Abstract
Quantitative magnetic resonance imaging (qMRI) goes beyond conventional MRI, which aims primarily at local image contrast. It provides specific physical parameters related to the nuclear spin of protons in water, such as relaxation times. These parameters carry information about the local microstructural environment of the protons (such as myelin in the brain). Non-invasive in vivo histology using MRI (hMRI) aims to use this information to directly characterize biological tissue microstructure, partially replacing or complementing classical invasive histology. The understanding of MRI tissue contrast provided by hMRI is, in turn, crucial for further improvements of qMRI, and they should be considered closely interlinked. We discuss concepts, models and validation approaches, pointing out challenges and the latest advances in this field. Further, we point out links to physics, including computational and analytical approaches and developments in materials science and photonics, that aid in reference data acquisition and model validation.
Key points
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Quantitative magnetic resonance imaging (qMRI) provides quantitative measurements of specific physical parameters related to the nuclear spin of protons in water.
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Water proton spins act as intrinsic probes of the surrounding tissue microstructure.
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qMRI parameters, including longitudinal and transverse relaxation rates, magnetic susceptibility, proton density and magnetization transfer, carry important information about myelination, iron and cell membranes in the living brain.
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In vivo histology using MRI (hMRI) aims to provide quantitative whole-brain measures of brain microstructure in health and disease.
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qMRI and hMRI promise much needed sensitive biomarkers in health and disease.
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Model building and validation require comprehensive reference data of brain microstructure that capture all features relevant for the MRI contrast.
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References
Boesch, C. Nobel Prizes for nuclear magnetic resonance: 2003 and historical perspectives. J. Magn. Reson. Imaging 20, 177â179 (2004).
Lauterbur, P. C. Image formation by induced local interactions: examples employing nuclear magnetic resonance. Nature 242, 190â191 (1973).
Mansfield, P. & Grannell, P. K. NMR âdiffractionâ in solids? J. Phys. C Solid State Phys. 6, L422âL426 (1973).
Thompson, A. J. et al. Diagnosis of multiple sclerosis: 2017 revisions of the McDonald criteria. Lancet Neurol. 17, 162â173 (2018).
Geraldes, R. et al. The current role of MRI in differentiating multiple sclerosis from its imaging mimics. Nat. Rev. Neurol. 14, 199â213 (2018).
Brownlee, W. J., Hardy, T. A., Fazekas, F. & Miller, D. H. Diagnosis of multiple sclerosis: progress and challenges. Lancet 389, 1336â1346 (2017).
Young, I. R. et al. Nuclear magnetic resonance imaging of the brain in multiple sclerosis. Lancet 2, 1063â1066 (1981).
Rees, J. H. Diagnosis and treatment in neuro-oncology: an oncological perspective. Br. J. Radiol. 84, S82âS89 (2011).
Fiebach, J. B. et al. Stroke magnetic resonance imaging is accurate in hyperacute intracerebral hemorrhage: a multicenter study on the validity of stroke imaging. Stroke 35, 502â506 (2004).
Ross, M. A., Biller, J., Adams, H. P. Jr & Dunn, V. Magnetic resonance imaging in Wallenbergâs lateral medullary syndrome. Stroke 17, 542â545 (1986).
Moseley, M. E. et al. Diffusion-weighted MR imaging of acute stroke: correlation with T2-weighted and magnetic susceptibility-enhanced MR imaging in cats. Am. J. Neuroradiol. 11, 423â429 (1990).
Miller, K. L. et al. Multimodal population brain imaging in the UK Biobank prospective epidemiological study. Nat. Neurosci. 19, 1523â1536 (2016).
German National Cohort (GNC) Consortium. The German National Cohort: aims, study design and organization. Eur. J. Epidemiol. 29, 371â382 (2014).
Rosen, B. R. & Savoy, R. L. fMRI at 20: has it changed the world? Neuroimage 62, 1316â1324 (2012).
Bandettini, P. A. fMRI. The MIT Press Essential Knowledge Series (MIT Press, 2020).
Whitaker, K. J. et al. Adolescence is associated with genomically patterned consolidation of the hubs of the human brain connectome. Proc. Natl Acad. Sci. USA 113, 9105â9110 (2016).
Natu, V. S. et al. Apparent thinning of human visual cortex during childhood is associated with myelination. Proc. Natl Acad. Sci. USA 116, 20750â20759 (2019).
Good, C. D. et al. A voxel-based morphometric study of ageing in 465 normal adult human brains. Neuroimage 14, 21â36 (2001).
Callaghan, M. F. et al. Widespread age-related differences in the human brain microstructure revealed by quantitative magnetic resonance imaging. Neurobiol. Aging 35, 1862â1872 (2014).
Fox, N. C. et al. Imaging of onset and progression of Alzheimerâs disease with voxel-compression mapping of serial magnetic resonance images. Lancet 358, 201â205 (2001).
Shah, N. J. et al. Quantitative cerebral water content mapping in hepatic encephalopathy. Neuroimage 41, 706â717 (2008).
Freund, P. et al. MRI investigation of the sensorimotor cortex and the corticospinal tract after acute spinal cord injury: a prospective longitudinal study. Lancet Neurol. 12, 873â881 (2013).
Maguire, E. A. et al. Navigation-related structural change in the hippocampi of taxi drivers. Proc. Natl Acad. Sci. USA 97, 4398â4403 (2000).
Draganski, B. et al. Changes in grey matter induced by training newly honed juggling skills show up as a transient feature on a brain-imaging scan. Nature 427, 311â312 (2004).
Zatorre, R. J., Fields, R. D. & Johansen-Berg, H. Plasticity in gray and white: neuroimaging changes in brain structure during learning. Nat. Neurosci. 15, 528â536 (2012).
Sagi, Y. et al. Learning in the fast lane: new insights into neuroplasticity. Neuron 73, 1195â1203 (2012).
Sereno, M. I., Lutti, A., Weiskopf, N. & Dick, F. Mapping the human cortical surface by combining quantitative T1 with retinotopy. Cereb. Cortex 23, 2261â2268 (2013). Demonstrates systematic mapping of visual brain areas based on non-invasive R1 myelin measures, including a comparison with functional neuroanatomy.
Kuehn, E. et al. Body topography parcellates human sensory and motor cortex. Cereb. Cortex 27, 3790â3805 (2017).
Attar, F. M. et al. Mapping short association fibers in the early cortical visual processing stream using in vivo diffusion tractography. Cereb. Cortex 30, 4496â4514 (2020).
