Mesh Phantom Research Articles

Flexi-EIT: A Flexible and Reconfigurable Active Electrode Electrical Impedance Tomography System.

Electrical Impedance Tomography (EIT) systems have shown great promise in many fields such as real-time wearable healthcare imaging, but their fixed number of electrodes and placement locations limit the system's flexibility and adaptability for further advancement. In this article, we propose a flexible and reconfigurable EIT system (Flexi-EIT) based on digital active electrode (DAE) architecture to address these limitations. By integrating a reconfigurable number of up to 32 replaceable DAEs into the flexible printed circuit (FPC) based wearable electrode belt, we can enable rapid, reliable, and easy placement while maintaining high device flexibility and reliability. We also explore hardware-software co-optimization image reconstruction solutions to balance the size and accuracy of the model, the power consumption, and the real-time latency. Each DAE is designed using commercial chips and fabricated on a printed circuit board (PCB) measuring 13.1 mm × 24.4 mm and weighing 2 grams. In current excitation mode, it can provide programmable sinusoidal current signal output with frequencies up to 100 kHz and amplitudes up to 1 mA p-p that meets IEC 60601-1 standard. In voltage acquisition mode, it can pre-amplify, filter, and digitize the external response voltage signal, improving the robustness of the system while avoiding the need for subsequent analog signal processing circuits. Measured results on a mesh phantom demonstrate that the Flexi-EIT system can be easily configured with different numbers of DAEs and scan patterns to provide EIT measurement frames at 38 fps and real-time EIT images with at least 5 fps, showing the potential to be deployed in a variety of application scenarios and providing the optimal balance of system performance and hardware resource usage solutions.

Design and Implementation of a Linear Resistor Mesh Phantom for Evaluating the Linear ERT System

Design and Implementation of a Linear Resistor Mesh Phantom for Evaluating the Linear ERT System

A body-size-dependent series of Chinese adult standing phantoms for radiation dosimetry

Phantoms of different sizes, as indicated by several studies, have a significant impact on the accuracy of dose calculations. Therefore, it is necessary to establish a body-size-dependent series of Chinese standing adult phantoms to improve the accuracy of radiation dosimetry. In this study, the Chinese reference polygon-mesh phantoms have been refined and a method for automatically constructing lymph nodes in a mesh phantom has been proposed. Then, based on the refined phantoms, this study has developed 42 anthropometric standing adult computational phantoms, 21 models for each gender, with a height range of 145–185 cm and weight as a function of body mass index corresponding to healthy, overweight and obese. The parameters were extracted from the National Occupational Health Standards (GBZ) document of the People’s Republic of China, which covers more than 90% of the Chinese population. For a given body height and mass, phantoms are scaled in proportion to a factor reflecting the change of adipose tissue and the internal organs. The remainder is adjusted manually to match the target parameters. In addition, the constructed body-size-specific phantoms have been implemented in the in-house THUDose Monte Carlo code to calculate the dose coefficients (DCs) for external photon exposures in the antero-posterior, postero-anterior and right lateral geometries. The results showed that organ DCs varied significantly with body size at low energies () and high energies () due to the differences in anatomy. Organ DC differences between a phantom of a given size and a reference phantom vary by up to 40% for the same height and up to 400% for the whole phantom. The influence of body size differences on the DCs demonstrates that the body-size-dependent Chinese adult phantoms hold great promise for a wide range of applications in radiation dosimetry.

