Physics:History of magnetic resonance imaging

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The history of magnetic resonance imaging (MRI) includes the work of many researchers who contributed to the discovery of nuclear magnetic resonance (NMR) and described the underlying physics of magnetic resonance imaging, starting early in the twentieth century. One researcher was American physicist Isidor Isaac Rabi who won the Nobel Prize in Physics in 1944 for his discovery of nuclear magnetic resonance, which is used in magnetic resonance imaging. MR imaging was invented by Paul C. Lauterbur who developed a mechanism to encode spatial information into an NMR signal using magnetic field gradients in September 1971; he published the theory behind it in March 1973.[1][2]

The factors leading to image contrast (differences in tissue relaxation time values) had been described nearly 20 years earlier by physician and scientist Erik Odeblad and Gunnar Lindström.[3][4] Among many other researchers in the late 1970s and 1980s, Peter Mansfield further refined the techniques used in MR image acquisition and processing, and in 2003 he and Lauterbur were awarded the Nobel Prize in Physiology or Medicine for their contributions to the development of MRI. The first clinical MRI scanners were installed in the early 1980s and significant development of the technology followed in the decades since, leading to its widespread use in medicine today.

Nuclear magnetic resonance

Isidor Isaac Rabi won the Nobel Prize in Physics in 1944 for his discovery of nuclear magnetic resonance, which is used in magnetic resonance imaging. In 1950, spin echoes and free induction decay were first detected by Erwin Hahn[5][6] and in 1952, Herman Carr produced a one-dimensional NMR spectrum as reported in his Harvard PhD thesis.[7][8][9]

The next step (from spectra to imaging) was proposed by Vladislav Ivanov in Soviet Union, who filed in 1960 a patent application for a Magnetic Resonance Imaging device.[10][11][12] Ivanov's main contribution was the idea of using magnetic field gradient, combined with a selective frequency excitation/readout, to encode the spatial coordinates. In modern terms, it was only proton-density (not relaxation times) imaging, which was also slow, since only one gradient direction was used at a time and the imaging had to be done slice-by-slice. Nevertheless, it was a true magnetic resonance imaging procedure. Originally rejected as "improbable", Ivanov's application was finally approved in 1984 (with the original priority date).[13]

Relaxation times and early development of MRI

By 1959, Jay Singer had studied blood flow by NMR relaxation time measurements of blood in living humans.[14][15] Such measurements were not introduced into common medical practice until the mid-1980s, although a patent for a whole-body NMR machine to measure blood flow in the human body was filed by Alexander Ganssen in early 1967.[15][16][17][18][19]

In the 1960s, the results of work on relaxation, diffusion, and chemical exchange of water in cells and tissues of various types appeared in the scientific literature.[16] In 1967, Ligon reported the measurement of NMR relaxation of water in the arms of living human subjects.[16] In 1968, Jackson and Langham published the first NMR signals from a living animal, an anesthetized rat.[16][20]

In the 1970s, it was realized that the relaxation times are key determinants of contrast in MRI and can be used to detect and differentiate a range of pathologies. A number of research groups had showed that early cancer cells tended to exhibit longer relaxation times than their corresponding normal cells and as such stimulated initial interest in the idea of detecting cancer with NMR. These early groups include Damadian,[21] Hazlewood and Chang[22] and several others. This also initiated a program to catalog the relaxation times of a wide range of biological tissues, which became one of the main motivations for the development of MRI.[23]

Raymond Damadian's "Apparatus and method for detecting cancer in tissue".