Bernstein, M. A., King, K. F. & Zhou, X. J. Handbook of MRI Pulse Sequences (Academic Press, 2004).
Filo, S. et al. Disentangling molecular alterations from water-content changes in the aging human brain using quantitative MRI. Nat. Commun. 10, 3403 (2019). Shows that lipid composition of myelin may be captured by combination of qMRI parameters.
Stüber, C. et al. Myelin and iron concentration in the human brain: a quantitative study of MRI contrast. Neuroimage 93, 95â106 (2014).
Koenig, S. H. Classes of hydration sites at protein-water interfaces: the source of contrast in magnetic resonance imaging. Biophys. J. 69, 593â603 (1995).
Langkammer, C. et al. Quantitative MR imaging of brain iron: a postmortem validation study. Radiology 257, 455â462 (2010).
Möller, H. E. et al. Iron, myelin, and the brain: neuroimaging meets neurobiology. Trends Neurosci. 42, 384â401 (2019).
Jespersen, S. N., Leigland, L. A., Cornea, A. & Kroenke, C. D. Determination of axonal and dendritic orientation distributions within the developing cerebral cortex by diffusion tensor imaging. IEEE Trans. Med. Imaging 31, 16â32 (2012).
Beaulieu, C. & Allen, P. S. Water diffusion in the giant axon of the squid: implications for diffusion-weighted MRI of the nervous system. Magn. Reson. Med. 32, 579â583 (1994).
Palombo, M. et al. SANDI: a compartment-based model for non-invasive apparent soma and neurite imaging by diffusion MRI. Neuroimage 215, 116835 (2020).
Cercignani, M., Dowell, N. G. & Tofts, P. S. (eds) Quantitative MRI of the Brain: Principles of Physical Measurement 2nd edn (CRC Press, 2018).
Weiskopf, N. et al. Quantitative multi-parameter mapping of R1, PD*, MT, and R2* at 3T: a multi-center validation. Front. Neurosci. 7, 95 (2013).
Gracien, R.-M. et al. How stable is quantitative MRI? â Assessment of intra- and inter-scanner-model reproducibility using identical acquisition sequences and data analysis programs. Neuroimage 207, 116364 (2020).
Leutritz, T. et al. Multiparameter mapping of relaxation (R1, R2*), proton density and magnetization transfer saturation at 3 T: A multicenter dual-vendor reproducibility and repeatability study. Hum. Brain Mapp. 41, 4232â4247 (2020).
Damadian, R. Tumor detection by nuclear magnetic resonance. Science 171, 1151â1153 (1971).
Bakker, C. J., de Graaf, C. N. & van Dijk, P. Derivation of quantitative information in NMR imaging: a phantom study. Phys. Med. Biol. 29, 1511â1525 (1984).
Tofts, P. S. & du Boulay, E. P. Towards quantitative measurements of relaxation times and other parameters in the brain. Neuroradiology 32, 407â415 (1990).
Edwards, L. J., Kirilina, E., Mohammadi, S. & Weiskopf, N. Microstructural imaging of human neocortex in vivo. Neuroimage 182, 184â206 (2018).
Does, M. D. Inferring brain tissue composition and microstructure via MR relaxometry. Neuroimage 182, 136â148 (2018).
Sled, J. G. Modelling and interpretation of magnetization transfer imaging in the brain. Neuroimage 182, 128â135 (2018).
David, G. et al. Traumatic and nontraumatic spinal cord injury: pathological insights from neuroimaging. Nat. Rev. Neurol. 15, 718â731 (2019).
Enzinger, C. et al. Nonconventional MRI and microstructural cerebral changes in multiple sclerosis. Nat. Rev. Neurol. 11, 676â686 (2015).
Albers, G. W. Diffusion-weighted MRI for evaluation of acute stroke. Neurology 51, S47âS49 (1998).
Barkhof, F., Jäger, R., Thurnher, M. & Rovira, A. (eds) Clinical Neuroradiology: The ESNR Textbook (Springer, 2019).
Setsompop, K. et al. Pushing the limits of in vivo diffusion MRI for the human connectome project. Neuroimage 80, 220â233 (2013).
Medgadget Editors. FDA gives first clearance to Siemens high-field 7 Tesla MRI scanner. Medgadget https://www.medgadget.com/2017/10/fda-gives-first-clearance-high-field-7-tesla-mri-scanner.html (2017).
Medgadget Editors. EU gives first approval for ultra-high-field MRI scanner, the Siemens Magnetom Terra. Medgadget https://www.medgadget.com/2017/08/eu-gives-first-approval-ultra-high-field-mri-scanner-siemens-magnetom-terra.html (2017).
Zhu, B., Liu, J. Z., Cauley, S. F., Rosen, B. R. & Rosen, M. S. Image reconstruction by domain-transform manifold learning. Nature 555, 487â492 (2018).
Ma, D. et al. Magnetic resonance fingerprinting. Nature 495, 187â192 (2013). Introduces non-repetitive MRI pulse sequences to estimate qMRI parameters.
Tabelow, K. et al. hMRI â a toolbox for quantitative MRI in neuroscience and clinical research. Neuroimage 194, 191â210 (2019).
Karakuzu, A. et al. qMRLab: Quantitative MRI analysis, under one umbrella. J. Open Source Softw. 5, 2343 (2020).
Novikov, D. S., Fieremans, E., Jespersen, S. N. & Kiselev, V. G. Quantifying brain microstructure with diffusion MRI: theory and parameter estimation. NMR Biomed. 32, e3998 (2019).
Weiskopf, N., Mohammadi, S., Lutti, A. & Callaghan, M. F. Advances in MRI-based computational neuroanatomy: from morphometry to in-vivo histology. Curr. Opin. Neurol. 28, 313â322 (2015).
Deistung, A. et al. Toward in vivo histology: A comparison of quantitative susceptibility mapping (QSM) with magnitude-, phase-, and R2*-imaging at ultra-high magnetic field strength. Neuroimage 65, 299â314 (2013).
Bridge, H. & Clare, S. High-resolution MRI: in vivo histology? Philos. Trans. R. Soc. Lond. B Biol. Sci. 361, 137â146 (2006).
Alexander, D. C., Dyrby, T. B., Nilsson, M. & Zhang, H. Imaging brain microstructure with diffusion MRI: practicality and applications. NMR Biomed. 32, e3841 (2019).
