ENHANCED MULTISPECTRAL POLARIMETRIC IMAGING TECHNIQUES UTILIZING AN OPTICAL TUMOR PHANTOM A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Srinivasan Sukumar August, 2005 ENHANCED MULTISPECTRAL POLARIMETRIC IMAGING TECHNIQUES UTILIZING AN OPTICAL TUMOR PHANTOM Srinivasan Sukumar Thesis Approved: Accepted: _______________________________ _______________________________ Advisor Dean of the College Dr. George C. Giakos Dr. George K. Haritos _______________________________ _______________________________ Faculty Reader Dean of the Graduate School Dr. Narender P. Reddy Dr. George R. Newkome _______________________________ _______________________________ Department Chair Date Dr. Daniel B. Sheffer ii ABSTRACT The purpose of this research was to investigate the potential of a laser-based optical polarimetric imaging system, operating under light backscattering geometry, for tumor detection utilizing an optical tumor phantom. Image plays a key role in tumor detection studies. The polarization state of the scattered light from a tumor-like structure and the discrimination of randomly polarized light from weakly polarized light can provide meaningful information regarding the nature of the tumor itself. This information can be both physiological and structural. In this research study, experiments were performed at two optical wavelengths, one visible and one near-infrared wavelength. The weakly scattered light from the tumor tissue like phantom had the necessary information relevant to the structure of the tumor. A Rotating Retarder Polarimeter was used to analyze this weakly scattered light from the phantom. The images obtained from the Rotating Retarder Polarimeter were then processed by means of a data reduction algorithm, based on Polarimetric Measurement matrix method to calculate the Degree of Linear Polarization (DOLP) image. Then, the DOLP images obtained from the two different wavelength lasers were subtracted to enhance the information present in the image. The Signal-to-Background ratio, a measure of contrast, was calculated to determine the quality of the image. Results from the experiments and the contrast analysis procedures showed that, the subtracted DOLP images provides better contrast in terms of iii higher numerical value compared to the single DOLP image. Overall, this optical imaging system combined with data reduction algorithm and image processing technique served as an effective imaging methodology in optical tumor phantom study. iv DEDICATION I dedicate this thesis to my Grandmother, Laxmi Ammal. v ACKNOWLEDGEMENTS I still remember the first day when I went and met Dr. Giakos. He has truly inspired me in more than one ways. He has been supportive to me from day one and I am greatly indebted to him for that. I owe all my academic success during this master’s degree to Dr. Giakos who has been more than an advisor to me. Thank you so much for all that you have done to me during this past 12 months. My committee members, Dr. Daniel Sheffer and Dr. Narender Reddy have been very much understanding and I am thankful to them for their support and valuable advices. Ms. Bonnie Hinds, what should I say, she had been a wonderful person and was always ready to help me, whenever I needed them the most. I would like to thank Mr. Rick Nemer from the Biomedical Engineering department. I would also like to extend my sincere thanks to all the faculty members of the Biomedical Engineering department. Dad, I owe you everything that I have achieved in my life till now. You have stood by me in almost all my endeavors and I feel I am nowhere without your support. Mom, I just love you for your innocence and unconditional love for me. Your prayers have worked wonders for me. Ramesh, you have been the best brother I could ever ask for. Also, my sister in law, Vahini has been supporting me right from the day she walked into my life. Thank you for being there for me. At this point I would like to extend my sincere gratitude to my uncle Pitchandi and aunt Parimala. They are the sole reason for me being here in United States. vi My colleagues, Abhilasha and Shadi Sumrain were always there to help me during my nervous initial days in the lab. Abhilasha has been a great friend and philosopher to me. I am very thankful to her for her advices and support. Shadi, you have amazed me by your activities and the starting point of my thesis was mainly due to your DOLP algorithm. I am extremely thankful to you for that, as well as, your valuable advices. My friends Senthil ram, Rajdeep and Praveen have been very supportive to me and went out of the way to help me out in most of the occasions. I am extremely thankful to them for being there for me. My FFSG friends are my greatest possession