Phantom Boundary Research Articles

Resistivity Imaging of a Phantom with Irregular Inhomogeneities with 32 Silver Electrodes based Sensory System in Two Dimensional Electrical Impedance Tomography

Abstract In this paper, 32-silver electrodes based electrical impedance tomography (EIT) system has been modeled, fabricated and tested with different irregular inhomogeneities. In order to execute the proposed work, a simulation study using Finite Element Method (FEM) based Multiphysics software has been performed, in which we have imaged perfectly the shape, position and sizes of irregular shaped objects situated within a specified phantom area in a two dimensional (2-D) plane. Simultaneously, we have developed a real-time system consists of 32 silver electrodes (placed equidistantly) to detect non-conducting objects like plastic container and stone in normal saline solution. We have injected a constant current to the phantom boundary and the surface potentials are being measured using neighbouring method. The output voltages are collected and stored in the form of data sets for reconstructing the voltage density distribution plot using forward solver algorithm of EIT in FEM based Multiphysics Software. The resulting images show the resistivity profiles within the phantom area through which the presence of those objects are successfully observed.

SU-E-T-501: Perturbation of TG-43 Parameters of the Brachytherapy Sources under Insufficient Scattering Materials.

According to the TG-43 recommendations of American Association of Physicist in Medicine (AAPM), the dosimetry parameters of brachytherapy sources are obtained in a water phantom with full scattering conditions. However, in many actual clinical treatments the source are not surrounded with sufficient tissue in all directions to provide the full scattering condition. HDR brachytherapy of the breast or 125I eye-plaque treatment of the ocular melanoma are among the treatment sites that fits this category. In this project, the impact of insufficient phantom material surrounding the 137Cs, 192Ir, and 103Pd brachytherapy source on their TG43 dosimetric characteristics has been investigated. In this study, the effect of the insufficient tissue (referred here as missing tissues) around the brachytherapy sources on their TG-43 dosimetric parameters have been investigated using MCNP5 Monte Carlo code. The brachytherapy sources were simulated in different locations inside a cubical water phantom with the dimensions of 30*30*30 cm3 . The variation of the dosimetric parameters of the three sources (i.e. Î>, g(r), and F(r,θ)) were compared to the values from full scattering conditions (i.e. source at the center of the phantom). The results of this study indicate the variation of g(r)and 2D anisotropy function of the brachytherapy sources as a function of the missing tissue thickness. These changes increase by decreasing the energy of the photons emitted by the brachytherapy sources. These differences are mainly due to the lack of full scattering condition for the points near the phantom boundary. Unlike the published data for symmetric, but insufficient phantom material around the source, the impact of asymmetric phantom materials have been evaluated on dosimetric characteristics of the brachytherapy sources.

Crossing the phantom boundary in f(R) modified gravity: Jordan vs. Einstein frames

We study the capability of f(R) gravity models to allow for crossing the phantom boundary in both Jordan and Einstein conformal frames. In the Einstein frame, these models are equivalent to Einstein gravity with a scalar field minimally coupled to gravity. This scalar degree of freedom appears as a quintessence field with a coupling to the matter sector. We investigate the evolution of the equation of state parameter for some cosmologically viable f(R) gravity models in both conformal frames. This investigation (beyond mere theoretical arguments) acts as an operational tool to distinguish the physical status of the two conformal frames. It shows that this status is not the same.

Studying the resistivity imaging of chicken tissue phantoms with different current patterns in Electrical Impedance Tomography (EIT)

A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IRMean and IRMax neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom.

TIME VARIABLE COSMOLOGICAL CONSTANT OF HOLOGRAPHIC ORIGIN WITH INTERACTION IN BRANS–DICKE THEORY

Time variable cosmological constant (TVCC) of holographic origin with interaction in Brans–Dicke theory is discussed in this paper. We investigate some characters for this model, and show the evolutions of deceleration parameter and equation of state (EOS) for dark energy. It is shown that in this scenario an accelerating universe can be obtained and the evolution of EOS for dark energy can cross over the boundary of phantom divide. In addition, a geometrical diagnostic method, jerk parameter, is applied to this model to distinguish it with cosmological constant.

Cosmological constraints on the generalized holographic dark energy

We use the Markov Chain Monte Carlo method to investigate global constraints on the generalized holographic (GH) dark energy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic dark energy can cross over the phantom boundary w de =−1.

