横窦血液流率MR测量的影响因素分析

Blood flow measurement of transverse sinuses by using MR:a phantom study of its influence factors

目的 (1)探讨稳定流动状态下磁共振信号强度与液体速率关系。 (2 )探讨流动液体速度矢量与编码梯度方向夹角 (θ)、翻转角和层面厚度对倾斜流动液体速率和流率测量的影响。 (3 )为测量横窦血液流率提供合理方案。方法 在实验水模上将内径 3 4mm塑胶管沿横断面弯曲成环状 ,模拟横窦血流状态 ,使用 1 5T超导磁共振仪梯度回返回波速度 (VIGRE)序列进行速度测量。合理方案基于以下几方面考虑 :(1)速率和面积测量的准确性 ;(2 )信噪比。结果 (1)磁共振信号强度 (y)和流动液体实际速率 (x)呈线性关系 ,y =68 914x+3 5 7 2 0 6,R2 =0 998。 (2 )随着θ角的增大 ,流动液体横截面积增加 ,而速率下降。 (3 )随翻转角度增大 ,信噪比的变化范围为 5 7～ 11 2。最大值由 3 0°翻转角获得。 (4)随着层厚增加 ,信噪比和信号面积有增大。结论 相位对比法是 1种实用的液体流率测量方法。θ角影响速率和液体面积测量 。

Objective (1) To determine the relationship between the MR signal intensity and the actual flow velocity under steady flow condition (2) to analyze the influence produced by the angle (θ) between the flow direction and the velocity encoded gradient direction, and flip angle as well as section thickness on the velocity measurement under oblique flow condition (3) to develop a suitable protocol for using this method to measure volumetric flow rate in the transverse sinus system Methods Flow phantom, which simulated blood flow conditions in the transverse sinus system, consisted of a fluid filled cylinder and a bent tube with a 3 4 mm internal diameter A 1 5 T superconductive MR imager and VIGRE sequence were used for these studies A suitable protocol was based on consideration of the effects of (1) the accuracy of velocity and transverse area measurement of flow, and (2) signal to noise ratio (SNR) Results (1) Signal intensity (y) determined by MR and the actual flow velocity (x) showed straight line correlation, y=68 914x+357 206, R 2=0 998 (2) As the angle (θ) increased, the transverse area of the signal determined by MR also increased, but the value of flow velocity decreased (3) As the flip angle increased, the SNR varied from 5 7 to 11 2 The maximum SNR was obtained with 30°flip angle (4) As the section thickness increased, the SNR and the transverse area of the signal determined by MR slightly increased Conclusions Phase contrast MR imaging is a practical method for measuring volumetric flow rates The angle (θ) influenced the accuracy of flow velocity and the measurement of transverse area of flow whereas the flip angle and the section thickness substantially influenced the signal to noise ratio and the transverse area of flow