Peter J Lally^1,2, Ben Statton³, Paul M Matthews^1,4, Mark Chiew⁵, Karla L Miller⁵, and Neal K Bangerter^6
1Department of Brain Sciences, Imperial College London, London, United Kingdom, ²UK Dementia Research Institute Centre for Care Research and Technology, London, United Kingdom, ³MRC London Institute of Medical Sciences, Imperial College London, London, United Kingdom, ⁴UK Dementia Research Institute Centre at Imperial College London, London, United Kingdom, ⁵Wellcome Centre for Integrative Neuroimaging, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, ⁶Department of Bioengineering, Imperial College London, London, United Kingdom

Steady state free precession (SSFP) imaging with unbalanced gradients (e.g. FISP, PSIF, DESS) causes aliasing in k-space which is often overlooked, or at best, minimised with large spoilers. Here we exploit this phenomenon and use the aliased signals to increase the SNR-efficiency of SSFP imaging.

Kartiga Selvaganesan¹, Yonghyun Ha², Gigi Galiana², and Todd Constable^2
1Biomedical Engineering, Yale University, New Haven, CT, United States, ²Radiology and Biomedical Imaging, Yale University, New Haven, CT, United States

Gradient-free imaging at low-fields can significantly reduce the cost of and increase access to MRI devices. Here we propose to exploit the Bloch-Siegert shift effect to perform gradient-free, RF spatial encoding at 24mT. We have developed a simulation algorithm that designs various nonlinear encoding schemes and evaluates their performance through image reconstruction. Our results indicate that this technique is tolerant to noise and B₀ inhomogeneities; this is an important step towards demonstrating the feasibility of performing low-field imaging with nonlinear RF spatial encoding using the Bloch-Siegert shift.  

Thomas Roos^1,2,3, Edwin Versteeg¹, and Jeroen Siero^1
1Highfield research group, University Medical Center Utrecht, Utrecht, Netherlands, ²Delft University of Technology, Delft, Netherlands, ³Spinoza Centre for Neuroimaging, Amsterdam, Netherlands

Acceleration techniques like SENSE have enabled significant decreases in scan time, but the $$$G$$$-factor penalty on SNR limits attainable accelerations.
Wave-CAIPI lowers this $$$G$$$-factor by spreading aliasing and taking advantage of the coil sensitivity distributions. A high performance single-axis insert gradient is utilised to increase the attainable wave amplitudes and thereby increasing the effectivity of Wave-CAIPI.

Simulations and 7T phantom & in-vivo acquisitions show significant improvements in $$$G$$$-factor when using Wave-CAIPI, especially when utilizing the higher performance of the insert gradient.
Not only are the $$$G$$$-factors lower but also show increased spreading and lack hard edges, allowing for even faster acquisitions.

 

 

Tobias Speidel¹, Patrick Metze¹, Kilian Stumpf¹, Thomas Hüfken¹, and Volker Rasche^1
1Internal Medicine II, Ulm University Medical Center, Ulm, Germany

The calculation of k-space trajectories in MRI usually involves prior knowledge of the FOV, since the desired FOV defines a minimum k-space sampling density. The reconstruction of a FOV, which is larger than what is represented by the primary sampling density, is equal to undersampling in k-space. Arising artefacts are strictly dependent on the underlying k-space trajectory which leads to advantages for k-space trajectories with low-coherent aliasing properties also for the combination with non-linear reconstruction techniques.Based on a generalised form of the Seiffert Spirals, this abstract describes a k-space trajectory that does not require prior commitment to an imaging FOV.

Dahan Kim¹, Dinghui Wang¹, Tzucheng Chao¹, and James G Pipe^1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States

T2-weighted imaging typically employs either TSE or multi-pass 2D SE acquisitions, but using a thick slice and/or a slice gap is often necessary to overcome SNR inefficiencies of these methods, to achieve high-resolution scans in reasonable scan time. We studied efficient T2-weighted SE technique which employed localized quadratic encoding to realize SNR-efficient slice encoding scheme that produced contiguous volumetric coverage. Combined with long-readout spiral acquisitions, the proposed method, a hybrid of 2D and 3D imaging, demonstrated the expected SNR benefit compared to standard 2D scans and produced T2-weighted images with SNR equivalent as 2D-TSE scans but with larger, contiguous coverage.

Jose Borreguero Morata¹, Jose Manuel González Hernández¹, Eduardo Pallás Lodeiro², Juan Pablo Rigla Pérez¹, Jose Miguel Algarín Guisado², Rubén Bosch Esteve¹, Fernando Galve Conde², Daniel Grau Ruíz¹, Rubén Pellicer Guridi², Alfonso Ríos Alonso¹, Jose María Benlloch Baviera², and Joseba Alonso^2
1Tesoro Imaging S.L., Valencia, Spain, ²MRI-lab, Institute for Molecular Imaging and Instrumentation (i3M), Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV), Valencia, Spain

Prepolarized Magnetic Resonance Imaging is a long established technique conceived to counteract the loss in signal strength inherent to low field MRI systems. When it comes to hard biological tissues and solid state matter, PMRI is severely restricted by their ultra short characteristic relaxation times. Here we demonstrate that hard tissue prepolarization is possible with a 0.26 T scanner designed for dental MRI. These results can be applied to clinical dental imaging, making low field PMRI scanners a possible replacement for hazardous X ray systems.