Density compensation functions for spiral MRI
Density compensation functions for spiral MRI
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DOI：
10.1002/mrm.1910380117
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发表时间：
1997-07-01
影响因子：
3.3
通讯作者：
Pike, GB
中科院分区：
文献类型：
--
作者：
Hoge, RD;Kwan, RKS;Pike, GB
在交错螺旋MRI中，沿着空间频率域（k空间）中的一组弯曲轨迹对对象的傅立叶变换进行沿着采样。然后通常通过将采样的傅立叶数据内插到笛卡尔网格上并应用快速傅立叶变换（FFT）算法来重建对象的图像。为了获得准确的结果，必须考虑k空间采样的不均匀密度。本文基于笛卡尔坐标系与螺旋采样参数时间和叶间旋转角之间的变换的雅可比行列式，推导了螺旋MRI的解析密度补偿函数（DCF），并将该函数与几种已发表的表达式进行了比较。各种非理想条件，包括相交的轨迹，被认为是。新的DCF消除了在用其他函数重建的图像中遇到的强度杯形，并且显著降低了当采用不均匀间隔的采样轨迹（例如用梯形梯度波形实现的那些）时观察到的伪影水平。发现该函数的修改形式在交叉轨迹使得螺旋-笛卡尔变换不可逆时提供类似的改进，以及当螺旋轨迹的形状在交错之间变化时。
In interleaved spiral MRI, an object's Fourier transform is sampled along a set of curved trajectories in the spatial frequency domain (k-space), An image of the object is then reconstructed, usually by interpolating the sampled Fourier data onto a Cartesian grid and applying the fast Fourier transform (FFT) algorithm, To obtain accurate results, it is necessary to account for the nonuniform density with which k-space is sampled. An analytic density compensation function (DCF) for spiral MRI, based on the Jacobian determinant for the transformation between Cartesian coordinates and the spiral sampling parameters of time and interleaf rotation angle, is derived in this paper, and the reconstruction accuracy achieved using this function is compared with that obtained using several previously published expressions. Various nonideal conditions, including intersecting trajectories, are considered. The new DCF eliminated intensity cupping that was encountered in images reconstructed with other functions, and significantly reduced the level of artifact observed when unevenly spaced sampling trajectories, such as those achieved with trapezoidal gradient waveforms, were employed, Modified forms of this function were found to provide similar improvements when intersecting trajectories made the spiral-Cartesian transformation noninvertible, and when the shape of the spiral trajectory varied between interleaves.