Ryan McNaughton^1,2, Ning Hua², Lei Zhang³, David Kennedy⁴, T. Michael O'Shea³, Karl Kuban², and Hernan Jara^2
1Mechanical Engineering, Boston University, Boston, MA, United States, ²Boston University Medical Center, Boston, MA, United States, ³University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ⁴University of Massachusetts, Worcester, MA, United States

Purpose: To describe the dependencies of multiparametric quantitative MRI (MP-qMRI) on myelin and iron content in the extremely preterm born brain at adolescence. Methods: Algorithms for a fast exchange relaxation (FER) model and MP-qMRI create maps of R1, R2, myelin, and iron in 30 participants using MR images obtained with the triple TSE pulse sequence at age 15 years. Results: R1 and R2 have linear dependencies with myelin and iron content, respectively. Conclusion: Application of a FER model produces coregistered maps of myelin and iron content which exhibit unique influences on the relaxation of white matter and gray matter regions.

Meike W.M. van Wijk¹, Joey Roosen¹, Lovisa E.L. Westlund Gotby¹, Mark J. Arntz¹, Marcel J.R. Janssen¹, Daphne Lobeek¹, Gerrit H. van de Maat², Christiaan G. Overduin¹, and J. Frank W. Nijsen^1
1Department of Medical Imaging, Radboud University Medical Center, Nijmegen, Netherlands, ²Imaging & Software Solutions, Quirem Medical B.V., Deventer, Netherlands

Transarterial radioembolization (TARE) is a treatment for liver cancer, during which radioactive microspheres are administered through the hepatic artery. Microspheres containing holmium-166 enable MRI-based dosimetry, based on subtraction of pre- and post-treatment $$$R_2^*$$$ values. This subtraction is performed using a mean pre-treatment $$$R_2^*$$$ value. This does however not take pre-existing differences of $$$R_2^*$$$ values into account, introducing an error in the dosimetry. In this work a voxelwise subtraction method is presented, using deformable registration to transform the pre-treatment $$$R_2^*$$$ map to the post-treatment $$$R_2^*$$$ map, enabling voxel-by-voxel subtraction. This method does take $$$R_2^*$$$ differences into account and improves MRI-based dosimetry.

Aurélien J Trotier¹, Bixente Dilharreguy², Serge Anandra³, Nadège Corbin¹, William Lefrançois¹, Valery Ozenne¹, Sylvain Miraux¹, and Emeline Julie Ribot^1
1Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS, Bordeaux, France, ²UMS3767, CNRS, Bordeaux, France, ³UMS3767, Université de Bordeaux, Bordeaux, France

A Compressed Sensing Magnetization prepared Two Rapid Gradient Echo (CS-MP2RAGE) sequence was developed to provide images in <10min including reconstruction time. It was applied on 13 participants each scanned 3 to 4 times with repositioning.  Compared to the standard MPRAGE sequence, it provides higher contrast morphological images. Similar intra-volunteer variabilities in volume segmentations of the brain structures were obtained. Additionally, high resolution T1 maps provided T1 values of white and gray matters and several deep grey nuclei consistent with the literature, and show very low variability (<1%). The CS-MP2RAGE can be used in future clinical research protocols.

Nadège Corbin^1,2, Aurélien J Trotier¹, Sylvain Miraux¹, and Emeline J Ribot^1
1Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, Bordeaux, France, ²Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom

T2 mapping is usually very time consuming and long acquisition time often result in high sensitivity to intra-scan motion. Here we propose a T2 mapping method relying on 3D radial sampling and advanced iterative reconstruction to retrospectively correct for motion and/or reduce the acquisition. First, in-vivo experiments at 3T showed the capability of the technique to correct for intra-scan motion and therefore improve the quality of resulting T2 maps. Second, acquisitions varying from 7 to 33 min of whole-brain single and multi-compartment T2 maps were obtained, showing the potential of the method to accelerate and therefore reduce sensitivity to motion.

Andreia C Freitas¹, Andreia S Gaspar¹, Nuno A Silva², José M Bioucas-Dias³, and Rita G Nunes^1
1ISR Lisboa/LARSyS and Department of Bioengineering, Instituto Superior Técnico - Universidade de Lisboa, Lisbon, Portugal, ²Hospital da Luz Learning Health, Luz Saúde, Lisbon, Portugal, ³Instituto de Telecomunicações, Instituto Superior Técnico - Universidade de Lisboa, Lisbon, Portugal

T₁ mapping provides valuable information regarding cardiovascular pathologies. Clinical approach consists of using a Cartesian MOLLI sequence and fitting a 3-parameter model. Although easy and straightforward, this method can require long breath-holds and does not explicitly include other factors affecting T₁ estimation. We propose coupling an accelerated golden-angle radial MOLLI with a model-based regularized reconstruction (SALSA). The proposed method was tested in phantom and in vivo data at 1.5T. Improved T₁ precision and good accuracy was found for the phantom data. Lower T₁ was estimated with SALSA compared to the commercial sequence in vivo, future work will address this.

