Institute for Biomedical Imaging, Hamburg University of Technology, Hamburg, Germany.
Section for Biomedical Imaging, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Phys Med Biol. 2023 Aug 22;68(17). doi: 10.1088/1361-6560/ace309.
Magnetic particle imaging (MPI) is capable of high temporal resolution measurements of the spatial distribution of magnetic nanoparticles and therefore well suited for perfusion imaging, which is an important tool in medical diagnosis. Perfusion imaging in MPI usually requires a fresh bolus of tracer material to capture the key signal dynamics. Here, we propose a method to decouple the imaging sequence from the injection of additional tracer material, without further increasing the administered iron dose in the body with each image.A bolus of physiological saline solution without any particles (negative contrast) diminishes the steady-state concentration of a long-circulating tracer during passage. This depression in the measured concentration contributes to the required contrast dynamics. The presence of a long-circulating tracer is therefore a prerequisite to obtain the negative contrast. As a quantitative tracer based imaging method, the signal is linear in the tracer concentration for any location that contains nanoparticles and zero in the surrounding tissue which does not provide any intrinsic signal. After tracer injection, the concentration over time (positive contrast) can be utilized to calculate dynamic diagnostic parameters like perfusion parameters in vessels and organs. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background.Perfusion parameters are calculated based on the time response of the proposed negative bolus and compared to a positive bolus. Results from phantom experiments show that normalized signals from positive and negative boli are concurrent and deviations of calculated perfusion maps are low.Our method opens up the possibility to increase the total monitoring time of a future patient by utilizing a positive-negative contrast sequence, while minimizing the iron dose per acquired image.
磁共振粒子成像(MPI)能够实现对磁性纳米粒子空间分布的高时间分辨率测量,因此非常适合用于灌注成像,这是医学诊断中的重要工具。MPI 中的灌注成像通常需要新鲜的示踪剂脉冲以捕捉关键的信号动态。在这里,我们提出了一种方法,可以将成像序列与额外示踪剂材料的注射分离,而不会在每次图像采集时增加体内的铁剂量。没有任何颗粒的生理盐水(负对比)脉冲会在通过时降低长循环示踪剂的稳态浓度。这种测量浓度的降低有助于产生所需的对比动态。因此,长循环示踪剂的存在是获得负对比的前提条件。作为一种基于定量示踪剂的成像方法,对于任何包含纳米粒子的位置,信号与示踪剂浓度呈线性关系,而在不提供任何固有信号的周围组织中为零。示踪剂注射后,随时间变化的浓度(正对比)可用于计算血管和器官中的灌注参数等动态诊断参数。因此,每幅采集的灌注图像都需要新的含有足够大铁剂量的示踪剂脉冲,以在背景之上可见。灌注参数是基于所提出的负脉冲的时间响应计算的,并与正脉冲进行比较。体模实验的结果表明,正、负脉冲的归一化信号是一致的,计算的灌注图的偏差较低。我们的方法通过使用正-负对比序列,为未来的患者增加了总监测时间,同时使每个获取图像的铁剂量最小化,从而为患者带来了更大的获益。
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