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Lawrence L Wald - One of the best experts on this subject based on the ideXlab platform.
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high fidelity high isotropic resolution diffusion imaging through gslider acquisition with b 1 and t 1 corrections and integrated δb 0 rx shim array
Magnetic Resonance in Medicine, 2020Co-Authors: Congyu Liao, Jason P Stockmann, Qiyuan Tian, Berkin Bilgic, Nicolas Arango, Mary Kate Manhard, Susie Y Huang, William A Grissom, Lawrence L WaldAbstract:PURPOSE: B1+ and T1 corrections and dynamic multicoil Shimming approaches were proposed to improve the fidelity of high-isotropic-resolution generalized slice-dithered enhanced resolution (gSlider) diffusion imaging. METHODS: An extended reconstruction incorporating B1+ inhomogeneity and T1 recovery information was developed to mitigate slab-boundary artifacts in short-repetition time (TR) gSlider acquisitions. Slab-by-slab dynamic B0 Shimming using a multicoil integrated ΔB0 /Rx shim array and high in-plane acceleration (Rinplane = 4) achieved with virtual-coil GRAPPA were also incorporated into a 1-mm isotropic resolution gSlider acquisition/reconstruction framework to achieve a significant reduction in geometric distortion compared to single-shot echo planar imaging (EPI). RESULTS: The slab-boundary artifacts were alleviated by the proposed B1+ and T1 corrections compared to the standard gSlider reconstruction pipeline for short-TR acquisitions. Dynamic Shimming provided >50% reduction in geometric distortion compared to conventional global second-order Shimming. One-millimeter isotropic resolution diffusion data show that the typically problematic temporal and frontal lobes of the brain can be imaged with high geometric fidelity using dynamic Shimming. CONCLUSIONS: The proposed B1+ and T1 corrections and local-field control substantially improved the fidelity of high-isotropic-resolution diffusion imaging, with reduced slab-boundary artifacts and geometric distortion compared to conventional gSlider acquisition and reconstruction. This enabled high-fidelity whole-brain 1-mm isotropic diffusion imaging with 64 diffusion directions in 20 min using a 3T clinical scanner.
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high fidelity high isotropic resolution diffusion imaging through gslider acquisition with b1 t1 corrections and integrated delta b0 rx shim array
arXiv: Medical Physics, 2018Co-Authors: Congyu Liao, Jason P Stockmann, Qiyuan Tian, Berkin Bilgic, Nicolas Arango, Mary Kate Manhard, William A Grissom, Lawrence L Wald, Kawin SetsompopAbstract:Purpose: B1+ and T1 corrections and dynamic multi-coil Shimming approaches were proposed to improve the fidelity of high isotropic resolution Generalized slice dithered enhanced resolution (gSlider) diffusion imaging. Methods: An extended reconstruction incorporating B1+ inhomogeneity and T1 recovery information was developed to mitigate slab-boundary artifacts in short-TR gSlider acquisitions. Slab-by-slab dynamic B0 Shimming using a multi-coil integrated {\Delta}B0/Rx shim-array, and high in-plane acceleration (Rinplane=4) achieved with virtual-coil GRAPPA were also incorporated into a 1 mm isotropic resolution gSlider acquisition/reconstruction framework to achieve an 8-11 fold reduction in geometric distortion compared to single-shot EPI. Results: The slab-boundary artifacts were alleviated by the proposed B1+ and T1 corrections compared to the standard gSlider reconstruction pipeline for short-TR acquisitions. Dynamic Shimming provided >50% reduction in geometric distortion compared to conventional global 2nd order Shimming. 1 mm isotropic resolution diffusion data show that the typically problematic temporal and frontal lobes of the brain can be imaged with high geometric fidelity using dynamic Shimming. Conclusions: The proposed B1+ and T1 corrections and local-field control substantially improved the fidelity of high isotropic resolution diffusion imaging, with reduced slab-boundary artifacts and geometric distortion compared to conventional gSlider acquisition and reconstruction. This enabled high-fidelity whole-brain 1 mm isotropic diffusion imaging with 64 diffusion-directions in 20 minutes using a 3T clinical scanner.
