Abstract not available.

The implementation of time-resolved reflectance, R(t), measurements via endoscopes during medical procedures may provide an important diagnostic tool for medicine. This paper presents initial studies on a prototype catheter device suitable for the biopsy channel of an endoscope. A pair of optical fibers, one a source and one a collector, were adjoined with epoxy to create a single catheter tip. Such close proximity of two fibers is a special case of the generic R(r,t) measurement, where the fiber separation (r) approaches zero. The influence of an air/tissue surface boundary on the time-resolved collection of photons backscattered by a turbid media is presented. The catheter was either (1) place on the surface of an aqueous turbid solution, or (2) imbedded deep within the volume and distant from the surface or any boundaries. The time course of photon collection was found to be strongly influenced by the surface boundary. Such boundary effects are pertinent to the design of time-resolved catheters which require close spacing of the source and collector fibers.

Several schemes for using time-resolved spectroscopy to determine changes in optical absorbance of a composite media are discussed. Mathematical division of measured transit-time probabilities yields a difference signal whose logarithmic decay is observable over an extended time range. This signal can be used to obtain reliable estimates of the absolute value of a change in the optical absorption of a sample. In homogeneous media, a ratio of absorbances can be determined from the ratio of the mean values of the transit-time distributions. A three optode detection system may improve the accuracy of detected absorption changes when composite media are examined.

We have investigated the effect of an absorbing object on the time- course and the migration paths of photons within a highly scattering cylindrical phantom. Experimentally, we injected photons into the phantom at one point on the circumference, and recorded the time course of the photons arriving at various detection positions round the cylinder. The simulations used both a Monte-Carlo approach and a diffusion approach to calculate the photon migration. The two computational approaches are similar. The calculated time-course signals agree well with the experimentally observed signals. Moreover, we are able to use a diffusion approximation to calculate the probable paths taken for photons which take a defined time to travel from source to detector.

When a picosecond light pulse is incident on an optically turbid medium such as tissue, the temporal distribution of diffusely reflected and transmitted photons depends on the optical absorption and scattering properties of the medium. From diffusion theory it is possible to derive analytic expressions for the pulse shape in terms of the optical interaction coefficients of a homogeneous semi-infinite medium. Experimental tests of this model in tissue-simulating liquid phantoms of different geometries are presented here.

Several measurement and analysis schemes have been explored, using simulated data, in an effort to identify new strategies for the determination of the macroscopic optical properties of multilayer random media. Several simple algorithms are described which are capable of identifying the values of important parameters such as the total cross- section, (summation)t, the ratio of the absorption to total-cross section, (summation)a/(summation)t, and depth of subsurface boundaries in two- and three- layer media. The albedo values of the media varied for 0.9 to 0.99 and the superficial layer had an absorptivity either greater or less than the subsurface layers. A novel feature of the algorithms is a comparison of the responses of coupled pairs of detectors. Their utility stems from the fact that variations in the orientation and location of collimated detectors permit the selective interrogation of subsurface regions in dense scattering media.

Laser Doppler velocimetry provides a method for non invasive measurements of the perfusion of tissue. Therefore the tissue is illuminated with a monochromatic light source and back scattered light from the tissue is collected at a detector at an adjacent site. Some of the back scattered photons have had interaction with moving red blood cells and are frequency shifted. Due to interference of frequency shifted and non-frequency shifted photons the intensity at the detector fluctuates. These fluctuations provide the information from which a rate for the perfusion can be derived. In this paper we present perfusion measurements and Monte Carlo (MC) simulations on both a scale model and human skin tissue. The Monte Carlo results are used to quantify the size and position of the probe volume. Three different ways are presented to vary the size and position of the probe volume.

Simulation of optical-CT imaging has been conducted using the Monte Carlo method to generate projection data for filtered back projection. A reference cylinder of 10 mm diameter is filled with an uniformly scattering medium, and an object cylinder filled with the same scattering medium as the reference has an inner coaxial cylindrical portion with weak absorption. The time-resolved transmittances detected on the line of the incidence for object and the reference provide time- resolved data of the difference in the absorbances between the object and the reference. The difference in the absorbances which is temporally extrapolated to the shortest time of flight present projection data for filtered back projection usually used in CT reconstruction. The resulting reconstructed image reflects the difference in the absorption coefficients between the object and the reference with a satisfactory spatial resolution and accuracy.

