Motoki Oda

Visuospatial imagery is a fruitful strategy for the digit span backward task: A study with near-infrared optical tomography.

Our newly developed 64-channel time-resolved optical tomographic imaging system using near-infrared light enables us to obtain a quantitative image of hemoglobin concentration changes associated with neuronal activation in the human brain ¿H. Eda, I. Oda, Y. Ito, Y. Wada, Y. Oikawa, Y. Tsunazawa, M. Takada, Y. Tsuchiya, Y. Yamashita, M. Oda, A. Sassaroll, Y. Yamada, M. Tamura, Multi-channel time-resolved optical tomographic imaging system, Rev. Sci. Instrum., 70 (1999) 3595-3602. Here, we used this optical imaging system to demonstrate that the backward digit span (DB) task activated the dorsolateral prefrontal cortex (DLPFC) of each hemisphere more than the forward digit span (DF) task in healthy adult volunteers, and higher performance of the DB task was closely related to the activation of the right DLPFC. These results suggest that visuospatial imagery is a useful strategy for the DB task. Optical tomography described here is a new modality of neuropsychological studies.

Multichannel time-resolved optical tomographic imaging system

A time-resolved optical imaging system using near-infrared light has been developed. The system had three pulsed light sources and total 64 channels of detection, working simultaneously for acquisition of the time-resolved data of the pulsed light transmitted through scattering media like biological tissues. The light sources were provided by high power picosecond pulsed diode lasers, and optical switches directed one of the light sources to the object through an optical fiber. The light signals reemitted from the surface of the object were collected by optical fibers, and transmitted to a time-resolved detecting system. Each of the detecting channels consisted of an optical attenuator, a fast photomultiplier, and a time-correlated single photon counting circuit which contained a miniaturized constant fraction discriminator/time-to-amplitude converter module, and a signal acquisition unit with an A/D converter. The performance and potentiality of the imaging system have been examined by the image reconstr...

Cerebral hemodynamics evaluation by near-infrared time-resolved spectroscopy: Correlation with simultaneous positron emission tomography measurements

We compared pharmacologically-perturbed hemodynamic parameters (cerebral blood volume; CBV, and flow; CBF) by acetazolamide administration in six healthy human subjects studied with positron emission tomography (PET) and near-infrared (NIR) time-resolved spectroscopy (TRS) simultaneously to investigate whether NIR-TRS could measure in vivo hemodynamics in the brain tissue quantitatively. Simultaneously with the PET measurements, TRS measurements were performed at the forehead with four different optode spacing from 2 cm to 5 cm. Total hemoglobin and oxygen saturation (SO2) measured by TRS significantly increased after administration of acetazolamide at any optode spacing in all subjects. In PET study, CBV and CBF were estimated in the following three volumes of interest (VOIs) determined on magnetic resonance images, VOI1: scalp and skull, VOI2: gray matter region, VOI3: gray and white matter regions. Acetazolamide treatment elevated CBF and CBV significantly in VOI2 and VOI3 but VOI1. TRS-derived CBV was more strongly correlated with PET-derived counterpart in VOI2 and VOI3 when the optode spacing was above 4 cm, although optical signal from cerebral tissue could be caught with any optode spacing. As to increase of the CBV, 4 cm of optode spacing correlated best with VOI2. To support the result of TRS-PET experiment, we also estimated the contribution ratios of intracerebral tissue to observed absorption change based on diffusion theory. The contribution ratios at 4 cm were estimated as follows: 761 nm: 50%, 791 nm: 72%, 836 nm: 70%. These results demonstrated that NIR-TRS with 4 cm of optode spacing could measure cerebral hemodynamic responses optimally and quantitatively.

Near-infrared time-resolved spectroscopy system for tissue oxygenation monitor

We have developed a three-wavelength (759,797, and 833 nm) time-resolved spectroscopy (TRS) system as a tissue oxygenation monitor employing a time-correlated single photon counting method. This system achieved a high data acquisition rate and system miniaturization maintaining a high sensitivity and time resolution. Our system succeeded in accurately measuring concentrations of oxy-(HbO2) and deoxyhemoglobin (Hb) by means of TRS data observation through studies using a phantom model and living tissue.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A simple and novel algorithm for time-resolved multiwavelength oximetry

Using time-resolved spectroscopy, we have developed an experimental approach to obtain the absolute changes in concentration in the scattering medium of living tissues. The time-resolved Beer-Lambert equation can be applied to living tissue due to the fact that the optical attenuation by absorption can be separated from that by scattering, and the intensity of the light along the non-linear scattered optical path is exponentially attenuated by the absorption. Based on the above, the absolute concentration of haemoglobin as well as oxygen saturation in the rat head can be determined in situ under various respiratory conditions where multiwavelength measurements were performed. The optically assessed values agree with those determined directly by the gas analysis of our previous report. The present method is very simple and therefore opens up wide applications for time-resolved spectrophotometry in clinical medicine as a technique for quantitative near-infrared oxygen monitoring.

