Kawin Setsompop¹, Jason Stockmann¹, Qiuyun Fan¹, Thomas Witzel¹, and Lawrence L. Wald^1
1A.A. Martinos Center for Biomedical Imaging, charlestown, MA, United States

In this work, we propose generalized Slider (gSlider) method which utilizes RF encoding to markedly improve the ability of slice super-resolution in acquiring a large number of imaging slices simultaneously in diffusion imaging, to increase volume encoding and SNR. In particular, we show that gSlider can be use to acquire 5 slices simultaneously to provide close to the theoretical √5 SNR gain, while retaining sharp slice/partition resolution, comparable to that of conventional 2-D slice-selective imaging. Through a combined gSlider-SMS acquisition (5x-gSlider and MB-2), we demonstrate a highly efficient 10 simultaneous slice acquisition for high quality whole-brain 660μm isotropic diffusion imaging.  

Martijn A Cloos^1,2, Tiejun Zhao³, Florian Knoll^1,2, and Daniel K Sodickson^1,2
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, ²Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, NY, United States, ³Siemens Medical Solutions USA Inc., Malvern, PA, United States

Magnetic resonance fingerprinting (MRF) is a promising new approach for rapid quantitative imaging. So far, multi-slice acceleration (MSA) for MRF has been based on a gradient t-Blipped multi-slice scheme. However, for traditional MR sequences using thick slices, it has been shown that radiofrequency based phase encoding works better than the gradient blipped implementation. In this work we demonstrate an RF based MSA approach for radial sampled MRF experiments such as PnP-PTX including a fully integrated online image reconstruction pipeline that creates both quantitative maps (T1, T2, PD and B₁⁺) and synthesized contras weighted images (MP-RAGE, T1-TSE and T2-TSE).

Kangrong Zhu¹, Hua Wu², Robert F. Dougherty², Matthew J. Middione³, John M. Pauly¹, and Adam B. Kerr^1
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Center for Cognitive and Neurobiological Imaging, Stanford University, Stanford, CA, United States, ³Applied Sciences Laboratory West, GE Healthcare, Menlo Park, CA, United States

In simultaneous multi-slice (SMS) imaging, a commonly used method to compute the g-factor is the pseudo multiple replica method, whose accuracy depends on the number of simulated replicas. In this work, we derive analytical g-factor maps for SMS acquisitions with arbitrary Cartesian undersampling patterns basing on a hybrid-space SENSE reconstruction. Brain images demonstrate that the analytical g-factor maps agree with those calculated by the pseudo multiple replica method, but require less computation time for high quality maps. The analytical maps enable a fair comparison between coherent and incoherent Cartesian SMS undersampling patterns.

JaeJin Cho¹, Dongchan Kim¹, Hyunseok Seo¹, Kinam Kwon¹, Seohee So¹, and HyunWook Park^1
1Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, Republic of

Blipped-CAIPI imaging is widely used for fast imaging, which is one of the simultaneous multi-slice imaging methods. Conventional water-fat separation methods can be combined with the blipped-CAIPI technique. However, it results in the chemical-shift ghost artifact because fat signal on slightly shifted position is exited in the slice-selection process. This geometric error in slice-selection generates additional phase cycling, which causes the ghost artifacts on each slice’s fat image. In this abstract, a SENSE-based water-fat separation method is proposed, which considers the additional phase cycling on fat signal and obtains more accurate water-fat separated images.

Zahra Fazal¹, Jennifer Schulz¹, Jose P Marques¹, and David G Norris ^1,2
1Donders Center for Cognitive Neuroimaging, Radboud university, Nijmegen, Netherlands, ²Erwin L.Hahn institute for Magnetic Resonance Imaging, Essen, Germany

To reconstruct blood vessel in 2D and 3D MB TOF MRA without using coil sensitivity profile to reduce g-factor noise. The idea is to use CAIPRINHA on sparse angiographic data that first shift each slice/slab differently and then apply CAIPI reshift to shift each slab to its original position to form a continuous vessel tree. Results showed that the vessel reconstruction in 2D and 3D MB is comparable to standard single band MS TOF. Vessel reconstruction in MB angiography without using coil sensitivity profile can lead to high MB factors reducing the aquistion time and high sensitivity in detecting small vessels

