Highlights of the OSA Spring Topical Meeting in Orlando, Florida

NewsEtc., April, 1998. Steven Jacques, Oregon Medical Laser Center

The 3rd biennial Optical Society of America (OSA) Topical Meeting on biomedical optics was held in Orlando, FL, March 8-11, 1998. Here is a quick summary of the meeting and some highlights.

There were three meetings held with some simultaneous sessions and some joint sessions. The links to the original OSA website listing the conference schedule of talks with 25-word abstracts are:

This summary lists the session topics and mentions a few talks, but cannot cite all the excellent presentations. My apologies. It was a really good conference.

Advances in Optical Imaging and Photon Migration

The session topics were:

My favorite talk was by Britton Chance who discussed the use of a dual criteria for identifying malignant tumors of the breast. He used a source/detector array incorporating two wavelengths to map blood content and hemoglobin oxygenation. The dual criteria for identifying malignant tumors were: (1) an area of increased blood perfusion, AND (2) an area of increased deoxygenation of hemoglobin. The concept is that a malignant tumor will have recruited an enhanced blood supply and that the high metabolic rate of a malignant tumor will more vigorously deplete the oxygenation status of blood in that supply. Dr. Chance reported good performance of this dual criteria in discriminating malignant breast tumors from various benign lesions.

A session of "Light and sound" highlighted projects combining light and sound in optical diagnostics. The two major categories of measurements were:

  • opto-acoustic imaging: A pulsed laser generates pressure waves (sound) in absorbing objects (such as a vascularized tumor) within a turbid tissue and an array of pressure transducers on the tissue surface detects the pressure waves. The arrival time of the pressure wave at each transducer is proportional to the distance of the object from the transducer and the transducer signals can be backprojected to determine the position and shape of the object. An invited talk by Frits de Mul (Univ. of Twente, The Netherlands) on "Photoacoustic imaging of blood vessels" presented sharp images of 200-um capillaries within a 5-mm thickness of chicken breast created by Q-switched 8-ns 532-nm doubled Nd:YAG laser pulses and a PVDF-piezo-film hydrophone. Steven Jacques described how the opto-acoustic technique is useful for both superficial and deep tissue imaging. He and his colleagues Rinat Esenaliev and Alexander Oraevsky, now at Univ. of Texas Medical Branch-Galveston, sent Q-sw 1064-nm laser pulses through 10 cm of chicken breast in vitro and generated detectable sound in a 7-mm thickness of liver. The sound propagated through 1.5 cm of chicken before detection and the liver was imaged with about 1-mm resolution.

  • acousto-optic imaging: A focussed ultrasound transducer generates oscillating pressure at 1 MHz frequency in a 1-mm^3 region of tissue. A laser beam is transmitted through the tissue and a photodetector is locked-in to the 1 MHz ultrasound signal such that only photons which pass through the 1-mm^3 region of tissue are detected. The apparent mechanism of signal localization is that the ultrasound modulates the speckle pattern generated by photons that passed through the 1-mm^3 region of tissue (mechanism still subject to debate). A series of talks by Lihong Wang (Texas A&M Univ.), Charles DiMarzio (Northeastern Univ.), and S. Leveque (Ecole Superieure de Physique and Chimie Industrielle, France) presented examples of this technique. The acousto-optic technique uses ultrasound to select the volume of interest and photons to probe that volume.

    Biomedical Optical Spectroscopy and Diagnostics

    The session topics were:

    My favorite talk was by Michael Feld, M.I.T., who spoke on "Spectral pathology using reflected light." He discussed the work of his colleagues Lev Perelman et al. who are using simple white light reflectance spectroscopy to detect the onset of Barrett's esophagus, a condition which can result from chronic gastric acid reflux and may be regarded as a premalignant condition. The MIT group is delivering/collecting white light using two small closely spaced optical fibers such that the reflectance is dominated by the scattering near the fibers and is somewhat sensitive to the wavelength-dependent Mie scattering from the nuclei. Such Mie scattering causes slight but distinguishable oscillatory variations in the reflectance as a function of wavelength which are characteristic of nuclei size. In Barrett's esophagus, the nuclei of esophageal cells are enlarged from their normal approx. 7 um diameter to greater than 10 um diameter and with a broader range of diameters as well. The MIT group could spectrally detect these differences.

    The Mie scattering patterns observed by the MIT group supports the contention long championed by Irv Bigio and his colleagues at Los Alamos National Labs that Mie scattering patterns can detect cancer, although the Los Alamos group's work has emphasized shorter wavelength reflectance changes attributable to smaller scale structures than the nuclei. The Los Alamos group presented their recent work on scattering from cancer cell suspensions, Judith Mourant et al., "Scattering properties of biological cells", in which the wavelength dependence of the reduced scattering coefficient (mus') can be characterized by a value x which is related to the size distribution of scatterers in the cell suspension, mus' = constant*nm^(-x), where nm is the wavelength in the UV-VIS-NIR spectral range.

    Therapeutic Laser Applications

    The session topics were:

    This meeting was new at the OSA Spring Topical Meeting, expanding beyond purely optical techniques to consider the physics and chemistry of how lasers and light interact with tissue. Of particular interest were the invited talks by Tayyaba Hasan, Wellman Laboratory of Photomedicine, on "Photodynamic Therapy: current status and future directions", Raimund Hibst, Institut fuer Lasertechnologien in der medizin and Mestechnik, Ulm, Germany, on "Hard tissue laser ablation for caries removal", and Dr. Cornelius Borst, Utrecht Univ. Hospital, The Netherlands, on "The octopus tissue stabilizer for local cardiac wall immobilization during CABG without CPB", illustrating the wide range of topics covered in this meeting.

    In summary, the conference was very good. Next year, this biomedical optics community will meet at the SPIE meeting in San Jose, CA, January, 1999. The next OSA Spring Topical Meeting will be held in March, 2000.

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