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Ying-Chih Chen

Professor
 
Department :
Physics
Membership :
Full Member
Core Research :
Cancer
Office :
Room 1238 North
Email :
Office Phone :
(212) 772-4526
Lab Room:
(212) 772-5390
Education :
  • B.S., National Taiwan University
  • Ph.D., Columbia University
Research Interest :

My research has been focused in  the application of lasers to biomedical imaging.  There are two ongoing projects: photoacoustic imaging and convergence of light through optically diffusive media. 

Photoacoustic imaging of tissues

Ultrasound  is an imaging method commonly performed in pulse-echo mode, where a focused acoustic pulse is emitted by the transducer into the tissue and echoes produced wherever the pulse encounters a change in speed of ultrasound.  Like all detection techniques based on waves, such as ultrasound, light, and microwave, the ability to resolve small objects is limited by diffraction. As a rule, the ultimate limitation of resolution of imaging is on the order of one wavelength. For transducers with a center frequency of 20 MHz, the resolution is on the order of 200 microns. Photoacoustic imaging, which combines optics and ultrasound to produce images, has attracted considerable interests as complementary diagnostic imaging technique.  The generation of photoacoustic signal is based on thermal  expansion of tissue in response to an absorbed light pulse. This rapid expansion of tissue generates a broadband acoustic pulse, which can then be detected by an ultrasound  transducer.  Early studies of photoacoustic imagining utilized laser pulses to illuminate a large area where the spatial  resolution was still determined by the parameters of the  ultrasound transducer.  Recently, we have demonstrated that, by focusing the laser to a micron-sized spot which is far smaller than can be achieved with a weakly focused   ultrasound transducer,  the image resolution can be significantly improved by one order  of magnitude compared to that obtained with pulse-echo ultrasound or by photoacoustic imaging with a non-focused light source.  Images produced by the absorption-based contrast at   a particular wavelength is independent of those imaged by pulse-echo ultrasound and may be use to highlight specific tissues of interest. For example, the laser wavelength may be tuned to the absorption band of melanin to reveal the layers of retina and choroid  that have not been seen before with conventional ultrasound technique.  Potential applications of this technique include clinical examination of superficial and thin tissues containing optically absorbing pigments such as melanin or hemoglobin, including skin.

Focusing of light through optically diffusive media
Random scattering of light is what makes materials such as ground glass, milk,  thick fog, and human tissues opaque. In these materials, repeated scattering distorts the incident wavefront so strongly that the information carried by the input light is totally lost.   Recent studies show that by manipulating the wavefront, light can be re-converged total a point behind the surface of an opaque object and thereby to allow images to be formed.  We have demonstrated that by using the photoacoustic signals   generated by a light absorbing target underneath an opaque surface as a beacon,  randomly-scattered light can be converged through a diffusive medium towards the target.  In our approach, micro-manipulation of wavefront is done with a 12x12-element deformable mirror. After wavefront optimization, the intensity of light at the target is enhanced by two to three orders of magnitude.  This new capability opens the possibility of delivering intense focused laser beam deeper into tissues for  imaging and therapeutic applications. 

Selected Publications :
  • Guichen Tang, Fanting Kong, Y.C. Chen, and M. Xu, “ Full field photothermal dynamics microscopy”  SPIE Proceedings 8949,  Three-dimensional and multidimensional microscopy XXI, 89490X (2014).
  • Tianjie Chen, Shaoguang Duan, and Y.C. Chen, “Electrodynamics analysis on coherent perfect absorber and phase-controlled optical switch” Journal of Optical Society of America, A, 29, 689-693 (2012). 
  • Fanting Kong, Ronald Silverman, Liping Liu, Parag Chitnis, and Y.C. Chen, “Focusing of light through scattering media” SPIE Proceedings  Photos plus ultrasound imaging  Vol. 7899 , 789925 (2011).
  • Fanting Kong, Ronald Silverman, Liping Liu, P. V. Chitnis, Kotik K. Lee, and Y.C. Chen, "Photoacoustic-guided convergence of light through optically diffusive media", Opt. Lett. 36, 203 (2011).
  • Ronald H. Silverman, Fanting Kong, Harriet O. Lloyd,Y. C. Chen, 'Fine-resolution photoacoustic imaging of the eye', Imaging and Sensing 2010, edited by Alexander A. Oraevsky, Lihong V. Wang, Proc. of SPIE, Vol. 7564, 75640Y (2010)
  • R H. Silverman, Fanting Kong, Y. C. Chen, Harriet O. Lloyd, Hyung Ham Kim, Jonathant M. Cannata, K. Kirk Shung, and D. Jackson Coleman, "High-resolution photoacoustic imaging of Ocular tissues", Ultrasound in Med. & Biol., Vol. 36, No. 5, pp. 733–742, (2010).
  • Fanting Kong, Y. C. Chen, Harriet O. Lloyd, Ronald H. Silverman, Hyung Ham Kim, Jonathan M. Cannata,and K. Kirk Shung,"High-resolution photoacoustic imaging with focused laser and ultrasonic beams" Appl. Phys. Lett., 94, 033902 (2009).
  • Fanting Kong, Liping Liu, Yi Zhou, Shou-Huan Zhou , Y.C. Chen, ' Phase locking of short-pulse Q-switched lasers' Opt. Commun. 282, 1622 (2009).
  • Fanting Kong, Liping Liu, Charlotte Sanders, Y. C. Chen, and Kotik K. Lee, ' Phase locking of nanosecond pulses in a passively Q-switched two-element fiber laser array', Appl. Phys. Lett., 90, 151110 (2007).