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.

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 Expert opinion paper on cardiac imaging after ischemic stroke

2021 ◽  
Author(s):  
Renate B. Schnabel ◽  
Stephan Camen ◽  
Fabian Knebel ◽  
Andreas Hagendorff ◽  
Udo Bavendiek ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
Expert Opinion ◽  
Cardiac Imaging ◽  
Controlled Trial ◽  
Case Series ◽  
Stroke Care ◽  
Imaging Method ◽  
Cardiac Evaluation ◽  
Magnetic Resonance Imaging Mri ◽  
Ischemic Attack

AbstractThis expert opinion paper on cardiac imaging after acute ischemic stroke or transient ischemic attack (TIA) includes a statement of the “Heart and Brain” consortium of the German Cardiac Society and the German Stroke Society. The Stroke Unit-Commission of the German Stroke Society and the German Atrial Fibrillation NETwork (AFNET) endorsed this paper. Cardiac imaging is a key component of etiological work-up after stroke. Enhanced echocardiographic tools, constantly improving cardiac computer tomography (CT) as well as cardiac magnetic resonance imaging (MRI) offer comprehensive non- or less-invasive cardiac evaluation at the expense of increased costs and/or radiation exposure. Certain imaging findings usually lead to a change in medical secondary stroke prevention or may influence medical treatment. However, there is no proof from a randomized controlled trial (RCT) that the choice of the imaging method influences the prognosis of stroke patients. Summarizing present knowledge, the German Heart and Brain consortium proposes an interdisciplinary, staged standard diagnostic scheme for the detection of risk factors of cardio-embolic stroke. This expert opinion paper aims to give practical advice to physicians who are involved in stroke care. In line with the nature of an expert opinion paper, labeling of classes of recommendations is not provided, since many statements are based on expert opinion, reported case series, and clinical experience.

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.

Radial magnetic resonance imaging (MRI) using a rotating radiofrequency (RF) coil at 9.4 T

2017 ◽  
Vol 31 (2) ◽  
pp. e3860 ◽  
Author(s):  
Mingyan Li ◽  
Ewald Weber ◽  
Jin Jin ◽  
Thimo Hugger ◽  
Yasvir Tesiram ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Rf Coil ◽  
Resonance Imaging ◽  
Magnetic Resonance Imaging Mri

Feasibility Study of Force Measurement for Multi-digit Unconstrained Grasping via Fingernail Imaging and Visual Servoing

2020 ◽  
Vol 1 (2) ◽  
Author(s):  
Navid Fallahinia ◽  
Stephen A. Mascaro
Keyword(s):  
Visual Servoing ◽  
Degrees Of Freedom ◽  
Force Measurement ◽  
Field Of View ◽  
Imaging Method ◽  
Shear Forces ◽  
Maximum Value ◽  
6 Degrees Of Freedom ◽  
Finger Pad ◽  
Rms Errors

Abstract A fingernail imaging has been shown to be effective in estimating the finger pad forces along all three directions simultaneously in previous works. However, this method has never been used for the purpose of force measurement during a grasping task with multiple fingers. The objective of this paper is to demonstrate the grasp force-sensing capabilities of the fingernail imaging method integrated with a visual servoing robotic system. In this study, the fingernail imaging method has been used in both constrained and unconstrained multi-digit grasping studies. Visual servoing has been employed to solve the issue of keeping fingernail images in the field of view of the camera during grasping motions. Two grasping experiments have been designed and conducted to show the performance and accuracy of the fingernail imaging method to be used in grasping studies. The maximum value of root-mean-square (RMS) errors for estimated normal and shear forces during constrained grasping has been found to be 0.58 N (5.7%) and 0.49 N (9.2%), respectively. Moreover, a visual servoing system implemented on a 6-degrees-of-freedom (DOF) robot has been devised to ensure that all of the fingers remain in the camera frame at all times. Comparing unconstrained and constrained forces has shown that force collaboration among fingers could change based on the grasping condition.

scholarly journals Measuring Kidney Perfusion, pH, and Renal Clearance Consecutively Using MRI and Multispectral Optoacoustic Tomography

2019 ◽  
Vol 22 (3) ◽  
pp. 494-503 ◽  
Author(s):  
Atul S. Minhas ◽  
Jack Sharkey ◽  
Edward A. Randtke ◽  
Patricia Murray ◽  
Bettina Wilm ◽  
...  
Keyword(s):  
Renal Clearance ◽  
Clearance Rate ◽  
Area Under The Curve ◽  
Kidney Cortex ◽  
Imaging Method ◽  
Ph Measurements ◽  
Optoacoustic Tomography ◽  
Significant Difference ◽  
Kidney Perfusion ◽  
Magnetic Resonance Imaging Mri

Abstract Purpose: To establish multi-modal imaging for the assessment of kidney pH, perfusion, and clearance rate using magnetic resonance imaging (MRI) and multispectral optoacoustic tomography (MSOT) in healthy mice. Kidney pH and perfusion values were measured on a pixel-by-pixel basis using the MRI acidoCEST and FAIR-EPI methods. Kidney filtration rate was measured by analyzing the renal clearance rate of IRdye 800 using MSOT. To test the effect of one imaging method on the other, a set of 3 animals were imaged with MSOT followed by MRI, and a second set of 3 animals were imaged with MRI followed by MSOT. In a subsequent study, the reproducibility of pH, perfusion, and renal clearance measurements were tested by imaging 4 animals twice, separated by 4 days. The contrast agents used for acidoCEST based pH measurements influenced the results of MSOT. Specifically, the exponential decay time from the kidney cortex, as measured by MSOT, was significantly altered when MRI was performed prior to MSOT. However, no significant difference in the cortex to pelvis area under the curve (AUC) was noted. When the order of experiments was reversed, no significant differences were noted in the pH or perfusion values. Reproducibility measurements demonstrated similar pH and cortex to pelvis AUC; however, perfusion values were significantly different with the cortex values being higher and the pelvic values being lower in the second imaging time. We demonstrate that using a combination of MRI and MSOT, physiological measurements of pH, blood flow, and clearance rates can be measured in the mouse kidney in the same imaging session.

