41 research outputs found
A flexible low-cost, high-precision, single interface electrical impedance tomography system for breast cancer detection using FPGA
Typically, in multi-frequency Electrical Impedance Tomography (EIT) systems, a current is applied and the voltages developed across the subject are detected. However, due to the complexity of designing stable current sources, there has been mention in the literature of applying a voltage to the subject whilst measuring the consequent current flow. This paper presents a comparative study between the two techniques in a novel design suitable for the detection of breast cancers. The suggested instrument borrows the best features of both the injection of current and the application of voltage, circumventing their limitations. Furthermore, the system has a common patient-electrode interface for both methodologies, whilst the control of the system and the necessary signal processing is carried out in a field programmable gate array (FPGA). Through this novel system, wide-bandwidth, low-noise, as well as high-speed (frame rate) can be achieved
A feasibility study of a rotary planar electrode array for electrical impedance mammography using a digital breast phantom
A feasibility study of an electrical impedance mammography (EIM) system
with a rotary planar electrode array, named RPEIM, is presented. The RPEIM
system is an evolution of the Sussex MK4 system, which is a prototype
instrument for breast cancer detection. Comparing it with the other planar
electrode EIM systems, the rotation feature enables a dramatic increase in
the number of independent measurements. To assist impedance evaluation
exploiting electrode array rotation, a synchronous mesh method is proposed.
Using the synchronous mesh method, the RPEIM system is shown to
have superior performance in image accuracy, spatial resolution and noise
tolerance over the MK4 system. To validate the study, we report simulations
based on a close-to-realistic 3D digital breast phantom, which comprises of:
skin, nipple, ducts, acinus, fat and tumor. A digital breast phantom of a real
patient is constructed, whose tumor was detected using the MK4 system. The
reconstructed conductivity image of the breast phantom indicates that the
breast phantom is a close replica of the patient’s real breast as assessed by the
MK4 system in a clinical trial. A comparison between the RPEIM system and
the MK4 system is made based on this phantom to assess the advantages of
the RPEIM system
Finite element implementation of Maxwell's equations for image reconstruction in electrical impedance tomography
Traditionally, image reconstruction in electrical impedance tomography (EIT) has been based on Laplace's equation. However, at high frequencies the coupling between electric and magnetic fields requires solution of the full Maxwell equations. In this paper, a formulation is presented in terms of the Maxwell equations expressed in scalar and vector potentials. The approach leads to boundary conditions that naturally align with the quantities measured by EIT instrumentation. A two-dimensional implementation for image reconstruction from EIT data is realized. The effect of frequency on the field distribution is illustrated using the high-frequency model and is compared with Laplace solutions. Numerical simulations and experimental results are also presented to illustrate image reconstruction over a range of frequencies using the new implementation. The results show that scalar/vector potential reconstruction produces images which are essentially indistinguishable from a Laplace algorithm for frequencies below 1 MHz but superior at frequencies reaching 10 MHz.</p