As drug carriers, magnetic nanoparticles can specifically bind to tumors and have the potential for targeted therapy. It is of great significance to explore non-invasive imaging methods that can detect the distribution of magnetic nanoparticles. Based on the mechanism that magnetic nanoparticles can generate ultrasonic waves through the pulsed magnetic field excitation, the sound pressure wave equation containing the concentration information of magnetic nanoparticles was derived. Using the finite element method and the analytical solution, the consistent transient pulsed magnetic field was obtained. A three-dimensional simulation model was constructed for the coupling calculation of electromagnetic field and sound field. The simulation results verified that the sound pressure waveform at the detection point reflected the position of magnetic nanoparticles in biological tissue. Using the sound pressure data detected by the ultrasonic transducer, the B-scan imaging of the magnetic nanoparticles was achieved. The maximum error of the target area position was 1.56%, and the magnetic nanoparticles regions with different concentrations were distinguished by comparing the amplitude of the boundary signals in the image. Studies in this paper indicate that B-scan imaging can quickly and accurately obtain the dimensional and positional information of the target region and is expected to be used for the detection of magnetic nanoparticles in targeted therapy.
磁性纳米粒子作为药物载体能够与肿瘤特异性结合，具有靶向治疗的潜力。探索用于检测磁性纳米粒子分布的无创成像方法具有重要意义。本文基于磁性纳米粒子在脉冲磁场激励下产生超声波的机制，推导含有磁性纳米粒子浓度信息的声压波动方程。利用有限元法和解析解得到一致的瞬态脉冲磁场。建立三维模型用于电磁场和声场耦合计算，仿真结果验证了检测点处的声压波形能够反映磁性纳米粒子区域在生物组织中的位置信息。利用超声换能器采集的声压数据，实现磁性纳米粒子的 B 型扫描成像。目标区域位置的最大误差为 1.56%，通过比较图像中边界信号的幅值可以区分不同浓度的纳米粒子区域。本文研究表明 B 型扫描成像能够快速、准确地获取目标区域的尺寸和位置信息，有望用于靶向治疗中磁性纳米粒子的检测。.
Keywords: B-scan imaging; acoustic signal; magnetic nanoparticles; magnetoacoustic effect; pulsed magnetic field.