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The comparison was made to illustrate the factor, which leads to the difference of radiofrequency induced heating associated with implants between in-vivo and in-vitro. The simulations of virtual adult male and ASTM phantom, with a group of orthopedic plate implants, were performed in a body-sized birdcage coil driven at 128MHz. For femur and humerus orthopedic plate implants with various dimension,...
The objective of this study is to numerically compare the radio frequency (RF)-induced heating in transverse electromagnetic (TEM) coil and birdcage (BC) coil in the presence of circular leg fixator. We show that TEM coil generates a larger peak specific absorption rate averaged over 1 gram (SAR1g) than BC coil in the leg phantom with a generic circular external fixator. In the specific case, the...
Numerical studies of local specific absorption rate (SAR) were conducted for femoral plate implants in MRI 3T birdcage coil. Both the quadrature excitation and RF shimming conditions were evaluated in anatomical models of human body. All the results were normalized to 2W/kg average whole body SAR and Q-Matrices formalism method was used to improve the SAR calculation efficiency. The RF shimming procedure...
The objective of this study is to numerically compare the radio frequency (RF) — induced heating in transverse electromagnetic (TEM) coil and birdcage (BC) coil in the presence of circular leg fixator. We show that TEM coil generates a larger peak specific absorption rate averaged over 1 gram (SAR1g) than BC coil with circular external fixator. In the specific case, the peak SAR1g in TEM coil can...
In this study the helical stent is evaluated of the radio frequency (RF)-induced heating for the variation of gap and pitch under 1.5 T and 3 T magnetic resonance imaging (MRI). It is shown that the gap increment can reduce the peak 1 g averaged SAR and the pitch variation can also alter the heating. The detailed discussions are presented.
The comparison was made to illustrate the factor, which leads to the difference of radiofrequency induced heating associated with implants between in-vivo and in-vitro. The simulations of virtual adult male and ASTM phantom, with a group of orthopedic plate implants, were performed in a body-sized birdcage coil driven at 128MHz. For femur and humerus orthopedic plate implants with various dimension,...
In this paper, a fast prediction method using a 3-layer feed-forward neural network was proposed to estimate the radiofrequency (RF) — induced heating for generic implantable plate devices under magnetic resonance imaging (MRI). The peak local specific absorption rate averaged over 1 gram (SAR1g) was calculated to represent the heating level. A total number of 130 plate devices have been numerically...
Transfer function method was utilized to evaluate the RF-induced heating of implantable lead with 137 implanted lead trajectories under different shimming conditions. A coated wire is used to emulate medical leads. Two different shimming conditions were studied. One is to optimize the homogeneity of the B_(1+) field magnitude in human heart region, and second one is to estimate the possible worst-case...
In this study we present numerical simulations of the Specific Absorption Rate (SAR) for multi-component orthopaedic hip replacement systems. The SAR is used to evaluate the radio frequency (RF)-induced heating of the devices during magnetic resonance imaging (MRI). Because multi-component orthopaedic hip replacement systems have many combinations of components with various designs and sizes, it is...
The RF-induced heating is one of the main problems in diagnostic MRI. The standard way to assess the RF-induced heating is to perform experimental or computational phantom studies. Due to the inherent differences in geometry and electrical parameters between the phantom and the human body, the induced RF-induced heating assessed in the phantom is typically not be the same as in human body. In this...
In this work, a novel implantable medical stent is designed to reduce the radio frequency (RF)-induced heating from implantable medical stent under magnetic resonance imaging (MRI) procedure. By using segmented structure, the induced specific absorption rate (SAR) for a 100 mm length stent is reduced from 54.4 mW/g to 13.4 mW/g. Numerical simulation demonstrates the effectiveness of the designed structure.
One of the critical MRI safety concerns for patients with medical implants is the RF coil induced heating in the vicinity of electrode lead tip. Many works have been carried out to assess such risk for fully implanted leads. However studies on partially implanted, as well as minimally implanted electrodes have not been explored. In addition, effects of statures, weight, ages and many other factors...
One of the most critical MRI safety concerns for patients with medical implants is the RF coil induced heating in the vicinity of medical electrode lead tip. In this study, temperature rises for different lead path configurations are evaluated using transfer function method. Lead tip heating along three configurations: fully implanted, partially implanted, and minimum implanted medical electrode leads...
In this paper, a quick and efficient approach is proposed to estimate the in-vivo RF induced heating of small medical implants under MRI procedure. The method is based on scaling the in-vivo incident electric fields. Numerical and experimental studies demonstrate the efficiency and accuracy of the proposed method.
Using absorption materials to reduce RF heating during MRI procedure is studied in this paper. Materials with different electromagnetic absorption characteristics are used to alter the EM and current distributions on the device. Consequently, the RF induced heating behaviors of external fixation devices can be reduced. Numerical and experimental studies are provided to demonstrate the potentials of...
This paper focuses on control of hydrogen production via autothermal reforming of methanol. Owing to uncertainty of model parameters, a sliding mode controller is designed for regulating hydrogen yield by manipulating methanol flow and water flow. Theoretical analysis and simulations demonstrate its adaptability to shifts of model parameters. In addition, a variable ratio controller is proposed in...
A high voltage laterally insulated-gate-bipolar-transistor (LIGBT) built in ultra-thin silicon-on-insulator (SOI) is reported. A theoretical analysis about the efficient approach to increasing the holding voltage of LIGBT starting with BJT's has been proposed. Higher holding voltage and almost the same turn-on speed is achieved by segmenting the emitter area of LIGBT to increase the resistance.
In this letter, the small-scale variations of cross-polar discrimination (XPD) are shown to have a generalized Beta prime distribution in Nakagami-m fading channels. The cumulative distribution function of the distribution can be simply computed in mathematical software like MATLAB. Indoor measurements have been carried out at 2.4 GHz to validate the derived XPD model. The theoretical distribution...
With the complete system analysis framework which takes the effects of matching networks and the appropriate power constraint into account, a simple proof demonstrates the maximum achievable eigenvalues and capacity of MIMO systems with any possible transmit and receive matching networks.
A novel capacity estimator for low rank multiple-input multiple-output (MIMO) channels impaired with white noise is proposed by reducing the impact of noise on both the spatial multiplexing gain and on the power gain. Numerical results show that the estimator performs better than conventional methods in estimation accuracy, and the requirements on the number of observations as well as on the computation...
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