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Objective Speech production MRI benefits from lower magnetic fields due to reduced off-resonance effects at air-tissue interfaces and from the use of dedicated receiver coils due to higher SNR and parallel imaging capability. Here we present a custom designed upper airway coil for 1H imaging at 0.55 Tesla and evaluate its performance in comparison with a vendor-provided prototype 16-channel head/neck coil. Materials and methods Four adult volunteers were scanned with both custom speech and prototype head–neck coils. We evaluated SNR gains of each of the coils over eleven upper airway volumes-of-interest measured relative to the integrated body coil. We evaluated parallel imaging performance of both coils by computing g-factors for SENSE reconstruction of uniform and variable density Cartesian sampling schemes with R = 2, 3, and 4. Results The dedicated coil shows approximately 3.5-fold SNR efficiency compared to the head–neck coil. For R = 2 and 3, both uniform and variable density samplings have g-factor values below 1.1 in the upper airway region. For R = 4, g-factor values are higher for both trajectories. Discussion The dedicated coil configuration allows for a significant SNR gain over the head–neck coil in the articulators. This, along with favorable g values, makes the coil useful in speech production MRI.
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Performance of receive head arrays versus ultimate intrinsic SNR at 7 T and 10.5 T
Abstract PurposeWe examined magnetic field dependent SNR gains and ability to capture them with multichannel receive arrays for human head imaging in going from 7 T, the most commonly used ultrahigh magnetic field (UHF) platform at the present, to 10.5 T, which represents the emerging new frontier of >10 T in UHFs. MethodsElectromagnetic (EM) models of 31‐channel and 63‐channel multichannel arrays built for 10.5 T were developed for 10.5 T and 7 T simulations. A 7 T version of the 63‐channel array with an identical coil layout was also built. Array performance was evaluated in the EM model using a phantom mimicking the size and electrical properties of the human head and a digital human head model. Experimental data was obtained at 7 T and 10.5 T with the 63‐channel array. Ultimate intrinsic SNR (uiSNR) was calculated for the two field strengths using a voxelized cloud of dipoles enclosing the phantom or the digital human head model as a reference to assess the performance of the two arrays and field depended SNR gains. ResultsuiSNR calculations in both the phantom and the digital human head model demonstrated SNR gains at 10.5 T relative to 7 T of 2.6 centrally, ˜2 at the location corresponding to the edge of the brain, ˜1.4 at the periphery. The EM models demonstrated that, centrally, both arrays captured ˜90% of the uiSNR at 7 T, but only ˜65% at 10.5 T, leading only to ˜2‐fold gain in array SNR in going from 7 to 10.5 T. This trend was also observed experimentally with the 63‐channel array capturing a larger fraction of the uiSNR at 7 T compared to 10.5 T, although the percentage of uiSNR captured were slightly lower at both field strengths compared to EM simulation results. ConclusionsMajor uiSNR gains are predicted for human head imaging in going from 7 T to 10.5 T, ranging from ˜2‐fold at locations corresponding to the edge of the brain to 2.6‐fold at the center, corresponding to approximately quadratic increase with the magnetic field. Realistic 31‐ and 63‐channel receive arrays, however, approach the central uiSNR at 7 T, but fail to do so at 10.5 T, suggesting that more coils and/or different type of coils will be needed at 10.5 T and higher magnetic fields.
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- Award ID(s):
- 2313156
- PAR ID:
- 10529353
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Magnetic Resonance in Medicine
- Volume:
- 92
- Issue:
- 3
- ISSN:
- 0740-3194
- Page Range / eLocation ID:
- 1219 to 1231
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/mrm.30108
