The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Accurate Modelling of Tissue Properties in Diffuse Optical Imaging of the Human Brain

Juha Heiskala

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium TU2 at Helsinki University of Technology (Espoo, Finland) on the 19th of September, 2009, at 12 noon.

Overview in PDF format (ISBN 978-952-248-059-0)   [1156 KB]
Dissertation is also available in print (ISBN 978-952-248-058-3)

Abstract

Diffuse optical imaging (DOI) is an emerging imaging modality for non-invasive functional medical imaging, using near infrared (NIR) or visible red light. The innovation is to derive functional information about living tissue from measurements of light that has passed through it. Optical imaging can be applied to imaging of tissues as diverse as the central nervous system, female breast, muscle, and joints of fingers. This thesis addresses the application of DOI to studying the human brain.

In this thesis, the problems of modelling light propagation in the adult and infant human head, and reconstructing three-dimensional images of functional changes in the brain using optical measurements, are addressed. Difference imaging, where changes from baseline optical parameters rather than absolute parameter values are reconstructed, is considered. The goal was to develop methods for accurate modelling of light propagation and to clarify how specific aspects of the computational modelling affect the reconstruction of functional images from optical measurements of the human brain. Specifically, the significance of anisotropic light propagation in the white matter, and a priori knowledge of the anatomy and the optical properties of the head and brain are studied. Moreover, a generic probabilistic atlas model of the infant head to enhance image reconstruction is developed.

Significance of anisotropic light propagation was found to be small in optical imaging of the adult brain. Although anisotropic light propagation may have a larger impact on the measured signal when infants are imaged, results suggest that image reconstruction can be performed without taking anisotropy into consideration.

The use of a priori anatomical knowledge was found to significantly improve the accuracy and robustness of image reconstruction in difference imaging. The results suggest that for optimal reconstructions, individual MR imaging based anatomical data should be used when possible. For cases where individual anatomical data is not available, atlas models should be developed. An important consideration is how to obtain the baseline optical parameters of tissue classes in the anatomical model. Literature-derived parameters can be used as a starting point. For optimal results however, methods should be developed for estimating the baseline parameters from measured data.

This thesis consists of an overview and of the following 6 publications:

  1. Juha Heiskala, Ilkka Nissilä, Tuomas Neuvonen, Seppo Järvenpää, and Erkki Somersalo. 2005. Modeling anisotropic light propagation in a realistic model of the human head. Applied Optics, volume 44, number 11, pages 2049-2057. © 2005 Optical Society of America (OSA). By permission.
  2. Juha Heiskala, Tuomas Neuvonen, P. Ellen Grant, and Ilkka Nissilä. 2007. Significance of tissue anisotropy in optical tomography of the infant brain. Applied Optics, volume 46, number 10, pages 1633-1640. © 2007 Optical Society of America (OSA). By permission.
  3. Juha Heiskala, Kalle Kotilahti, and Ilkka Nissilä. 2005. An application of perturbation Monte Carlo in optical tomography. In: Proceedings of the 27th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE-EMBS 2005). Shanghai, China. 1-4 September 2005, pages 274-277. © 2005 IEEE. By permission.
  4. Juha Heiskala, Kalle Kotilahti, Lauri Lipiäinen, Petri Hiltunen, P. Ellen Grant, and Ilkka Nissilä. 2007. Optical tomographic imaging of activation of the infant auditory cortex using perturbation Monte Carlo with anatomical a priori information. In: Brian W. Pogue and Rinaldo Cubeddu (editors). Diffuse Optical Imaging of Tissue. Proceedings of SPIE, volume 6629, paper 66290T, 11 pages. © 2007 Society of Photo-Optical Instrumentation Engineers (SPIE). By permission.
  5. J. Heiskala, P. Hiltunen, and I. Nissilä. 2009. Significance of background optical properties, time-resolved information and optode arrangement in diffuse optical imaging of term neonates. Physics in Medicine and Biology, volume 54, number 3, pages 535-554. © 2009 Institute of Physics Publishing. By permission.
  6. Juha Heiskala, Mika Pollari, Marjo Metsäranta, P. Ellen Grant, and Ilkka Nissilä. 2009. Probabilistic atlas can improve reconstruction from optical imaging of the neonatal brain. Optics Express, volume 17, number 17, pages 14977-14992. © 2009 Optical Society of America (OSA). By permission.

Keywords: diffuse optical imaging, Monte Carlo, biomedical optics

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© 2009 Helsinki University of Technology

Last update 2011-05-26