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a 32 channel combined rf and b0 shim array for 3t brain imaging
Magnetic Resonance in Medicine, 2016Co-Authors: Jason P Stockmann, Lawrence L Wald, Azma Mareyam, Boris Keil, Thomas Witzel, Jonathan R Polimeni, Cristen Lapierre, Kawin SetsompopAbstract:Purpose 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. Methods Shim performance using constrained DC current (±2.5A) is simulated for brain arrays ranging from 8 to 128 elements. A 32-channel 3-tesla brain array is realized using inductive chokes to bridge the tuning capacitors on each RF loop. The RF and B0 Shimming performance is assessed in bench and imaging measurements. Results The addition of DC currents to the 32-channel RF array is achieved with minimal disruption of the RF performance and/or negative side effects such as conductor heating or mechanical torques. The Shimming results agree well with simulations and show performance superior to third-order spherical harmonic (SH) Shimming. Imaging tests show the ability to reduce the standard frontal lobe susceptibility-induced fields and improve echo planar imaging geometric distortion. The simulation of 64- and 128-channel brain arrays suggest that even further Shimming improvement is possible (equivalent to up to 6th-order SH shim coils). Conclusion Including user-controlled shim currents on the loops of a conventional highly parallel brain array coil is feasible with modest current levels and produces improved B0 Shimming performance over standard second-order SH Shimming. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
K Scheffler - One of the best experts on this subject based on the ideXlab platform.
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a 32 channel multi coil setup optimized for human brain Shimming at 9 4t
Magnetic Resonance in Medicine, 2020Co-Authors: A Aghaeifar, J Zhou, Rahel Heule, Behzad Tabibian, Bernhard Scholkopf, Feng Jia, Maxim Zaitsev, K SchefflerAbstract:Purpose 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. Methods 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. Results 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. Conclusions 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.
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dynamic b0 Shimming of the human brain at 9 4 t with a 16 channel multi coil shim setup
Magnetic Resonance in Medicine, 2018Co-Authors: A Aghaeifar, A Henning, C Mirkes, J Bause, Theodor Steffen, N Avdievitch, K SchefflerAbstract:PURPOSE A 16-channel multi-coil Shimming setup was developed to mitigate severe B0 field perturbations at ultrahigh field and improve data quality for human brain imaging and spectroscopy. METHODS The Shimming setup consisted of 16 circular B0 coils that were positioned symmetrically on a cylinder with a diameter of 370 mm. The latter was large enough to house a shielded 18/32-channel RF transceiver array. The shim performance was assessed via simulations and phantom as well as in vivo measurements at 9.4 T. The global and dynamic Shimming performance of the multi-coil setup was compared with the built-in scanner shim system for EPI and single voxel spectroscopy. RESULTS The presence of the multi-coil shim did not influence the performance of the RF coil. The performance of the proposed setup was similar to a full third-order spherical harmonic shim system in the case of global static and dynamic slice-wise Shimming. Dynamic slice-wise Shimming with the multi-coil setup outperformed global static Shimming with the scanner's second-order spherical-harmonic shim. The multi-coil setup allowed mitigating geometric distortions for EPI. The combination of the multi-coil shim setup with the zeroth and first-order shim of the scanner further reduced the standard deviation of the B0 field in the brain by 12% compared with the case in which multi-coil was used exclusively. CONCLUSION The combination of a multi-coil setup and the linear shim channels of the scanner provides a straightforward solution for implementing dynamic slice-wise Shimming without requiring an additional pre-emphasis setup.
A Aghaeifar - One of the best experts on this subject based on the ideXlab platform.
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a 32 channel multi coil setup optimized for human brain Shimming at 9 4t
Magnetic Resonance in Medicine, 2020Co-Authors: A Aghaeifar, J Zhou, Rahel Heule, Behzad Tabibian, Bernhard Scholkopf, Feng Jia, Maxim Zaitsev, K SchefflerAbstract:Purpose 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. Methods 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. Results 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. Conclusions 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.
