Nadège Corbin^1,2 and Martina F. Callaghan^1
1Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom, ²Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/University Bordeaux, Bordeaux, France

Imperfect spoiling introduces a bias in T₁ times estimated with the Variable Flip Angle approach. Correction factors accounting for B₁⁺ inhomogeneities have been proposed but a T₂ dependent bias is expected to remain. Here we assess the amplitude of this effect at 7T with a commonly used multi-echo protocol and multiple radiofrequency spoiling increments and gradient spoiler moments. The T₂ dependence is observed in-vivo and varies across spoiling conditions. Given that correction schemes don’t account for T₂ variability, we recommend to use the least sensitive increment, such as 117° or 144°, in association with sufficient spoiling gradient (6π per TR).

Kerrin J Pine¹, Nicolas Gross-Weege², Martina F Callaghan³, and Nikolaus Weiskopf^1,3,4
1Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Siemens Healthcare GmbH, Erlangen, Germany, ³Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom, ⁴Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, Leipzig, Germany

In this abstract we detail our first experiences using parallel transmission (pTx) to quantitatively map T₁ via a dual flip-angle approach. We present data from a human volunteer scanned on the 7T Siemens MAGNETOM Terra using the pTx system and a Nova 32-channel receive / 8-channel transmit coil, with online optimized kT-points RF pulses. Data from the same coil in static CP mode (without pTx) was additionally acquired. With the demonstrated reduction in B₁⁺ inhomogeneity, various bias correction schemes used at lower field strengths may become applicable.

Gabriele Bonanno^1,2,3, Patrick Leibig⁴, Tobias Kober^5,6,7, and Tom Hilbert^5,6,7
1Advanced Clinical Imaging Technology, Siemens Healthcare AG, Bern, Switzerland, ²Translational Imaging Center, sitem-insel AG, Bern, Switzerland, ³Departments of Radiology and Biomedical Research, University of Bern, Bern, Switzerland, ⁴Siemens Healthcare GmbH, Erlangen, Switzerland, ⁵Advanced Clinical Imaging Technology, Siemens Healthcare AG, Lausanne, Switzerland, ⁶Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland, ⁷LTS5, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

T₂ relaxometry has the potential to become an important quantitative MRI biomarker thanks to its sensitivity to pathology. However, acquiring high-resolution isotropic T₂ maps is challenging due to signal-to-noise and specific absorption rate constraints. We present a T₂-mapping method for ultra-high-field MRI based on an optimized T₂-prepared acquisition with compressed sensing acceleration. The T₂ preparation uses adiabatic pulses in conjunction with a segmented FLASH sequence to obtain uniform whole-brain T₂ weighting despite B₁ inhomogeneity. Preliminary tests show good signal homogeneity for images and maps obtained in a scan time compatible with volunteer studies.

Rosa Sanchez Panchuelo¹, Olivier Mougin¹, Robert Turner^1,2, and Susan Francis^1,3
1Sir Peter Mansfield Imaging Centre, UP, University of Nottingham, Nottingham, United Kingdom, ²Max Planck Institute for Human Cognitive and Brain Sciences, Leibzig, Germany, ³NIHR Nottingham Biomedical Research, University of Nottingham, Nottingham, United Kingdom

We report the quantitative T₁ values of the NIST/ISMRM system phantom T₁ and T₂ spheres at 7T. We compare the accuracy and repeatability of T₁ measurements using a 2D multi-slice multi-shot IR-EPI sequence, to 3D MP2RAGE and standard single-slice IR sequences at 3 and 7 T. We show that T₁ measurements are more accurate using MS-IR-EPI compared to MP2RAGE. The T₂-spheres of the NIST/ISMRM system phantom are shown to be best suited for T₁-mapping at 7T as they offer a wider range of T₁-values, better matched than those of the T₁-spheres to those found within the human brain.

Jochen Schmidt¹, Dvir Radunsky², Patrick Scheibe¹, Noam Ben-Eliezer^2,3,4, Nikolaus Weiskopf^1,5, and Robert Trampel^1
1Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, ³Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel, ⁴Center for Advanced Imaging Innovation and Research (CAI2R), New-York University Langone Medical Center, New York, NY, United States, ⁵Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, Leipzig, Germany

Accurate quantification of transverse relaxation times in vivo is of vital importance for research and clinical applications. At higher field-strength, the gain in signal enables T₂ mapping at sub-millimetre resolutions, but with infeasible scan time for standard spin-echo techniques. Using CPMG echo trains reduces the acquisition time. However, inhomogeneities of the transmit B₁ field hamper accurate T₂ quantification. Correcting for resulting bias effects is possible through signal response simulations via the Bloch equations using the specific sequence parameters. Matching acquired data to the simulated signal points allows accurate and robust fitting of T₂ values as shown by our 7T study.

