A highly phase-stable differential detector amplifier for magnetic induction tomography

Abstract

Magnetic induction tomography (MIT) has been proposed for the detection of cerebral oedema and haemorrhagic stroke. Achieving the required phase measurement precision for these applications is however a major technical challenge. A critical component within an MIT system is the detector amplifier and for this role an ultra-phase-stable, low noise instrumentation amplifier has been developed. The design of the amplifier is described and (i) the results of simulations and measurements of the amplifiers phase stability versus temperature and (ii) measurements of the phase noise and drift performance of the amplifier within a single-channel magnetic induction spectroscopy system are provided and discussed. For a 10 MHz signal the amplifier, with a gain of 21, displayed an average change in the measured phase of its output of just -0.1 ± 0.6 m° °C(-1) as the ambient temperature was varied between 35 and 50 °C, demonstrating a level of phase stability approaching that required for potential biomedical applications such as the detection of cerebral haemorrhage.

Application of the method of auxiliary source to the sensitivity analysis of high frequency magnetic induction tomography system

“…We assume that the magnetic field is quasi-static in the external region, combines with weak electric fields in the space exterior to the target, so the right side of (1) is eliminated which means that the exterior magnetic fields are irrotational and thus can be represented efficiently using a simple scalar potential M H (2) Here M is the magnetic scalar potential. …”

Advancements in Transmitters and Sensors for Biological Tissue Imaging in Magnetic Induction Tomography

“…In biological tissues, the conductivity component is always dominant compared to permittivity and permeability [1,37–39] as the permittivity term for biological tissues is much smaller than the conductivity, especially at frequencies within the β-dispersion range (10 kHz–10 MHz) [40]. In term of devices used, MIT is different from EIT since it does not require galvanic coupling between the device and the object, hence avoiding the ill defined electrode-skin interface [25,29,37–39]. MIT instruments consist of several components which are sensors (excitation coils, detection coils, and screen), interface electronics and host computer [3] as shown in Figure 1.…”

“…Latest, Watson et al [29] had introduced a highly phase stable differential detector amplifier for magnetic induction tomography for the purpose of achieving the required phase measurement precision. To reach this objective, he and his team had developed an ultra-phase-stable, low noise instrumentation amplifier with proven average change of −0.1 ± 0.6 m·°C −1 as the ambient temperature was varied between 35 and 50 °C, with gain of 21 at 10 MHz operational frequency as in Figure 28.…”

“…Their works have been continued by the new researchers who made MIT of interest to many researchers around the World with the new innovations and discoveries. Among the applications involved are lung monitoring and imaging [20,21], brain imaging and stroke related problem [20,22–28], liver tissue monitoring [29–31]physiological measurement [27] and several others not listed here.…”

“…One motivation for researchers who are involved in these passive electrical properties is their characteristic dependence on the state of hydration of biological tissue [23,25,29,31,32]. This provides an opportunity and alternative in studying the human body based on passive imaging modalities.…”