Electrical impedance tomography system: an open access circuit design

BACKGROUND: This paper reports a simple 2-D system for electrical impedance tomography EIT, which works efficiently and is low cost. The system has been developed in the Sharif University of Technology Tehran-Iran (for the author's MSc Project). METHODS: The EIT system consists of a PC in which an I/O card is installed with an external current generator, a multiplexer, a power supply and a phantom with an array of electrodes. The measurement system provides 12-bit accuracy and hence, suitable data acquisition software has been prepared accordingly. The synchronous phase detection method has been implemented for voltage measurement. Different methods of image reconstruction have been used with this instrument to generate electrical conductivity images. RESULTS: The results of simulation and real measurement of the system are presented. The reconstruction programs were written in MATLAB and the data acquisition software in C++. The system has been tested with both static and dynamic mode in a 2-D domain. Better results have been produced in the dynamic mode of operation, due to the cancellation of errors. CONCLUSION: In the spirit of open access publication the design details of this simple EIT system are made available here

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

Aim The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. Methods This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. Results Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. Conclusion One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

Magnetic Resonance - Electrical Impedance Tomography (MR-EIT) Research at METU

Following development of magnetic resonance current density imaging (MRCDI), magnetic resonance - electrical impedance tomography (MR-EIT) has emerged as a promising approach to produce high resolution conductivity images. Electric current applied to a conductor results in a potential field and a magnetic flux density distribution. Using a magnetic resonance imaging (MRI) system, the magnetic flux density distribution can be reconstructed as in MRCDI. The flux density is related to the current density distribution hence the relative conductivity distribution. The sensitivity of the MR-EIT measurements to conductivity distribution and the spatial resolution in the field of view are independent of position. The spatial resolution is in the order of a few millimeters which make MR-EIT an attractive modality to image tissue conductivity. In this talk, several MR-EIT reconstruction algorithms developed and implemented at Middle East Technical University (METU), their performance analysis on simulated data and the results of experiments performed on 0.15 Tesla METU-MRI system are given

Mumford-Shah Based Unsupervised Segmentation of Brain Tissue on MR Images

Automated segmentation of different tissues on medical images is a crucial concept for medical image analysis. In this study, unsupervised image segmentation problem is generalized as a Mumford-Shah energy minimization problem, and several solution proposals for the problem are investigated. Ambrosio-Tortorelli approximation method is implemented, and the performance of the algorithm on magnetic resonance (MR) images of brain is evaluated. First image used in the experiments is chosen among the ones which contain an edema formation due to a brain tumor, and the second one belongs to a healthy subject on which gray matter/white matter segmentation is aimed. Acquired results are presented in visual, tabular and numerical forms. Results and performance are discussed and quantitatively evaluated. © Springer International Publishing Switzerland 2014

J-substitution and equipotential-projection based hybrid MREIT reconstruction algorithm

Magnetic Resonance Electrical Impedance Tomography is an imaging modality which reconstructs true conductivity images by using current density distribution and surface potential measurements. In this study, two current based algorithms, namely equipotential projection [1] and J-substitution image reconstruction [2] algorithms are compared A novel reconstruction technique, J-substitution and equipotential-projection based hybrid reconstruction algorithm, is proposed In this technique, the image which is reconstructed with equipotential projection algorithm is assigned as the starting conductivity distribution for J-substitution algorithm. Moreover, true conductivity values can be reconstructed with two surface potential measurements. Simulation results on a thorax phantom show that the proposed method has a better performance in some regions

Analysis of Magnetic Resonance signal in inhomogenous main magnetic field

Nuclear Magnetic Resonance (NMR) systems with inhomogenous main magnetic fields, which are used to analyze material properties, have been developed before. Therefore, Magnetic Resonance Imaging (MRI) systems with inhomogenous main magnetic fields can be possibly developed to image tissues. To investigate the possibility of AM in inhomogenous main magnetic field, Magnenetic Resonance (MR) signal has to be analyzed. In this study, MR signal's parameters deviation due to inhomogeneity level change in the main magnetic field of a MRI system is investigated. Analyzed AM signal parameters are signal peak, energy and relaxation constant. Deviations of these parameters, because of inhomogeneity level change in the main magnetic field, are related to change in MRI system's properties. Thus, starting from the AM system's properties, tolerable inhomogeneity level in main magnetic field can be found

Anisotropie skeletal muscle conductivity in electrical impedance imaging

This work presents an analysis of the detectability of an anisotropic skeletal muscle conductivity in electrical impedance imaging, with a given measurement accuracy. A concentric circle model is used to develop a relationship between the anisotropic conductivity parameters and the measurement accuracy required to detect these parameters