1. 体動によるアーチファクト(MRI 撮像技術とその臨床評価 : アーチファクトの原因と対策)

Abstract

In clinical MRI, the motion artifact is a serious problem for the quality of image. Especially, the ghost image produced by the oscillation of abdominal fat tissue is one of the most significant technical problems for abdominal MRI. The ghost image is closely related to the respiratory pattern of the patient, but this correlation has not been reported clinically. Therefore, we analyzed the ghost image using a moving-phantom that can imitate the respiratory movement, after that, we clinically investigated and reconsidered the scan parameters to eliminate the ghost. The moving-phantom can produce various respiratory patterns. For example, the frequency, amplitude, and the rest time can be changed freely. Diluted Gd-DTPA solution was used as a sample. The standard scan condition was fixed as table 1. We changed each parameter individually, and took the MR image by the spin-echo sequence. Next, we measured the length of the ghost image (=the length between the ghost image and its actual source), and evaluated the correlation of the ghost image and each the variable parameters that were changed. The length of the ghost image was directry proportional to TR, NAV (number of avaraging), FOV, and was inversely proportional to cycle to oscillation. On other hand, the amplitude of oscillation was related to the reduction of signal intensity of the ghost. These ghost factors were specified by this experience, and as a result, we can estimate the location and intensity of the ghost image before the MR study by knowing the patient's respiratory pattern.