The motion of pseudo-sputum (20% solution of mucin) on a vibrating plate has been investigated using a function generator and an amplifier. Many finger-like liquid columns have appeared at appropriate frequencies (100-130 Hz) from a droplet of the solution on a vibrating plate. The viscosity of the mucin solution was measured using a capillary viscometer of the Maron-Krieger-Sisko type, and it was shown that the shear-thinning viscosity occurred in the lower frequency region contrary to the fact that the most abnormal viscosity of the rheological dilatancy fluid emerges in higher frequency than the frequency in which it behaves the normal one; the most important mechanical cause of this soliton-like phenomenon or the emergence of fingerlike column and wrinkles on the surface of fluid is thought to be the rheological dilatancy (shearthickening viscosity) of source liquid. In connection with this vibrating liquid column phenomenon, the spectrums of productive cough were also investigated, and it was proved that the effective low frequency vibration, which is a characteristic spectrum of productive cough, is essential for the expectoration and is a similar mechanism to the above-mentioned pug mechanism of the finger-like liquid columns seen on the vibrating plate.

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Phase mutual information as a similarity measure has been demonstrated to perform comparably to an intensity method even when there is no strong intensity relationship between images. The estimation of local phase is significantly affected by the choice of bandpass filter and its parameter selection. The effect of the parameter selection of Log-Gabor filter on local phase estimation and performance of registration has been studied. The Log-Gabor filter is mainly constructed using two parameters, the center frequency ω₀, and bandwidth B. Forty-two different transformations for magnetic resonance imaging (MRI) and simulated positron emission tomography (PET) data were used in this study, with mean and standard deviation of the distance between the gold standard position and the computed position taken as an error measure. The results showed that there was a tendency for wider B to be required to generate clear phase images with increasing of ω₀. However, wider B could not improve the performance of registration for a certain ω₀. Parameters (ω₀, B) with the values of (0.1,3) are recommended to obtain optimum performance. There were no large differences in the registration errors among noise levels of 5%,10%,15% and 20%, suggesting that phase-based registration is robust against noise. When using the Log-Gabor filter with parameters (ω₀, B) of (0.1,3), the registration errors were always smaller than those in intensity-based registration for both cases with intensity non-uniformity in MRI of 20% and 40%. These results suggest that phase-based registration can be used as an alternative to intensity-based registration even in intensity non-uniform MRI.

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To establish traceability of absorbed dose to water, a cobalt calibration coefficient is transferred to a reference ionization chamber by the standard dosimetry laboratory in the radiotherapy field. In Japan, the calibration is done against a set of an ionization chamber and an electrometer as system. Nowadays, solely electrometer calibration ^ desirable ^ measure absorbed dose witah. more than one combination of ionization chamber and electrometer. Unfortunately, there is no domestic electrometer calibration service for nano-ampere range appropriate for ionization curr e n measurement in the radiotherapy field. In this report, a relative electrometer calibration factor was determined by comparison between a calibrated combination and a non-calibrated electrometer under identical irradiation conditions at the user site. To estimate uncertainties of user electrometer calibration, comparison was made betw en calibration factor obtained by ionization current under a linac photon beam and DC current with a precision DC source instrument. It was found thatthe variation of electrometer readings to pulse ionization current is negligible under the steady photon beam output and dose monitor system. Therefore relative electrometer calibration under identical irradiation conditions at the user site was judged valid until a domestic nano-ampere electrometer calibration service becomes available.

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We developed a system for measuring the wall shear stress (WSS) in blood vessels using magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). The time-dependent velocity at the center of the blood vessel was measured by phase-contrast MRI and was approximated by finite Fourier series, which was used for generating the velocity profile at the inlet for the boundary condition to the CFD method. To validate the CFD method, we compared the WSS obtained by the CFD method with the theoretical value in a straight cylinder with vari ous radii for both steady and pulsatile flows. We also investigated the dependence of the WSS on the inlet velocity profile incorporated into the CFD method. For steady flow, there was a good agreement between the WSS obtained by the CFD method and the theoretical value. For pulsatile flow, there was a relatively good agreement between them when the radius of the cylinder was 2.5 mm and the inlet velocity profile was given by the Womersley solution for fully developed pulsatile flow in a straight circular cylinder. When the radius of the cylinder was 5 mm and/or the inlet velocity profile was assumed to be parabolic, large differences were observed between them, suggesting that the assumption of fully developed flow does not hold true in these cases. In human studies, the vortex due to the secondary blood flow in the carotid arterial sinus was clearly observed. The WSS in the bifurcation was the highest, while that in the carotid arterial sinus was the smallest. In conclusion, the system presented here appears to be useful for measuring the WSS in blood vessels and for analyzing the cause and/or extent of atherosclerosis, and our results suggest that the inlet velocity profile should be carefully considered.

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