Chao Ma^1,2, Paul K. Han^1,2, and Georges El Fakhri^1,2
1Radiology, Massachusetts General Hospital, Boston, MA, United States, ²Radiology, Harvard Medical School, Boston, MA, United States

Absolution quantification of metabolite concentration requires accurate measurement of the longitudinal relaxation times of metabolites. However, it will be very time consuming to access the spatial variations of metabolite T1 relaxation times using the conventional MRS-based methods. Inspired by the recent success of the subspace-based methods for fast high-resolution MRSI, we propose a subspace imaging-based method for simultaneous mapping of metabolite concentration and T1 relaxation time. We propose a fast Look-Locker EPSI sequence for data acquisition and a low-rank tensor-based method for simultaneous reconstruction of MRSI images at different TIs.

Marco Andrea Zampini^1,2, Jan Sijbers³, Marleen Verhoye², and Ruslan Garipov^1
1MR Solutions Ltd, Guildford, United Kingdom, ²Department of Biomedical Sciences, University of Antwerp, Wilrijk, Belgium, ³Department of Physics, University of Antwerp, Wilrijk, Belgium

Fast multiparametric mapping could ease the adoption of quantitative MRI in clinical practice. We propose a new 3D sequence (RAMSES) which toggles the readout modality between mono- and multi-gradient echo that, associated with the acquisition of one or several spoiled gradient echo images, can provide maps of T1, T2*, B1 and net magnetisation, M0. Results show the feasibility of RAMSES for accurate and precise relaxometry mapping within a clinically reasonable acquisition time.

Volkert Roeloffs¹, Nick Scholand^1,2, and Martin Uecker^1,2,3
1Institute for Diagnostic and Interventional Radiology, University Medical Center Göttingen, Goettingen, Germany, ²DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Germany, Goettingen, Germany, ³Campus Institute Data Science (CIDAS), University of Göttingen, Göttingen, Germany, Goettingen, Germany

Sensitivity to T1 and T2 in frequency-modulated SSFP sequences can be increased by choosing a higher modulation speed without prolonging the repetition time. In this work, we assess the boost in sensitivity by Cramér-Rao-bound analysis, combine the sequence with stack-of-stars sampling and subspace-constrained reconstruction, and demonstrate joint T1/T2/B1/off-resonance mapping in phantom and in vivo study. The results render fast-sweep frequency-modulated SSFP an excellent candidate for comprehensive 3D multi-parametric mapping.

Quan Chen¹, Huajun She¹, Ming Zhang¹, Hongjiang Wei ¹, and Yiping P. Du^1
1Shanghai Jiao Tong University, Shanghai, China

The feasibility of simultaneously obtaining the quantitative myelin water fraction (MWF) mapping and susceptibility mapping (QSM) is demonstrated by using the multi-echo gradient echo (mGRE) sequence in this study.  The retrospective and the perspective undersampling experiments have shown the potential of obtaining whole brain QSM/MWF quantifications in 1 minute.

Vishaal Sumra^1,2, Tobias C Wood³, and Sofia Chavez^1,2
1Institute of Medical Science, University of Toronto, Toronto, ON, Canada, ²Brain Health Imaging Centre - MRI, Centre for Addiction and Mental Health, Toronto, ON, Canada, ³Department of Neuroimaging, King's College London, London, United Kingdom

Multi-parametric mapping is often conducted using multiple separate scans, leading to errors in registration and long scan times. Multi-echo complex data was acquired for two flip angles, with a total scan time of 11 minutes at high resolution. Optimized processing allowed for the generation of high resolution qT1, R2*, QSM, SWI and B0 maps in the same space. The use of all echoes in processing, as well as long maximum TE allows for improvements in image quality. Future studies will investigate optimizing phase processing to further improve image quality while decreasing scan time.

