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Der Radiologe

, Volume 53, Issue 5, pp 401–410 | Cite as

Probleme und Chancen der Hochfeldmagnetresonanztomographie

  • M.E. Ladd
  • M. Bock
Leitthema

Zusammenfassung

Klinisches/methodisches Problem

Die räumliche, zeitliche oder spektrale Auflösung der MRT ist heute vielfach nicht ausreichend, um Submillimeterläsionen zu detektieren oder um die Dynamik des Herzschlags darzustellen.

Radiologische Standardverfahren

Zur Zeit sind MR-Tomographen bei 1,5 oder 3 T die Standardgeräte für klinische Untersuchungen.

Methodische Innovationen

Der Einsatz ultrahoher Magnetfelder von 7 T verspricht durch die Erhöhung des Signal-zu-Rausch-Verhältnisses eine deutliche Verbesserung der räumlichen und/oder zeitlichen Auflösung sowie die Generierung neuer Kontraste.

Leistungsfähigkeit

Mit der 7-T-MRT ist es gelungen, MR-Aufnahmen des Hirns routinemäßig mit 0,3 mm Auflösung zu akquirieren. Die theoretisch erwartete Verbesserung des Signal-zu-Rausch-Verhältnisses wird aber auf Grund von B1-Inhomogenitäten und Kontrastvariationen oft nicht erreicht.

Bewertung

Mit Hilfe der 7-T-MRT kann eine deutliche Erhöhung der räumlichen Auflösung erzielt werden. Techniken wie die Time-of-flight(TOF)-MR-Angiographie und suszeptibilitätsgewichtete Methoden (z. B. die neurofunktionelle MRT) profitieren in verstärktem Maße von den hohen Feldern. Sendefeldinhomogenitäten sind immer noch eine große Herausforderung für die Ultrahochfeld(UHF)-MRT und stellen auch ein nur teilweise gelöstes Sicherheitsproblem dar.

Empfehlung für die Praxis

Die UHF-MRT ist z. Z. auf spezielle Anwendungsgebiete beschränkt, und der erwartete Gewinn muss oft gegen technische Komplikationen bei der Datenaufnahme und Bildinterpretation abgewogen werden.

Schlüsselwörter

Ultrahohe Magnetfelder Signal-zu-Rausch-Verhältnis Gewebekontraste Time-of-flight(TOF)-MR-Angiographie Suszeptibilitätsgewichtete Methoden 

Problems and chances of high field magnetic resonance imaging

Abstract

Clinical/methodical issue

The spatial, temporal and spectral resolution in magnetic resonance imaging (MRI) is in many cases currently not sufficient to detect submillimeter lesions or to image the dynamics of the beating heart.

Standard radiological methods

At present MRI systems at 1.5 T and 3 T are the standard units for clinical imaging.

Methodical innovations

The use of ultrahigh magnetic fields of 7 T and higher increases the signal-to-noise ratio, which holds promise for a significant improvement of the spatial and/or temporal resolution as well as for new contrast mechanisms.

Performance

With 7 T MRI, images of the brain have been acquired routinely with a spatial resolution of 0.3 mm. The theoretical improvement of the signal-to-noise ratio is often not fully realized due to B1 inhomogeneities and contrast variations.

Achievements

With MRI at 7 T a notable increase in spatial resolution can be achieved. Methods such as time-of-flight MR angiography and susceptibility-weighted imaging (e.g. neurofunctional MRI, fMRI) profit especially from the higher field strengths. Transmission field inhomogeneities are still a major challenge for ultrahigh field (UHF) MRI and are also a partially unsolved safety problem.

Practical recommendations

The use of UHF MRI is currently limited to special applications and the expected gain of the high field must be weighed against technical limitations in both image acquisition and interpretation.

Keywords

Ultrahigh magnetic fields Signal to noise ratio Tissue contrast Time of flight magnetic resonance angiography Susceptibility-weighted methods 

Notes

Interessenkonflikt

Der korrespondierende Autor gibt für sich und seinen Koautor an, dass kein Interessenkonflikt besteht.

