Imaging through Turbidity

Overview
Over the past decade powerful optical methods for probing and imaging biological cells and tissues have been developed. Advances have been made from the microscopic scale to imaging of the whole brain, breast and other organs of the body. Most of this development has been intensity-based, in which the light-tissue interaction is viewed as a stream of bullets (photons) impinging on tissue scatterers. In this picture, elastic scattering, the origin of tissue turbidity, is considered to be a randomizing process. This picture is embodied in Monte-Carlo simulations.

Although this intensity-based picture can provide useful information, it is fundamentally incomplete, as the phase of the light wave is not considered. The light-tissue interaction is fundamentally a wave phenomenon, and the electric field picture, in which both phase and amplitude are included, is the correct one. From this perspective, elastic scattering is a deterministic process, and in principle reversible, not randomizing. Using this E-field picture, one can quantify the turbidity of scattering media and appropriately manipulate the incident optical beam for light delivery to deep tissue regions for imaging and therapeutic purposes – a major goal in biomedical optics research.

A central part of microscopy work at the MIT LBRC has been the development of novel methodologies to obtain and exploit quantitative amplitude and phase information of the sample under study. This has led to new scientific opportunities as well as practical laboratory instruments that extend phase microscopy to the realms of quantitative and 3-D microscopy. Researchers at LBRC are furthering extending these capabilities to devise methods for turbidity suppression in biological tissue. Following is the list of related core and collaborative projects:

Core Projects

• Digital phase conjugation
• Field-based assessment of scattering matrix
• Light transport phenomena in complex media

Collaborative Projects:

• FDTD simulation of light propagation in turbid media
• Efficient light delivery for photodynamic therapy

1. Popescu G, Deflores LP, Vaughan JC, Badizadegan K, Iwai H, Dasari RR, and Feld MS, "Fourier Phase Microscopy for investigation of biological structure and dynamics”, Optics Letters 29 (21), 2503-2505 (2004).
2. Ikeda T, Popescu G, Dasari RR, and Feld MS, “Hilbert phase microscopy for investigating fast dynamics in transparent systems,” Optics Letters 30 (10), 1165-1167 (2005).
3. Park YK, Popescu G, Badizadegan K, Dasari RR, Feld MS. Diffraction phase and fluorescence microscopy. Optics Express 14, 8263-8 (2006) PMID: 19529201.
4. Choi W, Fang-Yen C, Badizadegan K, Oh S, Lue N, Dasari RR, Feld MS. Tomographic phase microscopy. Nature methods. 4, 717-9 (2007) PMID: 17694065.
5. Yaqoob Z, Psaltis D, Feld MS, Yang C. Optical phase conjugation for turbidity suppression in biological samples. Nat Photonics. 2, 110-5 (2008). PMCID: PMC2688902