burning filters}},
  url          = {{https://lup.lub.lu.se/search/files/117175420/Avh_Alexander_B_web.pdf}},
  year         = {{2022}},
}