James Pipe^1
1Mayo Clinic, Rochester, MN, United States

This work presents a versatile new algorithm to design better spiral trajectories, by minimizing high spatial frequencies in the gradient waveform and dynamically compensating for preconditioning by adaptively changing the maximum gradient and slew rate limits.  It has been integrated into software, and example waveforms are given.

Xi Peng¹, Daniel Borup², and James Pipe^1
1Mayo Clinic, Rochester, MN, United States, ²Philips Healthcare, Rochester, MN, United States

Cartesian Turbo-spin-echo (TSE) has been widely used in routine clinical MRI but is subject to high specific absorption rate (SAR) and altered contrast due to long RF pulse train and reduced RF refocusing flip angles. As an alternative, spiral-TSE has been developed to produce low-SAR and improved contrast for fast T2-weighted imaging. In this work, we accelerate a previous spiral-TSE method by a factor of 2 using a split spiral-inout acquisition strategy with reversed arm orderings to intrinsically compensate for the T2-decay induced artifacts. In vivo brain experiment has been performed to demonstrate the feasibility of the proposed acquisition scheme.

Rolf F Schulte¹, Ana Beatriz Solana¹, and Scott R Hinks^2
1GE Healthcare, Munich, Germany, ²GE Healthcare, Waukesha, WI, United States

BURST MRI is a way of exciting magnetisation sequentially and storing it in k-space. In this work, gradient-echo BURST MRI is combined with the sampling efficient Echo-Planar Imaging (EPI) and Spiral gradient trajectories. High quality T₂^*-weighted images were acquired both in phantom and in vivo, demonstrating the potential of this combination for reducing B₀ related artefacts.

Zhiqiang Li¹, Melvyn B Ooi², and John P Karis^1
1Neuroradiology, Barrow Neurological Institute, Phoenix, AZ, United States, ²Philips Healthcare, Gainesville, FL, United States

DWI plays a critical role in many neurological applications but its adoption in spinal imaging has been significantly hindered by geometric distortions in EPI, which is widely used in the clinic. TSE-based DWI methods, including PROPELLER and turboPROP, are free from distortion artifacts but may not be optimal for spinal imaging. In this work we present a single-shot GRASE technique with whole-mode acquisition and reduced FOV imaging to provide rapid and robust high-resolution spinal DWI. The feasibility is demonstrated and compared with ssEPI and msEPI in sagittal and axial cervical spine, and sagittal thoracic and lumbar spine.

Yuan Zheng¹, Lele Zhao², Zhongqi Zhang², Yu Ding¹, and Jian Xu^1
1UIH America, Inc., Houston, TX, United States, ²United Imaging Healthcare, Shanghai, China

GRE sequences benefits from increased SNR at high field and do not suffer from banding artifacts and SAR issues as bSSFP sequences, which makes it a good alternative for some applications that typically use bSSFP at 1.5 T or  3T. We have implemented  the autocalibrated multiband GRE cardiac cine sequence at 5 T. The autocalibrated multiband acquisition increases the scan efficiency by reducing the scan time and simplifying the multiband imaging workflow. Iterative reconstruction with sparsity constraints was used which can also accommodate in-plane undersampling. We have evaluated this application on volunteers and achieved cardiac cine images with satisfactory quality.

Rüdiger Stirnberg¹, Philipp Ehses¹, Eberhard Daniel Pracht¹, and Tony Stöcker^1,2
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Department of Physics and Astronomy, University of Bonn, Bonn, Germany

We propose a simple Actual Flip angle Imaging (AFI) modification to an existing multi-echo 3D-EPI implementation with flexible segmented CAIPIRINHA sampling. The free EPI factor choice makes more efficient use of the long optimal TRs than traditional AFI. Whole-head B1 maps at 5mm isotropic resolution can be acquired in less than 2s, however at the expense of increased signal dropouts at 7T. We explore the benefits of both reduced TEs and increased resolutions to counteract this. We find that a 2.5mm isotropic resolution single-echo protocol acquired in about 10s results in robust whole-head B1 maps with negligible dropouts and distortions.