360º optoacoustic capsule endoscopy at 50 Hz for esophageal imaging

Gastrointestinal (GI) endoscopy is a common medical diagnostic procedure used for esophageal cancer detection. Current emerging capsule optoacoustic endoscopes, however, suffer from low pulse repetition rates and slow scanning units limit attainable imaging frame rates. Consequently, motion artifacts result in inaccurate spatial mapping and misinterpretation of data. To overcome these limitations, we report a 360º, 50 Hz frame rate, distal scanning capsule optoacoustic endoscope. The translational capability of the instrument for human GI tract imaging was characterized with an Archimedean spiral phantom consisting of twelve 100 µm sutures, a stainless steel mesh with a pitch of 3 mm and an ex vivo pig esophagus sample. We estimated an imaging penetration depth of ~0.84 mm in vivo by immersing the mesh phantom in intralipid solution to simulate light scattering in human esophageal tissue and validated our findings ex vivo using pig esophagus. This proof-of-concept study demonstrates the translational potential of the proposed video-rate endoscope for human GI tract imaging.

Design Automation of a Dynamic Thorax-Like Mesh Phantom for Evaluating the Performance of Electrical Impedance Tomography System

Abstract—Phantoms are used to evaluate, calibrate, and compare the performance of electrical impedance tomography (EIT) systems. This paper presents a dynamic thorax-like mesh phantom, which mimics the changes in electrical conductivity distribution within a human thorax at different time frames. Furthermore, element merging and contour smoothing, electrode placement techniques, and PCB design automation methods are proposed to simplify, optimize the mesh phantom, and reduce the hardware implementation cost. To verify the accuracy of the mesh phantom and its PCB, SPICE simulations and experimental testings are performed to obtain the conductance of the mesh phantom and reconstruct the images through the EIDORS software. These images achieve an image correlation coefficient (ICC) of 0.680 (model versus SPICE simulation) and 0.9098 (SPICE simulation versus measurement result), respectively. This demonstrates the validity of our proposed dynamic thorax-like mesh phantom.

High-resolution phantom of a nephron for radiation nephrotoxicity evaluation in biophysical simulations

<abstract> <p>Computer simulation plays an important role in medical physics. The aim of this study was to generate an accurate model to calculate the absorbed dose at the cell level in a voxelized phantom of nephrons. In order to implement a model of kidney microdosimetry, a 3D mesh phantom of a human kidney nephron, representing a cortical nephron, was digitized to create a 3D voxelized phantom of a nephron for use in Monte Carlo simulations. The phantom was fed to GATE Monte Carlo toolkits, and simulations were performed to calculate the absorbed dose/energy from alpha and electron sources over a range of energy levels. The results were compared to the results published in literature that were derived by using a stylized phantom. The dose estimated in subunits of the voxelized and stylized phantoms showed a considerable bias (average of relative differences). The maximum difference for self-absorption was 12.5%, and up to 20% for cross-absorption. The digital phantom showed very significant differences in dose distribution among the cells in different subunits of the nephron. The results demonstrated that a small dissimilarity in the size and shape of subunits can lead to a considerable difference in the microdosimetry results. The model presented in this study offers a phantom that not only presents the realistic geometry of a nephron, which has been neglected in previous stylized models, but also one that has the capability of plotting the spatial distribution of the absorbed dose for any distribution of radiopharmaceuticals in nephron cells.</p> </abstract>

Optimization of mask size for median-modified Wiener filter according to matrix size of computed tomography images

We investigated the variation in the noise level and image restoration efficiency as a function of the mask size of the median-modified Wiener filter (MMWF) as applied to computed tomography (CT) images of various matrix sizes. We applied the MMWF with various mask sizes to simulated images of various sizes, which were acquired images using the Shepp–Logan​ phantom and a Male Adult meSH phantom, and we found that for both phantoms, the noise level reduced as the mask size increased. In addition, we calculated the optimized mask size for each matrix size in the case of image-similarity evaluation. Moreover, we conducted an experimental study using the CT image of a chest phantom to evaluate the noise-reduction efficiency of the MMWF with the application of the optimized mask size by calculating the coefficient of variation (COV), signal to noise ratio (SNR), and contrast to noise ratio (CNR). As a result, compared to images without MMWF applied, the COV, SNR, and CNR of image with MMWF were improved by 2.01, 1.02, and 1.60 times, respectively. In conclusion, our findings demonstrate the importance of mask-size optimization (for a given matrix size) in improving the MMWF efficiency.