The use of time- and frequency-domain spectroscopy for the detection of brain oxygenation and the localization of tissue regions exhibiting brain-bleeding has been suggested recently by Chance and coworkers. In this study, we explore the effect of the skull (with minimal absorbance and greater scattering properties) upon measurements of photon migration within the underlying brain tissue (of comparatively greater absorbance and smaller scattering properties). Using the diffusion approximation to understand photon migration within the layered medium, we show that the effect of a transmitting layer can be significant, yet may considered negligible at significant source and detector separations in time- and frequency-domain measurements. Using Monte Carlo simulation of photons migrating within a model consisting of (i) a central core ((mu) sb equals 8 cm-1, (mu) ab equals 0) and (ii) an annulus ((mu) ss equals 24 cm-1, (mu) a equals 0), we demonstrate the contribution of an additional 'time-of-flight' to time-domain spectra (TDS) and an additional phase-shift to frequency-domain spectra (FDS) due to the presence of the highly scattering layer. Under conditions of changing absorbance ((mu) ab equals 0 - 0.075 cm-1) in the central core, our results show that the diffusion approximation also provides description of the changes seen in TDS and FDS derived from Monte Carlo simulation. Finally, upon mapping of volumes sampled by the migrating photons, we characterize the capacity for 'light-channelling' within the highly scattering layer as a function of source-detector separation and core absorbance.

Ballistic images of a fish in vivo and a Bar chart behind a piece of 4 mm thickness chicken tissue were measured using a picosecond optical Kerr gate imaging technique.

By the use of the picosecond laser pulse of near-infrared light at 1064 nm, the temporal profile of the transmitted light through the anesthetized rat head has been investigated. The light intensity at a certain time after the input pulse was exponentially attenuated by hemoglobin in the blood, although the transmitted pulse broadened markedly due to scattering of the cerebral tissue. The optical pathlength which is required for the quantitation of the absolute absorbance change, was directly determined by the measurement of time of flight of light pulses, as the product of v and t where v is the velocity of light in water (0.23 mm/ps) and t, time in picosecond. The temporal profiles of transmitted light through the rat head were measured with changing the oxygen concentration in the inspired gas and cerebral venous oxygen saturation of hemoglobin (SvO2) were obtained quantitatively in the various conditions. The SvO2 values obtained from the time of flight measurement agreed with those of gas analysis of blood withdrawn from the internal jugular vein. Thus, the picosecond laser pulse technique is essential to quantify SvO2.

We demonstrate a time-gated technique to reduce the effect of light scattering when transilluminating turbid media such as tissue. The concept is based on transillumination with picosecond laser pulses and time-resolved detection. By detecting only the photons with the shortest travelling time, and thus the least scattered photons, the contrast can be enhanced. Measurements on a tissue phantom as well as breast tissue in vitro are presented. It is demonstrated that differences in scattering properties may be more pronounced than differences in absorption properties when demarcating tumor from normal tissue.

Light propagation in turbid media can be described by photon diffusion. In the frequency domain, sinusoidally intensity-modulated light gives rise to diffusive waves which have a coherent front. In a homogeneous medium, the wave front propagates with a constant phase velocity and the amplitude attenuates exponentially as the diffusional wave advances. We have studied the diffusion approximation to the one-speed linear transport equation with a sinusoidally intensity modulated point source of particles and performed experiments using frequency domain detection methods on homogeneous scattering and absorbing media to test the applicability of the above mentioned transport equation to photon migration in turbid media. We have used the analytical solutions of the linear transport equation in homogeneous, infinite media to determine via a simple analysis of our frequency domain data the linear scattering and absorption coefficients.