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dynamic b0 Shimming of the human brain at 9 4 t with a 16 channel multi coil shim setup
Magnetic Resonance in Medicine, 2018Co-Authors: A Aghaeifar, A Henning, C Mirkes, J Bause, Theodor Steffen, N Avdievitch, K SchefflerAbstract:PURPOSE A 16-channel multi-coil Shimming setup was developed to mitigate severe B0 field perturbations at ultrahigh field and improve data quality for human brain imaging and spectroscopy. METHODS The Shimming setup consisted of 16 circular B0 coils that were positioned symmetrically on a cylinder with a diameter of 370 mm. The latter was large enough to house a shielded 18/32-channel RF transceiver array. The shim performance was assessed via simulations and phantom as well as in vivo measurements at 9.4 T. The global and dynamic Shimming performance of the multi-coil setup was compared with the built-in scanner shim system for EPI and single voxel spectroscopy. RESULTS The presence of the multi-coil shim did not influence the performance of the RF coil. The performance of the proposed setup was similar to a full third-order spherical harmonic shim system in the case of global static and dynamic slice-wise Shimming. Dynamic slice-wise Shimming with the multi-coil setup outperformed global static Shimming with the scanner's second-order spherical-harmonic shim. The multi-coil setup allowed mitigating geometric distortions for EPI. The combination of the multi-coil shim setup with the zeroth and first-order shim of the scanner further reduced the standard deviation of the B0 field in the brain by 12% compared with the case in which multi-coil was used exclusively. CONCLUSION The combination of a multi-coil setup and the linear shim channels of the scanner provides a straightforward solution for implementing dynamic slice-wise Shimming without requiring an additional pre-emphasis setup.
Robin A De Graaf - One of the best experts on this subject based on the ideXlab platform.
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dynamic multi coil technique dynamite Shimming for echo planar imaging of the human brain at 7 tesla
NeuroImage, 2015Co-Authors: Christoph Juchem, Terence W. Nixon, Umesh S Rudrapatna, Robin A De GraafAbstract:Abstract Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field Shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain Shimming or on specific areas with strong susceptibility-induced B0 distortions such as the prefrontal cortex (PFC). Excellent B0 homogeneity has been demonstrated recently in the human brain at 7 Tesla with the DYNAmic Multi-coIl TEchnique (DYNAMITE) for magnetic field Shimming (J Magn Reson (2011) 212:280–288). Here, we report the benefits of DYNAMITE Shimming for multi-slice EPI and T2* mapping. A standard deviation of 13 Hz was achieved for the residual B0 distribution in the human brain at 7 Tesla with DYNAMITE Shimming and was 60% lower compared to conventional Shimming that employs static zero through third order SH shapes. The residual field inhomogeneity with SH Shimming led to an average 8 mm shift at acquisition parameters commonly used for fMRI and was reduced to 1.5-3 mm with DYNAMITE Shimming. T2* values obtained from the prefrontal and temporal cortices with DYNAMITE Shimming were 10-50% longer than those measured with SH Shimming. The reduction of the confounding macroscopic B0 field gradients with DYNAMITE Shimming thereby promises improved access to the relevant microscopic T2* effects. The combination of high spatial resolution and DYNAMITE Shimming allows largely artifact-free EPI and T2* mapping throughout the brain, including prefrontal and temporal lobe areas. DYNAMITE Shimming is expected to critically benefit a wide range of MRI applications that rely on excellent B0 magnetic field conditions including EPI-based fMRI to study various cognitive processes and assessing large-scale brain connectivity in vivo. As such, DYNAMITE Shimming has the potential to replace conventional SH shim systems in human MR scanners.