Surface electrode switching of a 16-electrode wireless EIT system using RF-based digital data transmission scheme with 8 channel encoder/decoder ICs

A Radio Frequency (RF) based digital data transmission scheme with 8 channel encoder/decoder ICs is proposed for surface electrode switching of a 16-electrode wireless Electrical Impedance Tomography (EIT) system. A RF based wireless digital data transmission module (WDDTM) is developed and the electrode switching of a EIT system is studied by analyzing the boundary data collected and the resistivity images of practical phantoms. An analog multiplexers based electrode switching module (ESM) is developed with analog multiplexers and switched with parallel digital data transmitted by a wireless transmitter/receiver (Tx/Rx) module working with radio frequency technology. Parallel digital bits are generated using NI USB 6251 card working in LabVIEW platform and sent to transmission module to transmit the digital data to the receiver end. The transmitter/receiver module developed is properly interfaced with the personal computer (PC) and practical phantoms through the ESM and USB based DAQ system respectively. It is observed that the digital bits required for multiplexer operation are sequentially generated by the digital output (D/O) ports of the DAQ card. Parallel to serial and serial to parallel conversion of digital data are suitably done by encoder and decoder ICs. Wireless digital data transmission module successfully transmitted and received the parallel data required for switching the current and voltage electrodes wirelessly. 1mA, 50kHz sinusoidal constant current is injected at the phantom boundary using common ground current injection protocol and the boundary potentials developed at the voltage electrodes are measured. Resistivity images of the practical phantoms are reconstructed from boundary data using EIDORS. Boundary data and the resistivity images reconstructed from the surface potentials are studied to assess the wireless digital data transmission system. Boundary data profiles of the practical phantom with different configurations show that the multiplexers are operating in the required sequence for common ground current injection protocol. The voltage peaks obtained at the proper positions in the boundary data profiles proved the sequential operation of multiplexers and successful wireless transmission of digital bits. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn again indicates a sequential and proper operation of multiplexers as well as the successful wireless transmission of digital bits. Hence the developed RF based wireless digital data transmission module (WDDTM) is found suitable for transmitting digital bits required for electrode switching in wireless EIT data acquisition system.

F(R) GRAVITY AND ITS COSMOLOGICAL IMPLICATIONS

We have investigated the evolution of a homogeneous isotropic background of the Universe and inhomogeneous subhorizon matter density perturbations in viable f(R) models of present dark energy and cosmic acceleration analytically and numerically. It is found that viable f(R) models generically exhibit recent crossing of the phantom boundary w DE = -1. Furthermore, it is shown that the growth index of perturbations depends both on time and wavenumber. This anomalous growth may explain properties of the observational matter power spectrum from the SDSS data and can also partially counteract the spectrum suppression by massive neutrinos making larger values of the total sum of neutrino rest-masses possible.

A Chicken Tissue Phantom for Studying an Electrical Impedance Tomography (EIT) System Suitable for Clinical Imaging

The study of practical phantoms is essential for assessing the reconstruction algorithms and instrumentation used in Electrical Impedance Tomography (EIT). Responses of saline phantoms with insulator inhomogeneities differ from the real tissue phantoms in several aspects. Also, it is difficult to reconstruct the actual resistivity of the insulator inhomogeneity in a saline background because of their large resistivity difference. A practical biological phantom consisting of two different materials with low resistivity difference is more suitable for impedance imaging studies. In order to demonstrate this, a chicken tissue phantom was developed to study the resistivity imaging in EIT. A 16-electrode array was placed inside the phantom tank filled with chicken muscle tissue paste and chicken tissue. A 1 mA, 50 kHz sinusoidal current was injected at the phantom boundary and the boundary potentials are measured using opposite current injection protocol. Resistivity images were reconstructed from the boundary data using Electrical Impedance and Diffuse Optical Reconstruction Software (EIDORS) and the reconstruction was evaluated by calculating the contrast parameters of the images. Results show that the resistivity of the chicken fat is successfully reconstructed with a proper background resistivity. Impedance spectroscopic studies show that the chicken tissue phantom can be suitably used to evaluate a multifrequency EIT system.

Techniques for performing quantitative measurements of high intensity focused ultrasound intensity distributions noninvasively.

Estimation of the HIFU intensity field at clinically relevant power levels can be difficult due to the possibility of hydrophone damage or of sensor interference with the focused beam. To address this issue, we have developed two non‐invasive methods for determining the intensity in free field and in tissue‐mimicking material. In the first method, streaming field generated by the absorption of acoustic energy in liquid is measured using particle image velocimetry. The intensity distribution giving rise to the velocity field is computed by performing the operations of the Navier–Stokes equations upon the experimentally measured streaming field. The second technique (IR thermography) involves the use of an infrared camera to measure the temperature within a tissue‐phantom. An air interface is required at the phantom boundary in order for the IR camera to observe the temperature rise. Quantitative determination of the intensity can be difficult due to the presence of the air interface (at which the intensity is zero), heat conduction within the phantom, and convection currents arising in the air. Mathematical relations that address these complications and allow for intensity measurements have been derived. Intensity fields obtained using both methods will be shown, along with comparisons with hydrophone measurements.

