I Alex Vitkin, PhD

Medical Applications of Lasers
My research is in the field of biophotonics / biomedical optics. We harness the unique properties of light to examine and treat biological tissues. We use lasers, photodetectors, optical fibers and other photonic technologies to address fundamental and applied biomedical problems, such as early diagnosis and effective treatment of disease. Three specific research areas are outlined below.
  • (1) Optical coherence tomography
    OCT is an emerging medical imaging modality with micron-scale subsurface resolution in intact tissues, down to ~2 mm depth. It relies on the wave nature of light, and on the coherence properties of lasers, to generate high-resolution subsurface images of tissue. OCT is similar to ultrasound, except reflections of near-infrared light, and not sound echoes, are used. OCT holds promise to enable cellular visualization in-vivo. If realizable, exciting clinical applications exist, including early cancer detection, diagnosis, and staging, 'optical biopsy' and optically-guided physical biopsy, evaluation of treatment efficacy and monitoring of subsequent treatment response. We and others have also detected OCT phase-resolved Doppler shifts that enable blood flow detection down to the micro-vascular/perfusion level (Doppler OCT, DOCT). We've also demonstrated Doppler-free detection of microvasculature, based on inter-frame texture analysis of speckle in OCT images (speckle variance OCT, svOCT). OCT's ability to image blood perfusion in-vivo opens up several exciting possibilities to study diseases and treatments with significant microvascular involvement; for example, we are quantifying the functional tissue changes during and following radiation and photodynamic therapies, in an effort to understand tissue responses, derive appropriate response metrics, and optimize the delivery of these treatments.
  • (2) Tissue polarimetry
    Polarization properties of light are widely used in science, technology and industry for detailed examinations of materials (ellipsometry, nondestructive evaluation, remote sensing). However, polarized light uses in biomedicine are severely compromised by tissue multiple scattering which depolarizes the light. We are developing experimental and theoretical methods to enable tissue polarimetry, by maximizing the detection of polarization-preserving photons, accounting for the effects of multiple scattering, and deriving intrinsic tissue polarization metrics (e.g, linear birefringence, circular birefringence, depolarization) from the measured polarimetric data. These methods are used to study the anisotropic (birefringent) nature of cardiac tissues, and its alterations following a heart attack and then following stem-cell-based regenerative treatments. In addition, the potential to detect small values of optical activity (circular birefringence) may offer a way to non-invasively quantify the concentration of optically active (chiral) tissue metabolites such as glucose. Non-invasive glucose monitoring in diabetic patients continues to be a major unsolved problem in clinical medicine, and our ability to extract small chiral asymmetries from the measured tissue polarization signals suggests a promising route towards a possible solution. Cancer applications are also possible, in that pathologic tissue often exhibits altered extracellular matrix microstructure (anisotropy) that may have a distinct polarization signature.
  • (3) Opto-thermal therapies / optical fiber sensors
    Thermal therapies using laser, microwave, or ultrasound energy sources offer several potential advantages for the treatment of solid tumours, for example in the brain or prostate. They are minimally invasive because they employ thin interstitial sources (optical fibers, microwave antennas, ultrasound applicators) to heat the target volume, obviating the need for extensive surgery; they can preserve the underlying tissue architecture; and the dividing line between thermally necrosed and viable tissue is sharp, making it possible to spare surrounding normal tissue if the treatment volume conforms to the 3D shape of the tumour. One important but poorly understood issue is the biophysics of thermal lesion formation. This requires extensive experimental measurements and three-dimensional modeling of energy propagation, temperature increases, and damage kinetics; in particular, the effects of blood flow and changing tissue properties (which makes the treatment process highly dynamic and variable) are being examined. The progress of thermal therapy can be monitored via magnetic resonance or ultrasound imaging, enabling the physician to alter the treatment in real time as required; however, these methods are expensive and often impractical. We are interested in using intestitial point optical measurements (fluence or radiance) to infer the important events during the course of thermal therapy, such as the onset of coagulation, the three-dimensional extend and location of the coagulation boundary, and the undesirable (and hopefully avoidable) occurrence of tissue charring. The clinical utility of optical monitoring as a practical feedback/control method for interstitial thermal therapy is currently being examined.

Related Links

For a list of Dr. Vitkin's publications, please visit PubMed, Scopus, Publons or ORCID.

Professor, Department of Radiation Oncology, University of Toronto
Professor, Department of Medical Biophysics, University of Toronto
Clinical Physicist (CCPM Certification), Princess Margaret Hospital, University Health Network