Unique Acquisition Strategies 1

Monday 12 May 2014

Dan Ma¹, Vikas Gulani^1,2, and Mark Griswold^1,2
1Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, ²Radiology, Case Western Reserve University, Cleveland, OH, United States

The purpose of this study is to use MRF method to potentially mitigate the acoustic noise problem in normal MR scans while simultaneously quantifying multiple tissue parameters. Instead of producing quiet sequences, we instead take advantage of the extra degrees of freedom in MRF to design acquisitions to replicate music in the magnet. In this study, mp3 music files, which are converted to arbitrary readout encoding gradients, are used with varying flip angles and TRs in the MRF exam to quantify T1, T2, off-resonance and proton density maps simultaneously while providing pleasing sounds to the patient.

Ouri Cohen¹, Mathieu Sarracanie^1,2, Brandon D. Armstrong^1,2, Jerome L. Ackerman¹, and Matthew S. Rosen^1,2
1Department of Radiology, MGH/Athinoula A. Martinos Center for Biomedical Imaging, Massachussets General Hospital, Charlestown, MA, United States,²Department of Physics, Harvard University, Cambridge, MA, United States

Current implementations of MR fingerprinting typically require over 1000 measurements to obtain the desired tissue maps. The large number entails an increased specific absorption rate and, to avoid excessive scan times, a subsampling of k-space that may incur undersampling artifacts. Here we propose an optimization method which allows reduction of the needed measurements ~100 fold without affecting image quality.

Yun Jiang¹, Dan Ma¹, Katie Wright¹, Nicole Seiberlich¹, Vikas Gulani², and Mark A. Griswold^1,2
1Department of Biomedical Enginneering, Case Western Reserve University, Cleveland, OH, United States, ²Department of Radiology, Case Western Reserve University, Cleveland, OH, United States

MR Fingerprinting (MRF) is a novel platform for generating multiple parametric maps simultaneously by matching spatially and temporally incoherent signals to a pre-calculated dictionary. Here we explore MRF using a double-echo sequence with a spiral trajectory to simultaneously generate T₁, T₂, M₀and ADC maps. The result shows quantitative diffusion and relaxation estimates can be simultaneously generated within the MRF framework, extending the concept beyond relaxometry.

Hao Sun¹, Jeffrey A. Fessler¹, Douglas C. Noll², and Jon-Fredrik Nielsen^2
1Electrical Engineering and Computer Science, the University of Michigan, Ann Arbor, MI, United States, ²Biomedical Engineering, the University of Michigan, Ann Arbor, MI, United States

Small tip fast recovery (STFR) imaging has been proposed recently as a potential alternative to balanced steady state free precession (bSSFP). STFR relies on a tailored “tip-up” RF pulse to achieve comparable signal level and image contrast as bSSFP, but with reduced banding artifacts. Previous STFR implementations used 2D or 3D pulses spatially tailored to the accumulated phase calculated from a B0 field map. Here we propose to replace the spatially tailored pulse with a spectrally tailored pulse, which can be precomputed to a target frequency range. We show that this “spectral-STFR” sequence has reduced banding artifacts compared to bSSFP.

Jakob Assländer¹, Simone Köcher², Steffen Glaser², and Jürgen Hennig^1
1Dept. of Radiology - Medical Physics, University Medical Center, Freiburg, Germany, ²Dept. of Chemistry, Technische Universität München, Germany

It is shown that, for small flip angles, it is possible to form spin echoes after a single excitation pulse, where the time between the end of the pulse and the echo is longer than the length of the pulse itself. This is in contrast to standard Hahn-echo pulse sequences, where the length of the pulse sequence is in approximation equal to the time between the end of the composite pulse and the echo. The sequence is implemented into a FLASH sequence. At the example of lung pulmonary imaging signal enhancement is demonstrated in comparison to a standard FLASH sequence.