Previously, we have shown that time-resolved spectroscopy can monitor changes in the distribution of photon migration pathlengths which are reflective of the changes in the tissue absorption due primarily to oxygenated or deoxygenated hemoglobin. In this study, we have monitored mean photon migration pathlengths in the frequency domain in the rodent brain insulted by hypoxia, ischemia and spreading depression (SD) using phase modulated spectroscopy (PMS). This technique consisted of monitoring light which emerged from the exposed rodent skull at 8 mm form an incident light source of 754 nm and 816 nm whose intensity was modulated at 220 MHz. The changes in phase-shift, (theta), of the emergent light with respect to the incident light are reflective of the photon pathlengths and hemoglobin absorbance. A multiprobe assembly holding PMS source fiber, nicotinamide dinucleotide (NADH) fluorometric probe, electrocortigraph (ECoG) electrodes, and doppler blood flow probe was placed on the rodent brain to simultaneously monitor brain metabolism, electrical cortical activity (ECoG) and blood flow. The PMS detector fiber was placed 8 mm posterior to the multiprobe assembly. Correlations between changes in intracellular deoxygenation (NADH) and hemoglobin deoxygenation as measured by PMS changes at 754 nm and 816 nm during hypoxia, and ischemia were found. The depolarization phase of spreading depression resulted in a similar increase at both 754 nm and 816 nm. We attribute this result to vasoconstriction and/or the decrease of extracellular space due to water shift in the rodent brain.

We report on time-resolved reflectance imaging experiments on a scattering medium containing a spatially limited absorber. The medium is illuminated at two positions with pulses from a mode-locked and cavity dumped picosecond dye laser. Time-resolved imaging of the back-scattered light is realized by means of a RF-phase-sensitive camera, synchronized to the laser pulses. The camera consists of a sinusoidally modulated proximity-focused image intensifier, a thermo-electrically cooled CCD camera, and a digital image processor unit. In operation, at least two images are taken under different image intensifier modulation conditions, such as modulation phase or modulation degree. By processing the stored images, a final image can be created the contrast of which is based only on time differences of the back-scattered photons. We found that this image reveals the presence and, to a certain extent, the position of a spatially limited absorber within the scattering medium. These experiments have been performed to evaluate possible ways towards an eventual optical tomography in living tissue.

Optical path lengths of photon migration in tissue can be determined directly by pulse-time measurement. This makes it possible to quantify tissue hemoglobin concentrations. However, the bulky and expensive solid state/liquid dye laser system is unsuitable for clinical studies. Thus, the design of an efficient phase modulation technology simplifies the methodology and offers continuous reading of tissue photon propagation in tissue. This report describes a 200 MHz time shared Dual Wavelength Phase modulation system, which measures the essential characteristic of light propagation in the body tissues. This system has slow drift over the 7.5 hour period has maximum of 0.04 degree(s)/hr. The noise peak to peak corresponds to 0.9 mm. Noise is maximum when the separation between transmitter and detector is 5 cm in Intralipid solution, with high voltage at 850 v. Applications of the noninvasive devices include measurement of hemoglobin deoxygenation in brain and hemoglobin and myoglobin deoxygenation in human skeletal muscle and animal models. Numerous applications to medical and biological problems now become available.

We report here a method for measuring and eliminating artifacts caused by background in fluorescence lifetime or rotational correlation data using multiharmonic Fourier transform frequency domain fluorometry. A single measurement on a blank yields phase and amplitude values for multiple modulation frequencies simultaneously, and these may then be used to correct the sample's data. Experimental results demonstrate the applicability of the method over a wide range of background contributions.

Optical imaging of in vivo tissue and noninvasive optical assessment of deep tissue requires knowledge concerning photon migration paths in the medium. We used intralipid emulsion as a phantom medium to study the distribution of the migration paths. An incident and receiving optical fibers were placed on the medium surface. Light at 760 nm was used. An absorber was placed in the medium at different locations to intersect different photon paths. The study shows that the incident photons migrate to the detector through the paths distributed in a region shaped a 'banana', with its two end connecting the source and detector and it mid portion reaching deepest. This region has a core connecting the source and detector through which the photons have maximum probability to take. The path distribution in depth across the mid portion of the 'banana' and through the core can be described by a random walk model, with its maximum probability at a certain depth below the surface. In this study, this maximum probability depth ranged from 3 millimeters to about 7 or 8 millimeters. The path distribution across the mid portion of the 'banana' horizontally and through the core can be described by a normal probability function. These distributions are affected by the optical properties of the medium and the source-detector separation. This study indicated the capability of using surface optical measurement to image the optical property distribution of in vivo tissue and to assess deep tissue optical properties.

The ability to selectively probe a random medium, even in the limit of isotropic scattering, suggests it should be possible to reconstruct images of a dense scattering medium from the information contained in the backscatter surface emission profile. Consideration of the imaging problem also requires knowledge of the impact that localized absorption at any site in the medium would have on the response of detectors at the surface. By applying the concept of importance used in reactor theory, we have calculated this relationship for various homogeneous media. This information was subsequently incorporated into several image reconstruction algorithms which employ a backprojection strategy. The algorithms were tested by applying them to simulated surface emission profile data for homogeneous scattering media with embedded arrays of black-body absorbers. The algorithms correctly identified the size and location of the arrays, resolved internal structural features, and showed significant improvement upon iteration.