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dynamic multi coil technique dynamite Shimming of the rat brain at 11 7 t
NMR in Biomedicine, 2014Co-Authors: Christoph Juchem, Peter B. Brown, Scott Mcintyre, Terence W. Nixon, Peter Herman, Basavaraju G Sanganahalli, Dan Green, Fahmeed Hyder, Robin A De GraafAbstract:The in vivo rat model is a workhorse in neuroscience research, preclinical studies and drug development. A repertoire of MR tools has been developed for its investigation; however, high levels of B0 magnetic field homogeneity are required for meaningful results. The homogenization of magnetic fields in the rat brain, i.e. Shimming, is a difficult task because of a multitude of complex, susceptibility-induced field distortions. Conventional Shimming with spherical harmonic (SH) functions is capable of compensating for shallow field distortions in limited areas, e.g. in the cortex, but performs poorly in difficult-to-shim subcortical structures or for the entire brain. Based on the recently introduced multi-coil approach for magnetic field modeling, the DYNAmic Multi-coIl TEchnique (DYNAMITE) is introduced for magnetic field Shimming of the in vivo rat brain and its benefits for gradient-echo echo-planar imaging (EPI) are demonstrated. An integrated multi-coil/radiofrequency (MC/RF) system comprising 48 individual localized DC coils for B0 Shimming and a surface transceive RF coil has been developed that allows MR investigations of the anesthetized rat brain in vivo. DYNAMITE Shimming with this MC/RF set-up is shown to reduce the B0 standard deviation to a third of that achieved with current shim technology employing static first- through third-order SH shapes. The EPI signal over the rat brain increased by 31%, and a 24% gain in usable EPI voxels could be realized. DYNAMITE Shimming is expected to critically benefit a wide range of preclinical and neuroscientific MR research. Improved magnetic field homogeneity, together with the achievable large brain coverage of this method, will be crucial when signal pathways, cortical circuitry or the brain's default network are studied. Together with the efficiency gains of MC-based Shimming compared with SH approaches demonstrated recently, DYNAMITE Shimming has the potential to replace conventional SH shim systems in small-bore animal scanners.
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multicoil Shimming of the mouse brain
Magnetic Resonance in Medicine, 2011Co-Authors: Christoph Juchem, Peter B. Brown, Scott Mcintyre, Terence W. Nixon, Douglas L Rothman, Robin A De GraafAbstract:MR imaging and spectroscopy allow the noninvasive measurement of brain function and physiology, but excellent magnetic field homogeneity is required for meaningful results. The homogenization of the magnetic field distribution in the mouse brain (i.e., Shimming) is a difficult task due to complex susceptibility-induced field distortions combined with the small size of the object. To date, the achievement of satisfactory whole brain Shimming in the mouse remains a major challenge. The magnetic fields generated by a set of 48 circular coils (diameter 13 mm) that were arranged in a cylinder-shaped pattern of 32 mm diameter and driven with individual dynamic current ranges of ±1 A are shown to be capable of substantially reducing the field distortions encountered in the mouse brain at 9.4 Tesla. Static multicoil shim fields allowed the reduction of the standard deviation of Larmor frequencies by 31% compared to second order spherical harmonics Shimming and a 66% narrowing was achieved with the slice-specific application of the multicoil Shimming with a dynamic approach. For gradient echo imaging, multicoil Shimming minimized shim-related signal voids in the brain periphery and allowed overall signal gains of up to 51% compared to spherical harmonics Shimming.
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optimization of static magnetic field homogeneity in the human and animal brain in vivo
Progress in Nuclear Magnetic Resonance Spectroscopy, 2009Co-Authors: Kevin M Koch, Douglas L Rothman, Robin A De GraafAbstract:Samples studied with conventional magnetic resonance (MR) techniques are subjected to a polarizing static magnetic field B(r)=B0z^. Ideally, this magnetic field is assumed to be spatially homogeneous over the sample volume. However, the presence of any object of finite magnetic susceptibility (i.e. a sample) will inevitably perturb this magnetic field and provide the Larmor frequencies of MR-sensitive spins with an unwanted spatial dependence. These susceptibility-induced B0 perturbations, which are a fundamental result of Maxwell’s electromagnetic field theory, scale roughly linearly in magnitude with applied B0 field strengths. B0 inhomogeneity degrades the signal-to-noise ratio (SNR) of all MR measurements. While Hahn spin-echoes can be used to refocus B0 inhomogeneity at one instantaneous temporal point, the remainder of a spin-echo is tempered by