Noise Level and Similarity Analysis for Computed Tomographic Thoracic Image with Fast Non-Local Means Denoising Algorithm

Although conventional denoising filters have been developed for noise reduction from digital images, these filters simultaneously cause blurring in the images. To address this problem, we proposed the fast non-local means (FNLM) denoising algorithm which would preserve the edge information of objects better than conventional denoising filters. In this study, we obtained thoracic computed tomography (CT) images from a male adult mesh (MASH) phantom modeled by computer and a five-year-old phantom to perform both the simulation study and the practical study. Subsequently, the FNLM denoising algorithm and conventional denoising filters, such as the Gaussian, median, and Wiener filters, were applied to the MASH phantom image adding Gaussian noise with a standard deviation of 0.002 and practical CT images. Finally, the results were compared quantitatively in terms of the coefficient of variation (COV), contrast-to-noise ratio (CNR), peak signal-to-noise ratio (PSNR), and correlation coefficient (CC). The results showed that the FNLM denoising algorithm was more efficient than the conventional denoising filters. In conclusion, through the simulation study and the practical study, this study demonstrated the feasibility of the FNLM denoising algorithm for noise reduction from thoracic CT images.

Anthropomorphic left ventricular mesh phantom: a framework to investigate the accuracy of SQUEEZ using Coherent Point Drift for the detection of regional wall motion abnormalities.

We present an anthropomorphically accurate left ventricular (LV) phantom derived from human computed tomography (CT) data to serve as the ground truth for the optimization and the spatial resolution quantification of a CT-derived regional strain metric (SQUEEZ) for the detection of regional wall motion abnormalities. Displacements were applied to the mesh points of a clinically derived end-diastolic LV mesh to create analytical end-systolic poses with physiologically accurate endocardial strains. Normal function and regional dysfunction of four sizes [1, 2/3, 1/2, and 1/3 American Heart Association (AHA) segments as core diameter], each exhibiting hypokinesia (70% reduction in strain) and subtle hypokinesia (40% reduction in strain), were simulated. Regional shortening ( ) estimates were obtained by registering the end-diastolic mesh to each simulated end-systolic mesh condition using a nonrigid registration algorithm. Ground-truth models of normal function and of hypokinesia were used to identify the optimal parameters in the registration algorithm and to measure the accuracy of detecting regional dysfunction of varying sizes and severities. For normal LV function, values in all 16 AHA segments were accurate to within . For cases with regional dysfunction, the errors in around the dysfunctional region increased with decreasing size of dysfunctional tissue.

Image Optimization of Fast Non Local Means Noise Reduction Algorithm using Various Filtering Factors with Human Anthropomorphic Phantom : a Simulation Study

In this study we analyzed the tendency of the image characteristic by changing filtering factor for the proposed fast non local means (FNLM) noise reduction algorithm with designed Male Adult mesh (MASH) phantom through Geant4 application for tomographic emission (GATE) simulation program. To accomplish this purpose, MASH phantom for human copy was designed through the GATE simulation program. In addition, we acquired degraded image by adding Gaussian noise with a value of 0.005 using the MATALB program in MASH phantom. Moreover, in degraded image, the FNLM noise reduction algorithm was applied by changing the filtering factors, which set to 0.005, 0.01, 0.05, 0.1, 0.5, and 1.0 value, respectively. To quantitatively evaluate, the coefficient of variation (COV), signal to noise ratio (SNR), and contrast to noise ratio (CNR) were calculated in reconstructed images. Results of the COV, SNR and CNR were most improved in image with a filtering factor of 0.05 value. Especially, the COV was decreased with increasing filtering factor, and showed nearly constant values after 0.05 value of the filtering factor. In addition, SNR and CNR were showed that improvement with increasing filtering factor, and deterioration after 0.05 value of the filtering factor. In conclusion, we demonstrated the significance of setting the filtering factor when applying the FNLM noise reduction algorithm in degraded image.

