Analytical Modeling of Noise in MRI Scanners

2007 ◽  
Author(s):  
Chris K. Mechefske ◽  
Wei Shao
Keyword(s):  
Acoustic Noise ◽  
Sound Field ◽  
Gradient Coil ◽  
Analytical Models ◽  
Gradient Coils ◽  
Radiation Impedance ◽  
Advantages And Disadvantages ◽  
Resonance Frequencies ◽  
Cylindrical Duct ◽  
Good Agreement

Acoustic noise generated by MRI scanners is sometimes a significant problem for patients by heightening their anxiety and even causing temporary and permanent hearing impairment. This noise is caused by the Lorentz forces acting on the gradient coils of MRI scanner bound within an epoxy resin cylinder. Some acoustic analytical models were developed to describe the sound radiation characteristics of the gradient coil system. The gradient coil was modeled as a finite cylindrical duct with vibrating walls. The sound field in the duct satisfied both the boundary conditions at the wall and at the open ends. The wave reflection phenomenon at the open ends of the finite duct was described by general radiation impedance. Comparisons between the results obtained by these analytical models and calculated by a commercial (boundary element method) BEM code are presented in this paper. Both the advantages and disadvantages of both methods are discussed. The comparisons show that the results calculated by all these models reached good agreement especially at the cut-off frequencies (resonance frequencies). Corresponding experimental data have also shown a similar trend at the cut-off frequencies.

Vibration and Acoustic Noise Characterization of a Gradient Coil Insert in a 4 T MRI

2004 ◽  
Vol 10 (6) ◽  
pp. 861-880 ◽  
Author(s):  
Chris K. Mechefske ◽  
G. Yao ◽  
Fenglin Wang
Keyword(s):  
Magnetic Resonance ◽  
Velocity Distribution ◽  
High Speed ◽  
Acoustic Noise ◽  
Sound Field ◽  
Modal Testing ◽  
Gradient Coil ◽  
Surface Velocity ◽  
Fea Model ◽  
High Magnetic Field Strength

High magnetic field strength and high-speed gradient coil current switching are becoming ever more commonplace in magnetic resonance imaging scanners. These and other factors are combining to yield high acoustic sound pressure levels (SPLs) in and around magnetic resonance imagers. Studies have already been conducted which partially characterize this sound field, and various methods have been investigated to attenuate the noise generated. In order to predict the vibration and acoustic response of a gradient coil inside a scanner, finite element analysis (FEA) was carried out. The model was based on specific internal and external structural dimensions and the material physical properties of a gradient coil. The FEA results were verified through experimental modal testing of the same gradient coil. It was found that the experimental modal analysis results were in good agreement with the FEA results. The Lorentz force distribution on the gradient coil caused by the time varying current in the coil windings was then applied to the FEA model to obtain the velocity distribution of the coil surface as a function of time. A vibro-acoustic computational model was then developed based on the verified FEA model. The surface velocity distribution was then used to predict the sound field inside the gradient coil. The vibro-acoustic model was verified using experimental noise measurements with swept sinusoidal waveform inputs to the gradient coil conductors. The numerical methods developed in this study could provide a guide and virtual testing platform for the designer of gradient coils to predict the vibration and acoustic behavior of new designs and thereby offer the opportunity to redesign and/or optimize the design to reduce SPLs.

Acoustic Noise Reduction Liner for a 4T MRI Scanner

2005 ◽  
Author(s):  
Chris K. Mechefske
Keyword(s):  
High Speed ◽  
Acoustic Noise ◽  
Sound Field ◽  
Gradient Coil ◽  
Patient Anxiety ◽  
Noise Levels ◽  
Acoustic Liner ◽  
Imaging Research ◽  
Magnetic Resonance Imaging Mri ◽  
Passive Acoustic

High-field, high-speed Magnetic Resonance Imaging (MRI) can generate high levels of acoustic noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 Tesla MRI scanner under a variety of conditions. These measurement results show; 1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner, and 2) the true noise levels that are experienced by patients during echo planer imaging (EPI).

