Saw-tooth shaped legs birdcage RF coil for small animal NMR imaging at 1.5T MRI system
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In this paper we are demonstrating a novel method of designing and implementing a modified birdcage type Radio Frequency (RF) coil for small animal Nuclear Magnetic Resonance (NMR) imaging. This RF coil is basically a band pass type birdcage coil which is specifically designed to perform the whole body NMR imaging of small animal at 1.5T MRI systems. The designed RF coil contains the saw tooth shaped pattern as the leg conductors. The magnetic field produced at 63.85 MHz resonance frequency by this designed saw toothed shape leg pattern RF coil is significantly stronger than the magnetic field produced by a conventional straight leg band pass type birdcage coil designed with the same dimension. A full wave 3D electromagnetic simulation is carried out to optimize the RF coil dimensions, capacitor values and to study the RF coil electromagnetic characteristics.Keywords:
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The growth in the use of magnetic resonance imaging (MRI) data for radiation therapy (RT) treatment planning has been facilitated by scanner hardware and software advances that have enabled RT patients to be imaged in treatment position while providing morphologic and functional assessment of tumor volumes and surrounding normal tissues. Despite these advances, manufacturers have been slow to develop radiofrequency (RF) coils that closely follow the contour of a RT patient undergoing MR imaging. Instead, relatively large form surface coil arrays have been adapted from diagnostic imaging. These arrays can be challenging to place on, and in general do not conform to the patient's body habitus, resulting in sub optimal image quality. The purpose of this study is to report on the characterization of a new flexible and highly decoupled RF coil for use in MR imaging of RT patients. Coil performance was evaluated by performing signal-to-noise ratio (SNR) and noise correlation measurements using two coil (SNR) and four coil (noise correlation) element combinations as a function of coil overlap distance and comparing these values to those obtained using conventional coil elements. In vivo testing was performed in both normal volunteers and patients using a four and 16 element RF coil. Phantom experiments demonstrate the highly decoupled nature of the new coil elements when compared to conventional RF coils, while in vivo testing demonstrate that these coils can be integrated into extremely flexible and form fitting substrates that follow the exact contour of the patient. The new coil design addresses limitations imposed by traditional surface coil arrays and have the potential to significantly impact MR imaging for both diagnostic and RT applications.
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Abstract Three quadrature transmit/receive radiofrequency magnetic resonance imaging breast coils were designed and built. The coils are geometrically equivalent but were scaled for different breast sizes. The coils were tested using a 4‐T Bruker/Siemens whole‐body scanner. We used different coil sizes to establish whether it is necessary to match coil size to load size. Moreover, our work investigated how the coil configuration can be changed to improve signal uniformity in the acquired images. We found that improvements can be gained by carefully matching the coil to the sample. In addition, we propose a coil layout that allows images quality to be improved, as measured by the signal‐to‐noise ratio and field uniformity of the coil. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 50–56, 2012
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Objective To assess the value of radiofrequency coil in rat brain imaging with 3.0T MR system.Methods A kind of method that designed the coil structure was put forward.A saddle coil of cylinder high equal to the diameter was adopted,and the rat brain coil diameter was 5 cm.The capacitors and distributed capacitors were minimized and the coil bandwidth decreased,the coil quality factor(Q) raised as well.The coil with head coils and body coil were used to carry on scan to the self-made model respectively in same sequence,and the coils signal-to-noise ratio(SNR) of three groups images in same position slice were compared.The rat brain was carried on T1W FLAIR and T2W scan in three axes directions respectively to observe the imaging quality.Results The coil SNR was 5 times higher than that existing brain coil and could clearly distinguish grey matter from white matter,as well as the structure in the rat brain on T1WI and T2WI.Conclusion This coil has very high SNR and can obtain good results in the imaging researches of rat brain.
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Radiofrequency coils provide high-resolution magnetic resonance (MR) imaging of human tissues. A small RF coil produces MR images with a higher resolution compared to the commercial volume MR coils from mass limited samples. Signal to noise ratio (SNR) plays a key role in the optimal design of receiver radiofrequency coils. In this work, we present a three-loop saddle coil suitable for MR imaging of digits of the human body. The geometry of the introduced coil is optimized to achieve the highest SNR. The coil performance is evaluated through comparing the measured SNR maps of the optimal coil derived from MR images of a saline phantom with the corresponding measured SNR maps of a commercial head coil in axial and sagittal slices. Results verify that the image SNR of the introduced coil is 3.4 times higher than that of the head coil and 2 times higher than that of the similar saddle coils represented in the literature recently. To validate the measured results, SNR maps of the introduced saddle and head coils were simulated and their SNR difference was compared with the corresponding measured data of the two coils. Results show that the simulated and measured data are in agreement with less than 11.8% error.