In infrared absorption imaging, the requirement is to reconstruct the spatial distribution of the optical absorption coefficient, from boundary measurements of the flux intensity of light arising from a specific source distribution. An accurate and efficient model is required to simulate data for given experimental conditions and for any hypothesized solution (the Forward Problem). The Inverse Problem is then to derive the solution that best fits the data, subject to constraints imposed by a priori knowledge (e.g. positivity). The Forward Problem is denoted (chi) equals A(mu) + n where (mu) is the required functional map, (chi) the boundary data, A the Forward Transform and n noise, and the Inverse Problem is (mu) equals A+(chi) , where A+ is an approximation to the Inverse Transform. The experimental arrangement modelled assumes an inhomogeneous cylindrical object. A picosecond dye laser produces input pulses at N locations and a time resolved detector makes measurements at N output sites. This (chi) is an N2 by 1 vector and (mu) can be reconstructed to, at best, an N by N image. The Forward Model described here is an analytic approach using the Greens Function of the diffusion equation in a cylinder, (the P1 approximation to the radiative transfer equation). It may be parameterized by the global values of absorption and scattering coefficients ((mu) a, and (mu) s), which have to be adjusted to best fit the data. The Inverse Problem is highly ill-posed. To solve it, we use the Moore-Penrose generalized inverse A+ equals (A*A)-1A*, and two simple regularization techniques: truncated singular value reconstruction and Tikhovov regularization. Examination of the singular vectors of the kernel demonstrate that the solution is dominated by surface effects, unless a very high signal-to-noise ratio is obtained in the data. Results are shown for simulated mathematical phantoms and a tissue-equivalent phantom composed of polystyrene microspheres.

A Zeiss laser scanning microscope was fitted with a high powered Argon ion laser (10 W) which provided wavelengths in the following regions: 364 nm (multiline), 488 nm and 514 nm. A Zeiss water object of 40X, NA. 0.6, corrected for the UV was used to measure the fluorescence from optical sections of a freshly enucleated rabbit eye. The resolution in the transverse direction was about 0.5 micron and the range resolution was about 0.7 micron at 366 nm wavelengths. The confocal microscope was used in both the reflected mode and the confocal mode to image the endothelial cells of the enucleated eye. Reflected light images were obtained at all wavelengths from the argon laser, and also from the HeNe laser line at 633 nm was used to image the cells in reflected light. The same fields of cells were imaged in fluorescence light. The wavelengths of excitation of 366 nm for the excitation and 400-500 for the emission were used to image the pyridine nucleotides. The reduced pyridine nucleotides are suitable chromophores for the evaluation of cellular hypoxia in the living eye. This paper demonstrated the feasibility of two dimensional fluorescent imaging of the reduced pyridine nucleotides in the corneal endothelial cells. The confocal image was made through 400 microns of corneal tissue.

Preliminary results are presented of a study of the spatial resolution performance of a system which produces transmission images of highly scattering objects by recording and discriminating between the times-of- flight of transmitted photons. This system is being developed as a possible means of screening for breast cancer using harmless doses of visible or near-infrared radiation.

We propose a new method for reconstructing parameters of physiological interest within tissue. The novel aspect of this work is that we set out to determine not only the attenuation distribution but also the scattering characteristics of the unknown object. The model we propose contains, as a limiting case, the standard problem of X-ray tomography. In that case scattering (or diffusion) is usually ignored, and one only deals with straight paths between sources and detectors. The considerable increase in mathematical difficulty brought about by considering an unknown scattering distribution as part of the inversion problem is amply justified by the fact that at low energies - like those of an infrared laser - diffusion cannot be ignored. Numerical simulations based on a discretization of the appropriate equation describing the transport of photons through the medium are very encouraging.

This paper reports the study on dynamic speckle phenomena observed in the light fields scattered from living objects. The laser speckles produced from living objects are called 'bio-speckles' and fluctuate temporally due to various physiological movements. Time-varying properties of bio-speckles are experimentally investigated from the analyses of spectral powers and autocorrelation functions. Based on the knowledge of dynamic bio-speckles, some methods are also introduced for evaluating the blood flows in the skin surface, gastric mucous membrane, and human retina.

