超高速 MRI に用いる並列多重化電力増幅器と
そのディジタル最適制御系の構築

抄録

In recent years, MRI (Magnetic Resonance Imaging) systems have been actually requested to diagnose the moving parts of a human body such as the heart or the blood in angiography, where images should be taken in milliseconds instead of minutes. The gradient power supplies which are small but vital components for advanced MRI require higher output power capability as well as faster rise/fall dynamic response characteristics under a variety of specified current reference signals.
This paper presents a novel switch-mode gradient power amplifier using IGBTs which is connected in parallel with the conventional 4-switch full-bridge power conversion circuits at their inputs/outputs in order to realize further high-power density. To satisfy the design specifications which require minimized the ripple and improved the rise/fall dynamic response characteristics of the current in the gradient coil, a unique digital control scheme on the basis of optimal preview type-1 servo system is proposed and described in detail. The above effectiveness is discussed and evaluated through the computer-aided analysis. It is expected that the proposed techniques will highly enlarge the diagnostic target and improve the image quality of ultrahigh-speed scanning MRI.