Emily Louise Baadsvik¹, Markus Weiger¹, Romain Froidevaux¹, Manuela Barbara Rösler¹, David Otto Brunner¹, Lena Öhrström², Patrick Eppenberger², Frank J. Rühli², and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland, ²Institute of Evolutionary Medicine, University of Zurich, Zurich, Switzerland

Evolutionary medicine aims to study disease development over long timescales, and through the study of mummified human remains, tissue information dating back thousands of years becomes accessible. Due to their status as ancient relics, nonintrusive techniques are preferable, and to date CT imaging is the most common modality. However, CT images lack soft-tissue contrast, making complementary MRI data desirable. Due to the extensively dehydrated nature and short T2 times of mummified tissues, acquiring such data is challenging. This research explored the use of the zero echo-time sequences and a high-performance gradient in mummy MRI, yielding yet unparalleled image quality. 

Emil Ljungberg¹, Brian Burns², Tobias Wood¹, Ana Beatriz Solana³, Peder E.Z. Larson⁴, Gareth J. Barker¹, and Florian Wiesinger^1,3
1Neuroimaging, King's College London, London, United Kingdom, ²ASL West, GE Healthcare, Menlo Park, CA, United States, ³ASL Europe, GE Healthcare, Munich, Germany, ⁴Univeristy of California, San Francisco, San Francisco, CA, United States

Zero Echo Time (ZTE) imaging enables ultra-fast, near silent data acquisition. In this work we demonstrate how contrast-to-noise, between white and gray matter in the brain, with a ZTE acquisition changes with field strength. At low field strength, maximum contrast is achievable with low RF power, which is promising for implementation on low field systems. We demonstrate through in vivo experiment that ZTE imaging can be performed at 1.5T/3T/7T, and how variable flip angle data at, for instance, 1.5T can be used for synthesising high quality T₁-weighted MR images.

Romain Froidevaux¹, Markus Weiger¹, Manuela Barbara Rösler¹, David Otto Brunner¹, Benjamin Emanuel Dietrich¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

With recent developments in gradient hardware even tissues with T2s down to tens of microseconds have become accessible for MRI. Hence, mapping signal decay or imaging short-T2 tissues selectively is of particular interest.

This can be performed using ultra-short echo time imaging with multiple TEs. However, for typical resolutions this approach is limited to T2s down to hundreds of microseconds.

In this work, the PETRA and HYFI techniques are utilized to map the signal decay of samples with T2s down to 54 μs. Considerably larger scan efficiency is obtained for the HYFI approach.

Mukund Balasubramanian^1,2, Robert V. Mulkern^1,2, and Jonathan R. Polimeni^1,3,4
1Harvard Medical School, Boston, MA, United States, ²Department of Radiology, Boston Children's Hospital, Boston, MA, United States, ³Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ⁴Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

A novel “line-scan GESSE” pulse sequence was used to measure irreversible and reversible transverse relaxation rates—R₂ and R₂´, respectively—in the cerebral cortex of eight healthy human subjects, scanned at 7T with extremely high resolution (250 μm) in the radial direction, i.e., perpendicular to the cortical surface. Within primary visual (V1), motor (M1) and somatosensory (S1) cortex, we observed patterns of R₂ versus cortical depth that were quite consistent across subjects. These patterns are also consistent with the intracortical non-heme iron content in these areas, known from prior histology studies.

Yicun Wang¹, Peter van Gelderen¹, Jacco A. de Zwart¹, and Jeff H. Duyn^1
1AMRI, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

Brain tissue T₁ predominately reflects local macromolecular content and is magnetic field strength dependent. In this study, we quantified the field dependence of macromolecular proton T₁ (or rate R_m) in white matter by evaluating its effect exerted on the water signal through magnetization transfer. Inversion recovery and saturation recovery experiments were performed on a group of eight volunteers at 0.55, 1.5, 3 and 7 T, and were jointly analyzed using a two-pool exchange model. R_m was found to be close to inversely proportional to B₀, consistent with previous in vitro findings at very low fields.

