Abstract Doppler optical coherence tomography (DOCT) provides a non-disruptive, high resolution and real-time method for imaging flow velocity profiles inside small channels and capillaries. DOCT has been mostly used in the biomedical field to image blood flow. However, applications in the field of rheology have been rare. In this thesis, the time domain DOCT (TD-DOCT) was utilized to measure flow velocity profiles inside capillaries with high resolution. Time domain configuration was chosen due to the ability to implement dynamic focusing and, in addition, to have sufficient velocity range, especially at high speeds. The accuracy and reliability of the laboratory-built DOCT device was verified with Newtonian suspension and, further, the performance was compared to the commercial DOCT. In vivo measurements with slime mould Physarum polycephalum showed the versatility of DOCT to measure the flow velocity profile of a different kind of scattering suspension even with very low flow rates. The effects of multiple scattering on the accuracy of the measured flow velocity profiles were experimentally studied with two phantom configurations. The first case consisted of the static superficial layer, where the plain glass capillary with flowing Intralipid suspension was embedded into a cuvette. In the second case the moving superficial layer was made by introducing a second glass capillary in front of the studied flow. The results showed that multiple scattering has noticeable effect on the accuracy of the measured flow velocity profiles, especially at the deeper regions. Novel application of the DOCT technique is presented by implementing it to a capillary viscometer. As a result, the absolute viscosity of the Newtonian suspension is derived with high precision directly from the measured flow velocity profile and pressure drop without making any assumption of the flow under study. The results are consistent with the reference values measured with the commercial viscometer. / Tiivistelmä Doppler optinen koherenssitomografia (DOCT) on tekniikka, jolla on mahdollista mitata suspensioiden virtausnopeusprofiili virtausta häiritsemättömästi, reaaliaikaisesti ja tarkalla resoluutiolla ohuista kapillaareista. DOCT-tekniikkaa on hyödynnetty erityisesti lääketieteen alueella silmän rakenteen kuvantamisessa ja veren virtausmittauksissa. Tekniikan sovellukset nesteiden reologian tutkimuksessa ovat olleet harvinaisia. Tämän työn tarkoituksena on kehittää DOCT-tekniikkaa ja soveltaa sitä kapillaariviskometrissä viskositeetin määritykseen suoraan mitatusta virtausnopeusprofiilista. Tässä työssä hyödynnettiin laboratoriossa rakennettua aikatason DOCT-laitetta (TD-DOCT), jolla mitattiin virtausnopeusprofiili kapillaarin sisältä mikrometrien resoluutiolla. TD-DOCT valittiin, koska siinä voitiin käyttää dynaamista fokusointia parantamaan sivusuuntaista resoluutiota ja signaali-kohinasuhdetta. Tämän lisäksi se soveltuu laaja-alaisesti eri virtausnopeuksille, erityisesti nopeille virtauksille. Rakennetun DOCT-laitteen tarkkuus ja luotettavuus todennettiin mittaamalla Newtonista suspensiota ja vertaamalla mittaustuloksia kaupallisella DOCT:lla tehtyihin mittauksiin. Mittaukset elävässä organismissa, Physarum polycephalum -limasienessä, osoittavat laitteen soveltuvuuden erilaisten suspensioiden virtausnopeusprofiilin mittaukseen myös hyvin hitaissa virtauksissa. Moninkertaisen sironnan vaikutusta mitattujen profiilien tarkkuuteen tutkittiin kahdella eri konfiguraatiolla. Ensimmäisessä asetelmassa virtausnopeusprofiili mitattiin kapillaarista, joka oli upotettu valoa sirottavaan Intralipid-suspensioon, ja jonka upotussyvyyttä voitiin säätää. Toisessa asetelmassa muodostettiin dynaaminen valoa sirottava kerros asettamalla toinen Intralipidiä sisältävä kapillaari mitattavan kapillaarin eteen. Tulokset osoittavat, että monikertainen sironta vaikuttaa mitatun virtausnopeusprofiilin tarkkuuteen erityisesti kun valoa sirottava kerroksen paksuus kasvaa. Tässä työssä DOCT -tekniikkaa käytetään ensimmäistä kertaa kapillaariviskometrin yhteydessä. Newtonisen suspension absoluuttinen viskositeetti määritetään hyvin tarkasti suoraan mitatusta virtausnopeusprofiilista ja painehäviöstä ilman oletuksia virtaavasta nesteestä. Mitatut viskositeettiarvot vastaavat vertailumittauksia, jotka tehtiin kaupallisella rotaatioviskosimetrilla.

Abstract Light scattering diagnostics of turbid media containing both structural and dynamic inhomogeneities is currently of significant importance. One of the important directions in modern light scattering diagnostics is the development of methods for probing biological media with visible- and near-infrared radiation allowing for visualization of the biotissue structure. Optical methods for studying the biotissue structure and characterization of its optical properties are very promising and have been rapidly developing during the past decade. The present work is aimed at improving and discovering new potentials of currently existing methods of laser diagnostics of biological tissues containing both structural and dynamic inhomogeneities. In particular, the feasibilities of spatially resolved reflectometry and time-of-flight techniques for the problem of noninvasive determination of glucose level in human blood and tissues were examined both numerically and experimentally. The relative sensitivities of these methods to changes in glucose level were estimated. Time-of-flight technique was found to be more sensitive. The possibilities of Doppler optical coherence tomography for imaging of dynamic inhomogeneities with high resolution were considered. This technique was applied for the first time for the imaging of complex autowave cellular motility and cytoplasm shuttle flow in the slime mold Physarum polycephalum. The effect of multiple scattering on the accuracy of the measured flow velocity profiles for the case of single flow and for the case of the flow embedded into the static medium with strong scattering was studied. It was shown that this effect causes significant distortion to the measured flow velocity profiles and it is necessary to take this into account while making quantitative measurements of flow velocities.