With the technique of transillumination imaging, we can visualize the structure and the physiological change inside an animal body. The usefulness of this technique in animal experiments was demonstrated in the example of functional imaging of the rat brain. Using a fluorescent medium, we can apply this technique to the body part which light does not penetrate through. An example of transcutaneous fluorescent imaging was presented as the result of animal experiment. To improve the image blurred by the scattering effect in transcutaneous imaging, a deconvolution technique with a depth-dependent point spread function (PSF) was proposed. The PSF was derived theoretically as an analytical solution in a closed form. Using this PSF, the contrast of the fluorescent image was improved for depths of 1-15 mm in a scattering medium. The visible depth was more than doubled with this technique. An experiment with a rat demonstrated considerable improvement of a transcutaneous image of the cerebral vein at a specified depth. The spread image of the heart was reduced to the correct size using the PSF with the actual depth of the heart. With the proposed technique, the usefulness of transcutaneous fluorescent imaging is promoted significantly in practice.

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While application of near-infrared spectroscopy (NIRS) to monitoring of human brain function has attracted interest of many researchers and clinicians, it has been pointed out that only low quantitative and low spatial resolution data (or topographic images) could be obtained with NIRS due to highly light scattering properties of scalp, skull, and cortex. Currently prevailing multi-channel NIRS systems consist of several sets of incident and detecting optical fiber probes. Therefore, spatial resolution of two-dimensional topographic images obtained with the multi-channel NIRS depends on the number and the distance between incident and detecting optical fibers. To improve the spatial resolution and to obtain the depth information of absorbers buried in highly scattering material, we developed a noncontact backscatter-mode near-infrared time-resolved imaging system. It consists of mode-locked Ti-sapphire lasers (780 and 830 nm at 80 MHz and 10 psec of pulse width) as light sources and a CCD camera equipped with a time-resolved intensifier as a detector. Illumination and detection of light was conducted through a large-diameter objective lens system. The system was tested with a white polyacetal phantom as a light-scattering medium and black polyacetal particles as absorbers. Spatial resolution and accuracy of absorber positions were markedly improved compared with the conventional fiber-optic topographic instruments. Here, we report a backscatter-mode near-infrared time-resolved imaging system, which has a potential to overcome the currently prevailing multi-channel NIRS systems by achieving quantitative and high-resolution imaging.

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The optical coherence tomography(OCT)can be utilized to measure high-resolution cross-sectional in vivo and in situ images of microstructure in transparent and nontransparent biological tissues. OCT is based on the low-coherence interferometry and its axial and lateral resolutions are given by the half of coherence length of light source and the beam diameter of an incident beam at the beam waist. Using the solid state laser as a light source the OCT images of in vitro human colorectal adenocarcinoma cells have been measured with A:0.5-μm axial and L:2.5-μm transverse resolution. By the full-field OCT using CCD camera OCT images of biological tissues have also been measured with A:17-μm, L:4-μm and the speed of 100 frames/s. Developing the endoscopic OCT and the imaging catheter for OCT, the clinical applications of OCT is spreading into the fields of gastrointestinal system, cardiovascular system, ophthalmology, dermatology and so on.

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Optical coherence tomography (OCT) is a very promising technique for clinical diagnosis because high-resolution tomography is easily obtained by a compact imaging optics. The existing OCT, however, should be improved toward high-definition OCT which is comparable to a histology (or a microscopic photograph of tissue). In this paper, we summarized our recent effort to approach to high-definition OCT. In in-vitro tomographic imaging of the human stomach wall, in-focus OCT could provide a very clear image of the muscularis mucosae of a few tens of microns thickness. Furthermore, we demonstrated high-definition OCT of micro tissue structures including epidermis, dermis and stratum basale using a femtosecond Ti:sapphire laser.

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Optical Coherence Tomography (OCT) has become widely used in the field of ophthalmology. It enables us to observe retinochoroidal tomogram noncontactly and noninvasively at high resolution. Now OCT is essential and useful for understanding the effects of the treatment and regional change of disorder, which was not elucidated by ophthalmoscopy. In this article, we discuss the popular OCT devices and OCT diagnosis of common retinochoroidal disorder.

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Optical imaging methods by use of interaction between the ultrasonic wave and the light have been proposed for medical diagnosis using spectroscopic information. The optical absorption information was obtained from the dependence of ultrasonic velocity on the light intensity and wavelength. The ultrasonic velocity change caused by light illumination was detected even in the medium with high scattering coefficient equivalent to the reported value of human brain. Images of absorption objects hidden in a model tissue sample were reconstructed from ultrasonic velocity change due to light illumination.

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The author's group has proposed Optical Topography (OT) applying near-infrared spectroscopy ahead of everyone else in the world. OT has enabled measurements of changes in hemoglobin concentrations in brain tissue just by placing the cap fixing the optical fibers on the head. Also, the OT system has particular features that other conventional modalities do not have in measuring brain functions. We summarize basic principles, actual examples of brain function measurement results and an improvement strategy of spatial resolution in this report.

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Two versions of the Laser Speckle Flowgraphy system are presented - one version visualizes the microcirculation map of skin tissue and the other version analyzes the blood flow distribution of smaller tissue areas, such as the human retina. For the larger target tissue, the area is illuminated by the laser line spot, which is scanned across the tissue and the spot is imaged onto the line sensor. The signal is transmitted to a PC and the blood flow map is calculated from the difference of two successive scans for the regions of 60×60mm in a few seconds with 200×200 resolution. Similarly, the retina is illuminated with a diode laser spot through a retinal camera and the speckle field at the image plane of the spot is scanned by a CCD camera. More than 100 frames of the speckle image are captured by a PC and the square blur rate of the intensity variation at each pixel point is evaluated.. The results are displayed successively on 2-D color maps which allows real-time observation of retinal blood flow. Various applications of these versions are also demonstrated.

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