In a March 1971 paper in the journal Science,[21] Raymond Damadian, an Armenian-American doctor and professor at the Downstate Medical Center State University of New York (SUNY), reported that tumors and normal tissue can be distinguished in vivo by NMR. Damadian's initial methods were flawed for practical use,[24] relying on a point-by-point scan of the entire body and using relaxation rates, which turned out not to be an effective indicator of cancerous tissue.[25] While researching the analytical properties of magnetic resonance, Damadian created a hypothetical magnetic resonance cancer-detecting machine in 1972. He patented such a machine, U.S. Patent 3,789,832 on February 5, 1974.[26] Lawrence Bennett and Dr. Irwin Weisman also found in 1972 that neoplasms display different relaxation times than corresponding normal tissue.[27][28] Zenuemon Abe and his colleagues applied the patent for a targeted NMR scanner, U.S. Patent 3,932,805 in 1973.[29] They published this technique in 1974.[15][16][30] Damadian claims to have invented the MRI.[31]

The U.S. National Science Foundation notes "The patent included the idea of using NMR to 'scan' the human body to locate cancerous tissue."[32] However, it did not describe a method for generating pictures from such a scan or precisely how such a scan might be done.[33][34]

Imaging

Paul Lauterbur at Stony Brook University expanded on Carr's technique and developed a way to generate the first MRI images, in 2D and 3D, using gradients. In 1973, Lauterbur published the first nuclear magnetic resonance image [1][35] and the first cross-sectional image of a living mouse in January 1974.[36] In the late 1970s, Peter Mansfield, a physicist and professor at the University of Nottingham, England , developed the echo-planar imaging (EPI) technique that would lead to scans taking seconds rather than hours and produce clearer images than Lauterbur had.[37] Damadian, along with Larry Minkoff and Michael Goldsmith, obtained an image of a tumor in the thorax of a mouse in 1976.[38] They also performed the first MRI body scan of a human being on July 3, 1977,[39][40] studies they published in 1977.[38][41] In 1979, Richard S. Likes filed a patent on k-space U.S. Patent 4,307,343.

MRI Scanner Mark One
MRI Scanner Mark One. The first MRI scanner to be built and used, in Aberdeen Royal Infirmary in Scotland.

Full-body scanning

During the 1970s a team led by John Mallard built the first full-body MRI scanner at the University of Aberdeen.[42] On 28 August 1980 they used this machine to obtain the first clinically useful image of a patient's internal tissues using MRI, which identified a primary tumour in the patient's chest, an abnormal liver, and secondary cancer in his bones.[43] This machine was later used at St Bartholomew's Hospital, in London, from 1983 to 1993. Mallard and his team are credited for technological advances that led to the widespread introduction of MRI.[44]

In 1975, the University of California, San Francisco Radiology Department founded the Radiologic Imaging Laboratory (RIL).[45] With the support of Pfizer, Diasonics, and later Toshiba America MRI, the lab developed new imaging technology and installed systems in the United States and worldwide.[46] In 1981 RIL researchers, including Leon Kaufman and Lawrence Crooks, published Nuclear Magnetic Resonance Imaging in Medicine. In the 1980s the book was considered the definitive introductory textbook to the subject.[47]

In 1980 Paul Bottomley joined the GE Research Center in Schenectady, New York. His team ordered the highest field-strength magnet then available, a 1.5 T system, and built the first high-field device, overcoming problems of coil design, RF penetration and signal-to-noise ratio to build the first whole-body MRI/MRS scanner.[48] The results translated into the highly successful 1.5 T MRI product-line, delivering over 20,000 systems. In 1982, Bottomley performed the first localized MRS in the human heart and brain. After starting a collaboration on heart applications with Robert Weiss at Johns Hopkins, Bottomley returned to the university in 1994 as Russell Morgan Professor and director of the MR Research Division.[49]

Additional techniques

In 1986, Charles L. Dumoulin and Howard R. Hart at General Electric developed MR angiography[50] and Denis Le Bihan, obtained the first images and later patented diffusion MRI.[51] In 1988, Arno Villringer and colleagues demonstrated that susceptibility contrast agents may be employed in perfusion MRI.[52] In 1990, Seiji Ogawa at AT&T Bell labs recognized that oxygen-depleted blood with dHb was attracted to a magnetic field, and discovered the technique that underlies Functional Magnetic Resonance Imaging (fMRI).[53]