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities in 2D-electrical impedance tomography

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities is studied with a simple instrumentation and data acquisition system for Electrical Impedance Tomography. The reconfigurable phantom is developed with stainless steel electrodes and a sinusoidal current of constant amplitude is injected to the phantom boundary using opposite current injection protocol. Nylon and polypropylene cylinders with different cross sectional areas are kept inside the phantom and the boundary potential data are collected. The instrumentation and the data acquisition system with a DIP switch-based multiplexer board are used to inject a constant current of desired amplitude and frequency. Voltage data for the first eight current patterns (128 voltage data) are found to be sufficient to reconstruct the inhomogeneities and hence the acquisition time is reduced. Resistivity images are reconstructed from the boundary data for different inhomogeneity positions using EIDORS-2D. The results show that the shape and resistivity of the inhomogeneity as well as the background resistivity are successfully reconstructed from the potential data for single or double inhomogeneity phantoms. The resistivity images obtained from the single and double inhomogeneity phantom clearly indicate the inhomogeneity as the high resistive material. Contrast to noise ratio (CNR) and contrast recovery (CR) of the reconstructed images are found high for the inhomogeneities near all the electrodes arbitrarily chosen for the entire study.

Phantom Boundary Crossing and Anomalous Growth Index of Fluctuations in Viable f(R) Models of Cosmic Acceleration

Evolution of a background space-time metric and sub-horizon matter density perturbations in the Universe is numerically analyzed in viable $f(R)$ models of present dark energy and cosmic acceleration. It is found that viable models generically exhibit recent crossing of the phantom boundary $w_{\rm DE}=-1$. Furthermore, it is shown that, as a consequence of the anomalous growth of density perturbations during the end of the matter-dominated stage, their growth index evolves non-monotonically with time and may even become negative temporarily.

Near infrared tomographic system based on high angular resolution mechanism – Design, calibration, and performance

This study aims at the design, implementation, and verification of a near infrared (NIR) diffuse optical tomography (DOT) electro-optical imaging system based on a measuring instrument with single rotating source/detector scanning mechanism and an image reconstruction scheme implemented on an off-line PC. The developed measurement instrument possesses a high degree of angular resolution and is operated in a continuous-intensity scheme to acquire output NIR intensity signals. In this paper, some considerations of this measuring instrument are investigated such as phantom preparation, temporal stability, and container influence, etc. Experimental trials were conducted using both homogeneous and heterogeneous phantoms made of high-scattering microspheres or Intralipid. In order to verify the developed imaging system with tomographic image reconstruction, the intensity was acquired from the heterogeneous Intralipid phantom using NIR light at 800 nm, where the homogenous background as the normal tissue is inserted with an inclusion as the tumor. For the comparison of heterogeneous phantoms with homogeneous phantoms, 1-D measured intensity signals indicate the angular position of the inclusion, especially for the case of the inclusion near the phantom boundary. Furthermore, promising results of corresponding optical-property images can be reconstructed with the measured intensities as inputs of the image reconstruction scheme. Obviously, the developed NIR DOT tomographic system has been successfully built upon the experimental, analytical, and computational work.

Detection of mercury in the kidney via source‐excited x‐ray fluorescence

AbstractNon‐invasive detection of kidney Hg in vivo is important in order to prevent detrimental health effects in occupationally exposed persons. In this study, preliminary results of a 109Cd source‐based x‐ray fluorescence system for the detection of Hg in the kidney are presented. The system includes a single 50 mm diameter HPGe detector with a 109Cd source mounted on the detector face for backscatter measurement geometry. A detection limit of 3.9 ppm was obtained during a bare kidney phantom feasibility study. In order to simulate an in vivo measurement, kidney phantoms were also placed inside a water tank representing the torso. The detection limit was 5.0 ppm at 1 cm phantom depth, as measured to the phantom boundary. As expected, Hg sensitivity decreased with kidney depth owing to the attenuation of incident 109Cd γ‐rays and emitted characteristic Hg K x‐rays, so that at a phantom depth of 4 cm the detection limit was 44 ppm. Further improvements to the detection limit will allow future in vivo kidney Hg measurements of chronically exposed workers. Copyright © 2007 John Wiley & Sons, Ltd.

A fast and accurate treatment planning method for boron neutron capture therapy

Background and purpose: The aim of this study was to test the applicability of conventional semi-empirical algorithms for the treatment planning of boron neutron capture therapy (BNCT). Materials and methods: Beam data of a clinical epithermal BNCT beam obtained in a large cuboid water phantom were introduced into a commercial treatment planning system (TPS). For the calculation of thermal neutron fluence distributions, the Gaussian pencil beam model of the electron beam treatment planning algorithm was used. A simple photon beam algorithm was used for the calculation of the gamma-ray and fast neutron dose distribution. The calculated dose and fluence distributions in the central plane of an anthropomorphic head phantom were compared with measurements for various field sizes. The calculation time was less than 1 min. Results: At the normalization point in the head phantom, the absolute dose and fluence values agreed within the measurement uncertainty of approximately 2–3% (1 SD) with those at the same depth in a cuboid phantom of approximately the same size. Excellent agreement of within 2–3% (1 SD) was obtained between measured and calculated relative fluence and dose values on the central beam axis and at most off-axis positions in the head phantom. At positions near the phantom boundaries, generally in low dose regions, local differences of approximately 30% were observed. Conclusions: A fast and accurate treatment planning method has been developed for BNCT. This is the first treatment planning method that may allow the same interactive optimization procedures for BNCT as applied clinically for conventional radiotherapy.