Tomographic Imaging with Light and Sound Finnish Inverse Problems - - PowerPoint PPT Presentation

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Tomographic Imaging with Light and Sound Finnish Inverse Problems - - PowerPoint PPT Presentation

Aug 20, 2023 351 likes •707 views

Tomographic Imaging with Light and Sound Finnish Inverse Problems Summer School, Helsinki, June 3, 2019 Tanja Tarvainen, Computational Physics and Inverse Problems Group, Department of Applied Physics UEF // University of Eastern Finland This is

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UEF // University of Eastern Finland

Finnish Inverse Problems Summer School, Helsinki, June 3, 2019

Tanja Tarvainen, Computational Physics and Inverse Problems Group, Department of Applied Physics

Tomographic Imaging with Light and Sound

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UEF // University of Eastern Finland

This is joint work with

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Aki Pulkkinen, Senior Researcher Ultrasound physics and therapy Acousto-optic interaction Aleksi Leino, postdoc Light transport simulations Meghdoot Mozumder, postdoc Diffuse optical tomography Jenni Tick, PhD student Photoacoustic tomography Jarkko Leskinen, postdoc Ultrasonic and optical instrumentation Eero Koponen, PhD student Synthetic schlieren tomography Niko Hänninen, PhD student Quantitative photoacoustic tomography Teemu Sahlström, PhD student Photoacoustic tomography

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UEF // University of Eastern Finland

Optical imaging – Why the interest?

Early breast cancer imaging

  • In 1929 it was suggested that visible light could be used to detect

breast lesions

  • M. Cutler: "Transillumination of the breast", 1929
  • The method didn’t work

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UEF // University of Eastern Finland

Light has some properties which make it very appealing for biomedical studies

  • Capability of optical methods to

provide information on the internal properties of tissues based on endogenous (e.g. haemoglobin) or exogenous (e.g. dyes) contrast

  • Instrumentation is relatively simple

and low-cost

  • Non-ionizing

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Absorption coefficients of major chromophores in tissues (T. Näsi Multimodal applications of functional near-infrared spectroscopy, PhD thesis, Aalto University, 2013).

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UEF // University of Eastern Finland

  • Various visible and near-infrared light based measurement and

monitoring methods have been developed since 1930s

  • Pulse oximetry, NIR spectroscopy, ...

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Image from Wikimedia Commons, the free media repository.

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UEF // University of Eastern Finland

Diffuse optical tomography 1990-

  • Imaging through human body using

visible and near-infrared light

  • Reconstructing distributions of light

absorbers

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UEF // University of Eastern Finland

  • Light is guided into the

target from various direction

  • Amount of scattered and

transmitted light is measured

  • An image is reconstructed

from the measurements

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UEF // University of Eastern Finland 3.6.2019 Tomographic imaging with light and sound / Tanja Tarvainen 8

Diffusion approximation

  • Describes light propagation in highly

scattering medium

  • Diffuse model
  • Easy to solve using numerical

methods

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Image reconstruction in the framework of inverse problems

  • Solve the optical parameters which minimise functional

using methods of computational inverse problems

  • The minimisation problem is solved using optimization methods
  • The governing (partial) differential equation needs to be solved

using numerical methods

  • Both can be difficult tasks
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UEF // University of Eastern Finland

  • S. Arridge and M.

Schweiger: Inverse Methods for Optical Tomography, 1993

  • S. Arridge et al: A finite

element approach for modelling photon transport in tissue, 1993

  • Etc.

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UEF // University of Eastern Finland

However…

  • Diffuse optical tomography can only produce blurred (i.e. diffuse)

images

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UEF // University of Eastern Finland

Imaging using coupled physics 2000-

  • Utilise coupled physics to combine the benefits of different

imaging modalities

  • Photoacoustics, acousto-optics, ultrasound modulated diffuse
  • ptical tomography, thermoacoustics, etc.

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UEF // University of Eastern Finland

Photoacoustic imaging

First experiments

  • Photoacoustic effect was first reported

by Alexander Graham Bell in 1880

  • Generated audio waves using chopped

sunlight

  • A.G. Bell, On the production and

Reproduction of Sound by Light, American Journal of Science, 20:305, 1880

  • A.G. Bell, The Production of Sound by

Radiant Energy, Science, 2(48):242-253, 1881

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A.G. Bell, On the production and Reproduction

  • f Sound by Light, American Journal of Science,

20:305, 1880

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UEF // University of Eastern Finland

Photoacoustic effect 1. Tissue is illuminated by a short pulse (ns scale) of light 2. As light propagates within the tissue, it is absorbed by chromophores (light absorbing molecules)

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UEF // University of Eastern Finland

3. The absorbed energy causes pressure rise 4. This pressure increase propagates though the tissue as an acoustic wave and can be detected on the surface of the tissue using ultrasound sensors

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UEF // University of Eastern Finland

Photoacoustic imaging

  • Reconstruct the initial pressure (or absorbed
  • ptical energy density) from the photoacoustic

signal measured at the surface of the tissue

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UEF // University of Eastern Finland

  • Photoacoustic imaging combines the benefits of optical and

acoustic methods

  • Contrast though optical absorption

– Tissue chromophores: oxygenated and deoxygenated haemoglobin, water, lipids, melanin – Contrast agents

  • Resolution by ultrasound

– Low scattering in soft biological tissue

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J Laufer at al, Journal of Biomedical Optics, 2012

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UEF // University of Eastern Finland 3.6.2019 Tomographic imaging with light and sound / Tanja Tarvainen 18

Inverse problem in Bayesian framework

  • Model all parameters as random variables
  • The solution of the inverse problem (posterior probability

density) is given by the Bayes’ formula

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UEF // University of Eastern Finland

Quantitative photoacoustic tomography

  • Estimate the distribution of the optical parameters

from photoacoustic images

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Radiative transfer equation

  • Describes propagation of radiation in the presence of

scattering particles

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UEF // University of Eastern Finland 3.6.2019 Tomographic imaging with light and sound / Tanja Tarvainen 29

  • Is used to model light

transport in astrophysics, atmosphere,

  • ceanography, biomedical

studies

  • Analytical solutions are

limited to few geometries

  • Computationally

expensive and challenging

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UEF // University of Eastern Finland 3.6.2019 Tomographic imaging with light and sound / Tanja Tarvainen 30

  • Estimate optical parameters x from absorbed optical energy

density H

  • Forward model: radiative transfer equation or diffusion

approximation

  • Maximum a posteriori estimate

Optical inverse problem of QPAT

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UEF // University of Eastern Finland 3.6.2019 Tomographic imaging with light and sound / Tanja Tarvainen 31

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UEF // University of Eastern Finland

  • Example from a simulation study

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For more information

  • Computational physics and inverse problems research group:

www.uef.fi/inverse

  • Biomedical Optical Imaging and Ultrasound Laboratory:

www.uef.fi/opus

  • Open source Monte Carlo code and Matlab interface –ValoMC:

https://inverselight.github.io/ValoMC/

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Thank you!