B0 shimming in a small volume at 9.4T: irregular coil geometry setup vs. loop coil setup
0
Citation
0
Reference
20
Related Paper
Cite
Purpose : The purpose of the present study was to develop and optimize solenoid coil for animal- model in 3 T MRI system and investigate and compare with the birdcage coil concerning the image quality with the various parameters such as SNR and Q-factor. Materials and Methods : Solenoid coil for animal-model was made on the acryl structure (diameter 4 cm, length 10 cm) 3 times-winding cooper tape of width 2 cm, thickness 0.05 cm and length 10 cm with 2 cm interval between winded tapes. Capacitors from 2 pF to 100 pF were used, and the solenoid coil was designed for receiver only coil. Results : SNR of the developed solenoid was 985 in CuSO4 0.7 g/L and 995 in rat experiment. Q-factor was 84-89 in unloaded condition and 203-206 in loaded condition. Conclusion : The resolution of the image obtained from solenoid was relatively higher than that of the conventional birdcage coil. In addition, the homogeneity of RF field by coil simulation was significantly excellent. The present study demonstrated that the solenoid coil could be useful to obtain small animal images with better contrast, resolution, visibility than images from birdcage.
Solenoid
Radiofrequency coil
Cite
Citations (0)
Purpose Artifacts caused by large magnetic susceptibility differences between metallic needles and tissue are a persistent problem in many interventional MRI applications. The signal void caused by the needle can hide procedure targets and prevent accurate image‐based monitoring. In this paper, a solution to this problem is presented in the form of an active shim insert inspired from degaussing coils used in naval vessels, that is designed to correct the field disturbance (ΔB 0 ) caused by the needle. Methods The ΔB 0 induced by a 10 gauge hollow single‐beveled titanium needle at 3T is modeled in different orientations. A set of 63 orthogonal coil pairs with unique tip paths are evaluated for shimming performance, and an optimal coil pair is chosen. Shimming performance and current demands are evaluated over a range of needle orientations. Results Robust correction of the titanium needle induced ΔB 0 is predicted using a flat no‐loop coil combined with an orthogonal 1½ turn loop coil angled at the bevel angle for most orientations, with currents well below 1 amp per coil. Reductions in ΔB 0 standard deviations with shimming ranged from ~49% to ~10% depending on needle orientation, with performance worsening as the needle is aligned more along B 0 . Conclusion Simulations predict that it is possible to minimize metallic probe induced ΔB 0 and signal losses using externally supplied direct current shim coil inserts in arbitrary orientations for potential benefits in many interventional MRI applications.
Shim (computing)
Bevel
Radiofrequency coil
Cite
Citations (3)
Radiofrequency coil
Q factor
Cite
Citations (0)
Shim (computing)
Cite
Citations (0)
Purpose To theoretically describe, design, and test the new geometry of the birdcage coil for 7 Tesla anatomical brain imaging, which includes a large window on top, without deliberately jeopardizing its homogeneity and efficiency. This opencage will not only improve patient comfort but also enable the volunteer to follow functional MRI stimuli. This design could also facilitate the tracking of patient compliance and enable better correction of the movement. Methods Via the transfer matrix approach, a birdcage‐like coil with a nonperiodic distribution of rungs is constructed with optimized currents in the coil rungs. Subsequently, the coil is adjusted in full‐wave simulations. Then, the coil is assembled, fine‐tuned, and matched on the bench. Finally, these results are confirmed experimentally on a phantom and in vivo. Results Indeed, the computed isolation of −14.9 dB between the feeding ports of the coil and the symmetry of the circular polarized mode pattern transmit RF magnetic field ( ) showed that the coil was properly optimized. An experimental assessment of the developed coil showed competitive transmit efficiency and coverage compared with the conventional birdcage coil of similar size. Conclusion The proposed opencage coil can be designed and work without a dramatic drop of performance in terms of the field homogeneity, transmit efficiency ( / ), peak local specific absorption rate ( ) and SAR efficiency ( / ).
Radiofrequency coil
Specific absorption rate
Voice coil
Cite
Citations (7)
A multi-coil shim setup is designed and optimized for human brain shimming. Here, the size and position of a set of square coils are optimized to improve the shim performance without increasing the number of local coils. Utilizing such a setup is especially beneficial at ultrahigh fields where B0 inhomogeneity in the human brain is more severe.The optimization started with a symmetric arrangement of 32 independent coils. Three parameters per coil were optimized in parallel, including angular and axial positions on a cylinder surface and size of the coil, which were constrained by cylinder size, construction consideration, and amplifiers specifications. B0 maps were acquired at 9.4T in 8 healthy volunteers for use as training data. The global and dynamic shimming performance of the optimized multi-coil were compared in simulations and measurements to a symmetric design and to the scanner's second-order shim setup, respectively.The optimized multi-coil performs better by 14.7% based on standard deviation (SD) improvement with constrained global shimming in comparison to the symmetric positioning of the coils. Global shimming performance was comparable with a symmetric 65-channel multi-coil and full fifth-order spherical harmonic shim coils. On average, an SD of 48.4 and 31.9 Hz was achieved for in vivo measurements after global and dynamic slice-wise shimming, respectively.An optimized multi-coil shim setup was designed and constructed for human whole-brain shimming. Similar performance of the multi-coils with many channels can be achieved with a fewer number of channels when the coils are optimally arranged around the target.
Human brain
Radiofrequency coil
Cite
Citations (26)
Shim (computing)
Harmonic
Cite
Citations (0)
Cite
Citations (0)
Purpose Integrated parallel reception, excitation, and shimming (iPRES) coil arrays allow radio‐frequency currents and direct currents to flow in the same coils, which enables excitation/reception and localized B 0 shimming with a single coil array. The purpose of this work was to improve their shimming performance by adding the capability to shim higher‐order local B 0 inhomogeneities that are smaller than the radio‐frequency coil elements. Methods A novel design was proposed in which each radio‐frequency/shim coil element is divided into multiple direct current loops, each using an independent direct current current, to increase the number of magnetic fields available for shimming while maintaining the signal‐to‐noise ratio of the coil. This new design is termed iPRES( N ), where N represents the number of direct current loops per radio‐frequency coil element. Proof‐of‐concept phantom and human experiments were performed with an 8‐channel body coil array to demonstrate its advantages over the original iPRES(1) design. Results The average B 0 homogeneity in various organs before shimming and after shimming with the iPRES(1) or iPRES(3) coil arrays was 0.24, 0.11, and 0.05 ppm, respectively. iPRES(3) thus reduced the B 0 inhomogeneity by 53% and further reduced distortions in echo‐planar images of the abdomen when compared with iPRES(1). Conclusion iPRES(N) can correct for localized B 0 inhomogeneities more effectively than iPRES(1) with no signal‐to‐noise ratio loss, resulting in a significant improvement in image quality. Magn Reson Med 77:2077–2086, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Shim (computing)
Radiofrequency coil
Cite
Citations (28)
We add user-controllable direct currents (DC) to the individual elements of a 32-channel radio-frequency (RF) receive array to provide B0 shimming ability while preserving the array's reception sensitivity and parallel imaging performance.
Shim (computing)
Beamwidth
Radiofrequency coil
Cite
Citations (120)