In the early 1990s, Peter Basser and Le Bihan working at NIH,[54] and Aaron Filler, Franklyn Howe and colleagues published the first DTI and tractographic brain images.[55][56][57] Joseph Hajnal, Young and Graeme Bydder described the use of FLAIR pulse sequence to demonstrate high signal regions in normal white matter in 1992.[58] In the same year, arterial spin labelling was developed by John Detre and Alan P. Koretsky.[59] In 1997, Jürgen R. Reichenbach, E. Mark Haacke and coworkers at Washington University School of Medicine developed Susceptibility weighted imaging.[60]

Advances in semiconductor technology were crucial to the development of practical MRI, which requires a large amount of computational power.[61]

Although MRI is most commonly performed in the clinic at 1.5 T, higher fields such as 3 T for clinical imaging and more recently 7 T for research purposes are gaining popularity because of their increased sensitivity and resolution. In research laboratories, human studies have been performed at 9.4 T (2006)[62] and up to 10.5 T (2019).[63] Non-human animal studies have been performed at up to 21.1 T.[64]

Bedside imaging

In 2020, the United States Food and Drug Administration (USFDA) proffered 510(k)[clarification needed][65] approval of Hyperfine Research's bedside MRI system. The Hyperfine system claims 1/20th the cost, 1/35th the power consumption, and 1/10th the weight of conventional MRI systems.[66] It uses a standard electrical outlet for power.[67]

2003 Nobel Prize

Reflecting the fundamental importance and applicability of MRI in medicine, Paul Lauterbur of Stony Brook University and Sir Peter Mansfield of the University of Nottingham were awarded the 2003 Nobel Prize in Physiology or Medicine for their "discoveries concerning magnetic resonance imaging". The Nobel citation acknowledged Lauterbur's insight of using magnetic field gradients to determine spatial localization, a discovery that allowed the acquisition of 3D and 2D images. Mansfield was credited with introducing the mathematical formalism and developing techniques for efficient gradient utilization and fast imaging. The research that won the Prize was done almost 30 years earlier while Paul Lauterbur was a professor in the Department of Chemistry at Stony Brook University in New York.[1]

