Abstract A novel probe for laparoscopic in vivo detection of superparamagnetic iron oxide nanoparticles (SPIONs) has been developed. The main application for in vivo detection of SPIONs our research group aims at is sentinel node biopsy. This is a method to determine if a tumor has spread through the body, which helps to improve cancer patient care. The method we use to selectively detect SPIONs is Differential Magnetometry (DiffMag). DiffMag makes use of small magnetic field strengths in the mT range. For DiffMag, a handheld probe is used that contains excitation and detection coils. However, depth sensitivity of a handheld probe is restricted by the diameter of the coils. Therefore, excitation and detection coils are separated in our novel probe. As a result, excitation coils can be made large and placed underneath a patient to generate a sufficiently large volume for the excitation field. Detection coils are made small enough to be used in laparoscopic surgery. The main challenge of this setup is movement of detection coils with respect to excitation coils. Consequently, the detector signal is obscured by the excitation field, making it impossible to measure the tiny magnetic signature from SPIONs. To measure SPIONs, active compensation is used, which is a way to cancel the excitation field seen by the detection coils. SPIONs were measured in various amounts and at various distances from the excitation coils. Furthermore, SPIONs were measured in proximity to a surgical steel retractor, and 3 L water. It is shown that small amounts of SPIONs (down to 25 μg Fe) can be measured, and SPIONs can be measured up to 20 cm from the top of the excitation coil. Also, surgical steel, and diamagnetism of water – and thus of tissue – have minor influence on DiffMag measurements. In conclusion, these results make this novel probe geometry combined with DiffMag promising for laparoscopic sentinel node biopsy.

中文翻译：

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用于体内检测超顺磁性氧化铁纳米颗粒的激发线圈和检测线圈的分离

摘要 一种用于腹腔镜体内检测超顺磁性氧化铁纳米颗粒 (SPION) 的新型探针已被开发出来。我们研究小组针对的 SPION 体内检测的主要应用是前哨淋巴结活检。这是一种确定肿瘤是否已经扩散到全身的方法，有助于改善癌症患者的护理。我们用来选择性检测 SPION 的方法是微分磁力法 (DiffMag)。DiffMag 利用 mT 范围内的小磁场强度。对于 DiffMag，使用包含激励和检测线圈的手持式探头。然而，手持式探头的深度灵敏度受到线圈直径的限制。因此，在我们的新型探头中，激励线圈和检测线圈是分开的。因此，励磁线圈可以做得很大并放置在患者下方，以产生足够大的励磁场体积。检测线圈制作得足够小，可用于腹腔镜手术。这种设置的主要挑战是检测线圈相对于励磁线圈的移动。因此，检测器信号被激发场遮蔽，从而无法测量来自 SPION 的微小磁特征。为了测量 SPION，使用了主动补偿，这是一种消除检测线圈看到的激励场的方法。SPION 以不同的量和距励磁线圈的不同距离进行测量。此外，在手术钢牵开器和 3 L 水附近测量 SPION。结果表明，可以测量少量 SPION（低至 25 μg Fe），SPION 可以在距励磁线圈顶部 20 cm 处进行测量。此外，外科手术钢和水的抗磁性——以及组织的抗磁性——对 DiffMag 测量的影响很小。总之，这些结果使这种新型探针几何结构与 DiffMag 相结合，有望用于腹腔镜前哨淋巴结活检。