Alexander Joos¹, Olga Mykhaylyk², Norbert Löwa³, Dietmar Eberbeck³, Bernhard Gleich¹, and Axel Haase^1
1Zentralinstitut für Medizintechnik der Technischen Universität München, Garching, Germany, ²Department of Experimental Oncology, Klinikum rechts der Isar der TU München, Munich, Germany, ³Physikalisch-Technische Bundesanstalt, Berlin, Germany

Magnetic nanoparticles can be used for magnetic drug targeting while MRI can serve as non-invasive therapy monitoring. We investigated the influence of the assembling of magnetic nanoparticles with oncolytic viruses and their uptake into cancer cells on the MRI relaxivities r₁, r₂ and r₂^* and magnetically characterized all samples using magnetic particle spectroscopy. Our results show that R₂^* measurements seem most suitable for particle quantification while R₂ is sensitive to the uptake of the particles into the cells. Magnetic particle spectroscopy proves to be an important validation technique for MRI relaxometry.

Tom Hilbert^1,2,3, Jennifer Schulz⁴, Lauren J. Bains⁴, José P. Marques⁴, Reto Meuli², Jean-Philippe Thiran^2,3, Gunnar Krueger^2,3,5, David G. Norris⁴, and Tobias Kober^1,2,3
1Advanced Clinical Imaging Technology (HC CMEA SUI DI BM PI), Siemens Healthcare AG, Lausanne, Switzerland, ²Department of Radiology, University Hospital (CHUV), Lausanne, Switzerland, ³LTS5, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, ⁴Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, Netherlands, ⁵Siemens Medical Solutions USA, Inc., Boston, MA, United States

Long acquisition times of quantitative magnetic resonance imaging (qMRI) are one obstacle that prevents qMRI to be used in clinical routine. Acceleration methods, such as simultaneous-multi-slice and model-based iterative reconstruction proved in the past to allow high acceleration factors in MRI. Here we suggest combining these two methods to allow fast quantitative T2 mapping, yielding a high-resolution (0.7x0.7x3mm³) whole brain (40 slices) acquisition within a clinically acceptable acquisition time of less than 3 minutes. T2 values of the proposed method are similar to the values of the standard method as it is shown on phantom experiments.

Patrick Schuenke¹, Moritz Zaiss¹, Christina Koehler², Alexander Radbruch^2,3, Mark Edward Ladd¹, and Peter Bachert^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany, ³Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Recently it was demonstrated that on–resonant chemical–exchange–sensitive spin–lock (CESL) allows to observe the uptake of administered D–glucose in vivo and thus could be used for glucose metabolism studies. However, conventional spin–lock produces artifacts owing to B₁–field inhomogeneities, which are a common problem especially at high-field whole-body MR scanners. Therefore we developed an adiabatic water–T_1ρ mapping sequence which outperforms conventional spin-lock sequences with respect to its insensitivity to B₁–inhomogeneities; its sensitivity to glucose in the millimolar range as well as its applicability to in vivo studies is proven.

Evgeniya Kirilina^1,2, Juliane Dinse¹, Pierre-Louise Bazin¹, Carsten Stueber^3,4, Stefan Geyer¹, Robert Trample¹, Andreas Deistung⁵, Juergen R Reichenbach⁵, and Nikolaus Weiskopf^1,6
1Neurophysics, Max Plank Institute for Human Cognitive and Brain Science, Leipzig, Germany, ²Neurocomputation and Neuroimaging Unit, Department of Educational Science and Psychology, Free University Berlin, Berlin, Germany, ³Department of Radiology, Weill Cornell Medical College, New York, NY, United States, ⁴Department of Neurology, Yale School of Medicine, Yale University, New Haven, CT, United States,⁵Medical Physics Group, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, ⁶Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom

Subcortical white matter (SWM) incorporates U-fibers, the intra-hemispheric connections between adjacent gyri. Despite their importance for cortical connectivity little is known about the U-fiber distribution in humans due to the lack of appropriate imaging methods. Herein we investigate SWM using high-resolution in-vivo MRI at 7T. A clear-cut discrimination of SWM from the adjacent brain regions was obtained based on higher qR₂*, qR₂ and susceptibility in-vivo. These new findings may pave the way for future in-vivo segmentation strategies for this crucial brain region as well as potential U-fiber density mapping in humans.

