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.

Dual-energy computed tomography (DE-CT) is the promising technology, such as enabling material decomposition, generation of the virtual monochromatic image, and measurement of effective atomic numbers. There are reports that utilization of the virtual non-contrast (VNC) image, the iodine map image, and the virtual monochromatic image can contribute to the improvement of lesion detection and its characterization, compared with conventional contrast CT by single-energy computed tomography (SE-CT). In addition, acquisition of the VNC images makes it possible to skip scanning of true non-contrast CT, which is also expected to reduce exposure. However, a reliable evaluation of the accuracy of the VNC image has not been established, and only a few reports have verified their accuracy. In this study, we evaluated the relationship between the quantitativeness of iodine and the CT value of VNC image. As a result of our study, when the iodine volume was overestimated, the CT value of the VNC image was lower than the reference value, and when the iodine volume was underestimated, the CT value was upper than the reference value. Moreover, we clarified that the CT value of the VNC image greatly diverges as the iodine volume increases.

Purpose: The purpose of this study was to assess the feasibility of high-speed CT technology for head without deterioration of low-contrast detectability using the brain LCD (Canon Medical Systems) of iterative reconstruction. Methods: System performance (SP) function analysis, low-contrast object specific contrast-to-noise ratio (CNR_LO) analysis, and visual evaluation using Scheffe’s paired comparison were performed. Additionally, analysis of the correlation of CNR_LO and visual scores was performed. SP was performed with the self-made phantom. CNR_LO was calculated with the catphan 504 phantom (CTP 515). Visual evaluation was performed using the brain phantom which simulated such as cerebral infarction and investigated on a fivepoint scale. All images were acquired with pitch factor of 0.61 (low pitch) and 1.40 (high pitch). All images were reconstructed with filtered back projection (FBP), brain LCD standard (LCD STD) and strong (LCD STR). Results: SP of brain LCD improved compared with FBP. CNR_LO of FBP decreased in high pitch compared with low pitch. CNR_LO of brain LCD images acquired by low- and high pitch were improved compared with FBP. Visual scores denoted similar trends to that of CNR_LO and there was high correlation with CNR_LO. Conclusion: It was suggested that using brain LCD can achieve the high speed CT technology for head without deterioration of low-contrast detectability.

To optimize the radiation protection of patients, we investigated the possibility of constructing the diagnostic reference levels (DRLs) by imaging objective/disease group using display value of the blood vessel imaging apparatus (air kerma-area product: P_KA, air kerma at the patient entrance reference point: K_{a, r}) in cerebral angiography. We used P_KA and K_{a, r} recorded during surgery of 997 patients at our hospital, and classified them according to the purpose of imaging (diagnostic cerebral angiography or neuro interventional radiology) and disease group. Neuro interventional radiology (P_KA: 268±155 Gy・cm², K_{a, r}: 2420±1462 mGy) was significantly higher than that of diagnostic cerebral angiography (P_KA: 161±70 Gy・cm², K_{a, r}: 1112±485 mGy), (Mann-Whitney test, P<0.01). Significant difference was found between P_KA and K_{a, r} for imaging purpose and disease group (Kruskal-Wallis test, P<0.05). It is highly probable that the DRL for cerebral angiography can be constructed by imaging purpose/disease group using display value (P_KA, K_{a, r}) of the blood vessel imaging apparatus.