A study on dose conversion from a material to human body using mesh phantom for retrospective dosimetry

In case of a radiation emergency, thermoluminescence (TL) and optically stimulated luminescence (OSL) measurements from materials in a mobile phone have been developed to enable classification of exposed individuals within a short period of time. A reconstructed dose from a mobile phone does not, however, correspond directly to a human body dose. Therefore, several studies were tried to convert a phone dose to a human body dose. Because of the difficulty in obtaining conversion factors experimentally, Monte Carlo simulations have been carried out using human phantoms for various accident situations. In recent years phantoms made of mesh have been developed to solve some problems in traditional voxel phantoms such as limited posture. In the present study, simulations using the GEANT4 computer code were performed to obtain conversion factors using mesh phantoms. The geometry of a mobile phone was designed, reflecting latest structures, and a display glass was selected as a dosimetric material due to its wide detection area with a high radiation sensitivity. Four different positions (chest, hip, thigh, and hand) of a mobile phone on the phantom were considered. In addition, six exposure conditions of anterior-posterior (AP), posterior-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), isotropic (ISO), and rotational (ROT) exposure geometries and three different postures of standing, kneeling, and squatting were selected to reflect actual working situations. Three commonly used radiation sources (Iridium-192, Cesium-137, and Cobalt-60) were applied.

Development and Validation of the Realistic Anthropomorphic Flexible (RAF) Phantom.

Voxel phantoms developed by segmenting computed tomography images are known to be more anatomically accurate than mathematical phantoms. However, due to their lack of flexibility and the complexity of voxel datasets, the use of voxel phantoms in dosimetry is often impractical. This paper describes the development of the realistic anthropomorphic flexible (RAF) polygonal mesh phantom, a novel phantom based on Boundary Representation (B-Rep) that merges anatomical accuracy and flexibility. Rather than using segmentation of tomography images, the modeling of the phantom's organs was based on freely and commercially available anatomical atlases, ICRP 89, and recent medical literature. To validate the phantom, a high-resolution voxel version was created for the MCNPx transport code. The voxelized RAF phantom was validated by comparing it with the ICRP 110 male phantom for external irradiations with parallel beams of photons and electrons. Dose coefficients obtained from simulations with the RAF phantom were compared with those from ICRP Publication 116. Relevant differences in organ doses were found.

EVALUATION OF EYE LENS DOSE TO WORKERS IN THE STEAM GENERATOR AT THE KOREAN OPTIMIZED POWER REACTOR 1000.

ICRP (2011) revised the dose limit to the eye lens to 20 mSv/y based on a recent epidemiological study of radiation-induced cataracts. Maintenance of steam generators at nuclear power plants is one of the highest radiation-associated tasks within a non-uniform radiation field. This study aims to evaluate eye lens doses in the steam generators of the Korean OPR1000 design. The source term was characterized based on the CRUD-specific activity, and both the eye lens dose and organ dose were simulated using MCNP6 combined with an ICRP voxel phantom and a mesh phantom, respectively. The eye lens dose was determined to be 5.39E-02-9.43E-02 Sv/h, with a negligible effect by beta particles. As the effective dose was found to be 0.81-1.21 times the lens equivalent dose depending on the phantom angles, the former can be used to estimate the lens dose in the SG of the OPR1000 for radiation monitoring purposes.