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Magnetic resonance imaging (MRI) systems must undergo quantitative evaluation through daily and periodic performance assessments. In general, the reference or standard radiofrequency (RF) coils for these performance assessments of 1.5 to 7.0 T MRI systems have been low-pass-type birdcage (LP-BC) RF coils. However, LP-BC RF coils are inappropriate for use as reference RF coils because of their relatively lower magnetic field (B1-field) sensitivity than other types of BC RF coils, especially in ultrahigh-field (UHF) MRI systems above 3.0 T. Herein, we propose a hybrid-type BC (Hybrid-BC) RF coil as a reference RF coil with improved B1-field sensitivity in UHF MRI system and applied it to an 11.7 T MRI system. An electromagnetic field (EM-field) analysis on the Hybrid-BC RF coil was performed to provide the proper dimensions for its use as a reference RF coil. Commercial finite difference time-domain program was used in EM-field simulation, and home-made analysis programs were used in analysis. The optimal specifications of the proposed Hybrid-BC RF coils for them to qualify as reference RF coils are proposed based on their B1+-field sensitivity under unnormalized conditions, as well as by considering their B1+-field uniformity and RF safety under normalized conditions.
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Abstract A general analytical framework is presented for the design of birdcage radiofrequency resonators on cylindrical formers having arbitrary cross‐sectional shape. The primary objective of such shapes would be to improve the sensitivity of the NMR experiment to noncircular regions of the human anatomy while maintaining field homogeneity and quadrature polarization comparable to those of standard circular birdcage coils. The shape of the corresponding radiofrequency screen, which is required to decouple the coil from the rest of the NMR system and which is key to the performance, is also provided by this methodology. The theory was tested by constructing a 3‐T, quadrature, proton coil on a shape conforming to the anthropomorphic mean of the human head, namely, the oval of Cassini. Both bench tests ( Q ) and in vivo spectral and imaging comparisons of the Cassinian coil with an equivalently dimensioned and constructed circular birdcage coil, respectively, predicted and demonstrated in vivo an improvement in SNR of ∼24% over the circular section coil. The experimental RF field homogeneity and quadrature performance were comparable for both coil geometries, with the circular coil being marginally superior. Magn Reson Med 53:201–211, 2005. © 2004 Wiley‐Liss, Inc.
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A novel simple design of birdcage type RF receiver coil for using in the 1 H NMR (Nuclear Magnetic Resonance) imaging system operating at 1.5 T and 3.0 T has been demonstrated. The RF coil is a band pass type coil composed of legs and end rings and both legs and end rings are made of epoxy-etched copper strips on a single flexible circuit board. The important feature of the coil with multiple resonance frequency is the use of multiple capacitors in each leg of the coil. The coil is capable to resonate at 64 MHz (1.5 T) and 127 MHz (3.0 T) simultaneously. We have analyzed the performance of the coil through simulations and experimental measurements.
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Over the last 30 years, there have been dramatic changes in phased array coil technology leading to increasing channel density and parallel imaging functionality. Current receiver array coils are rigid and often mismatched to patient's size. Recently there has been a move towards flexible coil technology, which is more conformal to the human anatomy. Despite the advances of so-called flexible surface coil arrays, these coils are still relatively rigid and limited in terms of design conformability, compromising signal-to-noise ratio (SNR) for flexibility, and are not designed for optimum parallel imaging performance. The purpose of this study is to report on the development and characterization of a 15-channel flexible foot and ankle coil, rapidly designed and constructed using highly decoupled radio-frequency (RF) coil elements. Coil performance was evaluated by performing SNR and g-factor measurements. In vivo testing was performed in a healthy volunteer using both the 15-channel coil and a commercially available 8-channel foot coil. The highly decoupled elements used in this design allow for extremely rapid development and prototyping of application-specific coils for different patient sizes (adult vs child) with minimal additional design consideration in terms of coil overlap and geometry. Image quality was comparable to a commercially available RF coil.
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The performance of radio frequency (RF) coils, used in MRI units, is determined by the image uniformity and the signal-to-noise ratio (SNR). Birdcage and surface coils are commonly used. A birdcage coil provides a good image uniformity while a surface coil produces a high SNR. In this study, therefore, a staircase coil was designed from a standard version of a birdcage coil, with some structural changes to increase SNR while maintaining image uniformity. In phantom experiments, the improvement of the image to uniformity and the SNR increase of the staircase coil compared with the values for the birdcage coil were about 3.5% and 35%, respectively. In clinical experiment, the SNR increase of the staircase coil, compared with the value for the birdcage coil was about 40% in bone, muscle and blood-vessel tissues. These results show that the performance of the staircase coil was very improved over the standard birdcage coil in terms of SNR, and that image uniformity was maintained. Therefore, the staircase coil designed by this study should be useful in experimental and clinical l.5T MRI systems, and this coil offers an alternative method of quadrature detection.
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