Difei Wang¹, Rüdiger Stirnberg¹, Eberhard Pracht¹, and Tony Stöcker^1,2
1German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Department of Physics and Astronomy, University of Bonn, Bonn, Germany

We propose a fast MPM protocol at 7T using skipped-CAIPI 3D-EPI with simple PTx water-excitation based on 3 k_T-points. By comparison to corresponding CP mode scans, the 3 k_T-points excitation mainly improves the B₁⁺ field homogeneity in the Cerebellum. Using MPM B₁⁺ field correction, this simple improvement is sufficient to achieve good and homogeneous T₁, PD and T₂* estimates throughout the brain. However, the lack of MT homogenization still results in the inadequate MT_sat CNR. By combining MPM with EPI and PTx, we obtained quantitative whole-brain parameter maps of high quality, except for Cerebellar MTsat within 3 minutes scan time.

Georg Schramm¹, Johan Nuyts¹, and Fernando Boada^2
1KU Leuven, Leuven, Belgium, ²New York University School of Medicine, New York City, NY, United States

The image quality in sodium MR is hampered by very fast T2* decay during readout and high levels of noise in the acquired data. In this work we propose a joint iterative framework, including signal decay modeling during readout and decay estimation, to reconstruct dual echo sodium MR data. Regularization is incorporated by using an anatomical prior based on a high-resolution hydrogen T1 image. In simulations and a real brain tumor data set acquired on a 3T MR we demonstrate that our framework allows to suppress noise while preserving anatomical detail.

Guangyu Dan^1,2, Kaibao Sun¹, 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

A growing number of clinical applications rely on quantitative mapping of relaxation times and apparent diffusion coefficient (ADC). In addition, research interest in understanding the interplay between relaxation and diffusion processes is rising. Conventional methods for mapping relaxation and diffusion parameters require separate scans, resulting in not only a long acquisition time but also image co-registration challenges when inter-scan motion is present. We herein report a stimulated multi-echo-train EPI sequence with diffusion-weighting to achieve simultaneous, co-registered T1, T2* and ADC mapping. This technique was implemented at 3T and demonstrated in the brain and the prostate of healthy human subjects.

Ryan McNaughton¹, Hernan Jara^1,2, Ning Hua^2,3, Andy Ellison^2,3, Lee Goldstein^1,2,3, and Stephan Anderson^2,3
1Boston University, Boston, MA, United States, ²Boston University Medical Center, Boston, MA, United States, ³Center for Translational Neuroimaging, Boston, MA, United States

Purpose: To test the PD-T1-T2 qMRI accuracy of ultra-high spatial resolution compressed sense Tri-TSE. Methods: A healthy male volunteer (35yo) was scanned with an ultra-high spatial resolution compressed sensing Tri-TSE pulse sequence. Maps of PD, T1, and T2 were generated with voxel size of 0.4 x 0.4 x 1.2 mm3. Results: PD, T1, and T2 accuracy are not affected by threefold compressed sensing acceleration. Conclusion: Compressed sensing does not appear to negatively impact MS-qMRI accuracy and opens the door to ultrafast brain MS-qMRI at current clinical spatial resolution or to a new high spatial resolution standard in the clinical context.

Miha Fuderer^1,2, Oscar van der Heide^1,2, Cornelis A. T. van den Berg^1,2, and Alessandro Sbrizzi^1,2
1Computational Imaging Group for MR Diagnostics and Therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands, ²Department of Radiology, Division of Imaging and Oncology, University Medical Center Utrecht, Utrecht, Netherlands

In MR-STAT, data from a sequence of time-varying RF pulses and gradient encodings is reconstructed into multiple quantitative parameter maps by solving a large scale inversion problem. The combined interaction of RF and gradient events determines the noise-propagation into the reconstructed maps. We derive a computationally efficient performance metric to study this effect, by analyzing the block-diagonal of the k-space representation of the Jacobian. This allows for extremely fast prediction of the noise spectrum of the reconstructed parameter maps.

Giorgia Milotta¹, Nadège Corbin^1,2, Christian Lambert¹, Antoine Lutti³, Siawoosh Mohammadi^4,5, and Martina Callaghan^1
1Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom, ²Centre de Résonance Magnétique des Systèmes Biologiques, UMR5536, CNRS/University Bordeaux, Bordeaux, France, ³Laboratory for Research in Neuroimaging, Department for Clinical Neuroscience, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ⁴Department of Systems Neurosciences, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, ⁵Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The apparent transverse relaxation rate (R₂*) has biologically-relevant dependence on iron content and myelination. However confounding factors, e.g. flip angle dependence owing to differential longitudinal relaxation rates of sub-compartments, hinder interpretation. Multi-compartment models have been used to estimate myelin-water fraction from multi-echo spoiled GRE images, but require rich datasets for reliable estimation leading to extended acquisition times. A time-efficient alternative is to assume mono-exponential intra-voxel decay. In this work, we characterise the residual FA-dependence of such R₂* estimates in vivo, and explore the biological origin of this dependence via simulations.