Berkin Bilgic¹, Huihui Ye¹, Lawrence L Wald¹, and Kawin Setsompop^1
1Martinos Center for Biomedical Imaging, Charlestown, MA, United States

Wave-CAIPI utilizes additional gradients during the readout to improve controlled aliasing and fully harness coil sensitivity encoding. Recently proposed CS-Wave extended Wave-encoding with Poisson sampling and wavelet regularization. This work proposes optimized CS-Wave with i) tailored data-sampling and ii) highly efficient reconstruction. At 15-fold acceleration, proposed CS-Wave provides 20% RMSE improvement over Wave-CAIPI, which nearly doubles the improvement achieved with previously proposed CS-Wave. This permits single head-orientation Quantitative Susceptibility Mapping at 1×1×2mm³resolution in 25s. Combining CS-Wave with SMS Echo-Shift strategy further increases the acceleration to 30-fold, thus enabling multi-orientation QSM at long-TE from three head-rotations at 1.5mm isotropic in 72s.

Alexander D. Cohen¹, Andrew S. Nencka^1,2, and Yang Wang^1,2
1Radiology, Medical College of Wisconsin, Milwaukee, WI, United States, ²Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States

In this study a novel technique was tested combining multiband and multishot imaging for functional MRI at 7T. Hadamard and segmented multi-shot encoding were applied to yield short TR, reduced distortion fMRI images without the need for parallel imaging reconstruction techniques. Furthermore, acquiring segmented data allows for datasets to be reconstructed with effective in-plane accelerations up to the number of segments. Thus, one can reconstruct a dataset with higher SNR and the reduced geometric distortion of a highly accelerated  acquisition. 

Suhyung Park¹ and Jaeseok Park^2
1Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Korea, Republic of, ²Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of

Simultaneous multi-slice (SMS) acquisition has recently gained attention in clinical and research applications. However, since the spatial variation of coil sensitivity along the slice direction is typically insufficient and thus SMS reconstruction including SENSE/GRAPPA and slice-GRAPPA is potentially ill-conditioned, it is challenging to separate the aliased slices in the presence of noise with increasing multi-band factors (MB). In this work, we propose a novel, SMS reconstruction method that exploits Hankel subspace learning (SMS-HSL) for aliasing separation in the slice direction, in which SMS signals are projected onto an individual subspace specific to each slice by incorporating the proposed SMS model into a constrained optimization with low rank and magnitude priors. Simulation and experiments were performed at high MB factors to demonstrate the effectiveness of the proposed SMS-HSL over conventional SMS methods.

Desmond H Y Tse¹, Christopher J Wiggins², and Benedikt A Poser^1
1Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands, ²Scannexus, Maastricht, Netherlands

RF inhomogeneity at ultra-high field MRI leads to unwanted variations in image contrast and SNR. RF homogenisation at 9.4T was achieved with parallel transmission (pTx) of slice-specific spokes pulses designed offline using acquired B0 and B1+ maps. These spokes pulses were combined on-the-fly on the scanner to form simultaneous multi-slice (SMS) excitations, with optimised inter-slice phases to minimise the SMS pulse amplitude. The pTx spokes SMS pulse allowed a time efficient high resolution 2D GRE T2*-weighted imaging at 9.4T with whole brain coverage and minimal artefacts caused by RF inhomogeneity. 

Yi Wang¹, Xingfeng Shao¹, Thomas Martin¹, Steen Moeller², Essa Yacoub², and Danny JJ Wang^1
1Neurology, UCLA, Los Angeles, CA, United States, ²Center of Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

The application of balanced SSFP (bSSFP) is limited by the banding artifact resulting from its sensitivity to field inhomogeneity.  A common approach for band reduction involves multiple measurements with different RF phase cycling, at the cost of lengthened total imaging time. In this work, we present a novel time-efficient bSSFP banding reduction technique by utilizing simultaneous multi-slice (SMS) imaging with CAIPIRINHA to acquire multiple phase-cycled images within the same imaging time of a single-band bSSFP scan. Effective band reduction is demonstrated in phantom, abdominal and brain imaging with SMS factor up to four.