Niklas Wallstein¹, André Pampel ¹, Andrea Capucciati², Carsten Jäger¹, Fabio A. Zucca³, Luigi Casella², Luigi Zecca³, and Harald E. Möller^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Department of Chemistry, University of Pavia, Pavia, Italy, ³Institute of Biomedical Technologies, National Research Council of Italy, Segrate, Milan, Italy

Neuromelanin (NM) MRI has received increasing interest in applications to diagnosis of Parkinson’s disease. A reduction of T1 associated with paramagnetic melanin-iron complexes is assumed to be the primary contrast mechanism. NM is able to chelate large quantities of iron but also, to a lesser extent, other transition metals, in particular copper. Here, we investigated the effect of different copper/iron concentrations bound to NM on water T1 and T2. Our results corroborate previous studies suggesting a concentration-dependent decrease of T1 for iron-loaded melanin. Additionally, we found a synergetic effect if both metals are simultaneously present leading to a pronounced T1-shortening.

Stefano Tambalo^1,2, Alberto Finora², Diego Cavalli², and Jorge Jovicich^1
1CIMeC, University of Trento, Trento, Italy, ²Department of Radiology, G.B. Rossi Hospital, University of Verona, Verona, Italy

The gold standard T1 mapping method is the Inversion Recovery (IR). Volumetric sequences such as MP2RAGE without or with compressed sensing (csMP2RAGE) allow faster T1-mapping, but potential biases are not well characterized. Here we investigated T1-mapping and test-retest reproducibility effects of sequence (IR, MP2RAGE, csMP2RAGE) and head RF coil (64 and 20-channel), both in-vitro and in-vivo. The 64-channel coil results are more accurate and reliable, showing good agreement with the gold standard and a beneficial reduction of scan time.

Jonas Kielmann*¹, Ana-Maria Oros-Peusquens*¹, Nora Bittner², Svenja Caspers², and N. Jon Shah^1,3,4,5
1INM-4, Research Centre Juelich, Juelich, Germany, ²INM-1, Research Centre Juelich, Juelich, Germany, ³Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany, ⁴INM-11, JARA, Research Centre Juelich, Juelich, Germany, ⁵Department of Neurology, RWTH Aachen University, Aachen, Germany

Multicontrast quantitative MRI is used to characterize left-right and sulcal-gyral asymmetries of the brain in 26 volunteers. Several regions with significant asymmetries are found in different parameters (H2O, fbound, R2*, R1, kex, QSM). Good correlation between sulcal-gyral H2O-defined asymmetry and local gyrification index is found.

Elior Drori¹, Shir Filo¹, and Aviv Mezer^1
1The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel

The striatum is a heterogeneous brain structure with microstructural gradients along its main axes. Changes in its organization are associated with normal aging and disease. Yet the spatial variability in the human striatum is not well characterized and is mostly limited to postmortem studies. We propose a robust non-invasive method for detection and quantification of microstructural gradients along axes of the striatum in individuals in vivo, using qMRI. We show distinct profiles of spatial and aging-related changes in the striatum, associated with different biophysical sources such as tissue density and iron content, estimated in vivo.

Naoki Maeda¹, Yuki Kanazawa², Masafumi Harada², Yo Taniguchi³, Yuki Matsumoto², Hiroaki Hayashi⁴, Kosuke Ito³, Yoshitaka Bito³, and Akihiro Haga^2
1Graduate of Health Science, Tokushima University, Tokushima, Japan, ²Graduate School of Biomedical Sciences, Tokushima University, Tokushima, Japan, ³Healthcare Business Unit, Hitachi, Ltd., Tokyo, Japan, ⁴College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan

We developed a method for deriving water exchange rate based on mcDESPOT approach between two structures using quantitative parameters calculated from QPM-MRI. Our method was performed with human study for ten healthy volunteers and one patient with brain tumor. There was a significant negative correlation between k_FS and k_SF derived from QPM in each region, e.g., white matter, gray matter, and cerebral spinal fluid of healthy volunteers. (R = -0.75, P < 0.001). In conclusion, water exchange rates derived from QPM make it possible to obtain more detailed information of the brain associated with proton diffusion between structures, i.e., cross-relaxation.