Luke A. Reynolds¹, Alex L. MacKay^1,2,3, and Carl A. Michal^1
1Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada, ²Radiology, University of British Columbia, Vancouver, BC, Canada, ³MRI Research Centre, University of British Columbia, Vancouver, BC, Canada

Adiabatic pulses are commonly used in clinical MRI due to their insensitivity to B₁ inhomogeneity and uniform flip angle over a selected bandwidth. When applied to white matter, they are generally assumed to saturate the magnetization of the non-aqueous protons in myelin.  We performed adiabatic inversion recovery experiments on bovine brain in vitro using a solid state NMR spectrometer to directly observe the effects of adiabatic inversions on the non-aqueous signal. Substantial non-aqueous magnetization remains after typical adiabatic pulses. The state of the non-aqueous magnetization seriously impacts measurement of T₁, yielding values dependent on the form of inversion pulse used.

Zhao Wei^1,2,3, Yajun Ma¹, Hyungseok Jang¹, Wenhui Yang³, and Jiang Du^1
1Department of Radiology, UC San Diego, San Diego, CA, United States, ²University of Chinese Academy of Sciences, Beijing, China, ³Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing, China

In magnetic resonance imaging (MRI), T₁ is an important biomarker for many diseases and plays a key role in affecting image contrast. We propose a novel T₁ measurement method combining adiabatic inversion recovery with 3D ultrashort echo time cones pulse sequences (3D IR-UTE-Cones). This study aimed to verify the feasibility of using 3D IR-UTE-Cones to accurately calculate T₁s of short T₂* tissues. The results indicated that this method could precisely measure a broad range of T₁s and that it performed better than commonly used clinical protocols in ultrashort T₁ measurement.

Zijing Dong^1,2, Fuyixue Wang^1,3, Kwok-Shing Chan⁴, Timothy G. Reese¹, Berkin Bilgic¹, José P. Marques⁴, and Kawin Setsompop^1,3
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, United States, ³Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, United States, ⁴Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, Netherlands

Multi-compartment models have been developed to detect the microstructure properties of brain tissue using multi-modal MRI, but are limited by the long scan time of multi-contrast multi-parametric acquisition. In this work, a novel variable flip angle EPTI (vFA 3D-EPTI) technique is developed to quickly acquire rich multi-contrast information for multi-compartment analysis. The optimized ‘temporal variant CAIPI’ sampling was used, and an augmented subspace reconstruction with multi-compartment modelling is also developed to accurately reconstruct complex signal evolution. Through this approach, myelin water fraction, proton density, multi-compartment T₁, T₂^* maps can be acquired simultaneously in 12 minutes at 1-mm isotropic resolution.

Maximilian Gram^1,2, Daniel Gensler^1,3, Patrick Winter^1,2, Michael Seethaler^2,3, Peter Jakob², and Peter Nordbeck^1,3
1Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany, ²Experimental Physics 5, University of Würzburg, Würzburg, Germany, ³Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Würzburg, Germany

T_1ρ dispersion imaging is a very time-consuming process because full T_1ρ-mapping at different spin-lock amplitudes is required. Due to this issue, investigation of T_1ρ dispersion is hardly feasible in the limited measurement time of a small animal experiment. In this work, we present a novel approach for the rapid measurement of cardiac T_1ρ dispersion called dispersion reconstruction. With our new concept a T_1ρ dispersion image is generated by only acquiring a fraction of the required mapping data. Phantom and in vivo experiments confirm the applicability of our new method as part of a conventional protocol for small animal studies.

Hassaan Elsayed^1,2, Jouni Karjalainen^1,2, Nina Hänninen^1,3, Isabel Stavenuiter³, Stefan Zbyn^1,4, Mikko Nissi^1,3, Miika T. Nieminen^1,2,5, and Matti Hanni^1,2,5
1Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland, ²Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland, ³Department of Applied Physics, University of Eastern Finland, Kuopio, Finland, ⁴Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ⁵Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland

In this study, we determined correlation time ($$$\tau_c$$$ ), a parameter that we propose as MRI contrast indicative of the structure of articular cartilage. $$$T_{1\rho}$$$ dispersion data were acquired from intact patellar bovine cartilage samples and $$$\tau_c$$$ maps were obtained by fitting a Lorentzian model function to the $$$T_{1\rho}$$$ dispersion. The association between $$$\tau_c$$$ and the tissue properties was assessed by correlation analysis between $$$\tau_c$$$ and histology. The results suggest that the proposed parameter $$$\tau_c$$$ as well as other fitting parameters can reveal cartilage structure. More investigation is needed to establish correlation between $$$\tau_c$$$ and histology.