Jin Jin^1,2, Monique Tourell², Pascal Sati³, Sunil Patil⁴, Kecheng Liu⁵, John Derbyshire⁶, Fei Han⁷, Saskia Bollmann², Simon Robinson², Josef Pfeuffer⁸, Steffen Bollmann², Markus Barth², and Kieran O'Brien^1
1Siemens Healthcare, Brisbane, Australia, ²The University of Queensland, Brisbane, Australia, ³Cedars-Sinai Medical Center, Los Angeles, CA, United States, ⁴Siemens Medical Solutions USA, Baltimore, MD, United States, ⁵Siemens Medical Solutions USA, Baltimore, OH, United States, ⁶National Institute of Mental Health, Bethesda, MD, United States, ⁷Siemens Medical Solutions USA, Los Angeles, CA, United States, ⁸Siemens Healthcare, Sydney, Australia

In this work, a highly accelerated 3D EPI prototype sequence implementation and scanner in-line reconstruction are introduced. The proposed sequence provides a flexible combination of single-/multi-shot schemes, in-plane segmentation, image resolution, echo-train length, partial Fourier factors, 2D-CAIPIRINHA/2D-GRAPPA-based acceleration, and CAIPIRINHA shift. Initial tests presented herein indicate suitability for highly accelerated high-resolution susceptibility-based imaging with significantly reduced scan time, such as whole-head coverage at 0.65 mm isotropic resolution within 2 minutes.

Hao Chen¹, Shiwei Yang¹, Sijie Zhong¹, and Zhiyong Zhang^1
1School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China

EPI is a versatile MRI acquisition method, which can ultrafast yield an image and has been widely applied. However, EPI is well-known sensitive to B₀ inhomogeneities and susceptibility effects, which leading to geometrical image distortions. In order to reduce the geometric distortion on EPI images, this work presents a new interleaved single-shot EPI method, in which k_y-t line can be sampled with higher slope rate such that the geometric distortion can be alleviated. The experimental results of phantom and human brain at 3T demonstrate the capability of the new method.

Zhenliang Lin¹, Qikang Li¹, Huanhuan Liu², Ming Liu², Qiufeng Yin², Rui Wang³, Guobin Li³, Dengbin Wang², and Jie Luo^1
1Shanghai Jiao Tong University, Shanghai, China, ²Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China, ³Shanghai United Imaging Healthcare Co., Ltd, Shanghai, China

Single-shot echoplanar imaging (EPI) sequence is a commonly used readout scheme for functional and diffusion magnetic resonance imaging (fMRI and dMRI). It features fast alternating gradient that generate loud acoustic noise, often causing discomfort for patients and even pose risk for sensitive populations. In this study, we used genetic algorithm to optimize both sound pressure level and spectral entropy for single-shot EPI sequence by varying the duration of each readout unit with a sinusoidal waveform, changing the timbre significantly with increased entropy and reduced loudness. The sequence was implemented on a 3.0T pediatric uMR Alpha system.

Kaibao Sun¹, Zheng Zhong^1,2, Guangyu Dan^1,2, Muge Karaman^1,2, Qingfei Luo¹, and Xiaohong Joe Zhou^1,2,3
1Center for MR Research, University of Illinois at Chicago, Chicago, IL, United States, ²Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ³Departments of Radiology and Neurosurgery, University of Illinois at Chicago, Chicago, IL, United States

Reduced field-of-view (rFOV) imaging has been achieved in 2D imaging. Although 2D rFOV can reduce image distortion and produce high in-plane resolution in EPI, the through-plane resolution remains poor and signal voids persist. We report a 3D reduced field-of-view imaging (3D-rFOVI) sequence to extend the conventional 2D rFOV imaging to 3D by using a slab-selection 2D RF pulse in conjunction with through-slab phase-encoding. This sequence features high isotropic spatial resolution in EPI images while reducing off-resonance effects that cause image distortion and signal voids. We have successfully applied the 3D-rFOVI technique to fMRI and DWI.