Literatur

  1. 1.
    Fuchs VR, Sox HC Jr (2001) Physicians‘ views of the relative importance of thirty medical innovations. Health Aff (Millwood) 20:30–42Google Scholar
  2. 2.
    International Electrotechnical Commission (IEC) (2010) Medical electrical equipment – Part 2–33: particular requirements for the safety of magnetic resonance equipment for medical diagnosis. Edition 3.0. 60601-2-33Google Scholar
  3. 3.
    Norris DG (2003) High field human imaging. J Magn Reson Imaging 18:519–529PubMedCrossRefGoogle Scholar
  4. 4.
    Ugurbil K, Adriany G, Andersen P et al (2003) Ultrahigh field magnetic resonance imaging and spectroscopy. Magn Reson Imaging 21:1263–1281PubMedCrossRefGoogle Scholar
  5. 5.
    Hoult DI, Phil D (2000) Sensitivity and power deposition in a high-field imaging experiment. J Magn Reson Imaging 12:46–67PubMedCrossRefGoogle Scholar
  6. 6.
    Kowalski ME, Jin JM, Chen J (2000) Computation of the signal-to-noise ratio of high-frequency magnetic resonance imagers. IEEE Trans Biomed Eng 47:1525–1533PubMedCrossRefGoogle Scholar
  7. 7.
    Ocali O, Atalar E (1998) Ultimate intrinsic signal-to-noise ratio in MRI. Magn Reson Med 39:462–473PubMedCrossRefGoogle Scholar
  8. 8.
    Otazo R, Mueller B, Ugurbil K et al (2006) Signal-to-noise ratio and spectral linewidth improvements between 1.5 and 7 Tesla in proton echo-planar spectroscopic imaging. Magn Reson Med 56:1200–1210PubMedCrossRefGoogle Scholar
  9. 9.
    Vaughan JT, Garwood M, Collins CM et al (2001) 7 T vs. 4 T: RF power, homogeneity, and signal-to-noise comparison in head images. Magn Reson Med 46:24–30PubMedCrossRefGoogle Scholar
  10. 10.
    Haacke EM, Brown RW, Thompson MR, Venkatesan R (1999) Magnetic resonance imaging: physical principles and sequence design. Wiley, New YorkGoogle Scholar
  11. 11.
    Aime S, Dastru W, Gobetto R et al (2008) Agents for polarization enhancement in MRI. Handb Exp Pharmacol 247–272Google Scholar
  12. 12.
    Schenck JF (1996) The role of magnetic susceptibility in magnetic resonance imaging: MRI magnetic compatibility of the first and second kinds. Med Phys 23:815–850PubMedCrossRefGoogle Scholar
  13. 13.
    Bloembergen N, Purcell EM, Pound RV (1948) Relaxation effects in nuclear magnetic resonance absorption. Phys Rev 73:679–712CrossRefGoogle Scholar
  14. 14.
    Wright PJ, Mougin OE, Totman JJ et al (2008) Water proton T1 measurements in brain tissue at 7, 3, and 1.5 T using IR-EPI, IR-TSE, and MPRAGE: results and optimization. MAGMA 21:121–130PubMedCrossRefGoogle Scholar
  15. 15.
    Van de Moortele PF, Auerbach EJ, Olman C et al (2009) T1 weighted brain images at 7 Tesla unbiased for proton density, T2* contrast and RF coil receive B1 sensitivity with simultaneous vessel visualization. Neuroimage 46:432–446CrossRefGoogle Scholar
  16. 16.
    Kang CK, Park CW, Han JY et al (2009) Imaging and analysis of lenticulostriate arteries using 7.0-Tesla magnetic resonance angiography. Magn Reson Med 61:136–144PubMedCrossRefGoogle Scholar
  17. 17.
    Golay X, Petersen ET (2006) Arterial spin labeling: benefits and pitfalls of high magnetic field. Neuroimaging Clin North Am 16:259–268, xCrossRefGoogle Scholar
  18. 18.
    Wehrli FW, MacFall JR, Shutts D (1984) Mechanisms of contrast in NMR imaging. J Comput Assist Tomogr 8:369–380PubMedCrossRefGoogle Scholar
  19. 19.
    Yacoub E, Duong TQ, Van De Moortele PF et al (2003) Spin-echo fMRI in humans using high spatial resolutions and high magnetic fields. Magn Reson Med 49:655–664PubMedCrossRefGoogle Scholar
