Electromagnetic analysis of the slotted-tube resonator with a circular cross section for MRI applications

“…A series of previously published planar micro-sensor designs 20,34 along with some novel designs were manufactured to demonstrate the capability of using CNC micro-milling for NMR micro-coil development. In addition, a series of microstrip designs 34 were optimized for analysing 13 C-labelled D. magna adults as well as a slotted-tube resonator (STR) 35 for the study of neonates. It was found that cavities and sample holders could be made from copper/Teflon sheet at the same time as the coils were made.…”

Section: Introductionmentioning

confidence: 99%

5-Axis CNC Micromilling for Rapid, Cheap, and Background-Free NMR Microcoils

et al. 2020

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The superior mass sensitivity of micro-coil technology in Nuclear Magnetic Resonance (NMR) Spectroscopy provides potential for the analysis of extremely small mass-limited samples such as eggs, cells, and tiny organisms. For optimal performance and efficiency, the size of the micro-coil should be tailored to the size of the mass-limited sample of interest, which can be costly as mass-limited samples come in many shapes and sizes. Therefore, rapid and economic micro-coil production methods are needed. One method with great potential is 5-axis Computer Numerical Control (CNC) micro-milling, commonly used in the jewelry industry. Most CNC milling machines are designed to process larger objects and commonly have a precision >25 µm (making the machining of common spiral micro-coils, for example, impossible). Here, a 5-axis MiRA6 CNC milling machine, specifically designed for the jewelry industry, with a 0.3 µm precision was used to produce working planar micro-coils, microstrips, and novel micro-sensor designs, with some tested on the NMR in less than 24 hours after the start of the design process. Sample wells could be built into the micro-sensor and could be machined at the same time as the sensors themselves, in some cases leaving a sheet of Teflon as thin as 10 µm between the sample and sensor. This provides the freedom to produce a wide array of designs and demonstrates 5-axis CNC micro-milling as a versatile tool for the rapid prototyping of NMR micro-sensors. This approach allowed the experimental optimization of a prototype microstrip for the analysis of two intact adult Daphnia magna organisms. In addition, a 3D volume slotted tube resonator was produced that allowed for 2D 1 H-13 C NMR of D. magna neonates and exhibited 1 H sensitivity (nLOD ꙍ 600 = 1.49 nmol s 1/2 ) close to that of double striplines, which themselves offer the best compromise between concentration and mass sensitivity published to date.

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“…Therefore, hybridising MoM and FEM produces an exceptionally capable full-wave numerical technique that is particularly suited for modelling MRI RF coils and analysing RF field behaviour. The hybrid MoM/FEM used by our group is commercially available from FEKO, and its mathematical formulation has been discussed extensively (84,(97)(98)(99)(100)(101)(102)(103). For the purposes of illustration, we will give two examples to demonstrate the effectiveness and accuracy of the hybrid MoM/FEM method for MRI RF coil modelling.…”

Section: Hybrid Mom/femmentioning

confidence: 99%

Hybrid numerical techniques for the modelling of radiofrequency coils in MRI

Weber

et al. 2008

NMR in Biomedicine

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Radiofrequency (RF) coils for use in MRI can have a significant effect on both the signal-to-noise-ratio of MR images and the specific absorption rate inside the biological sample. In the past, prototypes were constructed and tested to investigate the performance of the RF coils and often required several iterations to achieve an acceptable result. However, with the advancement in computational electromagnetic techniques, RF coil modelling has now become the modus operandi of coil design because it can produce accurate numerical results, thus reducing the time and effort spent in designing and prototyping RF coils. Two hybrid methods -method of moments (MoM)/finite difference time domain (FDTD) and MoM/finite element method (FEM) - for RF coil modelling are presented herein. The paper provides a brief overview of FDTD, FEM and MoM. It discusses the hybridisation of these methods and how they are integrated to form versatile techniques. The numerical results obtained from these hybrid methods are compared with experimental results from prototype coils over a range of operating frequencies. The methods are then applied to the design of a new type of phased-array coil - the rotary phased array. From these comparisons, it can be seen that the numerical methods provide a useful aid for the design and optimisation of RF coils for use in MRI.

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Electromagnetic analysis of the slotted-tube resonator with a circular cross section for MRI applications

Cited by 7 publications

References 5 publications

Assessment of the efficacy of MRI for detection of changes in bone morphology in a mouse model of bone injury

Assessment of the efficacy of MRI for detection of changes in bone morphology in a mouse model of bone injury

5-Axis CNC Micromilling for Rapid, Cheap, and Background-Free NMR Microcoils

Hybrid numerical techniques for the modelling of radiofrequency coils in MRI

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