Rubin J B, Enzmann D R
AJR Am J Roentgenol. 1987 May;148(5):983-94. doi: 10.2214/ajr.148.5.983.
The effects of pulsatile motion on MR imaging of spinal CSF were quantitatively evaluated with a spine phantom that simulated spinal CSF pulsation. Two fundamental interdependent pulsation flow phenomena were observed: variable reductions in signal intensity of pulsatile CSF (signal loss) and spatial mismapping of this signal beyond the confines of the subarachnoid space (phase-shift images). Phase-shift images were observed as multiple regions of signal intensity conforming morphologically to the subarachnoid space but displaced symmetrically from it along the phase-encoding axis, either added to or subtracted from stationary signal intensity. Both CSF pulsation flow phenomena occurred secondary to harmonic modulation of proton precessional phase (temporal phase shift) by the unique pulsatile motion of spinal CSF when the repetition time was not an integral multiple of the pulsation period. Each flow phenomenon was analyzed with the spine phantom independently to control individual imaging and physiologic parameters including imaging plane, repetition time, echo time, slice thickness, number of echoes, number of excitations, CSF pulsation amplitude, and CSF pulsation period. In the axial plane, signal loss was present on both first- and second-echo images and was more pronounced with larger pulsation amplitudes and smaller slice thicknesses. A quantitative relationship between these two parameters allowed the prediction of CSF pulsation amplitude when the slice thickness was known and the CSF signal intensity was measured. In the sagittal plane, signal loss was present on first-echo images, was more pronounced with larger pulsation amplitudes, and underwent incomplete even-echo rephasing on second-echo images. Phase-shift images were influenced by the relationship between repetition time and CSF pulsation period. They were partly eliminated on sagittal but not on axial second-echo images because of incomplete even-echo rephasing. Both signal loss and phase-shift images were completely eliminated with CSF gating or pseudogating, indicating the rationale for gating during clinical spinal MR. The clinical significance of these findings is that awareness of the existence of spinal CSF pulsation flow phenomena avoids diagnostic confusion, whereas understanding their etiology provides a rational approach, such as CSF gating, to eliminate them.
使用模拟脊髓脑脊液搏动的脊柱模型对搏动运动对脊髓脑脊液磁共振成像的影响进行了定量评估。观察到两种基本的相互依存的搏动血流现象：搏动性脑脊液信号强度的可变降低（信号丢失）以及该信号在蛛网膜下腔范围之外的空间错配（相移图像）。相移图像表现为多个信号强度区域，其形态上符合蛛网膜下腔，但沿相位编码轴相对于蛛网膜下腔对称移位，与静止信号强度相加或相减。当重复时间不是搏动周期的整数倍时，这两种脑脊液搏动血流现象均继发于脊髓脑脊液独特的搏动运动对质子进动相位的谐波调制（时间相移）。使用脊柱模型对每种血流现象进行独立分析，以控制各个成像和生理参数，包括成像平面、重复时间、回波时间、层厚、回波数量、激励次数、脑脊液搏动幅度和脑脊液搏动周期。在轴位平面上，首次回波和第二次回波图像上均存在信号丢失，搏动幅度越大且层厚越小，信号丢失越明显。当已知层厚并测量脑脊液信号强度时，这两个参数之间的定量关系可用于预测脑脊液搏动幅度。在矢状位平面上，首次回波图像上存在信号丢失，搏动幅度越大信号丢失越明显，并且在第二次回波图像上经历不完全的偶数回波重聚相。相移图像受重复时间与脑脊液搏动周期之间关系的影响。由于不完全的偶数回波重聚相，它们在矢状位第二次回波图像上部分消除，但在轴位第二次回波图像上未消除。脑脊液门控或伪门控可完全消除信号丢失和相移图像，这表明了临床脊髓磁共振成像期间进行门控的基本原理。这些发现的临床意义在于，认识到脊髓脑脊液搏动血流现象的存在可避免诊断混淆，而了解其病因可提供一种合理的方法，如脑脊液门控，以消除这些现象。