Patel, Y. et al. Virtual histology of multi-modal magnetic resonance imaging of cerebral cortex in young men. Neuroimage 218, 116968 (2020).
Kessler, L. G. et al. The emerging science of quantitative imaging biomarkers terminology and definitions for scientific studies and regulatory submissions. Stat. Methods Med. Res. 24, 9â26 (2015).
European Society of Radiology (ESR). ESR statement on the validation of imaging biomarkers. Insights Imaging 11, 76 (2020).
Haller, S. et al. Arterial spin labeling perfusion of the brain: emerging clinical applications. Radiology 281, 337â356 (2016).
Germuska, M. & Wise, R. G. Calibrated fMRI for mapping absolute CMRO2: Practicalities and prospects. Neuroimage 187, 145â153 (2019).
Demetriou, E., Kujawa, A. & Golay, X. Pulse sequences for measuring exchange rates between proton species: From unlocalised NMR spectroscopy to chemical exchange saturation transfer imaging. Prog. Nucl. Magn. Reson. Spectrosc. 120â121, 25â71 (2020).
van Zijl, P. C. M., Lam, W. W., Xu, J., Knutsson, L. & Stanisz, G. J. Magnetization transfer contrast and chemical exchange saturation transfer MRI. Features and analysis of the field-dependent saturation spectrum. Neuroimage 168, 222â241 (2018).
McRobbie, D. W., Moore, E. A., Graves, M. J. & Prince, M. R. MRI from Picture to Proton (Cambridge Univ. Press, 2017).
Seiberlich, N. et al. Quantitative Magnetic Resonance Imaging (Academic Press, 2020).
Vlaardingerbroek, M. T. & den Boer, J. A. in Magnetic Resonance Imaging 9â54 (Springer, 2003).
Brown, R. W., Cheng, Y.-C. N., Haacke, E. M., Thompson, M. R. & Venkatesan, R. Magnetic Resonance Imaging: Physical Principles and Sequence Design 2nd edn (Wiley, 2014).
Bloch, F. Nuclear induction. Phys. Rev. 70, 460â474 (1946).
Hanson, L. G. Is quantum mechanics necessary for understanding magnetic resonance? Concepts Magn. Reson. 32A, 329â340 (2008).
Edzes, H. T. & Samulski, E. T. Cross relaxation and spin diffusion in the proton NMR or hydrated collagen. Nature 265, 521â523 (1977).
McConnell, H. M. Reaction rates by nuclear magnetic resonance. J. Chem. Phys. 28, 430â431 (1958).
Henkelman, R. M. et al. Quantitative interpretation of magnetization transfer. Magn. Reson. Med. 29, 759â766 (1993).
Torrey, H. C. Bloch equations with diffusion terms. Phys. Rev. 104, 563â565 (1956).
Spencer, R. G. & Bi, C. A tutorial introduction to inverse problems in magnetic resonance. NMR Biomed. 33, e4315 (2020).
Venkatesan, R., Lin, W. & Haacke, E. M. Accurate determination of spin-density and T1 in the presence of RF-field inhomogeneities and flip-angle miscalibration. Magn. Reson. Med. 40, 592â602 (1998).
Helms, G., Dathe, H. & Dechent, P. Quantitative FLASH MRI at 3T using a rational approximation of the Ernst equation. Magn. Reson. Med. 59, 667â672 (2008).
Mackay, A. et al. In vivo visualization of myelin water in brain by magnetic resonance. Magn. Reson. Med. 31, 673â677 (1994).
Helms, G., Dathe, H., Kallenberg, K. & Dechent, P. High-resolution maps of magnetization transfer with inherent correction for RF inhomogeneity and T1 relaxation obtained from 3D FLASH MRI. Magn. Reson. Med. 60, 1396â1407 (2008).
Basser, P. J. & Pierpaoli, C. Microstructural and physiological features of tissues elucidated by quantitative-diffusion-tensor MRI. J. Magn. Reson. B 111, 209â219 (1996).
McCollough, C. H., Leng, S., Yu, L. & Fletcher, J. G. Dual- and multi-energy CT: principles, technical approaches, and clinical applications. Radiology 276, 637â653 (2015).
Preibisch, C. & Deichmann, R. Influence of RF spoiling on the stability and accuracy of T1 mapping based on spoiled FLASH with varying flip angles. Magn. Reson. Med. 61, 125â135 (2009).
Haskell, M. W. et al. Network accelerated motion estimation and reduction (NAMER): convolutional neural network guided retrospective motion correction using a separable motion model. Magn. Reson. Med. 82, 1452â1461 (2019).
Tamir, J. I. et al. Computational MRI with physics-based constraints: application to multicontrast and quantitative imaging. IEEE Signal Process. Mag. 37, 94â104 (2020).
Assländer, J. A perspective on MR fingerprinting. J. Magn. Reson. Imaging 53, 676â685 (2021).
Novikov, D. S., Kiselev, V. G. & Jespersen, S. N. On modeling. Magn. Reson. Med. 79, 3172â3193 (2018).
West, D. J. et al. Inherent and unpredictable bias in multi-component DESPOT myelin water fraction estimation. Neuroimage 195, 78â88 (2019).
Fiedler, T. M., Ladd, M. E. & Bitz, A. K. SAR simulations & safety. Neuroimage 168, 33â58 (2018).
Davids, M., Guérin, B., Vom Endt, A., Schad, L. R. & Wald, L. L. Prediction of peripheral nerve stimulation thresholds of MRI gradient coils using coupled electromagnetic and neurodynamic simulations. Magn. Reson. Med. 81, 686â701 (2019).
Pohmann, R., Speck, O. & Scheffler, K. Signal-to-noise ratio and MR tissue parameters in human brain imaging at 3, 7, and 9.4 tesla using current receive coil arrays. Magn. Reson. Med. 75, 801â809 (2016).
Budinger, T. F. & Bird, M. D. MRI and MRS of the human brain at magnetic fields of 14 T to 20 T: Technical feasibility, safety, and neuroscience horizons. Neuroimage 168, 509â531 (2018).
Sadeghi-Tarakameh, A. et al. In vivo human head MRI at 10.5 T: a radiofrequency safety study and preliminary imaging results. Magn. Reson. Med. 84, 484â496 (2020).
Schmitt, M. et al. A 128-channel receive-only cardiac coil for highly accelerated cardiac MRI at 3 Tesla. Magn. Reson. Med. 59, 1431â1439 (2008).
