Yukio Oikawa

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...

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.

Near-infrared optical imager for cerebral blood flow and oxygenation detection

This paper describes the theory and the apparatus on our newly developed 64 channel optical imager that enables imaging of three components, indocyanine green (ICG), oxyHb and deoxyHb. Knowledge on blood flow is obtainable using ICG as a blood flow indicator that is to be introduced via injection. ICG has a strong absorption at 805nm, therefore the changes in ICG is detectable with NIR spectroscopy separating from oxyHb and deoxyHb using proper three wavelengths. In addition to the system description, it describes an animal experiment and a phantom test for the validation study. It discusses independence features of ICG on Hb values. Using a simple quasi Lambert Beers law, it proved the excellent separation of the three components. It also discusses the factors that affect the performance of signal separation.