No abstract

No abstract

Purpose Simultaneous multi-slice (SMS) acquisitions have recently received much attention as a means of increasing single-shot imaging speed. SMS acquisitions combine the advantages of single-shot sampling and acceleration along the slice dimension which was previously limited to 3D volumetric acquisitions. A 2D description of SMS sampling and reconstruction has become established in the literature. Here, we present a more general 3D Fourier encoding and reconstruction formalism for SMS acquisitions that can easily be applied to non-Cartesian SMS acquisitions. Theory and Methods A “SMS 3D” k-space is defined in which the field of view along the slice select direction is equal to the number of excited slices times their separation. In this picture, SMS acceleration can be viewed as an under sampling of SMS 3D k-space that can be freely distributed between the in-plane and slice directions, as both are effective phase encoding directions. Results Use of the SMS 3D k-space picture is demonstrated in phantom and in-vivo brain acquisitions including data obtained with blipped-CAIPI sampling. SMS SENSE reconstruction is demonstrated as well as non-Cartesian SMS imaging using blipped spiral trajectories. Conclusion The full framework of reconstruction methods can be applied to SMS acquisitions by employing a 3D k-space approach. The blipped-CAIPI method can be viewed as a special case of undersampling an SMS 3D k-space. The extension of SMS methods to non-Cartesian 3D sampling and reconstruction is straightforward.

MR-Encephalography (MREG) is a technique that allows real time observation of functional changes in the brain that appears within 100 msec. The high sampling rate is achieved at the cost of some spatial resolution. The article describes a novel imaging method for fast three-dimensional-MR-encephalography whole brain coverage based on rosette trajectories and the use of multiple small receiver coils. The technique allows the observation of changes in brain physiology at very high temporal resolution. A highly undersampled three-dimensional rosette trajectory is chosen, to perform single shot acquisition of k-space data within 23 msec. By using a 32-channel head coil array and regularized nonuniform Fourier transformation reconstruction, the spatial resolution is sufficient to detect even subtle centers of activation (e.g. human MT1). The method was applied to visual block design paradigms and compared with echo planar imaging-based functional MRI. As a proof-of-principle of the method's ability to detect local differences in the hemodynamic response functions, the analyzed MR-encephalography data revealed a spatially dependent delay of the arrival of the blood oxygenation level dependent response within the visual cortex. Magn Reson Med 65:1260-1268,

MR-encephalography is a technique that allows real-time observation of functional changes in the brain with a time-resolution of 100 ms. The high sampling rate is enabled by the use of undersampled image acquisition with regularized reconstruction. The article describes a novel imaging method for fast three-dimensional-MR-encephalography whole brain coverage based on undersampled, single-shot concentric shells trajectories and the use of multiple small receiver coils. The technique allows the observation of changes in blood oxygenation level dependent signal as a measure of brain physiology at very high temporal resolution. Magn Reson Med 68:484-494,

Purpose Simultaneous multi-slice (SMS) acquisitions play an import role in the challenge of increasing single-shot imaging speed. We show that 2D-SENSE can be used to reconstruct SMS acquisitions with periodic but otherwise arbitrary undersampling patterns. Theory and Methods By adopting a 3D k-space representation of the SMS sampling process, the accelerated in-plane and slice encoding directions form a 2D reconstruction problem that is equivalent to volumetric CAIPIRINHA. 2D-SENSE does otherwise not distinguish between standard volumetric and SMS imaging with arbitrary CAIPIRINHA sampling. Results Use of the SENSE algorithm is demonstrated for in-vivo brain data obtained with blipped-CAIPRINHA sampling in 2D SMS-EPI and RARE acquisitions and 3D EPI with various in-plane and through-plane acceleration factors and CAIPIRINHA shifts. The proposed SENSE reconstruction works for any combination of SMS-factor and CAIPIRINHA shift by the addition of “dummy slices”, allowing for non-integer undersampling in the slice direction. Images with commonly used Slice-GRAPPA reconstruction are shown for reference. Conclusion SENSE is conceptually simple and provides a one-step reconstruction along both undersampled dimensions. It also provides a “contrast independent” parallel imaging reconstruction for SMS.

No abstract

No abstract