B0 inhomogeneity-induced signal relaxation (commonly referred to as T2∗). Furthermore, many techniques cannot utilize spin-echo procedures, and are thus susceptible to the full evolution of T2∗ relaxation. The spatial variation of Larmor frequencies within a spectro-scopic voxel will broaden and distort spectral lineshapes. Standard spectroscopic techniques such as frequency-selective resonance suppression and spectral editing are easily degraded by these effects. MR images are susceptible to the same B0-induced SNR deterioration as spectroscopic acquisitions. Additionally, they can further suffer from spatial distortion in regions of high B0 inhomogeneity. In particular, commonly utilized rapid imaging strategies such as steady-state free precession (SSFP), spiral, and echo-planar imaging (EPI) are often compromised by B0 inhomogeneity. Broadly speaking, B0 Shimming refers to the optimized application of external magnetic fields to compensate unwanted inhomogeneity of the B0 magnetic field. For applications that require high-degrees of B0 homogeneity, fine-tuned Shimming has historically been accomplished using sets of dedicated electromagnets. These electromagnet coils, or ‘active shims’, can be adjusted on a subject-specific basis. This review is focused on high-field B0 Shimming of the brain, specifically within small rodents and humans. B0 field perturbations within the brain are particularly prominent near the air-tissue interfaces at the sinus and auditory cavities. The recent increases of B0 field strengths used in both clinical and research MR systems necessitates maximal utility of conventional shim technology. For some applications, this conventional technology cannot adequately homogenize designated shim volumes (particularly larger volumes). Therefore, along with the development of automated optimization protocols for conventional active shim systems, recent investigations have explored alternative approaches to shim hardware design. A theoretical treatment of B0 inhomogeneity and its effects on magnetic resonance acquisitions are presented in the next section. Section 3 then presents the techniques utilized in MR-based mapping of static magnetic fields, which is now a standard tool in automated Shimming methods. The hardware and methods utilized in room-temperature Shimming (also commonly referred to as ‘active’ Shimming) are developed in Section 4. The challenges of optimizing B0 homogeneity over extended volumes are introduced in Section 5, followed by a discussion of the methods and capabilities of Dynamic Shim Updating (DSU) of room-temperature shims. Finally, recent novel approaches to Shimming that deviate from any previous technological methodologies, such as local active Shimming and subject-specific passive Shimming, are presented.
Jason P Stockmann - One of the best experts on this subject based on the ideXlab platform.
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high fidelity high isotropic resolution diffusion imaging through gslider acquisition with b 1 and t 1 corrections and integrated δb 0 rx shim array
Magnetic Resonance in Medicine, 2020Co-Authors: Congyu Liao, Jason P Stockmann, Qiyuan Tian, Berkin Bilgic, Nicolas Arango, Mary Kate Manhard, Susie Y Huang, William A Grissom, Lawrence L WaldAbstract:PURPOSE: B1+ and T1 corrections and dynamic multicoil Shimming approaches were proposed to improve the fidelity of high-isotropic-resolution generalized slice-dithered enhanced resolution (gSlider) diffusion imaging. METHODS: An extended reconstruction incorporating B1+ inhomogeneity and T1 recovery information was developed to mitigate slab-boundary artifacts in short-repetition time (TR) gSlider acquisitions. Slab-by-slab dynamic B0 Shimming using a multicoil integrated ΔB0 /Rx shim array and high in-plane acceleration (Rinplane = 4) achieved with virtual-coil GRAPPA were also incorporated into a 1-mm isotropic resolution gSlider acquisition/reconstruction framework to achieve a significant reduction in geometric distortion compared to single-shot echo planar imaging (EPI). RESULTS: The slab-boundary artifacts were alleviated by the proposed B1+ and T1 corrections compared to the standard gSlider reconstruction pipeline for short-TR acquisitions. Dynamic Shimming provided >50% reduction in geometric distortion compared to conventional global second-order Shimming. One-millimeter isotropic resolution diffusion data show that the typically problematic temporal and frontal lobes of the brain can be imaged with high geometric fidelity using dynamic Shimming. CONCLUSIONS: The proposed B1+ and T1 corrections and local-field control substantially improved the fidelity of high-isotropic-resolution diffusion imaging, with reduced slab-boundary artifacts and geometric distortion compared to conventional gSlider acquisition and reconstruction. This enabled high-fidelity whole-brain 1-mm isotropic diffusion imaging with 64 diffusion directions in 20 min using a 3T clinical scanner.