scholarly journals Model forB1Imaging in MRI Using the Rotating RF Field

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Adnan Trakic ◽  
Jin Jin ◽  
Ewald Weber ◽  
Stuart Crozier
Keyword(s):  
Degrees Of Freedom ◽  
Acoustic Noise ◽  
Bloch Equation ◽  
Gradient Coil ◽  
Imaging Method ◽  
Nonuniform Field ◽  
Rf Coil ◽  
Image Encoding ◽  
Magnetic Resonance Imaging Mri ◽  
Space Requirements

Conventionally, magnetic resonance imaging (MRI) is performed by pulsing gradient coils, which invariably leads to strong acoustic noise, patient safety concerns due to induced currents, and costly power/space requirements. This modeling study investigates a new silent, gradient coil-free MR imaging method, in which a radiofrequency (RF) coil and its nonuniform field (B1+) are mechanically rotated about the patient. The advantage of the rotatingB1+field is that, for the first time, it provides a large number of degrees of freedom to aid a successfulB1+image encoding process. The mathematical modeling was performed using flip angle modulation as part of a finite-difference-based Bloch equation solver. Preliminary results suggest that representative MR images with intensity deviations of <5% from the original image can be obtained using rotating RF field approach. This method may open up new avenues towards anatomical and functional imaging in medicine.

High Amplitude Sound Propagation at Low Frequencies in a Flow Duct Lined With Resonators: A Time Domain Solution

1988 ◽  
Vol 110 (4) ◽  
pp. 545-551 ◽  
Author(s):  
A. Cummings ◽  
I.-J. Chang
Keyword(s):  
Time Domain ◽  
Internal Combustion Engines ◽  
Sound Propagation ◽  
Sound Field ◽  
High Amplitude ◽  
Combustion Engines ◽  
Low Frequencies ◽  
The Time Domain ◽  
Flow Duct ◽  
Good Agreement

A quasi one-dimensional analysis of sound transmission in a flow duct lined with an array of nonlinear resonators is described. The solution to the equations describing the sound field and the hydrodynamic flow in the neighborhood of the resonator orifices is performed numerically in the time domain, with the object of properly accounting for the nonlinear interaction between the acoustic field and the resonators. Experimental data are compared to numerical computations in the time domain and generally very good agreement is noted. The method described here may readily be extended for use in the design of exhaust mufflers for internal combustion engines.

Analysis of Collective Resonances in Clusters: Metals and Carbon

1992 ◽  
Vol 272 ◽  
Author(s):  
Vitaly V. Kresin
Keyword(s):  
Random Phase Approximation ◽  
Sum Rules ◽  
Random Phase ◽  
Closed Shell ◽  
Dynamical Response ◽  
Many Body ◽  
Resonance Frequencies ◽  
Unified View ◽  
Small Clusters ◽  
Good Agreement

ABSTRACTDipole photoabsorption spectra of small clusters are analyzed. Two types of systems are considered: metal clusters and the carbon fullerenes. Both have been found to exhibit strong collective photoabsorption modes associated with the motion of delocalized electrons. We describe analytical results for the resonance frequencies in both spherical (closed-shell metallic, C60 ) and spheroidal (openshell metallic, C70) particles. The calculation is based on the techniques of many-body physics (random-phase approximation, sum rules), affords a unified view of the dynamical response of microscopic clusters, and leads to good agreement with experimental data.

