Wood M L, Runge V M
Department of Radiation Oncology, New England Medical Center, Boston, Massachusetts.
Med Phys. 1988 Nov-Dec;15(6):825-31. doi: 10.1118/1.596299.
An artifact is identified in magnetic resonance images produced by the three-dimensional FLASH technique, which features a short repetition time TR. The artifact is caused by differential spoiling of transverse magnetization by the phase-encoding gradients. The image intensity in different slices becomes altered, especially for short TR and large flip angle, which are conditions for achieving strong T1-weighted contrast. The effectiveness of spoiler gradient and rephasing gradients in suppressing the artifact is evaluated experimentally in images of a uniform phantom. Spoiler gradients that are incremented in amplitude cause even more slices to deviate in intensity, and are therefore less effective than in two-dimensional techniques. Rephasing gradients make the slices uniformly intense, but also enhance the intensity of tissues that have longer T2. The further addition of constant spoiler gradients has reduced this intensity increase by one-half and allowed for an intensity difference between white matter and gray matter comparable to without a rephasing gradient.
在采用短重复时间TR的三维快速低角度激发（FLASH）技术产生的磁共振图像中识别出一种伪影。该伪影是由相位编码梯度对横向磁化的不同程度扰相引起的。不同层面的图像强度会发生改变，尤其是在短TR和大翻转角的情况下，这是实现强T1加权对比度的条件。在均匀体模的图像中通过实验评估了扰相梯度和重聚相梯度抑制该伪影的效果。幅度递增的扰相梯度会导致更多层面的强度出现偏差，因此其效果不如二维技术中的扰相梯度。重聚相梯度使各层面强度均匀，但也增强了T2较长的组织的强度。进一步添加恒定扰相梯度可将这种强度增加降低一半，并使白质和灰质之间的强度差异与不使用重聚相梯度时相当。