in my life. Their influence on me is way beyond explanation and I am more than thankful to them for their unconditional love and support. At this point I would like to thank Sowjanya, who had made me mature in more than one ways. I am thankful to all my friends over here and back in India for their love, support, criticism and encouragement. My fiancé and my better half, Shyamala has been my lover, friend, philosopher. Right from the day she entered my life, she has took me by surprise in most of the occasions. She has been thoroughly supportive and understanding throughout, especially during the lean patches of my life. Shyamala, I love you so much. vii TABLE OF CONTENTS Page LIST OF TABLES…………………………………………………………………. ….. xi LIST OF FIGURES…………………………………………………………………...... xii CHAPTER I. INTRODUCTION..………………………………………………………………... 1 1.1 General Introduction…………………………………………………………... 1 1.2 Problem Definition…………………………………………………………….. 3 1.3 Objectives of the Study………………………………………………………... 4 1.4 Research Hypothesis……………………………………………………........... 5 1.5 Limitations of the Study……………………………………………………….. 5 II. LITERATURE REVIEW………………………………………………………….. 6 2.1 Optical imaging techniques using polarization……………………………….. 6 2.2 Optical imaging techniques based on Mueller matrix formalism…………….. 7 2.3 Image subtraction techniques…………………………………………………. 8 2.4 Optical properties of biological tissues……………………………………….. 9 III. THEORY…………………………………………………………………………. 10 3.1 Laser interaction with tissue…………………………………………………. 10 3.2 Polarized light………………………………………………………………... 11 3.3 Multispectral imaging………………………………………………………... 13 viii 3.4 Polarimetric imaging…………………………………………………………. 13 3.5 Stokes parameter………………………………………………....................... 14 3.6 Mueller matrix……………………………………………………………….. 14 3.7 Multispectral Polarimetric imaging………………………………………….. 15 IV. EXPERIMENTAL SETUP AND PROCEDURES………………………………. 17 4.1 Preclinical Phantom Design………………………………………………….. 17 4.2 Experimental Setup…………………………………………………………... 19 4.3 Experimental Procedure……………………………………………………… 20 4.4 Alignment and Calibration Procedures………………………………………. 21 4.5 Data Reduction Algorithm…………………………………………………… 22 4.6 Analysis Technique…………………………………………………………... 25 V. MATERIALS……………………………………………………………………... 27 5.1 Optical Tabletop………………………………………………………...……. 27 5.2 Lasers………………………………………………………………………… 28 5.2.1 Semiconductor Laser…..…………………………………………… 28 5.2.2 Infrared Laser……………………………………………………….. 28 5.3 Linear Polarizer………………………………………………………………. 29 5.4 Retarder………………………………………………………………………. 29 5.4.1 Berek compensator………………………………………………….. 30 5.5 Beam Expander………………………………………………………………. 31 5.6 CCD Camera…………………………………………………………………. 32 5.7 Polystyrene sphere………………………………………………………........ 32 5.8 Intralipid…………………………………………………………………….... 32 ix VI. RESULTS AND DISCUSSIONS………………………………………………… 35 6.1 Single DOLP images………………………..………………………………... 35 6.2 Back-Scattered Mode Single DOLP images and their intensity plots……….. 37 6.3 Inferences from single DOLP images………………………………………... 43 6.4 Subtracted DOLP images………………………..………………………........ 44 6.5 Subtracted DOLP images and their intensity plots…………………………... 46 6.6 Inferences from subtracted DOLP images………………………………........ 52 6.7 Intensity measurements of the signal and the background and inferences....... 53 6.8 Signal-to-Background contrast ratio measurements and inferences…………. 54 VII. CONCLUSION AND FUTURE WORK………………………………………… 56 REFERENCES…………………………………………………………………………. 57 x LIST OF TABLES Table Page 5.1 Specifications of the 1135P JDS Uniphase Helium-Neon laser…………………… 28 5.2 Specifications of the IS785-25 model, IR Laser system…………………………… 29 5.3 Specifications for the beam expander…………………………………………........ 31 5.4 Specifications for the CCD Camera………………………………………………... 32 6.1 Average intensity value measurements of the signal and the background for solution 1……………………………………………………………………….. 53 6.2 Average intensity value measurements of the signal and the background for solution 2………………………………………………………………….......... 53 6.3 Signal-to-Background contrast ratio measurements for solution 1………………… 55 6.4 Signal-to-Background contrast ratio measurements for solution 2………………… 55 xi LIST OF FIGURES Figure Page 3.1 Paths traced by light in a tissue…………………………………………………….. 10 3.2 Linearly polarized light……………………………………………………….......... 12 3.3 Circularly polarized light………………………………………………………....... 12 4.1 Phantom for tissue infected with tumor…………………………………………..... 18 4.2 The experimental Setup……………………………………………………............. 19 5.1 The Melles Griot StableTop™ tabletop with triple-plate, double-honey comb-core construction includes TurboClean™ sealed mounting holes….….…… 27 5.2 Berek compensator…………………………………………………………………. 30 5.3 Side view of