Benoît Vernier^1,2, Eric Van Reeth^1,3, Frank Pilleul^1,4, Olivier Beuf¹, and Hélène Ratiney^1
1CREATIS, Université de Lyon, INSA Lyon, UCBL Lyon 1, UJM Saint Etienne, Unité CNRS UMR 5220, INSERM U1206, F69621, Lyon, France, ²Siemens Healthineers, Saint-Denis, France, ³CPE, Lyon, France, ⁴Centre Léon Bérard, Lyon, France

Optimal control in MRI has demonstrated its potential in the design of magnetization preparation in order to enhance relaxation based contrast. However, previous studies require full magnetization recovery between each TR, which induces long acquisition times and restricts its use to specific sequences.  Here, a generic optimal control framework that considers a longitudinal steady state is introduced, and applied to a MP-RAGE sequence.   In vitro and in vivo (rat brain) experiments validate the improvement of the contrast-to-noise ratio per unit of time when compared with an inversion-recovery preparation.

Jessica Schäper^1,2, Grzegorz Bauman^1,2, Carl Ganter³, and Oliver Bieri^1,2
1Department of Biomedical Engineering, University of Basel, Basel, Switzerland, ²Department of Radiology, Division of Radiological Physics, University Hospital Basel, Basel, Switzerland, ³Department of Diagnostic and Interventional Radiology, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany

For some tissues bSSFP shows a distinct asymmetry in its frequency response function. Theoretical considerations indicate that this asymmetry disappears in the limit of $$$\mathit{TR} \rightarrow 0$$$. This was studied experimentally at $$$3\,\mathrm{T}$$$ in the present work. The frequency response of bSSFP was investigated for in vivo brain for varying repetition time $$$\mathit{TR} = \{1.5,3,5\}\,\mathrm{ms}$$$.  Our results give strong evidence that the asymmetry vanishes in the limit of $$$\mathit{TR} \sim 1\,\mathrm{ms}$$$ and therefore indicate that bSSFP forgets about the spectral composition and thus becomes ''pure''.

Aidin Arbabi¹ and David G Norris^1
1Donders Institute, Radboud University, Nijmegen, Netherlands

Half-Fourier acquisition single-shot turbo spin-echo diffusion-weighted (HASTE DW) is a clinically established magnetic resonance imaging tool for the detection of small lesions, especially, primary and relapsing cholesteatoma at 1.5T field. HASTE DW imaging at high field strengths (3T and above) is challenging due to the intrinsic high radio frequency power deposition of the method, resulting from the extended echo train. We present a HASTE DW with smooth transition between pseudo-steady states, especially developed for 3T imaging, which features a low specific absorption rate and high quality images, without any loss of sensitivity.

Michael Mullen¹ and Michael Garwood^1
1Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States

Clinical MRI sequences for imaging near metallic implants are mainly multi-spectral approaches, with fast spin-echo acquisitions and large acceleration factors to achieve clinically relevant scan times. The authors previously reported a broadband, low flip angle method at 1.5T to image with large field inhomogeneity, such as near metallic implants, quickly relative to non-spatially selective multispectral approaches. Herein it is demonstrated that this approach, dual polarity missing pulse steady-state free precession, can achieve high spatial resolutions at 3T with a large 3D FOV in a clinically relevant scan time, ~8.74 minutes.

Dan Zhu¹ and Qin Qin^2,3
1Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States, ²The Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, United States, ³F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

Fast image acquisition is commonly used in quantitative MRI after contrast preparation, such as turbo-filed-echo (TFE), balance steady-state-free-precession (bSSFP), and turbo-spin-echo (TSE). k-Space data acquired are filtered by a modulation transfer function (MTF), causing contrast loss and blurring. Here, we derived the analytical formulation of the corresponding point spread function (PSF) of Cartesian TFE, bSSFP and TSE with 180° refocusing. The contrast-to-noise ratio (CNR) is defined and maximized, providing an analytically optimized selection of TFE/TSE factors and flip angles. bSSFP serves high CNR, small FWHM and large TFE factors. Long TR and short TE are suggested for TFE studies.