Wiggins, G. C. et al. 96-Channel receive-only head coil for 3 Tesla: design optimization and evaluation. Magn. Reson. Med. 62, 754â762 (2009).
Pruessmann, K. P., Weiger, M., Scheidegger, M. B. & Boesiger, P. SENSE: sensitivity encoding for fast MRI. Magn. Reson. Med. 42, 952â962 (1999).
Griswold, M. A. et al. Generalized autocalibrating partially parallel acquisitions (GRAPPA). Magn. Reson. Med. 47, 1202â1210 (2002).
Setsompop, K. et al. Blipped-controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g-factor penalty. Magn. Reson. Med. 67, 1210â1224 (2012).
Padormo, F., Beqiri, A., Hajnal, J. V. & Malik, S. J. Parallel transmission for ultrahigh-field imaging. NMR Biomed. 29, 1145â1161 (2016).
Lutti, A. et al. Robust and fast whole brain mapping of the RF transmit field B1 at 7T. PLoS ONE 7, e32379 (2012).
Pohmann, R. & Scheffler, K. A theoretical and experimental comparison of different techniques for B1 mapping at very high fields. NMR Biomed. 26, 265â275 (2013).
Turner, R. Gradient coil design: a review of methods. Magn. Reson. Imaging 11, 903â920 (1993).
Littin, S. et al. Development and implementation of an 84-channel matrix gradient coil. Magn. Reson. Med. 79, 1181â1191 (2018).
Veraart, J. et al. Noninvasive quantification of axon radii using diffusion MRI. eLife 9, e49855 (2020). Addresses accuracy issues of MRI-based effective axon diameter measurements.
Veraart, J., Raven, E. P., Edwards, L. J., Weiskopf, N. & Jones, D. K. The variability of MR axon radii estimates in the human white matter. Hum. Brain Mapp. 42, 2201â2213 (2021).
Kirilina, E. et al. Superficial white matter imaging: Contrast mechanisms and whole-brain in vivo mapping. Sci. Adv. 6, eaaz9281 (2020). Derives a biophysical model of iron-driven contrast in superficial white matter from first principles.
Triantafyllou, C. et al. Comparison of physiological noise at 1.5 T, 3 T and 7 T and optimization of fMRI acquisition parameters. Neuroimage 26, 243â250 (2005).
Federau, C. & Gallichan, D. Motion-correction enabled ultra-high resolution in-vivo 7T-MRI of the brain. PLoS One 11, e0154974 (2016).
Zaitsev, M., Dold, C., Sakas, G., Hennig, J. & Speck, O. Magnetic resonance imaging of freely moving objects: prospective real-time motion correction using an external optical motion tracking system. Neuroimage 31, 1038â1050 (2006).
Callaghan, M. F. et al. An evaluation of prospective motion correction (PMC) for high resolution quantitative MRI. Front. Neurosci. 9, 97 (2015).
Atkinson, D., Hill, D. L. G., Stoyle, P. N. R., Summers, P. E. & Keevil, S. F. in Information Processing in Medical Imaging (eds Duncan, J. & Gindi, G.) 341â354 (Springer, 1997).
Mohammadi, S., Hutton, C., Nagy, Z., Josephs, O. & Weiskopf, N. Retrospective correction of physiological noise in DTI using an extended tensor model and peripheral measurements. Magn. Reson. Med. 70, 358â369 (2013).
Callaghan, M. F., Mohammadi, S. & Weiskopf, N. Synthetic quantitative MRI through relaxometry modelling. NMR Biomed. 29, 1729â1738 (2016).
Stockmann, J. P. & Wald, L. L. In vivo B0 field shimming methods for MRI at 7 T. Neuroimage 168, 71â87 (2018).
Versluis, M. J. et al. Origin and reduction of motion and f0 artifacts in high resolution T2*-weighted magnetic resonance imaging: application in Alzheimerâs disease patients. Neuroimage 51, 1082â1088 (2010).
Vannesjo, S. J. et al. Retrospective correction of physiological field fluctuations in high-field brain MRI using concurrent field monitoring. Magn. Reson. Med. 73, 1833â1843 (2015).
Prasloski, T., Mädler, B., Xiang, Q.-S., MacKay, A. & Jones, C. Applications of stimulated echo correction to multicomponent T2 analysis. Magn. Reson. Med. 67, 1803â1814 (2012).
Ben-Eliezer, N., Sodickson, D. K. & Block, K. T. Rapid and accurate T2 mapping from multi-spin-echo data using Bloch-simulation-based reconstruction. Magn. Reson. Med. 73, 809â817 (2015).
Teixeira, A. G., P., R., Malik, S. J. & Hajnal, J. V. Fast quantitative MRI using controlled saturation magnetization transfer. Magn. Reson. Med. 81, 907â920 (2019).
Barker, G. J. et al. A standardised method for measuring magnetisation transfer ratio on MR imagers from different manufacturers â the EuroMT sequence. MAGMA 18, 76â80 (2005).
Stikov, N. et al. On the accuracy of T1 mapping: Searching for common ground. Magn. Reson. Med. 73, 514â522 (2015).
Bloembergen, N., Purcell, E. M. & Pound, R. V. Relaxation effects in nuclear magnetic resonance absorption. Phys. Rev. 73, 679â712 (1948).
Whittall, K. P., MacKay, A. L. & Li, D. K. Are mono-exponential fits to a few echoes sufficient to determine T2 relaxation for in vivo human brain? Magn. Reson. Med. 41, 1255â1257 (1999).
Knight, M. J., Wood, B., Couthard, E. & Kauppinen, R. Anisotropy of spin-echo T2 relaxation by magnetic resonance imaging in the human brain in vivo. Biomed. Spectrosc. Imaging 4, 299â310 (2015).
Pampel, A., Müller, D. K., Anwander, A., Marschner, H. & Möller, H. E. Orientation dependence of magnetization transfer parameters in human white matter. Neuroimage 114, 136â146 (2015).
Wharton, S. & Bowtell, R. Fiber orientation-dependent white matter contrast in gradient echo MRI. Proc. Natl Acad. Sci. USA 109, 18559â18564 (2012). Explains the orientation dependence of gradient echo signal based on a hollow cylinder multi-compartment model of myelinated axons and myelin susceptibility tensor.
Pakkenberg, B. et al. Aging and the human neocortex. Exp. Gerontol. 38, 95â99 (2003).
