Bookwalter Candice A, Griswold Mark A, Sunshine Jeffrey L, Duerk Jeffrey L
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.
Magn Reson Med. 2007 Oct;58(4):819-24. doi: 10.1002/mrm.21321.
Image signal-to-noise ratio (SNR) limits many MRI applications. Here we propose a method to improve SNR based on continuous sampling (CS) during each TR without significant increases in acquisition time. The general concept of CS is defined here as sampling the NMR signal immediately after slice excitation including ramp times, both the dephase and rephase lobes, the phase-encoding (PE) gradient application, and the slice refocusing gradient. This study analyzes several cases of CS and demonstrates a specific case where sampling occurs during an isolated and balanced readout gradient in order to increase SNR in a rectilinear Cartesian sequence without significantly increasing overall acquisition time. The noise correlation consequences of rectilinear CS are mathematically derived and proven through simulation. The SNR improvement of up to approximately 40% measured in both phantom and asymptomatic human volunteer images is comparable to theoretical prediction of increased SNR proportional to the increase in the square root of the sampling time.
图像信噪比（SNR）限制了许多MRI应用。在此，我们提出一种方法，在每个重复时间（TR）期间基于连续采样（CS）来提高信噪比，而采集时间不会显著增加。CS的一般概念在此定义为在层面激发后立即对NMR信号进行采样，包括斜坡时间、去相位和重相位叶、相位编码（PE）梯度应用以及层面重聚焦梯度。本研究分析了几种CS情况，并展示了一种特定情况，即在孤立且平衡的读出梯度期间进行采样，以提高直角笛卡尔序列中的信噪比，而不会显著增加总体采集时间。通过数学推导得出并通过模拟证明了直角CS的噪声相关性后果。在体模和无症状人类志愿者图像中测得的信噪比提高高达约40%，这与信噪比增加与采样时间平方根增加成比例的理论预测相当。