SU‐E‐CAMPUS‐I‐02: Estimation of the Dosimetric Error Caused by the Voxelization of Hybrid Computational Phantoms Using Triangle Mesh‐Based Monte Carlo Transport

Purpose:Computational voxel phantom provides realistic anatomy but the voxel structure may result in dosimetric error compared to real anatomy composed of perfect surface. We analyzed the dosimetric error caused from the voxel structure in hybrid computational phantoms by comparing the voxel‐based doses at different resolutions with triangle mesh‐based doses.Methods:We incorporated the existing adult male UF/NCI hybrid phantom in mesh format into a Monte Carlo transport code, penMesh that supports triangle meshes. We calculated energy deposition to selected organs of interest for parallel photon beams with three mono energies (0.1, 1, and 10 MeV) in antero‐posterior geometry. We also calculated organ energy deposition using three voxel phantoms with different voxel resolutions (1, 5, and 10 mm) using MCNPX2.7.Results:Comparison of organ energy deposition between the two methods showed that agreement overall improved for higher voxel resolution, but for many organs the differences were small. Difference in the energy deposition for 1 MeV, for example, decreased from 11.5% to 1.7% in muscle but only from 0.6% to 0.3% in liver as voxel resolution increased from 10 mm to 1 mm. The differences were smaller at higher energies. The number of photon histories processed per second in voxels were 6.4×104, 3.3×104, and 1.3×104, for 10, 5, and 1 mm resolutions at 10 MeV, respectively, while meshes ran at 4.0×104 histories/sec.Conclusion:The combination of hybrid mesh phantom and penMesh was proved to be accurate and of similar speed compared to the voxel phantom and MCNPX. The lowest voxel resolution caused a maximum dosimetric error of 12.6% at 0.1 MeV and 6.8% at 10 MeV but the error was insignificant in some organs. We will apply the tool to calculate dose to very thin layer tissues (e.g., radiosensitive layer in gastro intestines) which cannot be modeled by voxel phantoms.

Tetrahedral-mesh-based computational human phantom for fast Monte Carlo dose calculations

Although polygonal-surface computational human phantoms can address several critical limitations of conventional voxel phantoms, their Monte Carlo simulation speeds are much slower than those of voxel phantoms. In this study, we sought to overcome this problem by developing a new type of computational human phantom, a tetrahedral mesh phantom, by converting a polygonal surface phantom to a tetrahedral mesh geometry. The constructed phantom was implemented in the Geant4 Monte Carlo code to calculate organ doses as well as to measure computation speed, the values were then compared with those for the original polygonal surface phantom. It was found that using the tetrahedral mesh phantom significantly improved the computation speed by factors of between 150 and 832 considering all of the particles and simulated energies other than the low-energy neutrons (0.01 and 1 MeV), for which the improvement was less significant (17.2 and 8.8 times, respectively).

A Resistive Mesh Phantom for Assessing the Performance of EIT Systems

Assessing the performance of electrical impedance tomography (EIT) systems usually requires a phantom for validation, calibration, or comparison purposes. This paper describes a resistive mesh phantom to assess the performance of EIT systems while taking into account cabling stray effects similar to in vivo conditions. This phantom is built with 340 precision resistors on a printed circuit board representing a 2-D circular homogeneous medium. It also integrates equivalent electrical models of the Ag/AgCl electrode impedances. The parameters of the electrode models were fitted from impedance curves measured with an impedance analyzer. The technique used to build the phantom is general and applicable to phantoms of arbitrary shape and conductivity distribution. We describe three performance indicators that can be measured with our phantom for every measurement of an EIT data frame: SNR, accuracy, and modeling accuracy. These performance indicators were evaluated on our EIT system under different frame rates and applied current intensities. The performance indicators are dependent on frame rate, operating frequency, applied current intensity, measurement strategy, and intermodulation distortion when performing simultaneous measurements at several frequencies. These parameter values should, therefore, always be specified when reporting performance indicators to better appreciate their significance.

