Mitsunori Nishizawa

A Clinical Tissue Oximeter Using NIR Time-Resolved Spectroscopy.

The tNIRS-1, a new clinical tissue oximeter using NIR time-resolved spectroscopy (TRS), has been developed. The tNIRS-1 measures oxygenated, deoxygenated and total hemoglobin and oxygen saturation in living tissues. Two-channel TRS measurements are obtained using pulsed laser diodes (LD) at three wavelengths, multi-pixel photon counters (MPPC) for light detection, and time-to-digital converters (TDC) for time-of-flight photon measurements. Incorporating advanced semiconductor devices helped to make the design of this small-size, low-cost and low-power TRS instrument possible. In order to evaluate the correctness and reproducibility of measurement data obtained with the tNIRS-1, a study using blood phantoms and healthy volunteers was conducted to compare data obtained from a conventional SRS device and data from an earlier TRS system designed for research purposes. The results of the study confirmed the correctness and reproducibility of measurement data obtained with the tNIRS-1. Clinical evaluations conducted in several hospitals demonstrated a high level of usability in clinical situations and confirmed the efficacy of measurement data obtained with the tNIRS-1.

New femtosecond streak camera with temporal resolution of 180 fs

We describe a new design and measure data of a femtosecond streak camera with an electromagnetic focusing type streak tube. In order to reduce the temporal dispersion of photoelectrons in the streak tube, an acceleration electric field near the photocathode was achieved to 8.75 kV/mm applying a high voltage pulse to the dc biased-photocathode. We have developed a high speed deflection circuit and a Meander-type traveling wave deflector, and obtained high sweep speed of 8.76 X 108 m/s on the phosphor screen. A measured data of 180 fs was obtained with 100 photoelectrons using colliding-pulse passively modelocked ring dye laser for the light source. Dynamic ranges of 10 and 20 were achieved at the temporal resolutions of 200 fs and 330 fs, respectively.

New femtosecond streak camera

This paper presents a new design and measured data of a femtosecond streak camera. In order to reduce the temporal dispersion of photoelectrons in the new streak tube, an acceleration electric field near the photocathode was achieved to 8.75 kV/mm applying a high voltage pulse to the dc biased-photocathode. We have developed a high speed deflection circuit and a meander-type traveling wave deflector, and obtained high sweep speed of 8.76 X 108 m/s on the phosphor screen. A temporal resolution of 180 fs was obtained with 100 photoelectrons using colliding-pulse passively modelocked ring dye laser for the light source. Dynamic ranges of 10 and 20 were achieved at the temporal resolutions of 200 fs and 330 fs, respectively.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Femtosecond synchroscan streak tube

A femtosecond synchroscan streak tube has been developed. In order to achieve femtosecond time resolution, the following conditions were adopted in the tube design: high electric field application near the photocathode, high positive voltage application to the focusing electrode to reduce photoelectron transit time spread in the focusing region, and setting the anode electric potential as low as possible to obtain a very high deflection sensitivity for sweep due to low photoelectron drift velocity between the anode and the sweeping screen. The electrode structure and the applied voltages were designed by computer simulation of electron trajectory, and the theoretical time resolution obtained is ~520 fs. Based on the above design parameters, a prototype tube was fabricated and evaluated. A time resolution of ~660 fs was experimentally obtained at the synchroscan frequency of ~80 MHz.

Tissue spectroscopy with a newly developed phase modulation system based on the microscopic Beer-Lambert law

We have developed a phase and intensity-modulated spectroscopy system (PMS) using a newly developed algorithm based on the microscopic Beer-Lambert law. Experiments with phantoms and the human body demonstrate the feasibility and reliability of the system as well as the new algorithm. Our goal is to develop compact, cost-effective, highly reliable, and user-friendly medical equipment for the quantitative monitoring of oxygen metabolism, and so on. The PMS system consists of three time-shared wavelength laser diodes with a 70MHz modulation frequency as sources and a 3mm diameter silicon PIN photodiode as a detector with an in-phase quadrature demodulator (IQD) for AC amplitude and phase detection. The PIN photodiode is operated at a low voltage and is durable against strong extraneous light. In addition, a specially designed low-noise amplifier is achieve a high S/N and reliable measurement. Our algorithm is independent of boundary conditions, exterior shape, scattering properties of the medium, and optode separation for measurement. We can therefore quantify the absolute concentration for oxy- deoxy-hemoglobin and hemoglobin saturation in living tissue of various shapes precisely.

Femtosecond streak tube

A new magnetic focusing streak tube with a traveling wave deflection electrode has been developed. In the operation, a pulse voltage is applied between the photocathode and the accelerating mesh electrode. The limiting time resolution of approximately 180 fs has been experimentally obtained.