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In response to the conference organizer's request, I am presenting a summary of the current status of medical optical imaging and spectroscopy. This is a topic which is advancing rapidly and on which there have been a number of conferences recently, and yet there has not been presented an overview of the field and some idea of what the advantages and disadvantages of the photon diffusion technology may be. Thus, this paper emphasizes diffusion waves for spectroscopy and imaging deep within the tissue and, at the same time, for providing specificity information of both absorption and scattering. In achieving this goal, I will not be able to cite all of the advantages of technologies that view the superficial layers of skin, retina, etc., on the one hand, nor those that measure the photons that have been scattered minimally on the transit between input and output. One of the main reasons for this is that specificity of the optical methods requires all of the information available: absorption and scattering of intrinsic signals naturally in the tissue, and of extrinsic signal due to contrast agents that have been artificially lodged in strategic tissue volumes. Since this paper is essentially the transcript of a lecture, it is not proposed as a topic review and does not contain full-scale bibliographic references, some of which may be found in a recent review elsewhere. This paper highlights what we all might accomplish in order to bring to bear with maximal effectiveness the optical method for altering the outcome of medical problems. I have not emphasized the mathematics of photon diffusion so well represented by the papers of this symposium volume. The achievable goals of the optical methods are to speed detection, improve diagnosis, guide therapy, and what appears in the minds of most, contribute to the improvement of medical economics. In order to fulfill these objectives, we will in the end have to demonstrate by lengthy and expensive clinical studies that the medical devices we develop are really what we think they are as determined by accepted procedures for clinical studies. This is a difficult and expensive route and one track along which many technologies will 'fall by the wayside'. However, our technology is maturing: we are obtaining numbers for important medical problems. It is indeed difficult to make these kinds of contributions; medical devices are not new. The choice of methods is manifold and the niches or windows of opportunity are circumscribed.
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