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MREIT of Postmortem Swine Legs using Carbon-hydrogel Electrodes
Minhas, Atul S.,Jeong, Woo-Chul,Kim, Young-Tae,Kim, Hyung-Joong,Lee, Tae-Hwi,Woo, Eung-Je The Korean Society of Medical and Biological Engin 2008 의공학회지 Vol.29 No.6
Magnetic resonance electrical impedance tomography(MREIT) has been suggested to produce cross-sectional conductivity images of an electrically conducting object such as the human body. In most previous studies, recessed electrodes have been used to inject imaging currents into the object. An MRI scanner was used to capture induced magnetic flux density data inside the object and a conductivity image reconstruction algorithm was applied to the data. This paper reports the performance of a thin and flexible carbon-hydrogel electrode that replaces the bulky and rigid recessed electrode in previous studies. The new carbon-hydrogel electrode produces a negligible amount of artifacts in MR and conductivity images and significantly simplifies the experimental procedure. We can fabricate the electrode in different shapes and sizes. Adding a layer of conductive adhesive, we can easily attach the electrode on an irregular surface with an excellent contact. Using a pair of carbon-hydrogel electrodes with a large contact area, we may inject an imaging current with increased amplitude primarily due to a reduced average current density underneath the electrodes. Before we apply the new electrode to a human subject, we evaluated its performance by conducting MREIT imaging experiments of five swine legs. Reconstructed conductivity images of the swine legs show a good contrast among different muscles and bones. We suggest a future study of human experiments using the carbon-hydrogel electrode following the guideline proposed in this paper.
Minhas, Sachin,Bhalla, Sunita,Shokeen, Yogender,Jauhri, Mayank,Saxena, Renu,Verma, Ishwar Chandra,Aggarwal, Shyam Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.5
Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is an important protein involved in the regulation of the immune system. The +49 G/A polymorphism is the only genetic variation in the CTLA-4 gene that causes an amino acid change in the resulting protein. It is therefore the most extensively studied polymorphism among all CTLA-4 genetic variants and contributions to increasing the likelihood of developing cancer are well known in various populations, especially Asians. However, there have hiterto been no data with respect to the effect of this polymorphism on breast cancer susceptibility in our North Indian population. We therefore assayed genomic DNA of 250 breast cancer subjects and an equal number of age-, sex- and ethnicity-matched healthy controls for the CTLA-4 +49 G/A polymorphism but no significant differences in either the gene or allele frequency were found. Thus the CTLA-4 +49 G/A polymorphism may be associated with breast cancer in other Asians, but it appears to have no such effect in North Indians. The study also highlights the importance of conducting genetic association studies in different ethnic populations.
Minhas, Atul S.,Jeong, Woo Chul,Kim, Young Tae,Han, Yeqing,Kim, Hyung Joong,Woo, Eung Je Wiley Subscription Services, Inc., A Wiley Company 2011 Magnetic resonance in medicine Vol.66 No.4
<P><B>Abstract</B></P><P>Latest experimental results in magnetic resonance electrical impedance tomography (MREIT) demonstrated high‐resolution in vivo conductivity imaging of animal and human subjects using imaging currents of 5 to 9 mA. Externally injected imaging currents induce magnetic flux density distributions, which are affected by a conductivity distribution. Since we extract the induced magnetic flux density images from MR phase images, it is essential to reduce noise in the phase images. In vivo human and disease model animal experiments require reduction of imaging current amplitudes and scan times. In this article, we investigate a multi‐echo based MREIT pulse sequence where we utilize a remaining time after the first echo within one TR to obtain more echo signals. It also allows us to prolong the total current injection time. From phantom and animal imaging experiments, we found that this method significantly reduces the noise level in measured magnetic flux density images. We describe experimental validation of the multi‐echo sequence by comparing its performance with a single‐echo method using 3 mA imaging currents. The proposed method will be advantageous for an imaging region with long T2 values such as the brain and knee. Depending on T2 values, we suggest using two or three echoes in future experimental studies. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.</P>
Chemical Shift Artifact Correction in MREIT
Minhas, Atul S.,Kim, Young-Tae,Jeong, Woo-Chul,Kim, Hyung-Joong,Lee, Soo-Yeol,Woo, Eung-Je The Korean Society of Medical and Biological Engin 2009 의공학회지 Vol.30 No.6
Magnetic resonance electrical impedance tomography (MREIT) enables us to perform high-resolution conductivity imaging of an electrically conducting object. Injecting low-frequency current through a pair of surface electrodes, we measure an induced magnetic flux density using an MRI scanner and this requires a sophisticated MR phase imaging method. Applying a conductivity image reconstruction algorithm to measured magnetic flux density data subject to multiple injection currents, we can produce multi-slice cross-sectional conductivity images. When there exists a local region of fat, the well-known chemical shift phenomenon produces misalignments of pixels in MR images. This may result in artifacts in magnetic flux density image and consequently in conductivity image. In this paper, we investigate chemical shift artifact correction in MREIT based on the well-known three-point Dixon technique. The major difference is in the fact that we must focus on the phase image in MREIT. Using three Dixon data sets, we explain how to calculate a magnetic flux density image without chemical shift artifact. We test the correction method through imaging experiments of a cheese phantom and postmortem canine head. Experimental results clearly show that the method effectively eliminates artifacts related with the chemical shift phenomenon in a reconstructed conductivity image.