Luke J. Edwards¹, Siawoosh Mohammadi^1,2, Kerrin J. Pine¹, Martina F. Callaghan³, and Nikolaus Weiskopf^1,4
1Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, 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 vivo maps of R2* in human brain hold promise for neuroscientific investigations. We tested several R2* fitting routines (nonlinear least squares [NLLS; silver standard], auto-regression on linear operations [ARLO], log-linear weighted least square [WLS], and log-linear ordinary least squares [OLS]) for dual flip angle multi-echo FLASH data in simulations and challenging 400 µm resolution in vivo 7T data. Log-linear WLS was found to give a good trade-off between accuracy, precision, and computational time. The method will be available in a future version of the open source hMRI toolbox (hmri.info).

Amaresha Shridhar Konar¹, Akash Deelip Shah², Abhay Dave³, Suchandrima Banerjee⁴, Maggie Fung⁵, Vaios Hatzoglou², and Amita Shukla-Dave^1,2
1Medical Physics, Memorial Sloan Kettering Cancer Center, New York City, NY, United States, ²Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ³Touro College of Osteopathic Medicine, New York, NY, United States, ⁴GE Healthcare, New York, NY, United States, ⁵GE Healthcare, New York City, NY, United States

This work aims to assess the relaxometry maps generated using MRF and MAGiC in brain tumor (n=27). A total of 14 brain tumor tissue regions (Pre-Tx n=5, Post-Tx n=9) were used for comparison. The T₁ and T₂ values measured at tumor and normal appearing (contralateral) region showed significant difference in both MAGiC and MRF generated maps.  The results show that the relaxometry values estimated using MRF and MAGiC methods can differentiate Tumor and normal appearing tissues. The utility of this technique needs to be further explored in larger sample studies and it could be further extendable to classify tumor types.

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 whether multiple SPACE sequences accelerated using CAIPIRINHA and acquired with different echo times can be used to obtain high resolution isotropic whole brain T2 maps within a clinical feasible scan time. In a phantom study, we could show that the SPACE based T2 values are comparable with T2 values derived using multiple single spin echo sequences. By reducing the number of echoes we could acquire 1 mm isotropic in vivo whole brain T2 maps in under 3 minutes.

 

Elizabeth N. York¹, Rozanna Meijboom¹, Agniete Kampaite¹, Maria Valdes Hernandez¹, Michael J. Thrippleton¹, and Adam D. Waldman^1
1Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom

Magnetisation transfer saturation (MTsat) shows improved tissue contrast compared with magnetisation transfer ratio (MTR), due to T1 correction, and is more sensitive to subtle myelin loss in multiple sclerosis (MS).  It is not clear how MTsat performs in severely demyelinated tissue with markedly increased T1. We examine the relationship between T1app, MTsat and MTR in healthy and MS brains. We show a negative linear relationship between MTsat and T1app in white matter, which breaks down in grey matter and white matter lesions. MTsat is  sensitive to modest myelin disruption, while T1app may better reflect severe damage in MS lesions.

Gian Franco Piredda^1,2,3, Piotr Radojewski^4,5, Arun Joseph^5,6,7, Gabriele Bonanno^5,6,7, Karl Egger⁸, Shan Yang⁸, Punith B. Venkategowda⁹, Ricardo A. Corredor-Jerez^1,2,3, Bénédicte Maréchal^1,2,3, Roland Wiest^4,5, Jean-Philippe Thiran^2,3, Tom Hilbert^1,2,3, 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, ⁴Support Center for Advanced Neuroimaging, Institute for Diagnostic and Interventional Neuroradiology, Inselspital, Bern University, Bern, Switzerland, ⁵Translational Imaging Center, sitem-insel AG, Bern, Switzerland, ⁶Advanced Clinical Imaging Technology, Siemens Healthcare AG, Bern, Switzerland, ⁷Magnetic Resonance Methodology, Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland, ⁸Department of Neuroradiology, Medical Center – University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, ⁹Siemens Healthcare Pvt. Ltd., Bangalore, India

Previous studies at 3T have shown that T₁ relaxometry enables personalized characterization of brain tissues by comparing physical properties of a single patient to a normative atlas. Ultra-high field imaging allows exploiting this concept at even higher resolutions, which can be crucial to detect certain diseases. To this end, here we established an atlas of normative T₁ values at 7T from acquisitions with 0.6$$$\times$$$0.6$$$\times$$$0.6 mm³ isotropic resolution. Additionally, the clinical potential and improvement of 7T vs. 3T imaging is shown in two case reports from patients scanned at both field strengths.