  20. 20.
    Rohrer M, Bauer H, Mintorovitch J et al (2005) Comparison of magnetic properties of MRI contrast media solutions at different magnetic field strengths. Invest Radiol 40:715–724PubMedCrossRefGoogle Scholar
  21. 21.
    Laurent S, Elst LV, Muller RN (2006) Comparative study of the physicochemical properties of six clinical low molecular weight gadolinium contrast agents. Contrast Media Mol Imaging 1:128–137PubMedCrossRefGoogle Scholar
  22. 22.
    Hoult DI, Lauterbur PC (1979) The sensitivity of the zeugmatographic experiment involving human samples. J Magn Reson 34:425–433Google Scholar
  23. 23.
    Robitaille PM, Abduljalil AM, Kangarlu A et al (1998) Human magnetic resonance imaging at 8 T. NMR Biomed 11:263–265PubMedCrossRefGoogle Scholar
  24. 24.
    Weigel M, Hennig J (2006) Contrast behavior and relaxation effects of conventional and hyperecho-turbo spin echo sequences at 1.5 and 3 T. Magn Reson Med 55:826–835PubMedCrossRefGoogle Scholar
  25. 25.
    Weigel M, Zaitsev M, Hennig J (2007) Inversion recovery prepared turbo spin echo sequences with reduced SAR using smooth transitions between pseudo steady states. Magn Reson Med 57:631–637PubMedCrossRefGoogle Scholar
  26. 26.
    Conolly S, Nishimura DG, Macovski A, Glover G (1988) Variable-rate selective excitation. J Magn Reson 78:440–458Google Scholar
  27. 27.
    Gabriel C, Gabriel S, Corhout E (1996) The dielectric properties of biological tissues: I. literature survey. Phys Med Biol 41:2231–2249PubMedCrossRefGoogle Scholar
  28. 28.
    Van de Moortele PF, Akgun C, Adriany G et al (2005) B(1) destructive interferences and spatial phase patterns at 7 T with a head transceiver array coil. Magn Reson Med 54:1503–1518CrossRefGoogle Scholar
  29. 29.
    Homann H, Bornert P, Eggers H et al (2011) Toward individualized SAR models and in vivo validation. Magn Reson Med 66:1767–1776PubMedCrossRefGoogle Scholar
  30. 30.
    Voigt T, Homann H, Katscher U, Doessel O (2012) Patient-individual local SAR determination: in vivo measurements and numerical validation. Magn Reson Med 68:1117–1126PubMedCrossRefGoogle Scholar
  31. 31.
    Scheenen TW, Heerschap A, Klomp DW (2008) Towards 1H-MRSI of the human brain at 7 T with slice-selective adiabatic refocusing pulses. MAGMA 21:95–101PubMedCrossRefGoogle Scholar
  32. 32.
    Yang QX, Mao W, Wang J et al (2006) Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. J Magn Reson Imaging 24:197–202PubMedCrossRefGoogle Scholar
  33. 33.
    Abraham R, Ibrahim TS (2007) Proposed radiofrequency phased-array excitation scheme for homogenous and localized 7-Tesla whole-body imaging based on full-wave numerical simulations. Magn Reson Med 57:235–242PubMedCrossRefGoogle Scholar
  34. 34.
    Mao W, Smith MB, Collins CM (2006) Exploring the limits of RF shimming for high-field MRI of the human head. Magn Reson Med 56:918–922PubMedCrossRefGoogle Scholar
  35. 35.
    Orzada S, Maderwald S, Poser BA et al (2010) RF excitation using time interleaved acquisition of modes (TIAMO) to address B1 inhomogeneity in high-field MRI. Magn Reson Med 64:327–333PubMedGoogle Scholar
  36. 36.
    Raaijmakers AJ, Ipek O, Klomp DW et al (2011) Design of a radiative surface coil array element at 7 T: the single-side adapted dipole antenna. Magn Reson Med 66:1488–1497PubMedCrossRefGoogle Scholar
  37. 37.
    Vaughan JT, Snyder CJ, DelaBarre LJ et al (2009) Whole-body imaging at 7 T: preliminary results. Magn Reson Med 61:244–248PubMedCrossRefGoogle Scholar
  38. 38.
