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Alex Vitkin

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Professor

Ph.D., McMaster University
M-CCPM (Board Certification)
Fellow, OSA
Fellow, SPIE

 

Princess Margaret Cancer Centre

Toronto Medical Discovery Tower
101 College Street, Room 15-313
Toronto, Ontario
M5G 1L7

 

Phone: (416) 634-8727

Alex Vitkin's email address


For more information, please go to http://www.uhnres.utoronto.ca/labs/biophotonics/staff/avitkin.htm

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.

Selected Publications (a more complete list and corresponding PDFs are available at: 
                                     http://www.uhnres.utoronto.ca/labs/biophotonics/staff/avitkin.htm)

  • Davoudi B, Lindenmaier A, Standish BA, Bizheva K, Vitkin IA, Non-invasive morphological and vascular imaging of oral tissue with spectral domain optical coherence tomography, Biomed Opt Express 3 826-39 2012
  • Conroy L, DaCosta R, Vitkin IA, Quantifying tissue microvasculature with speckle variance optical coherence tomography, Opt Lett 37 3180-2, 2012
  • Ullah H, Mariampillai A, Atif M, Vitkin IA, Can temporal analysis of OCT statistics report on D-glucose levels in blood? Laser Phys Lett  21 1962-71, 2011
  • Standish BA, Mariampillai A, Leung MKK, Vitkin IA, Microvascular imaging and treatment response monitoring with biophotonics and OCT, in Handbook of Coherent Domain Optical Methods: 2nd ed, Tuchin VV, editor (Springer, NY, USA), chapter 11, 2011
  • Standish BA, Lee KKC, Mariampillai A, Munce NR, Leung MKK, Yang VDX, Vitkin IA, In-vivo endoscopic multi-beam optical coherence tomography, Phys Med Biol 55 615-22, 2010 (top-10 PMB downloads in 2010)
  • Douplik BA, Morofke D, Chiu S, Bouchelev V, Mao YI, Yang VXD, Vitkin IA, In vivo real time monitoring of vasoconstriction and vasodilation by a combined diffuse reflectance spectroscopy and Doppler optical coherence tomography approach, Lasers Surg Med40 323-31, 2008
  • Liu GY, Mariampillai A, Standish BA, Munce NR, Gu X, Vitkin IA, High power wavelength linearly swept mode locked fiber laser for OCT imaging, Opt Express 16 14095-105, 2008

(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. 

Selected Publications
(a more complete list and corresponding PDFs are available at: 
                                     http://www.uhnres.utoronto.ca/labs/biophotonics/staff/avitkin.htm)

  • Layden D, Wood MFG, Vitkin IA, Optimum selection of input polarization states in determining the sample Mueller matrix: a dual photoelastic polarimeter approach, Optics Express 20 20466-81, 2012
  • Alali S,  Ahmad M, Kim AJ, Wood MFG, Vitkin IA, Quantitative correlation between light depolarization and transport albedo of various porcine tissues, J Biomed Opt 17 045004-10, 2012
  • Ghosh N and Vitkin IA, Concepts, challenges and applications of polarized light in biomedicine: a tutorial review, J Biomed Opt 16 110801-29, 2011
  • Ahmad M, Alali S, Kim AJ, Wood MFG, Vitkin IA, Do different turbid media with matched bulk optical properties also exhibit similar polarization properties? Biomed Opt Express 2 3248-58, 2011
  • Wallenburg MA, Pop M, Wood MFG, Ghosh N, Wright GA, Vitkin IA, Comparison of optical polarimetry and diffusion  tensor MR imaging for assessing myocardial  anisotropy, J Innov Opt Health Sci 3 109-21, 2010
  • Wallenburg MA, Wood MFG, Vitkin IA, Effect of optical axis orientation on polarimetry-based linear retardance measurements, Opt Lett 35 2570-2, 2010
  • Wood MFG, Ghosh N, Wallenburg MA, Li S, Weisel RD, Wilson BC, Li R-K, Vitkin IA, Polarization birefringence measurements for characterizing the myocardium, including healthy, infracted, and stem cell regenerated tissues, J Biomed Opt 15 047009-9, 2010
  • Guo X, Wood MFG, Vitkin IA, A Monte Carlo study of penetration depth and sampling volume of polarized light in turbid media, Opt Communic 281 380-7, 2008

(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.

Selected Publications (a more complete list and corresponding PDFs are available at: 
                                     http://www.uhnres.utoronto.ca/labs/biophotonics/staff/avitkin.htm)

  • Chin LCL, Whelan WM, Vitkin IA, Interstitial optical fiber sensors in biomedicine, in Optical-Thermal Response of Laser Irradiated Tissue: 2nd edition, Welch AJ and van Gemert MG, editors (Springer, New York, USA), chapter 17, 2011
  • Chin LCL, Lloyd B, Whelan WM, Vitkin IA, Interstitial point radiance spectroscopy, J Appl Phys 105 102025-11, 2009
  • Chin LCL, Whelan WM, Vitkin IA, Determination of the optical properties of turbid media using relative interstitial radiance measurements: Monte Carlo study, experimental verification and sensitivity analysis, J Biomed Opt 12 036706, 2007
  • Rink A, Lewis DF, Varma S, Vitkin IA, Jaffray DA, Temperature and hydration effects on absorbance spectra and radiation sensitivity of a radiochromic medium, Med Phys 35 4545-55, 2008
  • Chin LCL, Whelan WM, Vitkin IA, Perturbative diffusion theory formalism for interpreting temporal light intensity changes during laser interstitial thermal therapy:  implications for point optical monitoring of coagulation boundary dynamics, Phys Med Biol 52 1659-74, 2007
  • Chin LCL, Whelan WM, Vitkin IA, Information content of point radiance measurements in turbid media:  Implications for interstitial optical property quantification, Appl Opt 45 2101-14, 2006

Link to Pubmed Publications

Graduate Students:

  • Bahar Davoudi (PhD) – Optical coherence tomography (OCT) for microstructural and microvascular assessment of tissue toxicity following radiation therapy
  • Sanaz Alali (PhD) – Polarized light investigation of tissue anisotropy in urology / obstructive bladder disease
  • Andras Lindenmaier (MSc) – OCT speckle and spectroscopic analysis for early radiobiological detection in irradiated tissues
  • Adam Gribble (MSc) – improved turbid polarimetry platform for tissue characterization and early cancer assessment
  • Andrew Weatherbee (MSc) – speckle variance OCT for tissue hydration and blood viscosity studies
  • Laura Burgess (MSc) – photodynamic therapy and OCT monitoring of oral cancers (co-supervised with Dr. Gang Zheng)

Recent MBP Graduates:

  • Michael Leung (MSc), Marika Wallenburg (MSc), Michael Wood (PhD), Adrian Mariampillai (PhD), Beau Standish (PhD), Lee Chin (PhD), Nigel Munce (PhD), Alexandra Rink (PhD, co-supervised with Dr. David Jaffray)
Post-doctoral Fellow(s):
  • Dr. Nirmalya Ghosh – Mueller matrix decomposition for extracting individual biological metrics from tissue polarimetry signals

 

 
Last Updated: February 28, 2014 All contents Copyright © 1995 - 2013, Department of Medical Biophysics. All Rights Reserved.