Jessica Schäper^1,2 and Oliver Bieri^1,2
1Department of Biomedical Engineering, University of Basel, Basel, Switzerland, ²Division of Radioligical Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland

Brain relaxometry with phase-cycled bSSFP shows systematically lower T₁ values, if compared to spoiled-GRE or inversion-recovery spin echo methods. One explanation can be the pronounced asymmetry in the bSSFP's frequency profile, observed for tissues. It was recently shown that this asymmetry decreases towards shorter TR, possibly leading to an adjustment of T₁ estimates from bSSFP to spoiled-GRE. Here, it was investigated how  T₁ and T₂ quantification is influenced by TR. Contrary to expectation, a stronger mismatch between bSSFP and spoiled-GRE was observed towards shorter TR. The origin of this mismatch can thus not be attributed to the bSSFP profile asymmetry.

Dvir Radunsky¹, Chen Solomon¹, Tamar Blumenfeld-Katzir¹, Neta Stern¹, Shir Filo², Aviv Mezer², Anita Karsa³, Karin Shmueli³, Lucas Soustelle ⁴, Guillaume Duhamel⁴, Olivier M. Girard⁴, and Noam Ben-Eliezer^1,5,6
1Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, ²The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel, ³Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, ⁴Aix Marseille University, CNRS, CRMBM, Marseille, France, ⁵Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel, ⁶Center for Advanced Imaging Innovation and Research (CAI2R), University Langone Medical Center, New York, Israel

The clinical utility of quantitative MRI (qMRI) techniques was demonstrated in numerous pathologies. This work investigated a range of qMRI pulse-sequences and processing methods with proven clinical applicability, aiming to establish a comprehensive and standard qMRI scan protocol for the brain. This multiparametric protocol provides a wide range of numeric maps (e.g., T₁, T₂, T₂*, PD, M₀, B₁⁺, water and macromolecular fractions, susceptibility, mean diffusivity, and more) with whole-brain coverage, diverse set of clinical biomarkers, and the ability for stable longitudinal and multi-center investigations. Limitations and practical tips are provided for users interested in quantitative brain imaging.

Jose M Guerrero-Gonzalez^1,2, Olivia Surgent^2,3, Nagesh Adluru^2,4, Steven R Kecskemeti², Gregory R Kirk², Douglas C Dean III^1,2,5, Brittany G Travers^2,6, and Andrew L Alexander^1,2,7
1Medical Physics, University of Wisconsin - Madison, Madison, WI, United States, ²Waisman Center, University of Wisconsin - Madison, Madison, WI, United States, ³Neuroscience Training Program, University of Wisconsin - Madison, Madison, WI, United States, ⁴Radiology, University of Wisconsin - Madison, Madison, WI, United States, ⁵Pediatrics, University of Wisconsin - Madison, Madison, WI, United States, ⁶Kinesiology Occupational Therapy Program, University of Wisconsin - Madison, Madison, WI, United States, ⁷Psychiatry, University of Wisconsin - Madison, Madison, WI, United States

Fiber orientation distributions (FOD) derived from diffusion magnetic resonance imaging (dMRI) enable resolution of multiple fiber populations within a voxel. FOD-based white matter studies include voxel-based analysis, atlas-based labeling, and group average fiber tracking. These methods require spatial normalization of the FODs. This work describes an alternative approach for FOD spatial normalization based on co-registering individual dMRI to the T1-weighted (T1w) images, non-linear spatial normalization of the T1w images to a template, and applying the transformations to the FOD maps. This approach is compared to the conventional approach of directly aligning FOD maps.

Daniel Z.L. Kor¹, Saad Jbabdi¹, Jeroen Mollink¹, Istvan N. Huszar¹, Sean Foxley², Menuka Pallebage-Gamarallage³, Connor Scott³, Adele Smart³, Olaf Ansorge³, Karla L. Miller¹, and Amy F.D. Howard^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, ²Department of Radiology, University of Chicago, Chicago, IL, United States, ³Neuropathology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

Acquisition of MRI and histology in the same ex-vivo tissue sample enables direct correlation between MR and histologically-derived metrics. Here, we analysed immunohistochemistry images of human visual cortex, anterior cingulate and hippocampus to produce stained area fraction maps for myelin, neurofilaments and microglia. We performed voxelwise correlations between MR parameters (FA, MD, R2*, R1) and histology maps to generally characterise the strength of relationships. We then used partial correlation to identify the unique variance in MR parameters explained by each histological feature, and multiple linear regression to explore how well multiple microstructural properties can together explain MR parameters.

Steven T. Whitaker¹, Jon-Fredrik Nielsen², and Jeffrey A. Fessler^1
1Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, United States, ²Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

Optimization techniques can be used to design scan parameters for quantitative imaging. The Cramér-Rao Lower Bound (CRLB) is often used for such designs, but it only characterizes unbiased estimators. We propose an end-to-end approach to scan design that optimizes scan parameters with a particular estimator in mind. We compare CRLB-based and end-to-end scan designs in the context of myelin water imaging. The end-to-end scan design results in lower estimation error in simulation and an in vivo myelin water fraction (MWF) map with improved contrast. The proposed end-to-end scan design approach is thus a promising alternative to using the CRLB.