Nieuwenhuys, R., Voogd, J. & van Huijzen, C. The Human Central Nervous System: A Synopsis and Atlas (Springer, 2007).
Kasthuri, N. et al. Saturated reconstruction of a volume of neocortex. Cell 162, 648â661 (2015).
Motta, A. et al. Dense connectomic reconstruction in layer 4 of the somatosensory cortex. Science 366, eaay3134 (2019).
Lazari, A. & Lipp, I. Can MRI measure myelin? Systematic review, qualitative assessment, and meta-analysis of studies validating microstructural imaging with myelin histology. Neuroimage 230, 117744 (2021).
Mancini, M. et al. An interactive meta-analysis of MRI biomarkers of myelin. eLife 9, e61523 (2020).
Kiselev, V. G. & Novikov, D. S. Transverse NMR relaxation in biological tissues. Neuroimage 182, 149â168 (2018).
Halle, B. & Denisov, V. P. A new view of water dynamics in immobilized proteins. Biophys. J. 69, 242â249 (1995).
Fullerton, G. D., Potter, J. L. & Dornbluth, N. C. NMR relaxation of protons in tissues and other macromolecular water solutions. Magn. Reson. Imaging 1, 209â226 (1982).
Chávez, F. V. & Halle, B. Molecular basis of water proton relaxation in gels and tissue. Magn. Reson. Med. 56, 73â81 (2006).
Barta, R. et al. Modeling T1 and T2 relaxation in bovine white matter. J. Magn. Reson. 259, 56â67 (2015).
Labadie, C. et al. Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields. Magn. Reson. Med. 71, 375â387 (2014).
Pine, K. J., Davies, G. R. & Lurie, D. J. Field-cycling NMR relaxometry with spatial selection. Magn. Reson. Med. 63, 1698â1702 (2010).
Weiger, M. et al. Advances in MRI of the myelin bilayer. Neuroimage 217, 116888 (2020).
Stanisz, G. J., Kecojevic, A., Bronskill, M. J. & Henkelman, R. M. Characterizing white matter with magnetization transfer and T2. Magn. Reson. Med. 42, 1128â1136 (1999). Introduces the four-compartment model for T2 and MT featuring exchange of the visible water pools.
West, K. L. et al. Myelin volume fraction imaging with MRI. Neuroimage 182, 511â521 (2018). Relates MRI-based myelin measures to the myelin volume fraction determined by gold standard electron microscopy in hypomyelinated and hypermyelinated mouse models.
Schmierer, K. et al. Quantitative magnetization transfer imaging in postmortem multiple sclerosis brain. J. Magn. Reson. Imaging 26, 41â51 (2007).
Laule, C. & Moore, G. R. W. Myelin water imaging to detect demyelination and remyelination and its validation in pathology. Brain Pathol. 28, 750â764 (2018).
Varma, G. et al. Interpretation of magnetization transfer from inhomogeneously broadened lines (ihMT) in tissues as a dipolar order effect within motion restricted molecules. J. Magn. Reson. 260, 67â76 (2015).
Manning, A. P., Chang, K. L., MacKay, A. L. & Michal, C. A. The physical mechanism of âinhomogeneousâ magnetization transfer MRI. J. Magn. Reson. 274, 125â136 (2017).
Duhamel, G. et al. Validating the sensitivity of inhomogeneous magnetization transfer (ihMT) MRI to myelin with fluorescence microscopy. Neuroimage 199, 289â303 (2019).
Mezer, A. et al. Quantifying the local tissue volume and composition in individual brains with magnetic resonance imaging. Nat. Med. 19, 1667â1672 (2013).
Zimmerman, J. R. & Brittin, W. E. Nuclear magnetic resonance studies in multiple phase systems: lifetime of a water molecule in an adsorbing phase on silica gel. J. Phys. Chem. 61, 1328â1333 (1957).
Schmierer, K., Scaravilli, F., Altmann, D. R., Barker, G. J. & Miller, D. H. Magnetization transfer ratio and myelin in postmortem multiple sclerosis brain. Ann. Neurol. 56, 407â415 (2004).
Menon, R. S., Rusinko, M. S. & Allen, P. S. Proton relaxation studies of water compartmentalization in a model neurological system. Magn. Reson. Med. 28, 264â274 (1992).
Dick, F. et al. In vivo functional and myeloarchitectonic mapping of human primary auditory areas. J. Neurosci. 32, 16095â16105 (2012).
Dinse, J. et al. A cytoarchitecture-driven myelin model reveals area-specific signatures in human primary and secondary areas using ultra-high resolution in-vivo brain MRI. Neuroimage 114, 71â87 (2015).
Helms, G. & Hagberg, G. E. In vivo quantification of the bound pool T1 in human white matter using the binary spin-bath model of progressive magnetization transfer saturation. Phys. Med. Biol. 54, N529âN540 (2009).
Koenig, S. H., Brown, R. D. 3rd, Spiller, M. & Lundbom, N. Relaxometry of brain: why white matter appears bright in MRI. Magn. Reson. Med. 14, 482â495 (1990).
Schyboll, F., Jaekel, U., Petruccione, F. & Neeb, H. Origin of orientation-dependent R1 (=1/T1) relaxation in white matter. Magn. Reson. Med. 84, 2713â2723 (2020).
Fukunaga, M. et al. Layer-specific variation of iron content in cerebral cortex as a source of MRI contrast. Proc. Natl Acad. Sci. USA 107, 3834â3839 (2010).
Brammerloh, M. et al. Measuring the iron content of dopaminergic neurons in substantia nigra with MRI relaxometry. Preprint at bioRxiv https://doi.org/10.1101/2020.07.01.170563 (2020).
Wen, J., Goyal, M. S., Astafiev, S. V., Raichle, M. E. & Yablonskiy, D. A. Genetically defined cellular correlates of the baseline brain MRI signal. Proc. Natl Acad. Sci. USA 115, E9727âE9736 (2018).
Yablonskiy, D. A. & Haacke, E. M. Theory of NMR signal behavior in magnetically inhomogeneous tissues: the static dephasing regime. Magn. Reson. Med. 32, 749â763 (1994).
Luo, J., Jagadeesan, B. D., Cross, A. H. & Yablonskiy, D. A. Gradient echo plural contrast imaging â signal model and derived contrasts: T2*, T1, phase, SWI, T1f, FST2*and T2*-SWI. Neuroimage 60, 1073â1082 (2012).
