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The purpose of this study was to investigate an influence of vibration waveform on magnetic resonance elastography (MRE). MRE is an innovative imaging technique for the non-invasive quantification of the elasticity of soft tissues through the direct visualization of propagating shear waves in vivo using a special phase-contrast magnetic resonance imaging sequence. Since the elasticity of soft tissue calculates from the wavelength of propagating shear waves, it is necessary to propagate sine-wave-shape shear wave at the target soft tissue. However, due to the various factors; i.e. overload of vibration generator, poor contact between imaging object and vibration pad, etc.; it may be difficult to generate a simple sine wave. This work was focused on change vibration waveforms; i.e. square wave, triangle wave, saw-tooth wave; which is induced by the various factors. Phantom experimental results demonstrated that when square and saw-tooth waveforms of 25 Hz vibration frequency, into the phantom, the waveform of propagating wave was not similar to sine waveform. It may influence on the MRE that in case of the waveforms has low frequency and square or saw-tooth like waveforms.

For security, boards containing lead are commonly used to partition off rooms adjacent to radiation facilities. From the viewpoints of environmental safety and of material recycling during the process of remodeling or repair, however, the trend is toward avoiding the use of lead-containing radiation-protection board. Consequently, we developed a lead-free board(W 910xH 1820xD 12.5 mm)composed of a mixed material incorporating calcium sulfate and barium sulfate to be used as a partition at a diagnostic X-ray institution. The mass attenuation coefficients of the lead-free board were lower by about 12% and 60% for energy ranges of 25 approximately 37 keV and 38 approximately 41 keV, respectively, as compared with those of lead. Lead equivalents for the newly developed board(12.5 mm thickness)were 0.87+/-0.01 mmPb at 100 kV tube voltage, 0.60+/-0.01 at 125 kV, and 0.47+/-0.01 at 150 kV. A double-layer lead-free board proved to have enough shielding ability even at usual photographic frequencies.