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Molin Zhang¹, Georgy Guryev¹, Nick Arango¹, Jason Stockmann^2,3, Jacob White¹, and Elfar Adalsteinsson^1,4,5
1EECS, MIT, Cambridge, MA, United States, ²Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ³Department of Radiology, Harvard Medical School, Charlestown, MA, United States, ⁴Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, United States, ⁵5 Institute for Medical Engineering and Science, MIT, Cambridge, MA, United States

Keywords: Pulse Sequence Design, RF Pulse Design & Fields

We explored the utility of shim array fields in the mitigation of in-plane B1+ inhomogeneity for a slice-selective excitation at 7T and achieved better magnitude of transverse magnetization compared with birdcage transmit using conventional single-channel RF excitation. Approximately 2:1 range of B1+ was mitigated, at the cost of increased peak RF power, shim array current demands up to 20 A, and minor out-of-slice sidelobes.

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

Keywords: Pulse Sequence Design, fMRI

Echo-volume imaging (EVI) can offer higher acquisition speed than echo-planar imaging (EPI) but is more sensitive to image distortion and blurring. In this study, we develop an EVI-based fast fMRI acquisition technique by employing three-dimension restricted field-of-view imaging (k-t rFOV-EVI) and (k, t)-space undersampling. Our human fMRI experiments covering the visual cortex demonstrate that k-t rFOV-EVI can provide higher image quality and fMRI detection sensitivity than the simultaneous multi-slice EPI at 2.5-mm-isotropic spatial resolution with a temporal resolution of 240 ms.

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Wan-Ting Zhao¹, Karl-Heinz Herrmann¹, Renat Sibgatulin¹, Janine Arlt², Weiwei Wei², Uta Dahmen², and Jürgen R. Reichenbach^1
1Medical Physics Group, Institute of Diagnostic Radiology, University hospital Jena, Jena, Germany, ²Experimental Transplantation Surgery, Department of General, Visceral and Vascular Surgery, University hospital Jena, Jena, Germany

Keywords: Pulse Sequence Design, Preclinical

This work demonstrates the use of echo-shifting in combination with an efficient variable flip angle 3D RARE to reconstruct fat fraction distribution in a liver sample, resolving the fine structure of the fat deposits in the tissue with a Dixon based analysis at 9.4T.

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Jon-Fredrik Nielsen¹ and Kawin Setsompop^2,3
1fMRI Laboratory and Biomedical Engineering, University Of Michigan, Ann Arbor, MI, United States, ²Radiology, Stanford University, Palo Alto, CA, United States, ³Electrical Engineering, Stanford University, Palo Alto, CA, United States

Keywords: Pulse Sequence Design, RF Pulse Design & Fields

We propose to use short (~1–1.5ms) multi-dimensional spatially selective RF pulses that saturate unwanted signal regions in spoiled gradient echo (SPGR/FLASH/T1-FFE) imaging. These pulses can be inserted at regular intervals in the sequence, e.g., immediately before each imaging excitation pulse. By reducing signal contamination from outside the region of interest (ROI), these pulses should enable more rapid and robust T1- and T2*-weighted imaging in many body and neuro applications.

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Samantha Hickey¹, Andreas Reichert¹, Lars Bielak^1,2, Wolfgang Ptacek³, Thomas Bortfeld⁴, and Michael Bock^1
1Division of Medical Physics, Dept. of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, ²German Cancer Consortium (DKTK), Partner Site Freiburg, Freiburg, Germany, ³ACMIT Gmbh, Wiener Neustadt, Austria, ⁴Division of Radiation Biophysics, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States

Keywords: Pulse Sequence Design, Radiotherapy, Interventional, T2-weighted

Radiotherapy, cryoablation, and percutaneous needle biopsy procedures profit from MR-guidance with real-time lesion tracking. T2-weighted images often provide superior lesion contrast, but the temporal resolution of conventional T2-weighted sequences is insufficient for real-time MRI. Here, we present a fast, T2-weighted sequence Ortho-SSFP-Echo, which simultaneously acquires two orthogonal images, to track breathing induced kidney motion.