Diana Khabipova^1,2, Rita Gil², Marcel Zwiers², and José Pedro Marques^2
1CIBM-AIT, EPFL, Lausanne, Switzerland, ²Centre for Cognitive Neuroimaging, Donders Institute, Nijmegen, Netherlands

Anisotropic microstructure of the white matter causes the apparent transverse relaxivity, $$$R_2^*$$$, to depend on the orientation of white matter fibres in respect to the applied magnetic field. Using the fibre orientation prior knowledge from DTI orientation dependent $$$R_{2,ANISO}^*$$$ and independent $$$R_{2,ISO}^*$$$ components of $$$R_2^*$$$ were calculated. For all studied WM fibres a consistency for the (an)isotropic components between both hemispheres was present. The isotropic component showed higher variability compared to the anisotropic component.

Weiqiang Dou¹ and Arend Heerschap^1
1Radiology, Radboud University Medical Centre, Nijmegen, Netherlands

Previously reported T₂^*quantification for calcium phosphate cement (CPC), a widely used bone material, remained unsatisfactory with a mono-exponential (ME) fit. A recently proposed Gaussian augmentation of the mono-exponential (GAME) model was reported to have robust fit for gradient echo (GRE) signals. To accurately evaluate GRE-signal decay of CPC, GAME and ME fits were applied in this study for multi-echo time GRE signals acquired at 11.7T. Compared to ME, GAME showed optimal fitting with significantly smaller sum of squared errors and larger R-squared values. Therefore, GAME model is demonstrated to be suitable for GRE signal modeling in CPC at ultra-high field.

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

Reversible and irreversible transverse relaxation rates were measured at 7T, using the GESSE pulse sequence, in basal ganglia structures in 11 volunteers (ages: 23-81 years). We found that, with a judicious choice of echo times, irreversible rates (R₂) in the globus pallidus were conspicuous for all subjects. Furthermore, both reversible and irreversible rates increased with age in a manner consistent with prior postmortem studies of iron concentration in these structures. Since these rates are differentially affected by field perturbations at different spatial scales, their consideration may provide information about the microscopic and mesoscopic distribution and concentration of iron in tissue. 

Avery J.L. Berman^1,2 and Bruce Pike^2
1Montreal Neurological Institute, McGill University, Montreal, QC, Canada, ²Department of Radiology and Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada

This study presents a closed-form analytical solution that describes transverse signal relaxation using the weak field approximation (WFA). The closed-form solution (CFS) fully describes the net signal dynamics under any train of 180° refocusing pulses, and we show that it is in close agreement with a commonly employed mono-exponential expression of the WFA. We compared the CFS to simulations from a medium containing spherical perturbers, with a focus on modelling red blood cells. The CFS and simulations were in close agreement but the results systematically varied depending on whether or not the spheres were allowed to overlap. This theory can be applied in areas such as tissue iron imaging or relaxometry of blood.

Silvia Mangia¹, Alena Svatkova^2,3, Peter Bednarik^1,3, Igor Nestrasil², Lynn E. Eberly⁴, Adam Carpenter⁵, and Shalom Michaeli^1
1Radiology, CMRR, University of Minnesota, Minneapolis, MN, United States, ²Department of Pediatrics, University of Minnesota, Minneapolis, MN, United States, ³Central European Institute of Technology, Masaryk University, Brno, Czech Republic, ⁴Division of Biostatistics, University of Minnesota, Minneapolis, MN, United States, ⁵Neurology, University of Minnesota, Minneapolis, MN, United States

Rotating frame MRI methods including adiabatic T1ρ, T2ρ, and RAFF4 were here employed for characterizing the white matter (WM) of relapsing-remitting Multiple Sclerosis (MS) patients. We calculated relaxograms from subcortical WM of MS patients (excluding lesions) and age-matched controls, and compared them with histograms of DTI outcomes. T1ρ, T2ρ and TRAFF4 were significantly different in the WM of MS patients vs controls, while DTI outcomes did not detect group differences. These findings are supported by recent validation studies using demyelination/dysmyelination animal models, where RAFF4 exhibited exceptional ability to probe myelin content/integrity which we attribute to enhanced sensitivity to slow/ultra-slow motion.

Wendy Ni^1,2, Thomas Christen², and Greg Zaharchuk^2
1Department of Electrical Engineering, Stanford University, Stanford, CA, United States, ²Department of Radiology, Stanford University, Stanford, CA, United States

Transverse MR spin relaxation rates, R₂*, R₂ and R₂’ have all been considered sensitive to brain tissue oxygenation.  In this study, we focus on a cohort of pre-operative Moyamoya disease patients and simultaneously map all three rates in addition to cerebral blood flow, both before and after the injection of the vasodilatory drug, acetazolamide.  We found our measurements to be consistent with physiology and previous studies, and to support the use of R₂’ for oxygenation mapping instead of R₂* and R₂.