Frequency reconfigurable antenna for cognitive radios with sequential UWB mode of perception and multiband mode of operation

2018 ◽  
Vol 10 (9) ◽  
pp. 1096-1102 ◽  
Author(s):  
Ali Mansoul ◽  
Farid Ghanem
Keyword(s):  
Narrow Band ◽  
Cognitive Radios ◽  
Dual Band ◽  
Uwb Antenna ◽  
Switch Operation ◽  
Resonance Frequencies ◽  
Mode Of Operation ◽  
The Mean ◽  
Conductive Strip ◽  
Good Agreement

AbstractIn this work, an UWB/narrow band reconfigurable elliptical-shaped monopole antenna for cognitive radio applications with sequential perception and operation modes is presented. The proposed approach consists in integrating a reconfigurable filter, in an UWB antenna ground plan, by the mean of four horizontal slots and integrated switches that allow inserting/removing/varying zeros and poles in the frequency response. By acting on the slot lengths in order to alter their resonance frequencies, the different switch configurations allow the antenna to switch between an UWB mode that could be used for the perception (sensing) and different narrowband modes, mono-band and dual-band, that could be used for the operation at 2.4 or/and 3.5 GHz. To validate the concept, an experimental prototype has been fabricated and a good agreement between the simulated and the measured S-parameters has been obtained. While the presented work uses the presence/absence of a perfect conductive strip (PEC) to model real switch operation, it is believed that the obtained results conjugated with previous work using real switches on a very similar structure allows validating approach.

scholarly journals Emergency department resource optimisation for improved performance: a review

2019 ◽  
Vol 15 (S1) ◽  
pp. 253-266 ◽  
Author(s):  
Kazi Badrul Ahsan ◽  
M. R. Alam ◽  
Doug Gordon Morel ◽  
M. A. Karim
Keyword(s):  
Nurse Practitioners ◽  
Patient Flow ◽  
Demand Management ◽  
Discrete Event ◽  
Healthcare Services ◽  
Models Of Care ◽  
Analytical Models ◽  
Fast Tracking ◽  
Advantages And Disadvantages ◽  
Modelling Techniques

AbstractEmergency departments (EDs) have been becoming increasingly congested due to the combined impacts of growing demand, access block and increased clinical capability of the EDs. This congestion has known to have adverse impacts on the performance of the healthcare services. Attempts to overcome with this challenge have focussed largely on the demand management and the application of system wide process targets such as the “four-hour rule” intended to deal with access blocks. In addition, EDs have introduced various strategies such as “fast tracking”, “enhanced triage” and new models of care such as introducing nurse practitioners aimed at improving throughput. However, most of these practices require additional resources. Some researchers attempted to optimise the resources using various optimisation models to ensure best utilisation of resources to improve patient flow. However, not all modelling approaches are suitable for all situations and there is no critical review of optimisation models used in hospital EDs. The aim of this article is to review various analytical models utilised to optimise ED resources for improved patient flow and highlight benefits and limitations of these models. A range of modelling techniques including agent-based modelling and simulation, discrete-event simulation, queuing models, simulation optimisation and mathematical modelling have been reviewed. The analysis revealed that every modelling approach and optimisation technique has some advantages and disadvantages and their application is also guided by the objectives. The complexity, interrelationships and variability of ED-related variables make the application of standard modelling techniques difficult. However, these models can be used to identify sources of flow obstruction and to identify areas where investments in additional resources are likely to have most benefit.

Studying the Patterns of the Universe

2011 ◽  
Vol 20 (2) ◽  
Author(s):  
T. Sepp ◽  
E. Tempel ◽  
M. Gramann ◽  
P. Nurmi ◽  
M. Haupt
Keyword(s):  
Dark Matter ◽  
Galaxy Cluster ◽  
Analytical Models ◽  
Matter Distribution ◽  
Galaxy Groups ◽  
The Galaxy ◽  
Dark Matter Distribution ◽  
Distribution Studies ◽  
The Universe ◽  
Good Agreement

AbstractThe SDSS galaxy catalog is one of the best databases for galaxy distribution studies. The SDSS DR8 data is used to construct the galaxy cluster catalog. We construct the clusters from the calculated luminosity density field and identify denser regions. Around these peak regions we construct galaxy clusters. Another interesting question in cosmology is how observable galaxy structures are connected to underlying dark matter distribution. To study this we compare the SDSS DR7 galaxy group catalog with galaxy groups obtained from the semi-analytical Millennium N-Body simulation. Specifically, we compare the group richness, virial radius, maximum separation and velocity dispersion distributions and find a relatively good agreement between the mock catalog and observations. This strongly supports the idea that the dark matter distribution and galaxies in the semi-analytical models and observations are very closely linked.