Bender, B. & Klose, U. The in vivo influence of white matter fiber orientation towards B0 on T2* in the human brain. NMR Biomed. 23, 1071â1076 (2010).
Rudko, D. A. & Klassen, L. M. Origins of R2* orientation dependence in gray and white matter. Proc. Natl Acad. Sci. USA 111, E159âE167 (2014).
Marques, J. P. & Bowtell, R. Application of a Fourier-based method for rapid calculation of field inhomogeneity due to spatial variation of magnetic susceptibility. Concepts Magn. Reson. B 25, 65â78 (2005).
Deistung, A., Schweser, F. & Reichenbach, J. R. Overview of quantitative susceptibility mapping. NMR Biomed. 30, e3569 (2017).
Song, S.-K. et al. Dysmyelination revealed through MRI as increased radial (but unchanged axial) diffusion of water. Neuroimage 17, 1429â1436 (2002).
Wheeler-Kingshott, C. A. M. & Cercignani, M. About âaxialâ and âradialâ diffusivities. Magn. Reson. Med. 61, 1255â1260 (2009).
Le Bihan, D. Looking into the functional architecture of the brain with diffusion MRI. Nat. Rev. Neurosci. 4, 469â480 (2003).
Jeurissen, B., Descoteaux, M., Mori, S. & Leemans, A. Diffusion MRI fiber tractography of the brain. NMR Biomed. 32, e3785 (2019).
Lynn, C. W. & Bassett, D. S. The physics of brain network structure, function and control. Nat. Rev. Phys. 1, 318â332 (2019).
Niendorf, T., Norris, D. G. & Leibfritz, D. Detection of apparent restricted diffusion in healthy rat brain at short diffusion times. Magn. Reson. Med. 32, 672â677 (1994).
Stanisz, G. J., Szafer, A., Wright, G. A. & Henkelman, R. M. An analytical model of restricted diffusion in bovine optic nerve. Magn. Reson. Med. 37, 103â111 (1997).
Lee, J.-H. & Springer, C. S. Jr. Effects of equilibrium exchange on diffusion-weighted NMR signals: the diffusigraphic âshutter-speedâ. Magn. Reson. Med. 49, 450â458 (2003).
Georgi, J., Metere, R., Jäger, C., Morawski, M. & Möller, H. E. Influence of the extracellular matrix on water mobility in subcortical gray matter. Magn. Reson. Med. 81, 1265â1279 (2019).
Niendorf, T., Dijkhuizen, R. M., Norris, D. G., van Lookeren Campagne, M. & Nicolay, K. Biexponential diffusion attenuation in various states of brain tissue: implications for diffusion-weighted imaging. Magn. Reson. Med. 36, 847â857 (1996).
Dhital, B., Labadie, C., Stallmach, F., Möller, H. E. & Turner, R. Temperature dependence of water diffusion pools in brain white matter. Neuroimage 127, 135â143 (2016).
Güllmar, D., Haueisen, J. & Reichenbach, J. R. Analysis of b-value calculations in diffusion weighted and diffusion tensor imaging. Concepts Magn. Reson. A 25A, 53â66 (2005).
Kiselev, V. G. Microstructure with diffusion MRI: what scale we are sensitive to? J. Neurosci. Methods 347, 108910 (2020).
Einstein, A. Ãber die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen. Ann. Phys. 322, 549â560 (1905).
Kiselev, V. G. & Ilâyasov, K. A. Is the âbiexponential diffusionâ biexponential? Magn. Reson. Med. 57, 464â469 (2007).
Callaghan, P. T., Coy, A., MacGowan, D., Packer, K. J. & Zelaya, F. O. Diffraction-like effects in NMR diffusion studies of fluids in porous solids. Nature 351, 467â469 (1991).
Panagiotaki, E. et al. Compartment models of the diffusion MR signal in brain white matter: a taxonomy and comparison. Neuroimage 59, 2241â2254 (2012).
Lampinen, B. et al. Searching for the neurite density with diffusion MRI: challenges for biophysical modeling. Hum. Brain Mapp. 40, 2529â2545 (2019).
Alexander, D. C. et al. Orientationally invariant indices of axon diameter and density from diffusion MRI. Neuroimage 52, 1374â1389 (2010).
Horowitz, A. et al. In vivo correlation between axon diameter and conduction velocity in the human brain. Brain Struct. Funct. 220, 1777â1788 (2015).
Innocenti, G. M., Caminiti, R. & Aboitiz, F. Comments on the paper by Horowitz et al. (2014). Brain Struct. Funct. 220, 1789â1790 (2015).
Horowitz, A., Barazany, D., Tavor, I., Yovel, G. & Assaf, Y. Response to the comments on the paper by Horowitz et al. (2014). Brain Struct. Funct. 220, 1791â1792 (2015).
Waxman, S. G. Determinants of conduction velocity in myelinated nerve fibers. Muscle Nerve 3, 141â150 (1980).
Jelescu, I. O. et al. One diffusion acquisition and different white matter models: how does microstructure change in human early development based on WMTI and NODDI? Neuroimage 107, 242â256 (2015).
Kiselev, V. G. & Posse, S. Analytical model of susceptibility-induced MR signal dephasing: effect of diffusion in a microvascular network. Magn. Reson. Med. 41, 499â509 (1999).
Chan, K.-S. & Marques, J. P. Multi-compartment relaxometry and diffusion informed myelin water imaging â promises and challenges of new gradient echo myelin water imaging methods. Neuroimage 221, 117159 (2020).
Veraart, J., Novikov, D. S. & Fieremans, E. TE dependent Diffusion Imaging (TEdDI) distinguishes between compartmental T2 relaxation times. Neuroimage 182, 360â369 (2018).
Gong, T. et al. MTE-NODDI: multi-TE NODDI for disentangling non-T2-weighted signal fractions from compartment-specific T2 relaxation times. Neuroimage 217, 116906 (2020).
Mohammadi, S. et al. Whole-brain in-vivo measurements of the axonal g-ratio in a group of 37 healthy volunteers. Front. Neurosci. 9, 441 (2015).
Stikov, N. et al. In vivo histology of the myelin g-ratio with magnetic resonance imaging. Neuroimage 118, 397â405 (2015).
Ellerbrock, I. & Mohammadi, S. Four in vivo g-ratio-weighted imaging methods: comparability and repeatability at the group level. Hum. Brain Mapp. 39, 24â41 (2018).
