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.

Instrumentation for Medical Optical Tomography with Applications

Ilkka Nissilä

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 10th of December, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7414-0)   [730 KB]
Dissertation is also available in print (ISBN 951-22-7413-2)


Near-infrared spectroscopy (NIRS) and imaging techniques based on it are a field which has been the subject of intensive research during the past 15 years. In NIRS, the tissue is illuminated with visible red or near-infrared (NIR) light of several wavelengths, and the light which is reflected back from the tissue or transmitted through it is measured using sensitive photodetectors. As the distance between the source and the detector is increased, the sensitivity of the measured intensity of light to changes in the internal parts of the tissue increases. Two main optical parameters can be defined which characterize the tissue: the scattering and absorption coefficients. The absorption coefficient is sensitive to the concentrations of oxygenated and deoxygenated hemoglobins in the tissue. The partial blood volume and oxygen saturation in the tissue studied can be calculated if the concentrations are known. The optical measurements are non-invasive and patient-friendly, and they can be performed in the presence of electromagnetic interference. The most interesting applications of optical imaging include the imaging of hemodynamic changes related to neural activity in adults and infants, the imaging of hematoma and circulatory defects in premature infants, mammography, and imaging of muscle tissue during exercise. The goal of this thesis was to develop a multichannel intensity-modulated optical imaging system, which can be used for the imaging of activation-related hemodynamic changes in the adult and neonatal cortex as well as optical tomography. The system can be calibrated to give absolute measurements of amplitude and phase, which reflect the absolute attenuation and temporal delay of the light as it passes through the tissue from source to detector. Both difference imaging (imaging of the differences between two functional states of a tissue, or between two phantoms) and absolute imaging are successfully demonstrated using phantoms which have realistic background values close to the optical properties of premature neonates' heads, and small targets with contrasts that occur between background tissue and, e.g., breast cancer, bone, or hematoma. Many activation measurements were also performed successfully using the system, including the measurement of hemodynamic changes in the right motor cortex during transcranial magnetic stimulation of the left motor cortex in adults, as well as bilateral auditory activation measurements on healthy full-term neonates.

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

  1. Nissilä I., Noponen T., Heino J., Kajava T., and Katila T., 2005. Diffuse optical imaging. Lin J. C. (editor), Advances in Electromagnetic Fields in Living Tissue 4. Springer Science, in press.
  2. Nissilä I., Kotilahti K., Fallström K., and Katila T., 2002. Instrumentation for the accurate measurement of phase and amplitude in optical tomography. Review of Scientific Instruments 73, number 9, pages 3306-3312. © 2002 American Institute of Physics. By permission.
  3. Nissilä I., Noponen T., Kotilahti K., Tarvainen T., Schweiger M., Lipiäinen L., Arridge S., and Katila T., 2004. Instrumentation and calibration methods for the multichannel measurement of phase and amplitude in optical tomography. Helsinki University of Technology, publications in Engineering Physics, Report A833 (TKK-F-A833).
  4. Nissilä I., Hebden J. C., Jennions D., Heino J., Schweiger M., Kotilahti K., Noponen T., Gibson A., Järvenpää S., Lipiäinen L., and Katila T., 2004. A comparison between difference data measured with a time-domain and a frequency-domain system for optical tomography. Helsinki University of Technology, publications in Engineering Physics, Report A834 (TKK-F-A834).
  5. Nissilä I., Kotilahti K., Komssi S., Kähkönen S., Noponen T., Ilmoniemi R. J., and Katila T., 2002. Optical measurement of hemodynamic changes in the contralateral motor cortex induced by transcranial magnetic stimulation. Proceedings of the 13th International Conference on Biomagnetism (BIOMAG 2002). Jena, Germany, 10-14 August 2002, pages 851-854. © 2002 VDE Verlag. By permission.
  6. Nissilä I., Kotilahti K., Huotilainen M., Mäkelä R., Lipiäinen L., Noponen T., Gavrielides N., Näätänen R., Fellman V., and Katila T., 2004. Auditory hemodynamic studies of newborn infants using near-infrared spectroscopic imaging. Proceedings of the 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. San Francisco, California, USA, 1-5 September 2004, pages 1244-1247.

Keywords: optical tomography, intensity modulation, instrumentation, near-infrared spectroscopy, activation studies

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© 2004 Helsinki University of Technology

Last update 2011-05-26