A multi-frequency EIT system design based on telecommunication signal processors

A multi-frequency electrical impedance tomography system for cardiopulmonary monitoring has been designed with specialized digital signal processors developed primarily for the telecommunications sector. The system consists of two modules: a scan-head and a base-station. The scan-head, located close to the patient's torso, contains front-end circuits for measuring transfer impedance with a 16-electrode array. The base-station, placed at the bedside, comprises 16 direct digital synthesizers, 32 digital down-converters, digital circuits to control the data acquisition sequence and a USB-2.0 microcontroller. At every step of the scan sequence, the system simultaneously measures four complex variables at eight frequencies. These variables are the potential difference between the selected pair of sense electrodes, the currents applied by the source and sink electrodes, and the current flowing through the ground electrode. Frequencies are programmable from 10 kHz to 2 MHz with a resolution of 2 mHz. Characterization tests were performed with a precision mesh phantom connected to the scan-head. For a 5 Hz frame rate, the mean signal-to-noise ratio and accuracy are, respectively, 43 dB and 95.4% for eight frequencies logarithmically spaced from 70 to 950 kHz. In vitro and in vivo time-difference images have been reconstructed.

Accounting for hardware imperfections in EIT image reconstruction algorithms

Electrical impedance tomography (EIT) is a non-invasive technique for imaging the conductivity distribution of a body section. Different types of EIT images can be reconstructed: absolute, time difference and frequency difference. Reconstruction algorithms are sensitive to many errors which translate into image artefacts. These errors generally result from incorrect modelling or inaccurate measurements. Every reconstruction algorithm incorporates a model of the physical set-up which must be as accurate as possible since any discrepancy with the actual set-up will cause image artefacts. Several methods have been proposed in the literature to improve the model realism, such as creating anatomical-shaped meshes, adding a complete electrode model and tracking changes in electrode contact impedances and positions. Absolute and frequency difference reconstruction algorithms are particularly sensitive to measurement errors and generally assume that measurements are made with an ideal EIT system. Real EIT systems have hardware imperfections that cause measurement errors. These errors translate into image artefacts since the reconstruction algorithm cannot properly discriminate genuine measurement variations produced by the medium under study from those caused by hardware imperfections. We therefore propose a method for eliminating these artefacts by integrating a model of the system hardware imperfections into the reconstruction algorithms. The effectiveness of the method has been evaluated by reconstructing absolute, time difference and frequency difference images with and without the hardware model from data acquired on a resistor mesh phantom. Results have shown that artefacts are smaller for images reconstructed with the model, especially for frequency difference imaging.

SU‐FF‐I‐125: Accuracy and Reliability of Manual Vessel Sizing Measurements Among Different Users and Systems

Purpose: Vessel sizing is an essential component of each vascular intervention. While the focus in the literature has been on sizing the stenosis, we have found that the critical interventional data are the proximal and distal vessel sizes and length of the interventional device, e.g., balloon or stent. We investigated the accuracy and reliability of these data for three clinical systems. Method and Materials: X‐ray images were obtained of cylindrical aluminum rod phantoms with different diameters and of patient angiograms of cardiac arteries with stenoses. The systems were manually calibrated using a wire mesh phantom (phantoms) or marker wire (patient) each having 1 cm spacing. Vessel sizes were measured using the same manual interactions on all three systems, indicating points at the edge of the vessel, proximal and distal to the lesion. The length for the device was measured as the distance from the proximal to distal measurement points. Three users performed calibrations and measurements with and without digital zoom. Measurements were repeated three times. Results: Accuracy of manual measurements is high . Using zoomed images improves accuracy and reliability . The variations across users and systems are comparable for clinical images (∼ 0.1 mm (sizes), ∼ 0.35 mm (lengths)). Conclusion: These results indicate that manual measurements of vessel sizes and lengths are accurate and reliable in the clinical arena, although there are variations between users and systems. Conflict of Interest: This study was supported by NIH Grant ♯ HL052567 and Toshiba Medical Systems Corporation.

Experimental acquisition system for impedance tomography with active electrode approach

An experimental system for impedance tomography has been constructed. The acquisition system uses 16 multifunctional active electrodes, each including a current source and a voltage buffer. Images of active and reactive parts of different target impedances in a phantom filled with liquid have been obtained. The system performance has been compared with those of other systems using either a mesh phantom or rods as point sources used for the determination of the modulation transfer function.