In the brain of the adult rat, the ratio of the absorption coefficient of hemoglobin to that of the cytochromes is approximately ten and in the newborn rat brain the ratio is even higher. Additionally the absorption spectra of these compounds overlap markedly. Under these circumstances the accurate determination of cytochrome concentration is difficult. There are many possible sources of error: (i) Non linear measuring equipment. (ii) Inaccurate hemoglobin and cytochrome spectra. (iii) A wavelength dependent effective optical pathlength. (iv) An absorption coefficient dependent effective optical pathlength. (v) Oxygenation dependent changes in tissue scattering. The first two sources of error can be solved with careful instrumental and experimental design. The last three are much more problematic, but can be addressed using time resolved measurements. These are the topic of this paper. A wavelength dependence of the optical pathlength leads to a distortion of the optical spectra of the chromophores in brain tissue. A simple method of examining the wavelength dependant effects is discussed. The selection of the correct wavelength range is important in minimizing these problems. Until recently, all near infrared data processing 'algorithms' have assumed a linear Beer Lambert relationship between the measured attenuation spectra and tissue absorption coefficient. However, picosecond optical techniques have shown that at a single wavelength, the optical pathlength in the rat brain can vary by 10% implying that the Beer Lambert law is not strictly valid. A non linear correction of tissue spectra which can be based on results from time of flight measurements is described.

Previously, Chance and coworkers have demonstrated the use of time- resolved spectroscopy to detect changes in deoxy- and oxy-hemoglobin concentrations in brain, muscle, and tumors. In this study, we examine the potential to quantitate hemoglobin saturation and tissue oxygenation from steady-state, dual-wavelength measurements in the frequency domain. Frequency-resolved spectroscopy depends upon monitoring light which emerges a known distance away from an incident light beam whose intensity is sinusoidally modulated. The phase-shift, (theta), of the emergent light with respect to the incident light is related to the light pathlengths traveled due to the scattering and absorption properties of the homogeneous medium. Using the diffusion approximation to describe the transport of photons through a highly scattering medium, we demonstrate the ability to detect changes in absorption and scattering properties from measurements of (theta) in model system if Intralipid/India ink and polystyrene microsphere suspensions using phase modulation spectroscopy. In addition, from measurements of (theta) at wavelengths that straddle the isosbestic point of hemoglobin, we demonstrate the ability to quantitatively follow changes in of absorption properties due to oxy- and deoxy- hemoglobin in an Intralipid/hemoglobin model. The advantages of using phase-modulation spectroscopy as an analytical tool in the clinic as well as the remaining problems associated with its use are discussed.

Human forearm oxygenation and scattering changes during ischemia were investigated using picosecond near infrared laser spectroscopy. Path lengths were calculated for different geometries. At 760 nm, a plateau phaser was reached after 4 min occlusion. No changes were observed during the occlusion at 800 nm, the hemoglobin isosbetic wavelength. Time-resolved Monte Carlo simulations were performed also to mimic the propagation of a light pulse in a forearm phantom containing different quantity and size of polystyrene spheres as scattering media. The influence of both the scattering and absorption effects was studied.

Using a near infrared (NIR) spectrophotometry, a compact instrument for monitoring the hemoglobin (Hb) oxygenation state in human brain was developed. Brian oxygen metabolism was non-invasively studied by simultaneous measurement of oxygenated Hb, deoxygnated Hb and total Hb content in rat and human head. After evaluating our method using anesthetized and artificially ventilated rats, this instrument was applied for clinical use, and was useful for the management of clinical patients. The same method was applied to develope the NIR computed tomography (CT). Human X-ray CT was modified for NIR-CT, and CT images were obtained using the back-projection (BP) method. NIR-CT could measure the oxygenation map of the tissues of anesthetized rats.

Noninvasive diffuse IR transmission spectroscopy is used to measure the attenuation of hemoglobin in the human cerebrovasculature. Experimental data demonstrating the intracranial, cerebrovascular source of the IR signal is presented. An algorithm to quantify per-cent hemoglobin oxygen saturation in the brain from these transmission spectra is outlined. The spectroscopic cerebrovascular hemoglobin saturation measured correlates well with the best clinical reference measurement of brain hemoglobin saturation (n equals 68, r equals 0.74, s equals 3.5), and IR spectroscopy is more sensitive to reduced brain oxygen than analogue or processed electroencephalography (EEG) data (p < .05).

