Wang Jau-Yi, Healey Timothy, Barker Anthony, Brown Brian, Monk Chris, Anumba Dilly
Academic Unit of Reproductive and Development Medicine, Jessop Wing, University of Sheffield and Sheffield Teaching Hospitals NHS Trust, Sheffield S10 2SF, United Kingdom.
Physiol Meas. 2017 May;38(5):729-744. doi: 10.1088/1361-6579/aa6b4e. Epub 2017 Apr 27.
Gradiometers have the advantage of increasing measuring sensitivity, which is particularly useful in magnetic induction spectroscopy (MIS) for bio-impedance measurements. Traditional gradiometers use a pair of field sensing coils equally distant and on opposite sides of a drive coil, which provides high immunity to interference. In this paper, a ferrite-cored coaxial gradiometer probe of 29 mm diameter has been developed for measuring the impedance spectra of cervical tissues in vivo.
It consists of a ferrite rod with outer ferrite confinement screening in order to eliminate the signals from surrounding tissue. The magnetic screening efficiency was compared with an air-cored gradiometer probe. For both gradiometer probes, a drive coil and two sensing coils were wound on a borosilicate glass former aligned coaxially with two sensing coils equidistant from the drive coil. The signal sensitivity of those two MIS gradiometers has been measured using saline samples with a conductivity range between 0.1 and 1.1 S m. Finite element methods using COMSOL Multiphysics have been used to simulate the distribution of sensitivity to conductivity over the face of each probe and with depth.
The ferrite-cored probe has a sensitivity confined to the volume defined by the gap between the ferrite core and outer tube of ferrite while the air-cored probe without any magnetic shielding had a wide sensitivity over the face and the side of the probe. Four saline samples and one of distilled water with conductivities from 0.1 to 1.1 S m have been used to make conductivity measurements at frequencies of 50 kHz, 100 kHz, and 300 kHz. The measurement accuracy of the air-cored MIS probe was 0.09 S m at 50 kHz, improving to 0.05 S m at 300 kHz. For the ferrite-cored MIS probe, the measurement accuracy was 0.28 S m at 50 kHz, improving to 0.04 S m at 300 kHz.
In vivo measurements on human hand have been performed using both types of gradiometers and the conductivity is consistent with reported data.
梯度仪具有提高测量灵敏度的优势，这在用于生物阻抗测量的磁感应光谱法（MIS）中尤为有用。传统的梯度仪使用一对与驱动线圈等距且位于其相对两侧的场感应线圈，这提供了高抗干扰能力。在本文中，已开发出一种直径为29毫米的铁氧体芯同轴梯度仪探头，用于测量体内宫颈组织的阻抗谱。
它由一根带有外部铁氧体约束屏蔽的铁氧体棒组成，以消除来自周围组织的信号。将磁屏蔽效率与空心梯度仪探头进行了比较。对于这两种梯度仪探头，一个驱动线圈和两个感应线圈缠绕在一个硼硅酸盐玻璃框架上，两个感应线圈与驱动线圈同轴且等距排列。已使用电导率范围在0.1至1.1 S m之间的盐水样品测量了这两种MIS梯度仪的信号灵敏度。使用COMSOL Multiphysics的有限元方法来模拟每个探头表面和深度上对电导率的灵敏度分布。
铁氧体芯探头的灵敏度局限于由铁氧体芯与铁氧体外管之间的间隙所定义的体积内，而没有任何磁屏蔽的空心探头在探头表面和侧面具有较宽的灵敏度。已使用四个电导率在0.1至1.1 S m之间的盐水样品和一个蒸馏水样品在50 kHz、100 kHz和300 kHz频率下进行电导率测量。空心MIS探头在50 kHz时的测量精度为0.09 S m，在300 kHz时提高到0.05 S m。对于铁氧体芯MIS探头，在50 kHz时的测量精度为0.28 S m，在300 kHz时提高到0.04 S m。
已使用这两种类型的梯度仪对手部进行了体内测量，并且电导率与报告数据一致。