Leo K. Tam¹, Gigi Galiana¹, Haifeng Wang¹, Emre Kopanoglu¹, Andrew Dewdney², Dana C. Peters¹, and R. Todd Constable^1
1Diagnostic Radiology, Yale University, New Haven, CT, United States, ²Siemens Healthcare AG, Erlangen, Bavaria, Germany

Local k-space, the spatial derivative of the encoded phase has been used to visualize and design strategies to mitigate the spatially-varying encoding of nonlinear gradient encoding. To reduce the local k-space asymmetry of O-space imaging, the phase prior to readout is adjusted for each readout in a technique called prephasing, first proposed by Gallichan et. al. Prephased O-space imaging shows reduced MSE, though artifacts from previous simulations of asymmetrical k-space were not corroborated. Parallel receiver information may sufficiently localize signal conditional on appropriate imaging parameters.

Kelvin J. Layton¹, Feng Jia², and Maxim Zaitsev^2
1Department of Electrical and Electronic Engineering, The University of Melbourne, Melbourne, Victoria, Australia, ²Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Spatial encoding magnetic fields (SEMs) that vary nonlinearly over the field-of-view have the potential to accelerate imaging and overcome current safety limitations. Encoding with combinations of linear and nonlinear SEMs offer great flexibility but also make trajectory design difficult, since traditional k-space is insufficient to represent the higher-dimensional encoding space. This work presents a new method for automated trajectory design based on the predicted variance of the reconstructed pixels. In this way, the condition of the reconstruction problem is explicitly considered during trajectory design. Images reconstructed from simulated data exhibit reduced artifacts and noise using the proposed trajectory.

Clarissa Zimmerman Cooley^1,2, Jason P. Stockmann^1,3, Brandon D. Armstrong^1,3, Mathieu Sarracanie^1,3, Matthew S. Rosen^1,3, and Lawrence L. Wald^1,4
1A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ²Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ³Dept. of Physics, Harvard University, Cambridge, MA, United States, ⁴Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States

MRI could find wider applicability if lightweight, portable systems were available for siting in unconventional locations. We have proposed a lightweight magnet whose inhomogeneous field pattern is physically rotated to form a rotating Spatial Encoding Magnetic field (rSEM). This is a way to lower the magnet weight and eliminate gradient coils. The resulting image resolution varies spatially in the FOV with minimal encoding in center, a common problem in non-linear gradient encoding schemes. With the goal of improving encoding throughout the FOV, we assess resolution in different rSEMs through simulations, and compare to experimentally acquired images.

Paul W. de Bruin¹, Maarten J. Versluis¹, Peter Koken², Sebastian A. Aussenhofer¹, Ingrid Meulenbelt³, Peter Börnert^1,2, and Andrew G. Webb^1
1Radiology Department, Leiden University Medical Center, Leiden, Netherlands, ²Innovative Technologies Research Laboratories, Philips Technologie GmbH, Hamburg, Germany, ³Molecular Epidemiology, Leiden University Medical Center, Leiden, Netherlands

A flexible sequence interleaving method for different nuclei is used to virtually simultaneously acquire 23Na and 1H scans. This results in a high time-efficiency that is essential for patient studies involving 23Na scans.

Jens T Rosenberg^1,2, Avigdor Leftin³, Eddy Solomon³, Fabian Calixto Bejarano¹, Lucio Frydman^1,3, and Samuel Colles Grant^1,2
1National High Magnetic Field Laboratory, The Florida State University, Tallahassee, FL, United States, ²Chemical & Biomedical Engineering, The Florida State University, Tallahassee, FL, United States, ³Chemical Physics, Weizmann Institute of Science, Rehovot, Israel

Fast imaging techniques such as echo planar imaging (EPI) are popular techniques for imaging of neuronal injuries. However, there is an inherent problem with these techniques with respect to susceptibility and geometric artifacts that distort not only anatomical information but also the quantification of relevant quantities, such as water diffusion. To provide robust and fast acquisitions at high field, this study utilizes an ultrafast single-shot spatiotemporally encoded (SPEN) imaging sequence with diffusion encoding to measure apparent diffusion coefficient (ADC) in stroke. Results show that SPEN images provide a more accurate way of measuring ADC at high field compared to EPI.