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Marcelo V. W. Zibetti¹, Hector L. De Moura¹, Mahesh B. Keerthivasan², and Ravinder R. Regatte^1
1Radiology, NYU Grossman School of Medicine, New York, NY, United States, ²Siemens Medical Solutions, Malvern, PA, United States

Keywords: Pulse Sequence Design, Quantitative Imaging

We proposed an efficient magnetization-prepared gradient echo (MP-GRE) sequence that uses optimized variable flip-angles (OVFA) to reduce acquisition time by 4x while increasing SNR when compared to magnetization-prepared angle-modulated partitioned k-space spoiled GRE snapshots (MAPSS), typically used for T1rho mapping. The proposed OVFA based sequence can improve the spatial resolution of T1rho mapping by 4x, with nearly same SNR and scan time as MAPSS.

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

Keywords: Pulse Sequence Design, New Trajectories & Spatial Encoding Methods, Spiral, WHIRL, analytical

This work introduces exact time-dependent analytical solutions, for both gradient waveforms and k-space trajectories, for an optimized spiral-based imaging strategy based on maximum frequency, perpendicular slew rate, and gradient magnitude constraints.

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Henric Rydén¹, Adam van Niekerk¹, Matea Borbas², and Mikael Skorpil^3
1Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden, ²Karolinska University Hospital, Stockholm, Sweden, ³Karolinska Institutet, Stockholm, Sweden

Keywords: Pulse Sequence Design, Data Acquisition, FSE, RARE, PROPELLER

A novel view ordering scheme for RARE (FSE/PROPELLER) imaging is proposed and compared with the vendor solution, particularly suited for MSK applications where intermediate TE is desired.

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Jiye Kim¹, Hongjun An¹, Chungseok Oh¹, Berkin Bilgic^2,3, and Jongho Lee^1
1Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of, ²Department of Radiology, Havard Medical School, Boston, MA, United States, ³Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States

Keywords: Pulse Sequence Design, Machine Learning/Artificial Intelligence

DeepRF¹ is a recently proposed RF pulse design method^2-5 using deep reinforcement learning and optimization, generating an RF pulse defined by a reward (e.g., slice profile and energy constraint) from self-learning. Here, we proposed an improved algorithm for DeepRF that incorporates a modulation function to design an simultaneous multislice⁶ RF pulse. The new algorithm is tested and compared with the original multiband⁹ pulses, reporting reduced RF energy while preserving the characteristics of the original slice profile. Additionally, a multiPINS⁸ like inversion pulse is designed to demonstrate the usefulness of DeepRF for a non-constant slice selective gradient. 

 

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Minyoung Kim^1,2, Jaeseok Park^3,4, Seunghong Choi⁵, and Taehoon Shin^1,2
1Department of Mechanical and Biomedical Engineering, Ewha Womans University, Seoul, Korea, Republic of, ²Graduate Program in Smart Factory, Ewha Womans University, Seoul, Korea, Republic of, ³Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ⁴Department of Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, Korea, Republic of, ⁵Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea, Republic of

Keywords: Pulse Sequence Design, Pulse Sequence Design, Variable Density Sampling Excitation

Velocity-selective (VS) magnetization preparation has shown great promise for non-contrast-enhanced MR angiography. Under the excitation k-space formalism, VS preparation pulse allocated RF weights to k-space at uniform intervals which leads to the aliased excitation at the inverse of the k-space interval (termed velocity FOV). In this study, we proposed a new version of VS preparation pulse with a diffused pattern of aliased saturation. The initial in-vivo test of the new version of VS-MRA shows a reduced effect of the aliased saturation compared with conventional VS-MRA.