Variation of temporal characteristics in human cerebral hemodynamic responses to electric median nerve stimulation: a near-infrared spectroscopic study.

Using near-infrared spectroscopy, we studied cerebral hemodynamic responses to electric median nerve stimulation in ten subjects. The recordings were conducted by optical fibers placed over the left scalp. Electric stimuli were delivered to contra- and ipsilateral median nerves, respectively. Hemodynamic responses in the secondary somatosensory cortex were observed following each median nerve stimulation, except for three drowsy subjects. The contralateral stimulation tended to induce a larger response. The degree of change in oxygenated hemoglobin was hardly related to stimulus intensities, and was augmented by attention. Four subjects showed long-lasting responses throughout the stimulus periods, while three other subjects revealed transient responses. Thus, taking account of the temporal activation patterns is necessary for proper interpretation of the hemodynamic response following electric nerve stimulation.

Clinical evaluation of time-resolved spectroscopy by measuring cerebral hemodynamics during cardiopulmonary bypass surgery

We developed a three-wavelength time-resolved spectroscopy (TRS) system, which allows quantitative measurement of hemodynamics within relatively large living tissue. We clinically evaluated this TRS system by monitoring cerebral circulation during cardiopulmonary bypass surgery. Oxyhemoglobin, deoxyhemoglobin, total hemoglobin and oxygen saturation (SO(2)) were determined by TRS on the left forehead attached with an optode spacing of 4 cm. We also simultaneously monitored jugular venous oxygen saturation (SjvO(2)) and arterial blood hematocrit (Hct) using conventional methods. The validity and usefulness of the TRS system were assessed by comparing parameters obtained with the TRS and conventional methods. Although the changes in SO(2) were lower than those in SjvO(2), SO(2) obtained by TRS paralleled the fluctuations in SjvO(2), and a good correlation between these values was observed. The only exceptions occurred during the perfusion period. Moreover, there was a good correlation between tHb and Hct values (r(2)=0.63). We concluded that time-resolved spectroscopy reflected the conditions of cerebral hemodynamics of patients during surgical operations.

Optical imaging of tumor vascularity associated with proliferation and glucose metabolism in early breast cancer: clinical application of total hemoglobin measurements in the breast.

BackgroundNear-infrared optical imaging targeting the intrinsic contrast of tissue hemoglobin has emerged as a promising approach for visualization of vascularity in cancer research. We evaluated the usefulness of diffuse optical spectroscopy using time-resolved spectroscopic (TRS) measurements for functional imaging of primary breast cancer.MethodsFifty-five consecutive TNM stageI/II patients with histologically proven invasive ductal carcinoma and operable breast tumors (<5 cm) who underwent TRS measurements were enrolled. Thirty (54.5%) patients underwent 18F-fluoro-deoxy-glucose (FDG) positron emission tomography with measurement of maximum tumor uptake. TRS was used to obtain oxyhemoglobin, deoxyhemoglobin, and total hemoglobin (tHb) levels from the lesions, surrounding normal tissue, and contralateral normal tissue. Lesions with tHb levels 20% higher than those present in normal tissue were defined as “hotspots,” while others were considered “uniform.” The findings in either tumor type were compared with clinicopathological factors.Results“Hotspot” tumors were significantly larger (P = 0.002) and exhibited significantly more advanced TNM stage (P = 0.01), higher mitotic counts (P = 0.01) and higher levels of FDG uptake (P = 0.0004) compared with “uniform” tumors; however, other pathological variables were not significantly different between the two groups.ConclusionsOptical imaging for determination of tHb levels allowed for measurement of tumor vascularity as a function of proliferation and glucose metabolism, which may be useful for prediction of patient prognosis and potential response to treatment.

Average Value Method: A New Approach to Practical Optical Computed Tomography for a Turbid Medium Such as Human Tissue.

We propose a new algorithm for optical computed tomography to determine the concentrations of absorber in turbid media such as human tissue. Our method does not require the measurement of a reference phantom, so that it is free from significant errors caused by geometric and structural differences between the target and reference media. We use an imaginary reference medium for which the optical properties are specified by the average or quasi-average values measured for the real target medium. Since we can calculate the weight function and re-emission for such an imaginary medium, tomographic images can be reconstructed based on the difference in values measured for the target medium and determined for the imaginary reference. The validity of our method was confirmed by measuring an 80-mm-diameter cylindrical, tissue-like phantom containing three different absorbers. The image quality such as image distortion and the capability for quantifying the concentrations of absorber are also discussed.

Reflectance Diffuse Optical Tomography: Its Application to Human Brain Mapping

We report the successful application of reflectance diffuse optical tomography (DOT) using near-infrared light with the new reconstruction algorithm that we developed to the observation of regional hemodynamic changes in the brain under specific mental tasks. Our results reveal the heterogeneous distribution of oxyhemoglobin and deoxyhemoglobin in the brain, showing complementary images of oxyhemoglobin and deoxyhemoglobin changes in certain regions. We conclude that our reflectance DOT has practical potential for human brain mapping, as well as in the diagnostic imaging of brain diseases.