Department of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany.
Magn Reson Med. 2009 Dec;62(6):1565-73. doi: 10.1002/mrm.22157.
A density-adapted three-dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k-space sampling than conventional three-dimensional projection reconstruction sequences. The gradients of the density-adapted three-dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k-space is constant. Due to hardware restrictions, an inner sphere of k-space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three-dimensional projection reconstruction sequence trajectories and an enhanced signal-to-noise ratio (SNR) efficiency akin to the commonly used three-dimensional twisted projection imaging trajectories. Benefits for low SNR applications, when compared to conventional three-dimensional projection reconstruction sequences, are demonstrated with the example of sodium imaging. In simulations of the point-spread function, the SNR of small objects is increased by a factor 1.66 for the density-adapted three-dimensional radial projection reconstruction pulse sequence sequence. Using analytical and experimental phantoms, it is shown that the density-adapted three-dimensional radial projection reconstruction pulse sequence allows higher resolutions and is more robust in the presence of field inhomogeneities. High-quality in vivo images of the healthy human leg muscle and the healthy human brain are acquired. For equivalent scan times, the SNR is up to a factor of 1.8 higher and anatomic details are better resolved using density-adapted three-dimensional radial projection reconstruction pulse sequence.
提出了一种密度自适应的三维径向投影重建脉冲序列，与传统的三维投影重建序列相比，该序列提供了更有效的 k 空间采样。密度自适应三维径向投影重建脉冲序列的梯度设计使得 k 空间中每个球形壳的平均采样密度保持恒定。由于硬件限制，k 空间的内球不进行密度自适应采样。这种方法结合了传统三维投影重建序列轨迹的直接处理方法，以及类似于常用的三维扭曲投影成像轨迹的增强的信噪比（SNR）效率。通过钠成像的例子展示了与传统三维投影重建序列相比，在低 SNR 应用中的优势。在点扩散函数的模拟中，对于密度自适应的三维径向投影重建脉冲序列，小物体的 SNR 提高了 1.66 倍。使用分析和实验体模，表明密度自适应的三维径向投影重建脉冲序列可以实现更高的分辨率，并且在存在磁场不均匀性时更稳健。获得了健康人腿部肌肉和健康人脑的高质量体内图像。在等效的扫描时间内，使用密度自适应三维径向投影重建脉冲序列，SNR 最高可提高 1.8 倍，并且可以更好地分辨解剖细节。