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Mark Armstrong¹ and Dan Xiao^1
1University of Windsor, Windsor, ON, Canada

Keywords: Pulse Sequence Design, New Trajectories & Spatial Encoding Methods

Pi Echo Planar Imaging (PEPI) has a significantly reduced gradient duty cycle compared to FSE. It has a great potential for low field MRI where concomitant fields are significant. However, its application is limited due to the requirement of a near perfect refocusing pulse to avoid coherence pathway artifacts. In this work an optimized phase cycling scheme is proposed which minimizes coherence pathway contributions to the signal. This method has been validated in simulations and experiments showing a reduced sensitivity to flip angle compared to the conventional XY-16 method. Artifact-free 2D PEPI was achieved.

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Qiuhong He¹, Hong Yuan^2,3, and Yen-Yu Ian Shih^2,4,5
1The School of Health Sciences, Purdue University, West Lafayette, IN, United States, ²Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ³Radiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ⁴Neurology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ⁵Center for Animal MRI, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States

Keywords: Pulse Sequence Design, Spectroscopy

A double-echo pi-SSelMQC method was developed to recover 100% biomarker signals, as compared to spin-echo pulse sequences, with excellent water and lipid suppression.  Signals from both ZQ→DQ and DQ→ZQ coherence transfer pathways were detected.  By synchronization of phase-encoding steps and RF phase increments of either MQ-preparation or MQ-transfer pulse, the biomarker images from different MQ-pathways were resolved and shifted away from residual lipid and water signals.   Full lactate and polyunsaturated fatty acids (PUFA) signals were recovered in pi-SSelMQC imaging using yogurt phantoms, vegetable oil, and murine 344SQ lung tumors grown subcutaneously on the right thigh of syngeneic 129X1/SvJ male mice. 

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Ke Dai^1,2, Zhiyong Zhang², and Lucio Frydman^1,3
1Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel, ²School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China, ³Azrieli National Center for Brain Imaging, Weizmann Institute of Science, Rehovot, Israel

Keywords: Pulse Sequence Design, New Trajectories & Spatial Encoding Methods

Single-shot cross-term SPatiotemporal ENcoding (xSPEN) is a single-shot approach to MRI with exceptional resilience to field inhomogeneities. xSPEN’s non-Fourier nature and sinc-like point-spread function demands SNR/resolution compromises which, so far, no post-processing has managed to solve. This study shows that introducing a quadratic phase modulation in conjunction with the hyperbolic phase modulation demanded by xSPEN can solve this, enabling the use of deconvolution principles providing resolution enhancement. The principles and examples of the ensuing quadratic xSPEN (QxSPEN) experiment, are presented on synthetic, phantom and human brain single-shot data.

Xue Yang¹, Ying Liu², Caixia Fu³, He Wang², Ying-Hua Chu⁴, Da-Xiu Wei¹, and Ye-Feng Yao^1
1East China Normal University, Shanghai, China, ²Fudan University, Shanghai, China, ³Siemens Shenzhen Magnetic Resonance Ltd., Shanghai, China, ⁴MR Collaboration, Siemens Healthineers Ltd., Shanghai, China

Keywords: Pulse Sequence Design, Spectroscopy

A new pulse sequence was developed to selectively probe the signals of γ-aminobutyric acid (GABA). Different with the previous pulse sequences, the signal selectivity of this pulse sequence is achieved by preparation and reconversion of the ¹H spin singlet order (SSO) of GABA. The optimal control method was used in the design of the pulse sequence. By using the developed pulse sequence, the ¹H signals of GABA in human brains were selectively probed.

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Roeland Christiaan Naaktgeboren¹, Chiara Coletti², Christal van de Steeg-Henzen³, and Sebastian Weingärtner^2
1Department of Imaging Physics, Delft University of Technology, Delft, Netherlands, ²Delft University of Technology, Delft, Netherlands, ³HollandPTC, Delft, Netherlands

Keywords: Pulse Sequence Design, Cartilage, RAFF

Spin-lock relaxation times can provide valuable markers for pathological remodelling, but their acquisition with constant amplitude spin-lock pulses is limited by SAR and sensitive to field inhomogeneities. Relaxation along a Fictitious Field (RAFF) can be used to measure spin-lock relaxation with reduced SAR burden. In this work, we evaluate the resilience of RAFF against field B₀ and B⁺₁ field inhomogeneities. Yet another RAFF (yaRAFF) pulse is introduced for fictitious field spin-locking with increased effective field strength. yaRAFF shows >5.9% reduced susceptibility for field inhomogeneities compared with RAFF in simulations and phantom measurements. In vivo images of yaRAFF in the calf show higher precision for small off-resonances, the mapping quality for large off-resonance is maintained for in phantom and in vivo  T_RAFF2 times at 3T.

