Examinando por Autor "Porter, David Andrew"

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Simultaneous whole-brain and cervical spine imaging at 7 T using a neurovascular head and neck coil with 8-channel transceiver array and 56-channel receiver array
(Magnetic Resonance in Medicine, 2025-01-29) Baskaran, Divya; Ding, Belinda; Chu, Son; McElhinney, Paul; Allwood-Spiers, Sarah; Williams, Sydney N.; Muir, Keith; Fullerton, Natasha Eileen; Porter, David Andrew; Gunamony, Shajan
Purpose: To develop a 7T neurovascular head and neck (NVHN) coil with an extended longitudinal coverage of the brain and cervical spine, with eight transceiver (TxRx) channels and 56 receive (Rx) channels for dynamic parallel-transmit (pTx) applications. Methods: A dual-row transceiver array with six elements in the upper row and two elements in the lower row was designed using combined electromagnetic and circuit optimization and constructed. A 56Rx array covering the brain and cervical spine was designed and combined with the transceiver array. The performance of the 8TxRx56Rx NVHN coil such as, signal-to-noise ratio, and g-factor were validated in phantom and in vivo studies and compared with an in-house 8Tx64Rx head coil. High-resolution in vivo images were acquired with the NVHN and head coil. Results: The average in phantom while exciting the upper six channels and all eight channels are 43.45 nT/V and 45.80 nT/V, respectively, demonstrating that the available field is seamlessly distributed in the brain and/or cervical spine, depending on the chosen excitation. The 8TxRx56Rx NVHN coil increases the SNR in the cervical spine and central brain by a factor of 2.18 and 1.16, respectively, compared with the 8Tx64Rx head coil. Furthermore, it demonstrates similar 1/g-factor performance for acceleration factors up to 5 × 5 compared with the head coil and provides diagnostic-quality images of the brain and spinal cord in a single acquisition. Conclusion: The extended longitudinal coverage of the NVHN coil promises to improve the clinical application of the current generation of pTx 7T MRI systems with 8Tx channels.
Slice-specific B1+ shimming improves the repeatability of multishot DWI at 7T
(Wiley, 2024-08-01) Ding, Belinda; Williams, Sydney Nicole; Dragonu, Iulius; Liebig, Patrick; Allwood-Spiers, Sarah; McElhinney, Paul; Gunamony, Shajan; Fullerton, Natasha; Porter, David Andrew
Purpose: Compared with lower field strengths, DWI at 7 T faces the combined challenges of increased distortion and blurring due to B0 inhomogeneity, and increased signal dropouts due to B1+ inhomogeneity. This study addresses the B1+ limitations using slice-specific static parallel transmission (pTx) in a multi-shot, readout-segmented EPI diffusion imaging sequence. Methods: DWI was performed in 7 healthy subjects using MRI at 7 T and readout-segmented EPI. Data were acquired with non-pTx circular-polarized (CP) pulses (CP-DWI) and static pTx pulses (pTx-DWI) using slice-specific B1+ shim coefficients. Each volunteer underwent two scan sessions on the same day, with two runs of each sequence in the first session and one run in the second. The sequences were evaluated by assessing image quality, flip-angle homogeneity, and intrasession and intersession repeatability in ADC estimates. Results: pTx-DWI significantly reduced signal voids compared with CP-DWI, particularly in inferior brain regions. The use of pTx also improved RF uniformity and symmetry across the brain. These effects translated into improved intrasession and intersession repeatability for pTx-DWI. Additionally, re-optimizing the pTx pulse between repeat scans did not have a negative effect on ADC repeatability. Conclusion: The study demonstrates that pTx provides a reproducible image-quality increase in multishot DWI at 7 T. The benefits of pTx also extend to quantitative ADC estimation with regard to the improvement in intrasession and intersession repeatability. Overall, the combination of multishot imaging and pTx can support the development of reliable, high-resolution DWI for clinical studies at 7 T.