scholarly journals Computer Simulation of Partial Discharges in Voids inside Epoxy Resins Using Three-Capacitance and Analytical Models

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 77 ◽  
Author(s):  
Johnatan M. Rodríguez-Serna ◽  
Ricardo Albarracín-Sánchez ◽  
Ming Dong ◽  
Ming Ren
Keyword(s):  
Epoxy Resins ◽  
Circuit Simulation ◽  
Electric Circuit ◽  
Real Data ◽  
Theoretical Background ◽  
General Purpose ◽  
Partial Discharges ◽  
Analytical Models ◽  
Advantages And Disadvantages ◽  
Capacitance Model

Epoxy resin is one of the most common polymers used as part of the insulation system in key electrical assets such as power transformers and hydrogenerators. Thus, it is necessary to know their main characteristics and to evaluate their condition when subjected to High Voltage (HV). A brief review of epoxy resins’ applications as insulating materials is made, their main characteristics as insulating media are given, the improvements with nano-fillers are summarized and the main electric properties required for Partial Discharges (PD) modelling are listed. In addition, the theoretical background and state-of-the-art of the three-capacitance and analytical models for simulating PD in solid dielectrics, such as epoxy resins, are reviewed in detail. Besides, their main advantages and disadvantages are presented, some critical arguments to the modelling procedure and assumptions are made and some improvements are proposed, taking into account conclusions made from other authors using models related to the PD development process. Finally, a case study was simulated using a modified three-capacitance model and the analytical model. The PD rate, q-φ-n diagrams and the minimum, mean and maximum PD electric charge are compared with measurements reported in the literature. Simulation results are in reasonable agreement with measured values. Capacitance models can be implemented in general purpose electric circuit simulation packages; however, its simulation is computationally expensive. Additional to this, although the modified three-capacitance model is not as accurate as finite elements or analytical models, results are also in agreement with real data.

RFID Loop Tags for Merchandise Identification Onboard Ships

2014 ◽  
Vol 1036 ◽  
pp. 969-974
Author(s):  
Daniela Deacu
Keyword(s):  
Radio Frequency Identification ◽  
Block Diagram ◽  
Simulated Data ◽  
Open Loop ◽  
Closed Loops ◽  
Passive Tags ◽  
Received Power ◽  
Resonance Frequencies ◽  
Frequency Identification ◽  
Good Agreement

Radio frequency identification (RFID) is one of the most actual techniques employed to control the circuit of merchandises, as an alternative to the classical barecode. RFID tags should be cheap and easy to reproduct on a multitude of dielectric supports. There are several types of RFID systems, depending on whether tag and/or reader are active or passive. For cost reasons, merchandise identification should use active reader and passive tag, as the latter might be manufactured on a cheap FR4 support or printed directly on paper, by using a conductive ink. Passive tags can be shaped as straight dipoles, meandered dipoles, or loops. When a small area is required, loops are more appropriated. Codes are made different one from another by using on the same tag antennas with different resonance frequencies. Another advantage of loops is that they can be placed one inside other, so the occupied area is even smaller compared to other multi-resonant tags. Firstly, a single loop is analyzed, in order to model the resonant behaviour, correlated to the loop geometry and size. Open and closed loops are studied; the lowest resonance frequency for a given loop length is achieved for the open loop. In that case, the loop is resonating as a dipole. Next, a tag with three concentric loops is investigated. Separately, a small loop is used on the tag, in order to couple the received power in a resistor. When the tag is close to the reader, the latter is triggered if power is absorbed simultaneously on the three expected frequencies. The proposed tag was simulated and manufactured. Results show a good agreement between measured and simulated data. Finally, a block diagram for the reader was proposed.

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