Lorentz force electrical impedance tomography using magnetic field measurements

Abstract

In this study, magnetic field measurement technique is investigated to image the electrical conductivity properties of biological tissues using Lorentz forces. This technique is based on electrical current induction using ultrasound together with an applied static magnetic field. The magnetic field intensity generated due to induced currents is measured using two coil configurations, namely, a rectangular loop coil and a novel xy coil pair. A time-varying voltage is picked-up and recorded while the acoustic wave propagates along its path. The forward problem of this imaging modality is defined as calculation of the pick-up voltages due to a given acoustic excitation and known body properties. Firstly, the feasibility of the proposed technique is investigated analytically. The basic field equations governing the behaviour of time-varying electromagnetic fields are presented. Secondly, the general formulation of the partial differential equations for the scalar and magnetic vector potentials are derived. To investigate the feasibility of this technique, numerical studies are conducted using a finite element method based software. To sense the pick-up voltages a novel coil configuration (xy coil pairs) is proposed. Two-dimensional numerical geometry with a 16-element linear phased array (LPA) ultrasonic transducer (1 MHz) and a conductive body (breast fat) with five tumorous tissues is modeled. The static magnetic field is assumed to be 4 Tesla. To understand the performance of the imaging system, the sensitivity matrix is analyzed. The sensitivity matrix is obtained for two different locations of LPA transducer with eleven steering angles from [Formula: see text] to [Formula: see text] at intervals of [Formula: see text]. The characteristics of the imaging system are shown with the singular value decomposition (SVD) of the sensitivity matrix. The images are reconstructed with the truncated SVD algorithm. The signal-to-noise ratio in measurements is assumed 80 dB. Simulation studies based on the sensitivity matrix analysis reveal that perturbations with [Formula: see text] mm size can be detected up to a 3.5 cm depth.

Finite element modelling and image reconstruction for Lorentz force electrical impedance tomography

“…Despite the good resemblance between the target and reconstructed images, the relative conductivity reconstruction error was computed at about 10%, significantly higher than the case with no electrode modelling errors. This is in agreement with the good results obtained by non-contact measurements in [5] and [7].…”

“…If ϕ ∈ C 2 (Ω) is a smooth function with continuous support over Ω both integral terms in (16) are well defined. However, when ϕ is compactly supported at a focal point as in [1], [7] or a planar surface transecting Ω as in the synthetic focusing approach [16], [19]; adopted in the study, the integrand in the second term of (16) becomes singular, leaving an analytic expression for the measurement as…”

Rotational magneto-acousto-electric tomography (MAET): theory and experimental validation

“…In addition to MAET, there exist several other hybrid modalities utilizing various combinations of magnetic field with ultrasound, such as, for example, magneto-acoustic tomography with magnetic induction (MAT-MI) (Mariappan and He 2003, Xu and He 2005, Li et al 2007, Hu et al 2011), Lorentz force electrical impedance tomography using magnetic field (Zengin and Gençer 2016), and some others. Like MAET, all these modalities are very new; they significantly differ from the present version of MAET by the physics of the signal acquisition.…”

Study on Reciprocal Models for Magneto-Acousto-Electrical Tomography With Coil Detection

“…Both the forward and inverse problems are verified by applying curl of the reciprocal current density, which will be described in future research. In recent studies, Zengin and Lorentz [15] proposed the use of a novel xy coil pair to measure the magnetic field intensity generated due to induced currents. In this paper, circular coil is used to detect the magnetic field intensity generated.…”