Haacke E M, Wielopolski P A, Tkach J A, Modic M T
Department of Radiology, Case Western Reserve University, Cleveland, OH.
Radiology. 1990 May;175(2):545-52. doi: 10.1148/radiology.175.2.2326480.
The authors discuss the appropriate FISP (fast imaging with steady-state precession) sequence structure to maintain constant phase at the radio-frequency pulse in the presence of motion. They present preliminary results of its application to head and spine imaging in an effort to maintain contrast between the cerebrospinal fluid (CSF) and the soft tissue. In the usual application of these FISP-like sequences, the gradient structure is modified to avoid unwanted signal (and contrast) variations due to field inhomogeneities. This change makes the signal sensitive to motion with a resulting decrease in signal intensity for moving tissue. The expected high contrast at large flip angles for tissues with low T1/T2 ratios such as CSF is not obtained. The technique discussed here overcomes the effects of field inhomogeneities and compensates for moving spins so that the transverse steady-state equilibrium and hence high contrast are obtained simultaneously.
作者们讨论了在存在运动的情况下，为在射频脉冲处保持恒定相位而采用的合适的快速成像稳态进动（FISP）序列结构。他们展示了将其应用于头部和脊柱成像的初步结果，旨在维持脑脊液（CSF）与软组织之间的对比度。在这些类似FISP序列的常规应用中，梯度结构会被修改，以避免由于场不均匀性导致的不必要的信号（以及对比度）变化。这种改变使得信号对运动敏感，从而导致运动组织的信号强度降低。对于诸如脑脊液等具有低T1/T2比值的组织，在大翻转角下预期的高对比度无法实现。这里讨论的技术克服了场不均匀性的影响，并补偿了移动的自旋，从而同时获得横向稳态平衡以及高对比度。