References

  1. ↑ 1.0 1.1 1.2 Lauterbur, P.C. (1973). "Image Formation by Induced Local Interactions: Examples of Employing Nuclear Magnetic Resonance". Nature 242 (5394): 190–191. doi:10.1038/242190a0. Bibcode: 1973Natur.242..190L. 
  2. ↑ Rinck, Peter A. (2024). Magnetic Resonance in Medicine. A critical introduction. e-Textbook. (14th ed.). TRTF – The Round Table Foundation: TwinTree Media.  "Magnetic Resonance in Medicine". http://magnetic-resonance.org/. 
  3. ↑ Odeblad, E.; Lindström, G. (1955). "Some preliminary observations on the proton magnetic resonance in biological samples". Acta Radiologica 43 (6): 469–476. doi:10.3109/00016925509172514. PMID 14398444. 
  4. ↑ Odeblad, Erik; Bhar, Baidya Nath; Lindström, Gunnar (July 1956). "Proton magnetic resonance of human red blood cells in heavy water exchange experiments". Archives of Biochemistry and Biophysics 63 (1): 221–225. doi:10.1016/0003-9861(56)90025-X. PMID 13341059. 
  5. ↑ Hahn, E. L. (1950). "Spin echoes". Physical Review 80 (4): 580–594. doi:10.1103/PhysRev.80.580. Bibcode: 1950PhRv...80..580H. 
  6. ↑ Hahn, E. L. (1950). "Nuclear Induction Due to Free Larmor Precession". Physical Review 77 (2): 297–298. doi:10.1103/physrev.77.297.2. Bibcode: 1950PhRv...77..297H. 
  7. ↑ Carr, Herman (1952). Free Precession Techniques in Nuclear Magnetic Resonance (PhD). Cambridge, MA: Harvard University. OCLC 76980558. [page needed]
  8. ↑ Carr, Herman Y. (July 2004). "Field Gradients in Early MRI". Physics Today 57 (7): 83. doi:10.1063/1.1784322. Bibcode: 2004PhT....57g..83C. 
  9. ↑ Carr, Herman (1996). "Free Precession Techniques in Nuclear Magnetic Resonance". in Grant, David M.; Harris, Robin K.. Encyclopedia of Nuclear Magnetic Resonance. 1. Hoboken, NJ: Wiley and Sons. p. 253. ISBN 978-0-47195-839-0. https://books.google.com/books?id=-OBvMgEACAAJ&q=Encyclopedia%20of%20Nuclear%20Magnetic%20Resonance. [yes|permanent dead link|dead link}}]
  10. ↑ MacWilliams, Bryon (November 2003). "Russian claims first in magnetic imaging". Nature 426 (6965): 375. doi:10.1038/426375a. PMID 14647349. Bibcode: 2003Natur.426..375M. 
  11. ↑ Bateneva, Tatiana (27 October 2003). "Привет Нобелю От Иванова: Как советский лейтенант-ракетчик перегнал Америку" (in ru). http://www.inauka.ru/science/article36826. 
  12. ↑ "Патенты автора Иванов Владислав Александрович" (in ru). http://www.findpatent.ru/byauthors/849010/. 
  13. ↑ Bateneva, Tatiana (29 October 2003). "Best Regards To Alfred Nobel". http://www.inauka.ru/english/article36919.html. 
  14. ↑ Singer, R.J. (1959). "Blood-flow rates by NMR measurements". Science 130 (3389): 1652–1653. doi:10.1126/science.130.3389.1652. PMID 17781388. Bibcode: 1959Sci...130.1652S. 
  15. ↑ 15.0 15.1 15.2 "A Short History of Magnetic Resonance Imaging from a European Point of View". http://www.emrf.org/FAQs%20MRI%20History.html. 
  16. ↑ 16.0 16.1 16.2 16.3 16.4 Rinck, P. (2017). "Chapter 20 : The history of MR imaging". Magnetic Resonance in Medicine (11th ed.). http://magnetic-resonance.org/ch/20-03.html. 
  17. ↑ de patent 1566148
  18. ↑ Braun, Bianca (June 24, 2013). "First MAGNETOM scanner in the USA in 1983". http://www.siemens.com/history/en/news/1204_magnetom.htm. 
  19. ↑ Haase, Axel (March 2012). "Nachruf auf Alexander Ganssen" (in de). Physik Journal 11 (3): 59. http://www.pro-physik.de/details/articlePdf/1492009/issue.html. 