Shohei Fujita^1,2, Akifumi Hagiwara¹, Koichiro Yasaka³, Hiroyuki Akai³, Akira Kunimatsu³, Shigeru Kiryu⁴, Issei Fukunaga¹, Shimpei Kato^1,2, Toshiaki Akashi¹, Koji Kamagata¹, Akihiko Wada¹, Osamu Abe², and Shigeki Aoki^1
1Department of Radiology, Juntendo University, Tokyo, Japan, ²Department of Radiology, The University of Tokyo, Tokyo, Japan, ³Department of Radiology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan, ⁴Department of Radiological Sciences, International University of Health and Welfare, Narita, Japan

Understanding the dependencies of radiomic features on the dictionary step size in MR fingerprinting is crucial in the clinical implementation of MR fingerprinting-based radiomics. We investigated the influence of dictionary design in the radiomic analysis of MR fingerprinting and observed that radiomic features vary significantly for different designs. Moreover, special attention is required when using datasets containing maps generated from different dictionaries. We also demonstrated that an inverse quantization process can mitigate the influence of dictionary design on the radiomic features obtained with MR fingerprinting.

Christoph Birkl¹, Christian Kremser², Alexander Rauscher³, and Elke Ruth Gizewski^1
1Department of Neuroradiology, Medical University of Innsbruck, Innsbruck, Austria, ²Department of Radiology, Medical University of Innsbruck, Innsbruck, Austria, ³UBC MRI research Centre, University of British Columbia, Vancouver, BC, Canada

We investigated how the sensitivity of spin-echo and turbo spin echo MRI sequences to diffusion processes affects the estimation of fiber orientation dependent R2 in white matter. Our results indicate that the strongest R2 orientation dependency is observed when R2 is estimated using multiple single spin echo sequences. The lowest R2 orientation dependency was observed for the multi-echo spin echo sequence.

Gunther Helms¹ and Hampus Olsson^1
1Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden

Fitting the inversion recovery (IR) at multiple TI provides T1 estimates of high accuracy if performed in a single slice with full relaxation. We present an isotropic 3D variant based on MP-RAGE, where a T1-weighted driven equilibrium is prepared prior to inversion by a second RAGE readout. This abolishes the need for long recovery times and provides volumes of similar contrast for co-registration. The method was tested at 3T on a small cohort and compared to 3D IR-TSE and 3D variable flip angle mapping.    

Gunther Helms^1
1Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden

Controlling the saturation of bound magnetization in variable flip angle (VFA) experiments improves the derived parameter maps. Instead of using special CSMT RF pulses, we kept the rmsB1 constant simply by increasing the RF pulse duration with the square of the flip angle. At 3T, VFA T1 mapping of human brain thus showed better compliance to the Ernst equation than at constant pulse duration or B₁ amplitude, but yielded shorter T₁.     

Luke A Reynolds¹, Sarah R Morris^1,2, Irene M Vavasour^2,3, Laura Barlow³, 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, ³UBC MRI Research Centre, Vancouver, BC, Canada

Adiabatic pulses have advantageous properties, such as an independently scalable bandwidth, which makes them more clinically versatile compared to standard soft pulses. However, their application to white matter has produced some unvalidated assumptions about the subsequent relaxation mechanisms. We examined the form of the longitudinal relaxation following adiabatic inversion in-vivo with simple inversion recovery experiments, which we found to be biexponential in character. This arises from cross-relaxation/exchange between aqueous and non-aqueous tissue components prepared in different magnetization states. We suggest a straightforward and accessible scheme for reproducible measurements of monoexponential T₁ using a specific saturation recovery method.

Zhitao Li^1,2, Zhiyang Fu³, and Maria I Altbach^4
1Department of Radiology, Stanford University, Palo Alto, CA, United States, ²Electrical Engineering, Stanford University, Palo Alto, CA, United States, ³Electrical and Computer Engineering, The University of Arizona, Tucson, AZ, United States, ⁴Department of Medical Imaging, The University of Arizona, Tucson, AZ, United States

A 3D IR-radFLASH pulse sequence and a corresponding model-based reconstruction algorithm is presented for in vivo brain T₁ mapping. The proposed pulse sequence can acquire data for high SNR 1.0mm isotropic resolution T₁ mapping within clinical time constraints. The proposed model-based reconstruction algorithm can reconstruct the acquired data with high temporal resolution, which can be used to map spin species with relatively low T₁ values. When combined with a slab-selective inversion pulse, the proposed technique can achieve whole brain coverage under 5 minutes.

