LIMITED FLIP ANGLE MR IMAGING OF BLOOD VESSELS

我们建议详细研究其技术特点、优点， 和有限翻转角（LFA）磁共振成像的局限性， 将其应用于血管投影成像的特定任务。 LFA成像的预期信号水平将根据理论预测 测量和实验。 重复次数和翻转角度将 优化用于区分规定的材料对。 算法 将被设计用于确定T1弛豫时间的图像， 在几个不同的翻转角下获得的测量值。 对比噪声 比率（CNR）和效率（CNR除以时间的平方根） 成像将与传统的自旋-翘曲方法进行严格的比较。 有限翻转角方法也将应用于不同的成像， 投影格式的血管。 信号的基础将是 相位的随机化以及因此由运动引起的信号的减少 血液沿着磁场梯度流动。 高速数据 （收缩期）和低速（舒张期）图像将在 在大约10个心动周期内以交错方式进行， 分别对应于相位相消图像和相位相干图像。 等 分配将根据额外的同时测量来确定 血压脉搏的变化。 不同阶段血管中的流速分布 将用多普勒超声测量犬的心动周期。 这些测量将用于优化MR技术。 LFA MR 将狗的血管造影图像与IV-DSA的结果进行比较。

We propose to study in detail the technical characteristics, advantages, and limitations of limited flip angle (LFA) magnetic resonance imaging and apply it to the specific task of projection imaging of blood vessels. Expected signal levels of LFA imaging will be predicted from theoretical grounds and measured experimentally. Repetition times and flip angles will be optimized for distinguishing prescribed pairs of materials. Algorithms will be devised for determining images of the T1 relaxation time from measurements acquired at several different flip angles. Contrast-to-noise ratios (CNR) and efficiency (CNR divided by the square root of time) of LFA imaging will be compared rigorously with conventional spin-warp methods. Limited flip angle methods will also be applied to the different imaging of blood vessels in projection format. The basis of the signal will be the randomization in phase and hence reduction in signal caused by the motion of flowing blood along a magnetic gradient. Data for a high velocity (systolic) and low velocity (diastolic) image will be acquired in interleaved fashion over approximately ten cardiac cycles and assigned respectively to the phase destructive and phase coherent images. Such assignment will be determined from an additional simultaneous measurement of blood pressure pulses. Velocity profiles in vessels at various phases of the cardiac cycle will be measured in dogs with Doppler ultrasound. Such measurements will be used to optimize the MR technique. LFA MR angiographic images of dogs will be compared with results from IV-DSA.