Alexander Loktyushin^1,2, Kai Herz^1,3, Nam Dang⁴, Felix Glang¹, Anagha Deshmane¹, Simon Weinmüller⁴, Arnd Doerfler⁴, Bernhard Schölkopf², Klaus Scheffler^1,3, and Moritz Zaiss^1,3
1Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Max Planck Institute for Intelligent Systems, Tübingen, Germany, ³Eberhard Karls University Tübingen, Tübingen, Germany, ⁴University Clinic Erlangen, Erlangen, Germany

We propose a framework — MRzero — that allows automatic invention of MR sequences. At the core of the framework is a differentiable forward process allowing to simulate image measurement and reconstruction. The sequence parameters are variables of optimization. As a cost function we use mean squared error distance to a certain given target contrast of interest. To avoid overfitting we propose a method that generates synthetic data that is used for training. In the experiments, we demonstrate the ability of the method to learn RF flip angles and spatial encoding from scratch given a target obtained with GRE sequence.

Felix Glang¹, Alexander Loktyushin¹, Kai Herz^1,2, Hoai Nam Dang³, Anagha Deshmane¹, Simon Weinmüller³, Arnd Doerfler³, Andreas Maier⁴, Bernhard Schölkopf⁵, Klaus Scheffler^1,2, and Moritz Zaiss^1,3
1High-field Magnetic Resonance Center, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Department of Biomedical Magnetic Resonance, Eberhard Karls University Tübingen, Tübingen, Germany, ³Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Neuroradiology, University Clinic Erlangen, Erlangen, Germany, ⁴Pattern Recognition Lab, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany, ⁵Empirical Inference, Max-Planck Institute for Intelligent Systems, Tübingen, Germany

Recently, MRzero has been proposed as a fully differentiable Bloch-equation-based MRI sequence invention framework. In this work, the approach is extended by parallel imaging capability, employing a CG SENSE reconstruction that allows optimizing for non-Cartesian sampling trajectories simultaneously with other sequence parameters like RF pulses and timings. The approach is tested herein by simulations on an in silico brain phantom and is found to yield improved reconstructions compared to regular Cartesian undersampling, and to simultaneously find variable flip angle patterns that compensate for transient signal induced blurring.

Matthijs de Buck ¹, Aaron Hess², and Peter Jezzard^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB Division, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, ²Oxford Centre for Clinical Magnetic Resonance Research, Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom

DANTE-SPACE can be used for visualizing intracranial vessel walls at 7T by simultaneously suppressing signal from the luminal blood and external CSF. However, vessel wall delineation is limited by the achieved contrast and resolution, and further improvement of the sequence is constrained by SAR. Here, an optimized protocol for the number of DANTE-pulses and the flip angle of each DANTE-pulse is proposed based on an EPG-based simulation framework. In-vivo data acquired using this DANTE preparation show an improved CNR and signal ratio between the vessel wall and both blood and CSF, while reducing the SAR compared to previous DANTE preparations.

Chenwei Tang¹, Laura B Eisenmenger², Steven Kecskemeti³, and Kevin M Johnson^1,2
1Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ²Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States, ³University of Wisconsin-Madison, Madison, WI, United States

 3D radial sampling can enable ultrashort echo times, reduce sensitivity to motion, and provide high levels of acceleration. These methods have recently been used to perform free-running pediatric body imaging. However, the optimization of projection sampling remains an open problem and current schemes often produce high acoustic noise with an unfavorable noise texture. In this work, we demonstrate the optimization of trajectories using  a joint consideration of sampling and acoustic performance. To perform this we introduce a neural network framework and investigate variable TR optimization as means to simultaneously distribute projections optimally and minimize acoustic noise autocorrelation.