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Jae-Youn Keum¹, Jeong Hee Yoon², Michael Garwood³, and Jang-Yeon Park^1,4
1Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ²Department of Radiology, Seoul National University Hospital and College of Medicine, Seoul, Korea, Republic of, ³Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States, ⁴Department of Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, Korea, Republic of

Keywords: Pulse Sequence Design, Diffusion/other diffusion imaging techniques, Hyperbolic-Secant Pulse

Blood flow artifacts sometimes occur in 2D spin-echo sequence despite its intrinsic flow-suppression effect. Pre-saturation pulses have widely been used for flow-suppression, but it has several disadvantages such as requirement of additional RF pulses and being not effective at suppressing relatively slow blood flow signal. In this study, we propose a more effective flow-suppressed spin-echo sequence using hyperbolic-secant (HS) pulses for π/2-excitation and π-refocusing. The proposed method was applied to 2D spin-echo diffusion EPI for liver imaging.

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Aidin Arbabi¹, Vitaliy Khlebnikov¹, Jose P. Marques¹, and David. G. Norris^1
1Radboud University, Nijmegen, Netherlands

Keywords: Pulse Sequence Design, Brain

Half-Fourier acquisition single-shot turbo spin-echo diffusion-weighted is a clinically established magnetic resonance imaging tool for the detection of small lesions, particularly cholesteatoma. However, in the standard approach, half of the available signal is sacrificed through displacing one echo parity out of the acquisition window to fulfill the Carr-Purcell-Meiboom-Gill condition. We present a selective parity approach to tackle this problem. The proposed method features a near full sensitivity, a low specific absorption rate for long echo trains, and more than two-fold increase in signal-to-noise ratio, compared to the manufacturer's method under the same conditions.

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Tayaba Gul¹, Omiar Inam², Abdul Basit², Nimra Naeem³, and Hammad Omer^2
1Electrical and Computer Engineering Department, Comsats University Islamabd, Islamabad, Pakistan, ²Electrical and Computer Engineering Department, Comsats University Islamabad, Islamabad, Pakistan, ³Comsats University Islamabad, Islamabad, Pakistan

Keywords: Parallel Imaging, Cardiovascular

Parallel MRI (e.g., SENSE, GRAPPA) accelerates the data acquisition in modern clinical scanners using multiple receiver coils. However, it results in more computational demands on general purpose computers. Coil compression is a promising way to address the computational cost and memory requirements associated with a large number of receiver coils. In this work, a novel FPGA based hardware accelerator is designed to perform coil compression using QR decomposition. In-vivo reconstruction results from 30 coil cardiac data set, show that the proposed accelerator elevates the speed and memory constraints while preserving the image quality.

Yihan Wu^1,2, Hamza Kebiri^1,3, Ali Gholipour¹, and Davood Karimi^1
1Harvard Medical School & Boston Children's Hospital, Boston, MA, United States, ²Zhejiang University, Hangzhou, China, ³Center for Biomedical Imaging & Lausanne University Hospital, Lausanne, Switzerland

Keywords: Machine Learning/Artificial Intelligence, Diffusion/other diffusion imaging techniques, NODDI

Deep learning has a great potential for estimating brain tissue micro-structure from diffusion MRI measurements. However, it is hard to understand and interpret how these models work. Therefore, until now these deep learning models have been designed using ad-hoc approaches. In this work, we propose a method for determining the contribution of different measurements to the prediction produced by these deep learning models. We apply this method for estimating the parameters of the NODDI model for the neonatal brain. Results show that this method is highly effective in determining the subsets of the measurements that result in lower estimation error.