Institute of Medical Engineering, University of Lübeck, 23538 Lübeck, Germany.
Med Phys. 2010 Feb;37(2):485-91. doi: 10.1118/1.3271258.
Magnetic particle imaging (MPI) is a new quantitative imaging technique capable of determining the spatial distribution of superparamagnetic nanoparticles at high temporal and spatial resolution. For reconstructing this spatial distribution, the particle dynamics and the scanner properties have to be known. To date, they are obtained in a tedious calibration procedure by measuring the magnetization response of a small delta sample shifted through the measuring field. Recently, first reconstruction results using a 1D model-based system function were published, showing comparable image quality as obtained with a measured system function. In this work, first 2D model-based reconstruction results of measured MPI data are presented.
To simulate the system function, various parameters have to be modeled, namely, the magnetic field, the particle magnetization, the voltage induced in the receive coils, and the transfer function of the receive chain. To study the accuracy of the model-based approach, 2D MPI data are measured and reconstructed with modeled and measured system functions.
It is found that the model-based system function is sufficiently accurate to allow for reconstructing experimental data. The resulting image quality is close to that obtained with a measurement-based reconstruction.
The model-based system function approach addresses a major drawback of the measurement-based procedure, namely, the long acquisition time. In this work, the acquisition of the measurement-based system function took 45 min, while the model-based system function was obtained in only 15 s. For 3D data, where the acquisition of the measurement-based system function takes more than 6 h, the need for an efficient system function generation is even more obvious.
磁共振粒子成像（MPI）是一种新的定量成像技术，能够以高时间和空间分辨率确定超顺磁纳米粒子的空间分布。为了重建这个空间分布，必须知道粒子动力学和扫描仪特性。迄今为止，它们是通过测量通过测量场移动的小 delta 样本的磁化响应在繁琐的校准过程中获得的。最近，使用基于 1D 的模型系统函数发布了第一个重建结果，显示出与使用测量系统函数获得的可比图像质量。在这项工作中，首先提出了基于模型的测量 MPI 数据的二维重建结果。
为了模拟系统函数，必须对各种参数进行建模，即磁场、粒子磁化、接收线圈中感应的电压和接收链的传递函数。为了研究基于模型的方法的准确性，使用建模和测量的系统函数测量和重建 2D MPI 数据。
发现基于模型的系统函数足够准确，可以重建实验数据。得到的图像质量接近基于测量的重建的图像质量。
基于模型的系统函数方法解决了基于测量的程序的一个主要缺点，即采集时间长。在这项工作中，基于测量的系统函数的采集需要 45 分钟，而基于模型的系统函数仅需 15 秒。对于采集基于测量的系统函数需要超过 6 小时的 3D 数据，对有效系统函数生成的需求更加明显。