Berman, S., West, K. L., Does, M. D., Yeatman, J. D. & Mezer, A. A. Evaluating g-ratio weighted changes in the corpus callosum as a function of age and sex. Neuroimage 182, 304â313 (2018).
Stikov, N. et al. Bound pool fractions complement diffusion measures to describe white matter micro and macrostructure. Neuroimage 54, 1112â1121 (2011). Introduces a biophysical model for in vivo measurement of the MRI-based g-ratio by combining myelin and diffusion MRI.
Callaghan, M. F., Helms, G., Lutti, A., Mohammadi, S. & Weiskopf, N. A general linear relaxometry model of R1 using imaging data. Magn. Reson. Med. 73, 1309â1314 (2015).
Mangeat, G., Govindarajan, S. T., Mainero, C. & Cohen-Adad, J. Multivariate combination of magnetization transfer, T2* and B0 orientation to study the myelo-architecture of the in vivo human cortex. Neuroimage 119, 89â102 (2015).
Draganski, B. et al. Regional specificity of MRI contrast parameter changes in normal ageing revealed by voxel-based quantification (VBQ). Neuroimage 55, 1423â1434 (2011).
DeWeerdt, S. How to map the brain. Nature 571, S6âS8 (2019).
Lee, H.-H. et al. Along-axon diameter variation and axonal orientation dispersion revealed with 3D electron microscopy: implications for quantifying brain white matter microstructure with histology and diffusion MRI. Brain Struct. Funct. 224, 1469â1488 (2019).
Kleinnijenhuis, M., Johnson, E., Mollink, J., Jbabdi, S. & Miller, K. L. A semi-automated approach to dense segmentation of 3D white matter electron microscopy. Preprint at bioRxiv https://doi.org/10.1101/2020.03.19.979393 (2020).
Lee, H.-H., Jespersen, S. N., Fieremans, E. & Novikov, D. S. The impact of realistic axonal shape on axon diameter estimation using diffusion MRI. Neuroimage 223, 117228 (2020).
Andersson, M. et al. Axon morphology is modulated by the local environment and impacts the noninvasive investigation of its structure-function relationship. Proc. Natl Acad. Sci. USA 117, 33649â33659 (2020).
Chung, K. et al. Structural and molecular interrogation of intact biological systems. Nature 497, 332â337 (2013).
Morawski, M. et al. Developing 3D microscopy with CLARITY on human brain tissue: towards a tool for informing and validating MRI-based histology. Neuroimage 182, 417â428 (2018).
Amunts, K., Mohlberg, H., Bludau, S. & Zilles, K. Julich-Brain: A 3D probabilistic atlas of the human brainâs cytoarchitecture. Science 369, 988â992 (2020).
Bulk, M. et al. Quantitative comparison of different iron forms in the temporal cortex of Alzheimer patients and control subjects. Sci. Rep. 8, 6898 (2018).
Davis, H. C. et al. Mapping the microscale origins of magnetic resonance image contrast with subcellular diamond magnetometry. Nat. Commun. 9, 131 (2018).
Leuze, C. et al. The separate effects of lipids and proteins on brain MRI contrast revealed through tissue clearing. Neuroimage 156, 412â422 (2017).
Kampmann, M. CRISPR-based functional genomics for neurological disease. Nat. Rev. Neurol. 16, 465â480 (2020).
Massner, C. et al. Genetically controlled lysosomal entrapment of superparamagnetic ferritin for multimodal and multiscale imaging and actuation with low tissue attenuation. Adv. Funct. Mater. 28, 1706793 (2018).
Cakir, B. et al. Engineering of human brain organoids with a functional vascular-like system. Nat. Methods 16, 1169â1175 (2019).
Schmierer, K. et al. Quantitative magnetic resonance of postmortem multiple sclerosis brain before and after fixation. Magn. Reson. Med. 59, 268â277 (2008).
Helbling, S. et al. Structure predicts function: combining non-invasive electrophysiology with in-vivo histology. Neuroimage 108, 377â385 (2015).
Novikov, D. S., Jensen, J. H., Helpern, J. A. & Fieremans, E. Revealing mesoscopic structural universality with diffusion. Proc. Natl Acad. Sci. USA 111, 5088â5093 (2014). Introduces universality classes of structural correlations and describes how they affect the MRI diffusion measurements.
Levitt, M. & Warshel, A. Computer simulation of protein folding. Nature 253, 694â698 (1975).
Noid, W. G. Perspective: Coarse-grained models for biomolecular systems. J. Chem. Phys. 139, 090901 (2013).
De Fauw, J. et al. Clinically applicable deep learning for diagnosis and referral in retinal disease. Nat. Med. 24, 1342â1350 (2018).
LeCun, Y., Bengio, Y. & Hinton, G. Deep learning. Nature 521, 436â444 (2015).
Silver, D. et al. Mastering the game of Go with deep neural networks and tree search. Nature 529, 484â489 (2016).
Alexander, D. C. et al. Image quality transfer and applications in diffusion MRI. Neuroimage 152, 283â298 (2017).
Wilm, B. J. et al. Diffusion MRI with concurrent magnetic field monitoring. Magn. Reson. Med. 74, 925â933 (2015).
Amunts, K. et al. BigBrain: an ultrahigh-resolution 3D human brain model. Science 340, 1472â1475 (2013).
Xu, Q. et al. CHIMGEN: a Chinese imaging genetics cohort to enhance cross-ethnic and cross-geographic brain research. Mol. Psychiatry 25, 517â529 (2020).
Meyer, A. Paul Flechsigâs system of myelogenetic cortical localization in the light of recent research in neuroanatomy and neurophysiology part II. Can. J. Neurol. Sci. 8, 95â104 (1981).
MacKay, A. L. & Laule, C. Magnetic resonance of myelin water: an in vivo marker for myelin. Brain Plast. 2, 71â91 (2016).
Panda, A. et al. Magnetic resonance fingerprinting â an overview. Curr. Opin. Biomed. Eng. 3, 56â66 (2017).
Papazoglou, S. et al. Biophysically motivated efficient estimation of the spatially isotropic component from a single gradient-recalled echo measurement. Magn. Reson. Med. 82, 1804â1811 (2019).
Gil, R. et al. An in vivo study of the orientation-dependent and independent components of transverse relaxation rates in white matter. NMR Biomed. 29, 1780â1790 (2016).