Qinqin Yang¹, Jiechao Wang¹, Qizhi Yang¹, Shuhui Cai¹, Hongjian He², Congbo Cai¹, Zhong Chen¹, and Jianhui Zhong^2,3
1Department of Electronic Science, Xiamen University, Xiamen, China, ²The Center for Brain Imaging Science and Technology, the Collaborative Innovation Center for Diagnosis, and the Treatment of Infectious Diseases, Zhejiang University, Hangzhou, China, ³Department of Imaging Sciences, University of Rochester, Rochester, NY, United States

Subject motion often leads to serious quality degradation of MR images, especially in quantitative MRI. In this study, a novel reconstruction method was proposed for single-shot T₂ mapping based on overlapping-echo detachment planar imaging and synthetic-data-driven learning (SDDL). This method was made robust to severe motion by improved parallel reconstruction and motion correction methods without extra scan. The proposed method was evaluated with human brain experiments. The results show that SDDL-based method can significantly reduce ghosting and motion artifacts in T₂ maps in the presence of randomly and continuously subject movement.

Simin Li¹, Jian Wu¹, Shuhui Cai¹, and Congbo Cai^1
1Department of Electronic Science, Xiamen University, Xiamen, China

Most quantitative magnetic resonance imaging (qMRI) techniques remain time-consuming and sensitive to motion, especially when large volume imaging is needed. Simultaneous multi-slice (SMS), which is not restricted by single-slice evolution time, is an acceleration method for MRI. Here we propose a flexible SMS T₂ mapping method based on overlapping echo detachment (OLED) planar imaging. Experimental results demonstrate the superior performance of our method. Reliable multi-slice T₂ maps can be obtained in a single shot within milliseconds for the first time.

Gian Franco Piredda^1,2,3, Tom Hilbert^1,2,3, Berkin Bilgic^4,5,6, Erick Jorge Canales-Rodríguez³, Marco Pizzolato^3,7, Reto Meuli², Jean-Philippe Thiran^2,3, and Tobias Kober^1,2,3
1Advanced Clinical Imaging Technology, Siemens Healthcare AG, Lausanne, Switzerland, ²Department of Radiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ³LTS5, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, ⁴Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ⁵Department of Radiology, Harvard Medical School, Boston, MA, United States, ⁶Harvard‐MIT Health Sciences and Technology, MIT, Cambridge, MA, United States, ⁷Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark

In previous work, CAIPIRINHA was implemented in multi-echo gradient and spin echo (GRASE) acquisitions for 3D myelin water imaging, achieving significant acceleration. However, residual undersampling artifacts prevented further acquisition time reduction. In this work, we propose a joint-CAIPI reconstruction across echoes of GRASE k-space data to remove aliasing artifacts and further accelerate the acquisition. Exploiting the redundant anatomical information across the different GRASE echoes helped mitigate aliasing artifacts in myelin water fraction maps and provided an additional ~40% reduction in scan time to 6:18$$$\,$$$minutes for a whole-brain acquisition at 1.6$$$\,$$$mm³ isotropic resolution.

Xinlin Zhang¹, Hengfa Lu², Zi Wang¹, Xi Peng³, Feng Huang⁴, Qin Xu⁴, Di Guo⁵, and Xiaobo Qu^1
1Department of Electronic Science, School of Electronic Science and Engineering (National Model Microelectronics College), National Institute for Data Science in Health and Medicine, Xiamen University, Xiamen, China, ²College of Optical Science and Engineering, Zhejiang University, Hangzhou, China, ³Department of Radiology, Mayo Clinic, Rochester, MN, United States, ⁴Neusoft Medical System, Shanghai, China, ⁵School of Computer and Information Engineering, Fujian Provincial University Key Laboratory of Internet of Things Application Technology, Xiamen University of Technology, Xiamen, China

Being the state-of-the-art parallel magnetic resonance imaging methods other than the deep learning approaches, the low-rank Hankel approaches embrace the advantage of holding low reconstruction errors. However, they demand intensive computations and high memory consumptions, thereby result in long reconstruction time. We proposed a new strategy for exploiting the low rankness and applied it to accelerate 2D imaging and T2 mapping. It is shown that the proposed method outperforms the state-of-the-art approaches in terms of lower reconstruction errors and more accurate mapping estimations. Besides, the proposed method required much less computation and memory consumption.

