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Purpose: Spatial encoding and shimming in MRI have traditionally been performed using dedicated coils that generate orthogonal spherical harmonic fields. The recently introduced multi‐coil hardware has proven that MRI‐relevant magnetic fields can also be created by a generic set of localized coils producing non‐orthogonal fields. As a step towards establishing a purely multi‐coil‐based MRI field generation system, the feasibility of performing conventional Cartesian k‐space encoding and echo‐planar imaging (EPI), as well as concurrent encoding and shimming is demonstrated in this study. Methods: We report the use of Dynamic Multi‐Coil Technique (DYNAMITE) for combined Cartesian encoding and shimming, and EPI using a 48‐channel multi‐coil system. Experiments were performed on phantom objects and biological specimens in a 9.4 T pre‐clinical scanner. Cartesian Fourier‐encoded MRI and EPI were implemented whereby the magnetic fields required for encoding of the three orthogonal spatial dimensions were entirely based on linear combinations of multi‐coil fields. Furthermore, DYNAMITE imaging was augmented by concurrent DYNAMITE shimming with the same hardware. Results: DYNAMITE‐based MR and echo‐planar images were indistinguishable from those acquired with the conventional linear imaging gradients provided by the scanner. In experiments with concurrent DYNAMITE shimming and imaging, shim challenges that would result in extreme spatial distortion and signal loss were corrected very effectively with more than 92% signal recovery in case of extreme Z2 shim challenge that resulted in complete signal dephasing in most slices. Conclusions: We demonstrate the first successful implementation of combined DYNAMITE imaging and shimming and show the feasibility of performing EPI with DYNAMITE hardware. Our results substantiate the potential of multi‐coil hardware as a full‐fledged imaging and shimming system, with additional potential benefits of reduced echo‐time and risk of peripheral nerve stimulation while performing EPI. [ABSTRACT FROM AUTHOR]

Purpose Tailored excitation (TEx) based on interspersing multiple radio frequency pulses with linear gradient and higher-order shim pulses can be used to obtain uniform flip angle in the presence of large radio frequency transmission (B [ABSTRACT FROM AUTHOR]

Purpose: Tailored excitation (TEx) based on interspersing multiple radio frequency pulses with linear gradient and higher-order shim pulses can be used to obtain uniform flip angle in the presence of large radio frequency transmission (B 1+) inhomogeneity. Here, an implementation of dynamic, multislice tailored excitation using the recently developed multi-coil nonlinear shim hardware (MC-DTEx) is reported., Methods: MC-DTEx was developed and tested both in a phantom and in vivo at 7 T, and its efficacy was quantitatively assessed. Predicted outcomes of MC-DTEx and DTEx based on spherical harmonic shims (SH-DTEx) were also compared., Results: For a planned 30 ° flip angle, in a phantom, the standard deviation in excitation improved from 28% (regular excitation) to 12% with MC-DTEx. The SD in in vivo excitation improved from 22 to 12%. The improvements achieved with experimental MC-DTEx closely matched the theoretical predictions. Simulations further showed that MC-DTEx outperforms SH-DTEx for both scenarios., Conclusion: Successful implementation of multislice MC-DTEx is presented and is shown to be capable of homogenizing excitation over more than twofold B 1+ variations. Its benefits over SH-DTEx are also demonstrated. A distinct advantage of MC hardware over SH shim hardware is the absence of significant eddy current effects, which allows for a straightforward, multislice implementation of MC-DTEx. Magn Reson Med 76:83-93, 2016. © 2015 Wiley Periodicals, Inc., (© 2015 Wiley Periodicals, Inc.)

Growing clinical evidence suggests critical involvement of spreading depolarizations (SDs) in the pathophysiology of neurological disorders such as migraine and stroke. MRI provides powerful tools to detect and assess co-occurring cerebral hemodynamic and cellular changes during SDs. This study reports the feasibility and advantages of two MRI scans, based on balanced steady-state free precession (b-SSFP) and diffusion-weighted multi-spin-echo (DT2), heretofore unexplored for monitoring SDs. These were compared with gradient-echo MRI. SDs were induced by KCl application in rat brain. Known for high SNR, the T2- and T1-based b-SSFP contrast was hypothesized to provide higher spatiotemporal specificity than T2*-based gradient-echo scanning. DT2 scanning was designed to provide simultaneous T2 and apparent diffusion coefficient (ADC) measurements, thus enabling combined quantitative assessment of hemodynamic and cellular changes during SDs. Procedures were developed to automate identification of SD-induced responses in all the scans. These responses were analyzed to determine detection sensitivity and temporal characteristics of signals from each scanning method. Cluster analysis was performed to elucidate unique temporal patterns for each contrast. All scans allowed detection of SD-induced responses. b-SSFP scans showed significantly larger relative intensity changes, narrower peak widths and greater spatial specificity compared with gradient-echo MRI. SD-induced effects on ADC, calculated from DT2 scans, showed the most pronounced signal changes, displaying about 20% decrease, as against 10-15% signal increases observed with b-SSFP and gradient-echo scanning. Cluster analysis revealed additional temporal sub-patterns, such as an initial dip on gradient-echo scans and temporally shifted T2 and proton density changes in DT2 data. To summarize, b-SSFP and DT2 scanning provide distinct information on SDs compared with gradient-echo MRI. DT2 scanning, with its potential to simultaneously provide cellular and hemodynamic information, can offer unique information on the inter-relationship between these processes in pathologic brain, which may improve monitoring of spreading depolarizations in (pre)clinical settings., (Copyright © 2015 John Wiley & Sons, Ltd.)