Resolution and Contrast in Magnetic Resonance Electrical Impedance Tomography (MREIT) and its Application to Cancer Imaging

Abstract

It has been reported that the electrical impedance of malignancies could be 20-40 times lower than healthy tissues and benign formations. Therefore, in vivo impedance imaging of suspicious lesions may prove to be helpful in improving the sensitivity and specificity of detecting malignant tumors. Several systems have been developed to map the conductivity distribution inside a volume of tissue, however they suffer from poor spatial resolution because the measurements are taken only from surface electrodes. MRI based impedance imaging (MREIT) is a novel method, in which weak electrical currents are injected into the tissue and the resulting perturbations in the magnetic field are measured using MRI. This method has been shown to provide better resolution compared to previous techniques of impedance imaging because the measurements are taken from inside the object on a uniform grid. Thus, it has the potential to be a useful modality that may detect malignancies earlier. Several phantom imaging experiments were performed to investigate the spatial resolution and dynamic range of contrast of this technique. The method was also applied to a live rat bearing a R3230 AC tumor. Tumor location was identified by contrast enhanced imaging.

Reconstruction of apparent orthotropic conductivity tensor image using magnetic resonance electrical impedance tomography

“…Fig. 5(b) shows a reconstructed isotropic conductivity by solving the over-determined system (15) under the assumption of isotropic (r ¼ r 11 ¼ r 22 ). The reconstructed isotropic conductivity image in Fig.…”

“…The matrix system (15) shows that each of r 11 and r 22 depends only on one component of the electrical fields u ' x and u ' y , respectively. Without the information of u ' , Fig.…”

“…[7][8][9] To avoid rotating the imaging object inside a MRI scanner, the latest image reconstruction algorithms in MREIT have focused on producing the isotropic or equivalent isotropic conductivity image using only B z data. 4,[10][11][12][13][14][15][16][17][18][19][20] For the isotropic conductivity reconstruction, we inject at least two currents in order to generate internal current flows with different pathways. Since there may exist infinitely many isotropic conductivity distributions which generate a same internal current density, at least two independent injection currents are definitely beneficial to determine the internal conductivity.…”

Equivalent Isotropic Conductivity Image Reconstruction in MREIT

“…Numerous conductivity image reconstruction algorithms have been developed and most of them assume an isotropic conductivity distribution [5][6][7][8][9][10][11][12][13][14]. Almost all reported experimental MREIT studies using phantoms also have assumed isotropic conductivity distributions [8,13,15,16].…”

Principles of electrical impedance tomography and its clinical application

“…A combination with magnetic resonance (so called magnetic resonance electrical impedance tomography) is now under development to image, e.g., cancer formation, in the breast (5). Heart (6,7) and gastrointestinal tract (8,9) were other organs of interest for imaging with EIT in dedicated articles.…”