  20. ↑ Jackson, J.A.; Langham, W.H. (April 1968). "Whole-body NMR spectrometer". Review of Scientific Instruments 39 (4): 510–513. doi:10.1063/1.1683420. PMID 5641806. Bibcode: 1968RScI...39..510J. https://digital.library.unt.edu/ark:/67531/metadc1032131/. 
  21. ↑ 21.0 21.1 Damadian, R. (March 1971). "Tumor detection by nuclear magnetic resonance". Science 171 (3976): 1151–1153. doi:10.1126/science.171.3976.1151. PMID 5544870. Bibcode: 1971Sci...171.1151D. 
  22. ↑ Hazelwood, C. F.; Chang, D.C.; Medina, D.; Cleveland, G.; Nichols, B. L. (1972). "Distinction between the preneoplastic and neoplastic state of murine mammary glands". Proceedings of the National Academy of Sciences of the United States of America 69 (6): 1478–1480. doi:10.1073/pnas.69.6.1478. ISSN 0027-8424. PMID 4504364. Bibcode: 1972PNAS...69.1478H. 
  23. ↑ Plewes, Donald; Kucharczyk, Walter (2012). "Physics of MRI: A Primer". Journal of Magnetic Resonance Imaging 35 (5): 1038–1054. doi:10.1002/jmri.23642. PMID 22499279. 
  24. ↑ "The man who did not win". The Sydney Morning Herald. 2003-10-17. http://www.smh.com.au/articles/2003/10/16/1065917548433.html. 
  25. ↑ Stracher, Cameron (2002-06-14). "Scan and Deliver". The Wall Street Journal. http://opinionjournal.com/taste/?id=110001844l. 
  26. ↑ "Apparatus And Method For Detecting Cancer In Tissue". http://www.google.com/patents?id=--AZAAAAEBAJ&printsec=abstract#v=onepage&q&f=false. 
  27. ↑ Schooley, Jim (2010). "NBS Examines a Mouse and Opens a New Medical Specialty". https://www.nist.gov/director/nist-culture-excellence-article-9. 
  28. ↑ Weisman, I. D.; Bennett, L. H.; Maxwell, L. R.; Woods, M. W.; Burk, D. (1972-12-22). "Recognition of cancer in vivo by nuclear magnetic resonance". Science 178 (4067): 1288–1290. doi:10.1126/science.178.4067.1288. ISSN 0036-8075. PMID 4640065. Bibcode: 1972Sci...178.1288W. 
  29. ↑ Abe, Zen-uemon; Tanaka, Kunio; Hotta, Masao (1974). "Non-invasive measurements of biological information with application of NMR". Transactions of the Society of Instrument and Control Engineers 10 (3): 290–297. doi:10.9746/sicetr1965.10.290. 
  30. ↑ Tanaka, K.; Yamada, T.; Shimizu, T.; Sano, F.; Abe, Z. (1974). "Fundamental investigations (in vitro) for a non-invasive method of tumor detection by nuclear magnetic resonance". Biotelemetry 1 (6): 337–350. PMID 4478948. 
  31. ↑ "The Inventor of the MRI on Real Science Radio". http://kgov.com/broadcast/stream/4772/lo. 
  32. ↑ "NSF history". http://www.sri.com/policy/csted/reports/techin/mri3.html. 
  33. ↑ Maugh, Thomas H. II; Piller, Charles (2003-10-11). "Scientist Claims Exclusion From Nobel Prize for MRI". Los Angeles Times. https://www.latimes.com/archives/la-xpm-2003-oct-11-sci-flap11-story.html. 
  34. ↑ Saryan, Levon A. (2003-11-08). "Does Dr. Raymond Damadian Deserve the Nobel Prize for Medicine?". The Armenian Reporter. http://www.highbeam.com/doc/1P1-89000528.html. 
  35. ↑ Filler, A. (October 2009). "Magnetic resonance neurography and diffusion tensor imaging: origins, history, and clinical impact of the first 50,000 cases with an assessment of efficacy and utility in a prospective 5000-patient study group". Neurosurgery 65 (4 Suppl): A29–43. doi:10.1227/01.NEU.0000351279.78110.00. PMID 19927075. 
