Albert Jang¹, Paul K Han¹, Chao Ma¹, Georges El Fakhri¹, and Fang Liu^1
1Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States

T₁ maps obtained using fast steady-state sequences are usually sensitive to B₁⁺ inhomogeneity and MT effects. We propose a novel method to achieve simultaneously B₁⁺- and MT-corrected T₁ quantification by introducing off-resonance RF pulses that create two effects: 1) direct saturation of macromolecules and 2) B₁⁺ dependent Bloch-Siegert phase shift. This method, termed BTS (Bloch-Siegert and magnetization transfer simultaneously), is presented and validated in both simulations and experiments, correcting for T₁ bias induced from B₁⁺ inhomogeneity and MT effects.

Rita Schmidt^1,2
1Brain Sciences, Weizmann Institute of Science, Rehovot, Israel, ²The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot, Israel

T₂ mapping can provide a valuable tool for monitoring and characterization of the tissue changes in the brain. Its implementation in 7T MRI will improve SNR and resolution, but also needs to overcome an increase in SAR and B₁ inhomogeneity. We developed a Steady-state T₂ And Rf Estimation (STARE) method capable to deliver T₂ and RF-field maps in 7T brain imaging. This work summarizes progress towards robust high-resolution whole brain T₂ mapping. The method was examined in phantoms and human imaging. Whole brain T₂ maps with 1mm resolution were acquired within 3:27 minutes, sufficiently fast to be used in clinics.

Jakob Assländer^1,2, Cem Gultekin³, Xiaoxia Zhang^1,2, Quentin Duchemin⁴, Kangning Liu⁵, Robert WE Charlson⁶, Timothy Shepherd¹, Carlos Fernandez-Granda^3,5, and Sebastian Flassbeck^1,2
1Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, ²Center for Advanced Imaging Innovation and Research, New York University School of Medicine, New York, NY, United States, ³Courant Institute of Mathematical Sciences, New York University, New York, NY, United States, ⁴Laboratoire d’analyse et de mathématiques appliquées, Université Gustave Eiffel, Paris, France, ⁵Center for Data Science, New York University, New York, NY, United States, ⁶Multiple Sclerosis Comprehensive Care Center, Department of Neurology, New York University School of Medicine, New York, NY, United States

We combine two recently proposed biophysical models, the hybrid state and the generalized-Bloch model, to describe magnetization transfer. Combined into a single model, they facilitate quantitative magnetization transfer imaging of the whole brain with 1mm isotropic resolution in 12 minutes. We optimized an MR-Fingerprinting-like pulse sequence, and validated the approach in two multiple sclerosis patients and two controls.

Guangyu Dan^1,2, Kaibao Sun¹, Qingfei Luo¹, 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

Studies on temporal diffusion characteristics can reveal a wealth of tissue microstructural information for disease evaluation, but typically require a long scan time because multiple diffusion times are need with each requiring a separate acquisition acquire. We herein report a time-efficient pulse sequence that acquires multiple diffusion-weighted images with different diffusion times in a single shot by utilizing multiple stimulated echoes with variable flip angles. This technique has been implemented on a 3T human scanner and successfully demonstrated in a quantitative diffusion phantom, the human brain gray and white matters, and the prostate peripheral zone and central grand.

Hongyan Liu¹, Tom Bruijnen¹, Maaike van Haandel¹, Oscar van den Heide¹, Miha Fuderer¹, Cornelis A.T. van den Berg¹, and Alessandro A.T. Sbrizzi^1
1Computational Imaging Group for MR diagnostics & therapy, Center for Image Sciences, UMC Utrecht, Utrecht, Netherlands

We propose a new method to increase the T2 encoding ability of MR-STAT sequences, according to a recently developed strategy for T2 mapping. Recent work has shown that RF phase modulated GRE sequences with small quadratic phase increments can effectively encode T2 information into the phase of the signal.  In this abstract, we show that by incorporating a simple and similar RF modulation strategy in 2D MR-STAT sequences, T2 sensitivity of transient-state gradient-spoiled sequences is improved, and therefore T2 maps as well as the proton density maps (PD) can be reconstructed with higher accuracy.

Gabriele Bonanno^1,2,3, Patrick Liebig⁴, Kurt Majewsky⁵, Tobias Kober^6,7,8, and Tom Hilbert^6,7,8
1Advanced Clinical Imaging Technology, Siemens Healthcare AG, Bern, Switzerland, ²Magnetic Resonance Methodology, Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland, ³Translational Imaging Center, sitem-insel, Bern, Switzerland, ⁴Siemens Healthcare GmbH, Erlangen, Germany, ⁵Siemens AG, Munich, Germany, ⁶Advanced Clinical Imaging Technology, Siemens Healthcare AG, Lausanne, Switzerland, ⁷Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland, ⁸LTS5, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

T₂ relaxometry at ultra-high field 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 a parallel transmit T₂-preparation (T₂p) module integrated in a compressed sensing accelerated segmented 3D FLASH sequence. The proposed parallel transmit T₂p module is investigated in phantom and in vivo experiments and compared to an adiabatic T₂p module. Preliminary tests show feasibility for sub-millimeter T₂ relaxometry at 7 T.

Nathan Tibbitts Roberts, BS^1,2, Diego Hernando, PhD^1,2,3,4, Nikolaos Panagiotopoulos, MD¹, and Scott B Reeder, MD, PhD^1,3,4,5,6
1Radiology, University of Wisconsin - Madison, Madison, WI, United States, ²Electrical and Computer Engineering, University of Wisconsin - Madison, Madison, WI, United States, ³Medical Physics, University of Wisconsin - Madison, Madison, WI, United States, ⁴Biomedical Engineering, University of Wisconsin - Madison, Madison, WI, United States, ⁵Medicine, University of Wisconsin - Madison, Madison, WI, United States, ⁶Emergency Medicine, University of Wisconsin - Madison, Madison, WI, United States

This work presents a complex-based fitting method to address concomitant gradient (CG) phase errors for time-interleaved (i.e., multi-pass) chemical shift-encoded (CSE) MRI estimation of proton density fat fraction (PDFF) and R2* through a joint estimation of pass-specific phase terms. The proposed method does not require prior knowledge of gradient waveforms. The proposed fitting method removed significant PDFF and R2* estimation errors in both phantom and in vivo evaluations away from isocenter. An evaluation in 29 clinical liver datasets demonstrated reduced PDFF bias and variability (8.4% improvement in the coefficient of variation), even when the imaging volume was centered at isocenter.