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).

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.

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.

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.

scholarly journals Characterization of Noise Level Inside a Vehicle under Different Conditions

Sensors ◽  
2020 ◽  
Vol 20 (9) ◽  
pp. 2471 ◽  
Author(s):  
Daniel Flor ◽  
Danilo Pena ◽  
Luan Pena ◽  
Vicente A. de Sousa ◽  
Allan Martins
Keyword(s):  
Regression Analysis ◽  
Noise Level ◽  
Acoustic Noise ◽  
Experimental Setup ◽  
Strongly Correlated ◽  
Noise Levels ◽  
Noise Sources ◽  
Statistical Tools ◽  
Window Position

Vehicular acoustic noise evaluations are a concern of researchers due to health and comfort effects on humans and are fundamental for anyone interested in mitigating audio noise. This paper focuses on the evaluation of the noise level inside a vehicle by using statistical tools. First, an experimental setup was developed with microphones and a microcomputer located strategically on the car’s panel, and measurements were carried out with different conditions such as car window position, rain, traffic, and car speed. Regression analysis was performed to evaluate the similarity of the noise level from those conditions. Thus, we were able to discuss the relevance of the variables that contribute to the noise level inside a car. Finally, our results revealed that the car speed is strongly correlated to interior noise levels, suggesting the most relevant noise sources are in the vehicle itself.

scholarly journals A New Approach to Assess the Quality of Small High-Speed Centrifugal Fans Using Noise Measurement

1999 ◽  
Vol 5 (2) ◽  
pp. 147-153 ◽  
Author(s):  
Dingjun Cui ◽  
Ian A. Craighead
Keyword(s):  
Signal Processing ◽  
Quality Assessment ◽  
Condition Monitoring ◽  
High Speed ◽  
Noise Levels ◽  
New Approach ◽  
Commercial Market ◽  
Centrifugal Fans ◽  
Special Approach

The requirements for a special approach for the quality assessment of small high-speed centrifugal fans are outlined and a new parameter designating the noise levels from the product in comprehensive form will be discussed and described as a criterion for such quality assessment.By applying techniques of signal processing and condition monitoring, the sources of the vibration and noise in different sections of the product can be identified, then the noise from each source from different components can be determined. Using this criterion, more aspects of the quality of the products can be assessed and suggestions to improve the quality of the products can be made. Finally, the assessment of a number ofvacuum cleaner motor/fan units available in the commercial market will be presented and compared with conventional specifications. It will be shown that the new parameter provides a more useful indication of appliance quality.

scholarly journals Canadian Association of Radiologists Recommendations for the Safe Use of MRI During Pregnancy

2021 ◽  
pp. 084653712110156
Author(s):  
Pejman Jabehdar Maralani ◽  
Anish Kapadia ◽  
Grace Liu ◽  
Felipe Moretti ◽  
Hournaz Ghandehari ◽  
...  
Keyword(s):  
Working Group ◽  
Energy Deposition ◽  
Expert Panel ◽  
Acoustic Noise ◽  
Evidence Based ◽  
Resonance Imaging ◽  
Canadian Association ◽  
Fetal Safety ◽  
Magnetic Resonance Imaging Mri ◽  
In Pregnancy

The use of magnetic resonance imaging (MRI) during pregnancy is associated with concerns among patients and health professionals with regards to fetal safety. In this work, the Canadian Association of Radiologists (CAR) Working Group on MRI in Pregnancy presents recommendations for the use of MRI in pregnancy, derived from literature review as well as expert panel opinions and discussions. The working group, which consists of academic subspecialty radiologists and obstetrician-gynaecologists, aimed to provide updated, evidence-based recommendations addressing safety domains related to energy deposition, acoustic noise, and gadolinium-based contrast agent use based on magnetic field strength (1.5T and 3T) and trimester scanned, in addition to the effects of sedative use and occupational exposure.

Using Wavelet Analysis to Distinguish Cavitation Acoustic Emissions From Blunt Impact Noise

2021 ◽  
Author(s):  
Christopher Eckersley ◽  
Joost Op 't Eynde ◽  
Mitchell Abrams ◽  
Cameron R. Bass
Keyword(s):  
Wavelet Transform ◽  
High Speed ◽  
Acoustic Noise ◽  
Bubble Formation ◽  
Acoustic Emissions ◽  
Wide Band ◽  
Water Tank ◽  
Impact Noise ◽  
Blunt Impact

Abstract Cavitation has been shown to have implications for head injury, but currently there is no solution for detecting the formation of cavitation through the skull during blunt impact. The goal of this communication is to confirm the wideband acoustic wavelet signature of cavitation collapse, and determine that this signature can be differentiated from the noise of a blunt impact. A controlled, laser induced cavitation study was conducted in an isolated water tank to confirm the wide band acoustic signature of cavitation collapse in the absence of a blunt impact. A clear acrylic surrogate head was impacted to induce blunt impact cavitation. The bubble formation was imaged using a high speed camera, and the collapse was synched up with the wavelet transform of the acoustic emission. Wideband acoustic response is seen in wavelet transform of positive laser induced cavitation tests, but absent in laser induced negative controls. Clear acrylic surrogate tests showed the wideband acoustic wavelet signature of collapse can be differentiated from acoustic noise generated by a blunt impact. Broadband acoustic signal can be used as a biomarker to detect the incidence of cavitation through the skull as it consists of frequencies that are low enough to potentially pass through the skull but high enough to differentiate from blunt impact noise. This lays the foundation for a vital tool to conduct CSF cavitation research in-vivo.

scholarly journals Ultrasonic image analysis and image-guided interventions

2011 ◽  
Vol 1 (4) ◽  
pp. 673-685 ◽  
Author(s):  
J. Alison Noble ◽  
Nassir Navab ◽  
H. Becher
Keyword(s):  
Image Analysis ◽  
Imaging Modality ◽  
Medical Image Analysis ◽  
Three Dimensional ◽  
Clinical Information ◽  
Image Guided ◽  
Software Algorithms ◽  
Positron Emission ◽  
Imaging Research ◽  
Magnetic Resonance Imaging Mri

The fields of medical image analysis and computer-aided interventions deal with reducing the large volume of digital images (X-ray, computed tomography, magnetic resonance imaging (MRI), positron emission tomography and ultrasound (US)) to more meaningful clinical information using software algorithms. US is a core imaging modality employed in these areas, both in its own right and used in conjunction with the other imaging modalities. It is receiving increased interest owing to the recent introduction of three-dimensional US, significant improvements in US image quality, and better understanding of how to design algorithms which exploit the unique strengths and properties of this real-time imaging modality. This article reviews the current state of art in US image analysis and its application in image-guided interventions. The article concludes by giving a perspective from clinical cardiology which is one of the most advanced areas of clinical application of US image analysis and describing some probable future trends in this important area of ultrasonic imaging research.

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