Peter Seres¹, Kelly C McPhee^1,2, Emily Stolz¹, Julia Rickard¹, Jeff Snyder¹, Christian Beaulieu¹, and Alan H Wilman^1
1Biomedical Engineering, University of Alberta, Edmonton, AB, Canada, ²CancerCare Manitoba, Winnipeg, MB, Canada

Transverse relaxation (T2) mapping from standard images is investigated in human brain using only a proton density and T2-weighted dual-echo turbo spin echo acquisition and applying Bloch fitting approach with transmit field map. In 24 subjects, repeatability of T2 maps was excellent with typically coefficient of variation (CoV) ~1% on the same scanner. In grey and white matter overall, CoV was 0.4%. The method is then applied to study T2 changes across the lifespan from 5-90 years old in 333 healthy participants, providing a normative population of true T2 values independent of refocusing flip angle effects.

Daiki Tamada¹ and Scott B. Reeder^1,2,3,4,5
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, ²Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ³Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, United States, ⁴Medicine, University of Wisconsin-Madison, Madison, WI, United States, ⁵Emergency Medicine, University of Wisconsin-Madison, Madison, WI, United States

A novel T2 mapping method is proposed using RF-phase modulated dual echo steady-state sequence (DESS). T2 information is encoded into the phase of the DESS signals by using a small RF phase increment. T2 value is estimated from the phase difference between the FISP and PSIF signal of the DESS acquisition. Phantom studies demonstrated that estimated T2 using the proposed method agrees closely with spin-echo-based T2 mapping, and volunteer studies demonstrate the feasibility of the proposed method in vivo. These results suggested that the proposed method enables fast and three-dimensional T2 mapping with a single acquisition.

Yuanyuan Liu¹, Yanjie Zhu¹, Yuxin Yang², Xin Liu¹, Hairong Zheng¹, and Dong Liang^1
1Shenzhen Institutes of Advanced Technology, Shenzhen, China, ²Chongqing University of Technology, Chongqing, China, Chongqing, China

Recent studies show that variations in the rate of $$$T_{1\rho} (R_{1\rho})$$$  reflect changes in the spectral density of the local dipolar fields experienced by protons due to slow molecular motions. The quantitative data for $$$R_{1\rho}$$$ dispersion requires multiple $$$T_{1\rho}$$$-weighted images with different spin lock times (TSLs) and different locking fields, which makes the acquisition time very long. In this work, a signal compensation strategy with low-rank plus sparse model (SCOPE) was used to reconstruct $$$T_{1\rho}$$$-weighted images from highly undersampled data. We provide the reconstructed images, the estimated $$$R_{1\rho}$$$ maps, and the results of $$$R_{1\rho}$$$ dispersion curves at different acceleration factors. 

Oliver Maier¹, Markus Bödenler^1,2, Rudolf Stollberger^1,3, Mary-Joan MacLeod⁴, Lionel M Broche⁵, and Hermann Scharfetter^1
1Graz University of Technology, Graz, Austria, ²Institute of eHealth, University of Applied Sciences FH JOANNEUM, Graz, Austria, ³BioTechMed Graz, Graz, Austria, ⁴Acute Stroke Unit, Aberdeen Royal Infirmary, Aberdeen, United Kingdom, ⁵Aberdeen Biomedical Imaging Centre, Univeresity of Aberdeen, Aberdeen, United Kingdom

T₁ maps from fast field-cycling (FFC) MRI can provide insights to structural information and dynamics of molecular system not accessible by traditional MRI. The low SNR associated with the lower field strength in FFC imaging (0.2 T - 50 µT) leads to long acquisition times, impairing its clinical applicability. Hence, we propose a model-based reconstruction strategy to reduce acquisition time and improve image quality of multi-field T₁ maps. The method is compared to standard fitting on numerical phantoms and a in vivo stroke patient. Model-based reconstruction clearly outperformed standard fitting, reducing noise and revealing previously unseen details in low-field T₁ maps.

Thomas O'Reilly¹ and Andrew Webb^1
1C.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands

Recent years have seen a renewal in interest in low field MRI systems due to its lower cost, increased portability and robustness to medical implants, with the obvious disadvantage of lower SNR compared to clinical high field systems. In this work we present T₁ and T₂ relaxation maps of the brain and lower leg to facilitate the optimization of sequence parameters. Generally the T₁ times are shorter and T₂ times are slightly longer than at clinical field strengths.