Monitoring of brain functions during neurosurgical conditions have been made by various groups of investigators. Attempts were made to monitor EEG or evoked potentials, cerebral blood flow, mitochondrial redox state during various neurosurgical procedures. In order to monitor various functions of the brain we have developed a new multiprobe (MPA) assembly, based on fiber optic probes and ion selective electrodes, enabling the assessment of relative CBF, mitochondrial redox state (NADH fluorescence) and ion homeostasis in real-time, intraoperatively. The base features of the multiprobe assembly were described previously (A. Mayevsky, J. Appl. Physiol. 54, 740-748, 1983). The multiprobe holder (made of Delarin) contained a bundle of fibers transmitting light to and from the brain as well as 3 ion selective electrodes (K+%/, Ca(superscript 2+, Na+) combined with DC steady potential electrodes (Ag/AgCl). The common part of the light guide contained 2 groups of fibers. For the Laser Doppler flowmetry one input fiber and two output fibers were glued in a triangular shape and connected to the standard commercial plug of the Laser Doppler flowmeter. For the monitoring of NADH redox state 10 excitation and 10 emission fibers were randomly mixed between and around the fibers used for the Laser Doppler flowmetry. This configuration of the fibers enabled us to monitor CBF and NADH redox state from about the same tissue volume. The ion selective electrodes were connected to an Ag/AgCl electrode holders and the entire MPA was protected by a Plexiglass sleeve. Animal experiments were used for the verification of the methods and recording of typical responses to various pathological situations. The entire multiprobe assembly was sterilized by the standard gas sterilization routine and was checked for electrodes integrity and calibration inside the operation room 24 hours later. The MPA was located on the exposed human cortex using a micromanipulator and data collection started immediately after, using a micro computer based data acquisition system. After recording of baseline levels of CBF, NADH redox state and extracellular ion levels, the responses to CBF decrease (occlusions of a blood vessel) were recorded followed by the recovery period. A significant correlation between the CBF and NADH redox state changes was recorded. This approach enabled us to correlate this change in energy supply, to those of extracellular ion concentration. The preliminary results obtained suggest that the usage of the MPA in the operating room may have a significant contribution to the neurosurgeon as a routine diagnostic tool. It seems to us that a simplified MPA which will enable to monitor only the relative CBF, NADH redox state as well as extracellular K+ is more appropriate for future usage.

The cardiac function is exquisitely sensitive to oxygen, because its energy production mainly depends on the oxidative phosphorylation at mitochondria. Thus, oxygenation state of the tissue is critical. Cytochrome a,a3, hemoglobin and myoglobin, which play indispensable role in the oxygen metabolism, have the broad absorption band in near infrared (NIR) region and the light in this region easily penetrates biological tissues. Using NIR spectrophotometry, we attempted to measure the redox state of the copper in cytochrome a,a3 in rat heart through thoracic wall without open chest. The result is given in this paper.

1 ) To enhance spatial resolution of near-infrared (NIR) imaging in vivo, we performed computer-aided refocusing of NIR-projection images of human forearm. Simple inverse, constrained least squares, and Wiener filters were tested as refocusing algorithms. Wiener filter gave the best result in terms of image quality and computation time. By applying Wiener filter, we obtained enhanced spatial resolution. 2) We also examined 2-dimensional visualization of Hb oxygenation state using NIR-projection images of human forearm. Forearm occlusion caused increase in 2-dimensional O.D. at 700 nm, while slight decrease was observed at 800 nm. On the basis of in vitro experiments using RBC suspension and test phantoms, we calculated 2-dimensional changes in Hb oxygenation in the human forearm caused by ischemia. 3) To confirm whether NIR-CT can detect changes in Hb quantity in the living tissues, we reconstructed CT images from NIR-projection data of mouse abdomen measured at 700 and 800 nm. Infusion of physiological saline into the liver caused decrease in gray level in the location of the liver in the CT images (700-800 nm), although uncertain artifacts were observed in the other areas. Although more detailed considerations are required for practical application of this technique, we have obtained NIR-projection and CT images which indicate regional changes in the state of Hb in the living tissues.