Electrical conductivity imaging via contactless measurements

A new imaging modality is introduced to image electrical conductivity of biological tissues via contactless measurements. This modality uses magnetic excitation to induce currents inside the body and measures the magnetic fields of the induced currents. In this study, the mathematical basis of the methodology is analyzed and numerical models are developed to simulate the imaging system. The induced currents are expressed using the (A) over right arrow-phi formulation of the electric field where (A) over right arrow is the magnetic vector potential and phi is the scalar potential function. It is assumed that (A) over right arrow describes the primary magnetic vector potential that exists in the absence of the body. This assumption considerably simplifies the solution of the secondary magnetic fields caused by induced currents. In order to solve phi for objects of arbitrary conductivity distribution a three-dimensional (3-D) finite-element method (FEM) formulation is employed. A specific 7 x 7-coil system is assumed nearby the upper surface of a 10 x 10 x 5-cm conductive body. A sensitivity matrix, which relates the perturbation in measurements to the conductivity perturbations, is calculated. Singular-value decomposition of the sensitivity matrix shows various characteristics of the imaging system. Images are reconstructed using 500 voxels in the image domain, with truncated pseudoinverse. The noise level is assumed to produce a representative signal-to-noise ratio (SNR) of 80 dB. It is observed that it is possible to identify voxel perturbations (of volume 1 cm(3)) at 2 cm depth. However, resolution gradually decreases for deeper conductivity perturbations.


Electrical conductivity Imaging via contactless measurements: An experimental study
KARBEYAZ, BAŞAK ÜLKER; Gençer, Nevzat Güneri (Institute of Electrical and Electronics Engineers (IEEE), 2003-05-01)
A data-acquisition system has been developed to image electrical conductivity of biological tissues via contactless measurements. This system uses magnetic excitation to induce currents inside the body and measures the resulting magnetic fields. The data-acquisition system is constructed using a PC-controlled lock-in amplifier instrument. A magnetically coupled differential coil is used to scan conducting phantoms by a computer controlled scanning system. A 10000-turn differential coil system with circular ...
Direct Reconstruction of Pharmacokinetic-Rate Images of Optical Fluorophores From NIR Measurements
Alacam, Burak; Yazici, Birsen (Institute of Electrical and Electronics Engineers (IEEE), 2009-09-01)
In this paper, we present a new method to form pharmacokinetic-rate images of optical fluorophores directly from near infra-red (NIR) boundary measurements. We first derive a mapping from spatially resolved pharmacokinetic rates to NIR boundary measurements by combining compartmental modeling with a diffusion based NIR photon propagation model. We express this mapping as a state-space equation. Next, we introduce a spatio-temporal prior model for the pharmacokinetic-rate images and combine it with the state...
Experimental results for 2D magnetic resonance electrical impedance tomography (MR-EIT) using magnetic flux density in one direction
Birgul, O; Eyüboğlu, Behçet Murat; Ider, YZ (IOP Publishing, 2003-11-07)
Magnetic resonance electrical impedance tomography (MR-EIT) is an emerging imaging technique that reconstructs conductivity images using magnetic flux density measurements acquired employing MRI together with conventional EIT measurements. In this study, experimental MR-EIT images from phantoms with conducting and insulator objects are presented. The technique is implemented using the 0.15 T Middle East Technical University MRI system. The dc current method used in magnetic resonance current density imaging...
Phonon Mean Free Path in Few Layer Graphene, Hexagonal Boron Nitride, and Composite Bilayer h-BN/Graphene
Gholivand, Hamed; Donmezer, Nazli (Institute of Electrical and Electronics Engineers (IEEE), 2017-09-01)
In this study, ab-initio calculations were performed to obtain the phonon dispersions of seven different structures: single layer graphene, bilayer graphene, graphite, single layer h-BN, bilayer h-BN, bulk h-BN, and finally composite bilayer h-BN/graphene. Using these dispersions specific heat, group velocity, and single mode relaxation times of phonons were obtained to calculate their thermal conductivities, and mean free paths at room temperature. Calculated variables were used to understand the effects o...
Current constrained voltage scaled reconstruction (CCVSR) algorithm for MR-EIT and its performance with different probing current patterns
Birgul, O; Eyüboğlu, Behçet Murat; Ider, YZ (IOP Publishing, 2003-03-07)
Conventional injected-current electrical impedance tomography (EIT) and magnetic resonance imaging (MRI) techniques can be combined to reconstruct high resolution true conductivity images. The magnetic flux density distribution generated by the internal current density distribution is extracted from MR phase images. This information is used to form a fine detailed conductivity image using an Ohm's law based update equation. The reconstructed conductivity image is assumed to differ from the true image by a s...
Citation Formats
N. G. Gençer, “Electrical conductivity imaging via contactless measurements,” IEEE TRANSACTIONS ON MEDICAL IMAGING, pp. 617–627, 1999, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/41749.