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high fidelity high isotropic resolution diffusion imaging through gslider acquisition with b1 t1 corrections and integrated delta b0 rx shim array
arXiv: Medical Physics, 2018Co-Authors: Congyu Liao, Jason P Stockmann, Qiyuan Tian, Berkin Bilgic, Nicolas Arango, Mary Kate Manhard, William A Grissom, Lawrence L Wald, Kawin SetsompopAbstract:Purpose: B1+ and T1 corrections and dynamic multi-coil Shimming approaches were proposed to improve the fidelity of high isotropic resolution Generalized slice dithered enhanced resolution (gSlider) diffusion imaging. Methods: An extended reconstruction incorporating B1+ inhomogeneity and T1 recovery information was developed to mitigate slab-boundary artifacts in short-TR gSlider acquisitions. Slab-by-slab dynamic B0 Shimming using a multi-coil integrated {\Delta}B0/Rx shim-array, and high in-plane acceleration (Rinplane=4) achieved with virtual-coil GRAPPA were also incorporated into a 1 mm isotropic resolution gSlider acquisition/reconstruction framework to achieve an 8-11 fold reduction in geometric distortion compared to single-shot EPI. Results: The slab-boundary artifacts were alleviated by the proposed B1+ and T1 corrections compared to the standard gSlider reconstruction pipeline for short-TR acquisitions. Dynamic Shimming provided >50% reduction in geometric distortion compared to conventional global 2nd order Shimming. 1 mm isotropic resolution diffusion data show that the typically problematic temporal and frontal lobes of the brain can be imaged with high geometric fidelity using dynamic Shimming. Conclusions: The proposed B1+ and T1 corrections and local-field control substantially improved the fidelity of high isotropic resolution diffusion imaging, with reduced slab-boundary artifacts and geometric distortion compared to conventional gSlider acquisition and reconstruction. This enabled high-fidelity whole-brain 1 mm isotropic diffusion imaging with 64 diffusion-directions in 20 minutes using a 3T clinical scanner.
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integrated rf shim coil allowing two degrees of freedom shim current
International Conference of the IEEE Engineering in Medicine and Biology Society, 2016Co-Authors: J Zhou, Jason P Stockmann, Yinghua Chu, Yicheng Hsu, Fahsuan LinAbstract:High-quality magnetic resonance imaging and spectroscopic measurements require a highly homogeneous magnetic field. Different from global Shimming, localized off-resonance can be corrected by using multi-coil Shimming. Previously, integrated RF and Shimming coils have been used to implement multi-coil Shimming. Such coils share the same conductor for RF signal reception and shim field generation. Here we propose a new design of the integrated RF-shim coil at 3-tesla, where two independent shim current paths are allowed in each coil. This coil permits a higher degree of freedom in shim current distribution design. We use both phantom experiments and simulations to demonstrate the feasibility of this new design.
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a 32 channel combined rf and b0 shim array for 3t brain imaging
Magnetic Resonance in Medicine, 2016Co-Authors: Jason P Stockmann, Lawrence L Wald, Azma Mareyam, Boris Keil, Thomas Witzel, Jonathan R Polimeni, Cristen Lapierre, Kawin SetsompopAbstract:Purpose 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. Methods Shim performance using constrained DC current (±2.5A) is simulated for brain arrays ranging from 8 to 128 elements. A 32-channel 3-tesla brain array is realized using inductive chokes to bridge the tuning capacitors on each RF loop. The RF and B0 Shimming performance is assessed in bench and imaging measurements. Results The addition of DC currents to the 32-channel RF array is achieved with minimal disruption of the RF performance and/or negative side effects such as conductor heating or mechanical torques. The Shimming results agree well with simulations and show performance superior to third-order spherical harmonic (SH) Shimming. Imaging tests show the ability to reduce the standard frontal lobe susceptibility-induced fields and improve echo planar imaging geometric distortion. The simulation of 64- and 128-channel brain arrays suggest that even further Shimming improvement is possible (equivalent to up to 6th-order SH shim coils). Conclusion Including user-controlled shim currents on the loops of a conventional highly parallel brain array coil is feasible with modest current levels and produces improved B0 Shimming performance over standard second-order SH Shimming. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
