Takao Jibiki

Development and feasibility study of a two-dimensional ultrasonic-measurement-integrated blood flow analysis system for hemodynamics in carotid arteries

Prevention and early detection of atherosclerosis are critical for protection against subsequent circulatory disease. In this study, an automated two-dimensional ultrasonic-measurement-integrated (2D-UMI) blood flow analysis system for clinical diagnosis was developed, and the feasibility of the system for hemodynamic analysis in a carotid artery was revealed. The system automatically generated a 2D computational domain based on ultrasound color Doppler imaging and performed a UMI simulation of blood flow field to visualize hemodynamics in the domain. In the UMI simulation, compensation of errors was applied by adding feedback signals proportional to the differences between Doppler velocities by measurement and computation while automatically estimating the cross-sectional average inflow velocity. The necessity of adjustment of the feedback gain was examined by analyzing blood flow in five carotid arteries: three healthy, one sclerosed, and one stenosed. The same feedback gain was generally applicable for the 2D-UMI simulation in all carotid arteries, depending on target variables. Thus, the present system was shown to be versatile in the sense that the parameter is patient independent. Moreover, the possibility of a new diagnostic method based on the hemodynamic information obtained by the 2D-UMI simulation, such as a waveform of the cross-sectional average inflow velocity and wall shear stress distributions, was suggested.

Investigation of twinkling artifact by controlling oscillating disturbance

Twinkling artifact (TA) is a phenomenon that rapidly alternating color pixels behind a stationary strongly reflecting medium where a comet tail artifact is expected in Doppler mode. Although this phenomenon has a potential in clinical diagnosis for example early detection of microcalcification in dense breast, the occurrence mechanism has not been clarified yet. There have been several hypotheses for underlying mechanism of this phenomenon: surface roughness of calcification, phase jitter noise of the ultrasound machine, and oscillation of reflecting medium. In this study, in-vitro experiments were conducted, and the effects of the oscillating disturbance on a microcalcification embedded in soft tissue were investigated. A transparent poly (vinyl alcohol) hydro (PVA-H) gel with 7 wt% concentration and graphite power with 7 wt% concentration were used. Glass beads were embedded in the phantom. Each diameter is approximately 569 and 213 μm, respectively. All scanning were performed using a medical ultrasound machine (LOGIQ S8 pilot unit, GE Healthcare) with a linear array probe (ML6-15, GE Healthcare). The probe and the phantom were fixed in several ways for the purpose of determining the factor of the TA. As results, when the probe and the phantom were fixed with a stage and the stage was placed on the same table with the ultrasound machine, the twinkling artifact appeared, and stable Doppler shift components appeared in the peak values of the amplitude of successive I/Q signals. When the stage was isolated from the external disturbance including the US machine, the twinkling artifact and Doppler shift components were suppressed. Suppression of the twinkling artifact by control of oscillating environment demonstrated that the twinkling artifact generates from variability among the acoustic signals, not phase jitter or surface roughness of microcalcification. Furthermore, the variability was caused by acoustical oscillation with the speaker.