MREIT conductivity imaging of the postmortem canine abdomen using CoReHA
Jeon, Kiwan,Minhas, Atul S,Kim, Young Tae,Jeong, Woo Chul,Kim, Hyung Joong,Kang, Byeong Teck,Park, Hee Myung,Lee, Chang-Ock,Seo, Jin Keun,Woo, Eung Je IOP PUBLISHING 2009 PHYSIOLOGICAL MEASUREMENT Vol.30 No.9
<P>Magnetic resonance electrical impedance tomography (MREIT) is a new bio-imaging modality providing cross-sectional conductivity images from measurements of internal magnetic flux densities produced by externally injected currents. Recent experimental results of postmortem and <I>in vivo</I> imaging of the canine brain demonstrated its feasibility by showing conductivity images with meaningful contrast among different brain tissues. MREIT image reconstructions involve a series of data processing steps such as <I>k</I>-space data handling, phase unwrapping, image segmentation, meshing, modelling, finite element computation, denoising and so on. To facilitate experimental studies, we need a software tool that automates these data processing steps. In this paper, we summarize such an MREIT software package called CoReHA (conductivity reconstructor using harmonic algorithms). Performing imaging experiments of the postmortem canine abdomen, we demonstrate how CoReHA can be utilized in MREIT. The abdomen with a relatively large field of view and various organs imposes new technical challenges when it is chosen as an imaging domain. Summarizing a few improvements in the experimental MREIT technique, we report our first conductivity images of the postmortem canine abdomen. Illustrating reconstructed conductivity images, we discuss how they discern different organs including the kidney, spleen, stomach and small intestine. We elaborate, as an example, that conductivity images of the kidney show clear contrast among cortex, internal medulla, renal pelvis and urethra. We end this paper with a brief discussion on future work using different animal models.</P>
Three-dimensional MREIT Simulator of Static Bioelectromagnetism and MRI
우응제,Atul S. Minhas,Zijun Meng,Young Tae Kim,김형중,김혜현 대한의용생체공학회 2011 Biomedical Engineering Letters (BMEL) Vol.1 No.2
Purpose Magnetic resonance electrical impedance tomography (MREIT) aims to produce high-resolution cross-sectional images of a conductivity distribution inside the human body. We perform conductivity image reconstructions based on a relation between the conductivity distribution and induced magnetic flux density distributions subject to externally injected currents. This induced magnetic flux density is measured in MREIT using an MRI scanner. To facilitate MREIT research, we need a numerical simulator including static bioelectromagnetism and MRI data collection process. In this paper, we describe the development of a threedimensional MREIT simulator (MREITSim). Methods We describe various features of MREITSim including geometry modeling, meshing, finite element modeling and numerical computations of magnetic flux density and k-space MR data. We demonstrate the underlying bioelectromagnetic phenomena and MR data collection process using phantom models of without and with anomaly. We illustrate effects of noise in MR data and echo time on magnetic flux density computations. Results We demonstrate numerical computations of current density and magnetic flux density distributions for current injections orthogonal to z-direction, the direction of the main magnetic field of an MRI scanner. The k-space MREIT data generation procedure is illustrated using a phantom model with an insulating anomaly. Conclusions The simulator functions as a virtual MREIT scanner and provides quantitative numerical results of intended experimental studies. We suggest the simulator as a basic research tool for future MREIT studies of its theory, algorithm,experimental techniques and pulse sequence design.