Wharton, S. & Bowtell, R. Gradient echo based fiber orientation mapping using R2* and frequency difference measurements. Neuroimage 83, 1011â1023 (2013).
Rabi, I. I., Ramsey, N. F. & Schwinger, J. Use of rotating coordinates in magnetic resonance problems. Rev. Mod. Phys. 26, 167â171 (1954).
Solomon, I. Relaxation processes in a system of two spins. Phys. Rev. 99, 559â565 (1955).
Wolff, S. D. & Balaban, R. S. Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo. Magn. Reson. Med. 10, 135â144 (1989).
Abragam, A. The Principles of Nuclear Magnetism (Clarendon Press, 1961).
Sled, J. G. & Pike, G. B. Quantitative imaging of magnetization transfer exchange and relaxation properties in vivo using MRI. Magn. Reson. Med. 46, 923â931 (2001).
Deoni, S. C. L., Rutt, B. K., Arun, T., Pierpaoli, C. & Jones, D. K. Gleaning multicomponent T1 and T2 information from steady-state imaging data. Magn. Reson. Med. 60, 1372â1387 (2008).
Stejskal, E. O. & Tanner, J. E. Spin diffusion measurements: spin echoes in the presence of a time-dependent field gradient. J. Chem. Phys. 42, 288â292 (1965).
Acknowledgements
The authors thank H. Möller (MPI-CBS, Leipzig), J. Schmidt (MPI-CBS, Leipzig) and R. Valiullin (Leipzig University) for their very helpful comments on earlier versions of the manuscript. They thank T. Reinert (MPI-CBS, Leipzig) and M. Morozova (MPI-CBS, Leipzig) for providing data for illustrations, including electron microscopy and PIXE. They also thank J. Grant (MPI-CBS, Leipzig) for proofreading an earlier version of the manuscript. N.W. received funding from the European Research Council under the European Unionâs Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 616905. N.W. also received funding from the European Unionâs Horizon 2020 research and innovation programme under the grant agreement no. 681094 and the Federal Ministry of Education and Research (BMBF; 01EW1711A and B) in the framework of ERA-NET NEURON. G.H. was funded by the Swedish Research Council (NT 2014-6193). S.M. was supported by the ERA-NET NEURON (hMRIofSCI), the BMBF (01EW1711A and B) and the German Research Foundation (DFG Priority Program 2041 âComputational Connectomicsâ (AL 1156/2-1; GE 2967/1-1; MO 2397/5-1; MO 2249/3-1), DFG Emmy Noether Stipend: MO 2397/4-1).
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The Max Planck Institute for Human Cognitive and Brain Sciences has an institutional research agreement with Siemens Healthcare. N.W. holds a patent on MRI data acquisition during spoiler gradients (United States Patent 10,401,453). N.W. was a speaker at an event organized by Siemens Healthcare and was reimbursed for the travel expenses.
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BRAIN Initiative: https://braininitiative.nih.gov/
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Glossary
- MRI pulse sequence
-
Sequence of radio frequency pulses, spatially varying magnetic field gradients and data acquisition periods executed on the MRI scanner for creating, manipulating and measuring the MRI signal.
- Longitudinal relaxation time
-
The characteristic time T1 for the return of the net magnetization of the spin ensemble to its thermal equilibrium value parallel to the external magnetic field (Box 1).
- Transverse relaxation time
-
The characteristic time T2 describing the irreversible loss of the magnetization transverse to the static magnetic field (Box 1).
- Effective transverse relaxation time
-
The characteristic time T2* describing the decay of the magnetization transverse to the static magnetic field due to reversible and irreversible processes (Box 1).
- Proton density
-
Proton density reflects the content of magnetic-resonance-visible free water in the tissue, which is often expressed as a percentage of the proton concentration in water.
- Iron
-
Iron is accumulated in the brain to cover demands for oxygen transport, myelination and neurotransmitter synthesis. Iron overload in ageing leads to cellular damage and neurodegeneration.
- Inverse problem
-
In physics, this refers to inferring unknown physical properties of a system from measurements.
- Forward model
-
A forward model predicts measurements from physical properties of a system.
- Ill-posed problem
-
A problem is regarded as ill-posed (in contrast to well-posed problems) when a solution either does not exist, is not unique (often the case in qMRI/hMRI) or is unstable in the presence of small perturbations (such as noise).
- Signal-to-noise ratio
-
A measure comparing the level of signal of interest to the level of noise. Noise may include thermal and instrumental noise, as well as physiological processes of no interest.
- Specific absorption rate
-
(SAR). Measure of radio frequency power deposition leading to tissue heating, typically given in Watts per kilogram of tissue.
- Peripheral nerve stimulation
-
(PNS). Stimulation of peripheral nerve fibres due to the electric field induced by the fast switching of magnetic field gradients.
- RF coil arrays
-
Coils for receiving and transmitting radio frequency fields used to manipulate the spin system and read out its magnetization state.
- Gradient systems
-
Systems consisting of a power amplifier and a set of three gradient coils providing switchable magnetic field gradients for spatial and diffusion encoding along the three spatial axes.
- Axon
-
Long projection of a neuronal cell body that transmits neuronal signals over long distances.
- Navigators
-
Short, low-resolution, self-contained acquisitions inserted into a pulse sequence to measure and correct for phase instabilities or motion.
- Shimming
-
Shimming increases the magnetic field (B0) spatial homogeneity in the imaged body part or object. This is achieved using additional resistive coils that can generate various field distributions (linear and higher order) to compensate for inhomogeneities.
- Voxel
-
The smallest 3D volume element in an imaging volume (typically represented as a cuboid in a 3D grid) as a logical extension of a 2D pixel (picture element).
- Glial cells
-
Non-neuronal cells in the nervous system that support and protect neurons, maintain homeostasis and form myelin.
- Myelin
-
A lipid-rich insulating substance surrounding axons that increases nerve conduction velocity.
- BloembergenâPurcellâPound theory
-
Explains that the main determinant of longitudinal and transverse relaxation rates in liquids is molecular motion stochastically modulating intramolecular and intermolecular dipolar interactions.
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Weiskopf, N., Edwards, L.J., Helms, G. et al. Quantitative magnetic resonance imaging of brain anatomy and in vivo histology. Nat Rev Phys 3, 570â588 (2021). https://doi.org/10.1038/s42254-021-00326-1
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DOI: https://doi.org/10.1038/s42254-021-00326-1