Alexandru V Avram^1,2, Joelle E Sarlls³, and Peter J Basser^1
1Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States, ²Center for Neuroscience and Regenerative Medicine, The Henry Jackson Foundation, Bethesda,, MD, United States, ³National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States

We develop a novel clinical pulse sequence with integrated inversion recovery (IR) and isotropic diffusion encoding (IDE) preparations for mapping correlation spectra of subvoxel T1 and mean diffusivities (MD) from measurements acquired with a wide range of joint T1-MD weightings. We evaluated the performance of the pulse sequence and spectral reconstruction pipeline using data from numerical simulations, a calibrated MRI phantom and healthy volunteers. Preliminary results suggest that maps of subvoxel T1-MD spectra show tissue-specific components in the human brain. Quantifying the heterogeneity of T1-diffusion properties in microscopic water pools could improve biological specificity in many clinical applications.

Zijing Zhang^1,2, Long Wang³, Hyeong-Geol Shin⁴, Jaejin Cho², Tae Hyung Kim², Jongho Lee⁴, Jinmin Xu¹, Tao Zhang³, Huafeng Liu¹, and Berkin Bilgic^2
1State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, China, ²Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts general hospital, Boston, MA, United States, ³Subtle Medical Inc, Menlo Park, CA, United States, ⁴Laboratory for Imaging Science and Technology (LIST), Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of

We propose BUDA-SAGE, an efficient echo‐planar imaging (EPI) sequence for quantitative mapping. The acquisition includes multiple T₂^*-, T₂^’- and T₂-weighted contrasts. We alternate the phase-encoding polarities across the shots in this multi-shot navigator-free acquisition to eliminate geometric distortion. An unsupervised Self2Self (S2S) neural network (NN) was utilized to perform denoising after BUDA reconstruction to achieve 1×1×2 mm³ resolution with high SNR. We demonstrate the ability of BUDA-SAGE to provide whole-brain, distortion-free, high-resolution multi-contrast images and quantitative T₂, T₂^* maps in 50 seconds, and separate para- and dia-magnetic susceptibility maps in 140 seconds.

Oscar van der Heide^1,2, Alessandro Sbrizzi^1,2, and Cornelis van den Berg^1
1Computational Imaging Group for MR Diagnostics and Therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands, ²Department of Radiology, Division of Imaging and Oncology, University Medical Center Utrecht, Utrecht, Netherlands

MR-STAT is a multi-parametric quantitative MR framework with computationally demanding reconstructions. In this work we implemented the reconstruction algorithm on the GPU using the Julia programming language, a language that allows for quick prototyping without sacrificing on performance. We demonstrate superior runtime-performance of the GPU implementation as compared to previously proposed implementations running on a cluster of CPU's. With the proposed implementation, high-resolution in-vivo parameter maps can be reconstructed in approximately two minutes. The proposed implementation can also be used to rapidly generate MR Fingerprinting dictionaries and is shown to outperform the native CUDA implementation from SnapMRF.

 

 

Arun Joseph^1,2,3, Quentin Raynaud⁴, Antoine Lutti⁴, Tobias Kober^5,6,7, and Tom Hilbert^5,6,7
1Advanced Clinical Imaging Technology, Siemens Healthcare AG, Bern, Switzerland, ²Translational Imaging Center, Sitem-Insel, Bern, Switzerland, ³Departments of Radiology and Biomedical Research, University of Bern, Bern, Switzerland, ⁴Laboratory for Neuroimaging Research, Department for Clinical Neuroscience, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland, ⁵Advanced Clinical Imaging Technology, Siemens Healthcare AG, Lausanne, Switzerland, ⁶Department of Radiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ⁷LTS5, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

Quantitative MRI (qMRI) provides biomarkers of microstructural properties of brain tissue and enables in-vivo monitoring of microscopic brain changes due to disease in patient populations. The widely used Multi Parameter Mapping qMRI protocol allows the computation of MTSat, PD, R1, and R2* maps. While it allows the assessment of multiple brain tissue properties, its acquisition time is excessive for clinical applications. Here, we propose a compressed sensing scheme based on a Cartesian spiral-phyllotaxis readout to reduce the total acquisition time of 1mm isotropic whole brain maps. A preliminary qualitative and quantitative validation is performed on healthy subjects.