  36. ↑ Lauterbur, P.C. (1974). "Magnetic resonance zeugmatography". Pure and Applied Chemistry 40 (1–2): 149–157. doi:10.1351/pac197440010149. 
  37. ↑ Mansfield, P.; Grannell, P. (1975). "Diffraction and microscopy in solids and liquids by NMR". Physical Review B 12 (9): 3618–3634. doi:10.1103/physrevb.12.3618. Bibcode: 1975PhRvB..12.3618M. 
  38. ↑ 38.0 38.1 Damadian, R.; Minkoff, L.; Goldsmith, M.; Stanford, M.; Koutcher, J. (1976). "Field focusing nuclear magnetic resonance (FONAR): visualization of a tumor in a live animal". Science 194 (4272): 1430–1432. doi:10.1126/science.1006309. PMID 1006309. Bibcode: 1976Sci...194.1430D. 
  39. ↑ "First MRI and ultrasound scanning". http://benbeck.co.uk/firsts/scanning.htm. 
  40. ↑ Wakefield, Julie (June 2000). "The "Indomitable" MRI". http://www.smithsonianmag.com/science-nature/object_jun00.html?c=y&page=2. 
  41. ↑ Hinshaw, W.S.; Bottomley, P.A.; Holland, G.N. (1977). "Radiographic thin-section image of the human wrist by nuclear magnetic resonance". Nature 270 (5639): 722–723. doi:10.1038/270722a0. PMID 593393. Bibcode: 1977Natur.270..722H. 
  42. ↑ "Celebrated scientist donates medal collection". 21 May 2009. http://www.abdn.ac.uk/news/3095/. 
  43. ↑ "John Mallard". http://www.bshr.org.uk/mallard.html. 
  44. ↑ "Mallard MRI body scanner, Aberdeen, Scotland, 1983". http://www.sciencemuseum.org.uk/broughttolife/objects/display.aspx?id=6765. 
  45. ↑ Crooks, Lawrence E.. "Radiologic Imaging Laboratory records, 1977-2000". http://ucsfcat.library.ucsf.edu/record=b1446128~S0. 
  46. ↑ Crooks, Lawrence E.. "Radiologic Imaging Laboratory Records". http://www.oac.cdlib.org/findaid/ark:/13030/kt3199s1qf/admin/#ref732. 
  47. ↑ Froelich, Jerry W. (17 February 1984). "Nuclear Magnetic Resonance (NMR) Imaging". Journal of the American Medical Association 251 (7): 967–968. doi:10.1001/jama.1984.03340310071034. 
  48. ↑ Sijbers, J.; Scheunders, P.; Bonnet, N.; Van Dyck, D.; Raman, E. (1996). "Quantification and improvement of the signal-to-noise ratio in a magnetic resonance image acquisition procedure". Magnetic Resonance Imaging 14 (10): 1157–1163. doi:10.1016/S0730-725X(96)00219-6. PMID 9065906. 
  49. ↑ "Biographical Sketch: Paul A. Bottomley, Ph.D.". 2003. http://icmic.rad.jhmi.edu/icmicpersonnel/BIOBottomleyP.pdf. 
  50. ↑ "Blood-flow checker". Popular Science 230 (4): 12. April 1987. https://books.google.com/books?id=IAEAAAAAMBAJ&pg=PA12. 
  51. ↑ Le Bihan, D.; Breton, E. (1987). "Method to Measure the Molecular Diffusion and/or Perfusion Parameters of Live Tissue". US Patent # 4,809,701. 
  52. ↑ Villringer, A.; Rosen, B. R.; Belliveau, J. W.; Ackerman, J. L.; Lauffer, R. B.; Buxton, R. B.; Chao, Y. S.; Wedeen, V. J. et al. (February 1988). "Dynamic imaging with lanthanide chelates in normal brain: contrast due to magnetic susceptibility effects". Magnetic Resonance in Medicine 6 (2): 164–174. doi:10.1002/mrm.1910060205. ISSN 0740-3194. PMID 3367774. 
  53. ↑ Faro, Scott H.; Mohamed, Feroze B. (2010-01-15). Bold fMRI. a guide to functional imaging for neuroscientists. Springer. ISBN 978-1-4419-1328-9. https://books.google.com/books?id=MkjTO4wx-bkC. Retrieved 10 June 2015. 
  54. ↑ Basser, Peter J. (2010). "Invention and Development of Diffusion Tensor MRI (DT-MRI or DTI) at the NIH". Diffusion MRI. pp. 730–740. doi:10.1093/med/9780195369779.003.0047. ISBN 978-0-19536-977-9. 
