Lee Nam G, Javed Ahsan, Jao Terrence R, Nayak Krishna S
Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA.
Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California, USA.
Magn Reson Med. 2020 Nov;84(5):2846-2857. doi: 10.1002/mrm.28304. Epub 2020 May 4.
To develop a numerical approximation to the general kinetic model for arterial spin labeling (ASL) quantification that will enable greater flexibility in ASL acquisition methods.
The Bloch-McConnell equations are extended to include the effects of single-compartment inflow and outflow on both the transverse and longitudinal magnetization. These can be solved using an extension of Jaynes' matrix formalism with piecewise constant approximation of incoming labeled arterial flow and a clearance operator for outgoing venous flow.
The proposed numerical approximation is compared with the general kinetic model using simulations of pulsed labeling and pseudo-continuous labeling and a broad range of transit time and bolus duration for tissue blood flow of 0.6 mL/g/min. Accuracy of the approximation is studied as a function of the timestep using Monte-Carlo simulations. Three additional scenarios are demonstrated: (1) steady-pulsed ASL, (2) MR fingerprinting ASL, and (3) balanced SSFP and spoiled gradient-echo sequences.
The proposed approximation was found to be arbitrarily accurate for pulsed labeling and pseudo-continuous labeling. The pulsed labeling/pseudo-continuous labeling approximation error compared with the general kinetic model was less than 0.002% (<0.002%) and less than 0.05% (<0.05%) for timesteps of 3 ms and 35 ms, respectively. The proposed approximation matched well with customized signal expressions of steady-pulsed ASL and MR fingerprinting ASL. The simulations of simultaneous modeling of flow, T , and magnetization transfer showed an increase in steady-state balanced SSFP and spoiled gradient signals.
We demonstrate a numerical approximation of the "Bloch-McConnell flow" equations that enables arbitrarily accurate modeling of pulsed ASL and pseudo-continuous labeling signals comparable to the general kinetic model. This enables increased flexibility in the experiment design for quantitative ASL.
开发一种用于动脉自旋标记（ASL）定量的通用动力学模型的数值近似方法，以在ASL采集方法上实现更大的灵活性。
布洛赫 - 麦康奈尔方程被扩展，以纳入单室流入和流出对横向和纵向磁化的影响。这些方程可以使用杰恩斯矩阵形式的扩展来求解，对进入的标记动脉血流采用分段常数近似，并对流出的静脉血流使用清除算子。
使用脉冲标记和伪连续标记的模拟以及组织血流为0.6 mL/g/min时广泛的通过时间和团注持续时间，将所提出的数值近似方法与通用动力学模型进行比较。使用蒙特卡罗模拟研究近似的准确性作为时间步长的函数。展示了另外三种情况：（1）稳态脉冲ASL，（2）磁共振指纹识别ASL，以及（3）平衡稳态自由进动和扰相梯度回波序列。
发现所提出的近似方法对于脉冲标记和伪连续标记具有任意精度。与通用动力学模型相比，对于3 ms和35 ms的时间步长，脉冲标记/伪连续标记的近似误差分别小于0.002%（<0.002%）和小于0.05%（<0.05%）。所提出的近似方法与稳态脉冲ASL和磁共振指纹识别ASL的定制信号表达式匹配良好。血流、T以及磁化传递的同时建模模拟显示稳态平衡稳态自由进动和扰相梯度信号增加。
我们展示了“布洛赫 - 麦康奈尔流”方程的一种数值近似方法，该方法能够对脉冲ASL和伪连续标记信号进行与通用动力学模型相当的任意精确建模。这在定量ASL的实验设计中增加了灵活性。