scholarly journals Improvements in MR imaging of solids through gradient waveform optimization

2011 ◽  
Vol 89 (7) ◽  
pp. 729-736
Author(s):  
Marco L.H. Gruwel ◽  
Peter Latta ◽  
Boguslaw Tomanek
Keyword(s):  
Mr Imaging ◽  
Acoustic Noise ◽  
Signal To Noise Ratio ◽  
Single Point ◽  
Waveform Optimization ◽  
Imaging Sequence ◽  
Wide Range ◽  
Gradient Waveform ◽  
Condensed Materials ◽  
Magnetic Resonance Imaging Mri

Magnetic resonance imaging (MRI) is known to provide a useful approach for the exploration of the chemistry and dynamics of a wide range of soft condensed materials. However, its application to solids has been limited to those materials with relatively narrow resonances. The time needed to obtain an image of a solid with a given resolution and signal-to-noise ratio (SNR) is directly proportional to the line width of the resonance. For MRI to become practical for the imaging of solids it will have to rely on the development and use of MR sequences that avoid the issues raised by line broadening of the resonance. In this paper we review the latest contributions towards MR imaging of solids from our laboratory, in particular, applications using optimized gradient waveforms. Acoustic noise reduction and SNR improvement obtained with modifications of the standard single-point imaging sequence are presented and discussed using examples.

scholarly journals Feasibility of Diffusion Weighting with a Local Inside-Out Nonlinear Gradient Coil for Prostate MRI

2021 ◽  
Author(s):  
Enamul Bhuiyan ◽  
Andrew Dewdney ◽  
Jeffrey Weinreb ◽  
Gigi Galiana
Keyword(s):  
Image Quality ◽  
Region Of Interest ◽  
Fold Increase ◽  
High Rate ◽  
Gradient Coil ◽  
Imaging Method ◽  
Ampli Tudes ◽  
Head Gradient ◽  
Spatially Varying ◽  
Inside Out

Purpose: Prostate cancer remains the 2nd leading cancer killer of men, yet it is also a disease with a high rate of overtreatment. Diffusion weighted imaging (DWI) has shown promise as a reliable, grade-sensitive imaging method, but it is limited by low image quality. Currently, DWI image quality is directly related to low gradient ampli-tudes, since weak gradients must be compensated with long echo times. Methods: We propose a new type of MRl accessory, an "inside-out" and nonlinear gradient, whose sole purpose is to deliver diffusion encoding to a region of interest. Performance was simulated in OPERA and the resulting fields were used to simulate DWI with two compartment and kurtosis models. Experiments with a nonlinear head gradient prove the accuracy of DWI and ADC maps diffusion encoded with nonlinear gradients. Results: Simulations validated thermal and mechanical safety while showing a 5 to 10-fold increase in gradient strength over prostate. With these strengths, lesion CNR in ADC maps approximately doubled for a range of anatomical positions. Proof-of-principle experiments show that spatially varying b-values can be corrected for accurate DWI and ADC. Conclusions: Dedicated nonlinear diffusion encoding hardware could improve prostate DWI.

scholarly journals ASSESSING BRAIN VOLUMETRICS IN THE AGING BRAIN USING COMPUTED TOMOGRAPHY

2019 ◽  
Vol 3 (Supplement_1) ◽  
pp. S588-S588
Author(s):  
Andrei Irimia ◽  
Alexander Maher ◽  
Kenneth Rostowsky
Keyword(s):  
Computed Tomography ◽  
Grey Matter ◽  
Aging Brain ◽  
Imaging Method ◽  
Segmentation Method ◽  
Dice Coefficient ◽  
Volumetric Assessment ◽  
Brain Changes ◽  
Magnetic Resonance Imaging Mri ◽  
Brain Volumetrics

Abstract Although broadly utilized, computed tomography (CT) has been superseded by magnetic resonance imaging (MRI) for the volumetric assessment of white matter (WM), grey matter (GM) and cerebrospinal fluid (CSF) in the aging human brain. Nevertheless, many scenarios remain where MRI is unavailable or discouraged; furthermore, in developing countries, CT can often be the only accessible imaging method for assessing brain structure in older patients with mild cognitive impairment or Alzheimer’s disease. Thus, there is merit in developing effective approaches for the estimation of brain volumetrics using CT. Here, MRI and CT scans were acquired from 10 older adults [mean (µ) ± standard deviation (σ) of age = 65 ± 7 yrs; 5 females]. To demarcate WM, GM and CSF from head CT, we developed a brain segmentation method based upon probabilistic, atlas-dependent classification. MRI-only segmentation was compared to CT-only segmentation; similarity was calculated through the Dice coefficient (DC). A normal distribution of DCs was found after contrasting the methods [µ ± σ across participants: 85.5% ± 4.6% (WM), 86.7% ± 5.6% (GM) and 91.3% ± 2.8% (CSF)], suggesting a satisfactory capacity of CT to assess brain volumetrics. Sensitivity was adequate: WM, GM and CSF volumes were estimated within ~5%, ~4% and ~3% of their MRI-based values. There was no indication of volume over- or under-estimation with CT [t (9) = 0.89, p &gt; 0.80]. These results facilitate the integration of CT-based brain volumetrics with MRI, thereby offering a wider range of methods for quantifying macroscale brain changes in neurodegenerative diseases.

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