  55. ↑ Howe, F. A.; Filler, A. G.; Bell, B. A.; Griffiths, J. R. (December 1992). "Magnetic resonance neurography". Magnetic Resonance in Medicine 28 (2): 328–338. doi:10.1002/mrm.1910280215. ISSN 0740-3194. PMID 1461131. 
  56. ↑ Filler, A. G.; Howe, F. A.; Hayes, C. E.; Kliot, M.; Winn, H. R.; Bell, B. A.; Griffiths, J. R.; Tsuruda, J. S. (1993-03-13). "Magnetic resonance neurography". The Lancet 341 (8846): 659–661. doi:10.1016/0140-6736(93)90422-D. ISSN 0140-6736. PMID 8095572. 
  57. ↑ Filler, Aaron (2009-10-01). "Magnetic Resonance Neurography and Diffusion Tensor Imaging". Neurosurgery 65 (suppl 4): A29–A43. doi:10.1227/01.neu.0000351279.78110.00. ISSN 0148-396X. PMID 19927075. 
  58. ↑ Hajnal, J. V.; De Coene, B.; Lewis, P. D.; Baudouin, C. J.; Cowan, F. M.; Pennock, J. M.; Young, I. R.; Bydder, G. M. (July 1992). "High signal regions in normal white matter shown by heavily T2-weighted CSF nulled IR sequences". Journal of Computer Assisted Tomography 16 (4): 506–513. doi:10.1097/00004728-199207000-00002. ISSN 0363-8715. PMID 1629405. 
  59. ↑ Koretsky, A.P. (August 2012). "Early development of arterial spin labeling to measure regional brain blood flow by MRI". NeuroImage 62 (2): 602–607. doi:10.1016/j.neuroimage.2012.01.005. PMID 22245338. 
  60. ↑ Reichenbach, J.R.; Venkatesan, R.; Schillinger, D.J.; Kido, D.K.; Haacke, E.M. (1997). "Small vessels in the human brain: MR venography with deoxyhemoglobin as an intrinsic contrast agent". Radiology 204 (1): 272–277. doi:10.1148/radiology.204.1.9205259. PMID 9205259. 
  61. ↑ Rosenblum, Bruce; Kuttner, Fred (2011). Quantum Enigma: Physics Encounters Consciousness. Oxford University Press. p. 127. ISBN 978-0-19979-295-5. https://books.google.com/books?id=I9kGFX1_oGAC&pg=PT127. 
  62. ↑ Vaughan, T.; DelaBarre, L.; Snyder, C.; Tian, J.; Akgun, C.; Shrivastava, D.; Liu, W.; Olson, C. et al. (December 2006). "9.4T human MRI: preliminary results". Magn Reson Med 56 (6): 1274–1282. doi:10.1002/mrm.21073. PMID 17075852. 
  63. ↑ Sadeghi‐Tarakameh, Alireza; De la Barre, Lance; Lagore, Russell L.; Torrado‐Carvajal, Angel; Wu, Xiaoping; Grant, Andrea; Adriany, Gregor; Metzger, Gregory J. et al. (2019-11-21). "In vivo human head MRI at 10.5T: A radiofrequency safety study and preliminary imaging results". Magnetic Resonance in Medicine 84 (1): 484–496. doi:10.1002/mrm.28093. ISSN 0740-3194. PMID 31751499. 
  64. ↑ Qian, C.; Masad, I.S.; Rosenberg, J.T.; Elumalai, M.; Brey, W.W.; Grant, S.C.; Gor'kov, P.L. (August 2012). "A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: ex and in vivo applications at 21.1T". J. Magn. Reson. 221: 110–116. doi:10.1016/j.jmr.2012.05.016. PMID 22750638. Bibcode: 2012JMagR.221..110Q. 
  65. ↑ "510(k) Clearances". 2018-04-19. https://www.fda.gov/medical-devices/device-approvals-denials-and-clearances/510k-clearances. 
  66. ↑ Wang, Brian. "First Bedside MRI Provides Images in 2 Minutes Instead of Hours" (in en-US). https://www.nextbigfuture.com/2020/02/first-bedside-mri-provides-images-in-2-minutes-instead-of-hours.html. 
  67. ↑ "US FDA grants 510(k) clearance to Hyperfine Research MRI system" (in en-GB). 2020-02-13. https://www.medicaldevice-network.com/news/fda-hyperfine-research-mri/. 

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