    Bergen B van den, Van den Berg CA, Bartels LW, Lagendijk JJ (2007) 7 T body MRI: B1 shimming with simultaneous SAR reduction. Phys Med Biol 52:5429–5441PubMedCrossRefGoogle Scholar
  39. 39.
    Katscher U, Bornert P (2006) Parallel RF transmission in MRI. NMR Biomed 19:393–400PubMedCrossRefGoogle Scholar
  40. 40.
    Zhu Y (2004) Parallel excitation with an array of transmit coils. Magn Reson Med 51:775–784PubMedCrossRefGoogle Scholar
  41. 41.
    Setsompop K, Wald LL, Alagappan V et al (2006) Parallel RF transmission with eight channels at 3 Tesla. Magn Reson Med 56:1163–1171PubMedCrossRefGoogle Scholar
  42. 42.
    Alt S, Muller M, Umathum R et al (2012) Coaxial waveguide MRI. Magn Reson Med 67:1173–1182PubMedCrossRefGoogle Scholar
  43. 43.
    Brunner DO, De Zanche N, Frohlich J et al (2009) Travelling-wave nuclear magnetic resonance. Nature 457:994–998PubMedCrossRefGoogle Scholar
  44. 44.
    Schenck JF (2005) Physical interactions of static magnetic fields with living tissues. Prog Biophys Mol Biol 87:185–204PubMedCrossRefGoogle Scholar
  45. 45.
    Frauenrath T, Hezel F, Heinrichs U et al (2009) Feasibility of cardiac gating free of interference with electro-magnetic fields at 1.5 Tesla, 3.0 Tesla and 7.0 Tesla using an MR-stethoscope. Invest Radiol 44:539–547PubMedCrossRefGoogle Scholar
  46. 46.
    Henneberg S, Hok B, Wiklund L, Sjodin G (1992) Remote auscultatory patient monitoring during magnetic resonance imaging. J Clin Monit 8:37–43PubMedCrossRefGoogle Scholar
  47. 47.
    Becker M, Frauenrath T, Hezel F et al (2010) Comparison of left ventricular function assessment using phonocardiogram- and electrocardiogram-triggered 2D SSFP CINE MR imaging at 1.5 T and 3.0 T. Eur Radiol 20:1344–1355PubMedCrossRefGoogle Scholar
  48. 48.
    Nassenstein K, Orzada S, Haering L et al (2012) Cardiac MRI: evaluation of phonocardiogram-gated cine imaging for the assessment of global und regional left ventricular function in clinical routine. Eur Radiol 22:559–568PubMedCrossRefGoogle Scholar
  49. 49.
    Glover PM, Cavin I, Qian W et al (2007) Magnetic-field-induced vertigo: a theoretical and experimental investigation. Bioelectromagnetics 28:349–361PubMedCrossRefGoogle Scholar
  50. 50.
    Chakeres DW, Bornstein R, Kangarlu A (2003) Randomized comparison of cognitive function in humans at 0 and 8 Tesla. J Magn Reson Imaging 18:342–345PubMedCrossRefGoogle Scholar
  51. 51.
    Chakeres DW, Kangarlu A, Boudoulas H, Young DC (2003) Effect of static magnetic field exposure of up to 8 Tesla on sequential human vital sign measurements. J Magn Reson Imaging 18:346–352PubMedCrossRefGoogle Scholar
  52. 52.
    Heinrich A, Szostek A, Meyer P et al (2012) Cognition and sensation in very high static magnetic fields: a randomized case-crossover study with different field strengths. Radiology, in pressGoogle Scholar
  53. 53.
    Schlamann M, Voigt MA, Maderwald S et al (2010) Exposure to high-field MRI does not affect cognitive function. J Magn Reson Imaging 31:1061–1066PubMedCrossRefGoogle Scholar
  54. 54.
    Vocht F de, Stevens T, Glover P et al (2007) Cognitive effects of head-movements in stray fields generated by a 7 Tesla whole-body MRI magnet. Bioelectromagnetics 28:247–255PubMedCrossRefGoogle Scholar
  55. 55.
    Nierop LE van, Slottje P, Zandvoort MJ van et al (2012) Effects of magnetic stray fields from a 7 Tesla MRI scanner on neurocognition: a double-blind randomised crossover study. Occup Environ Med 69:759–766PubMedCrossRefGoogle Scholar
  56. 56.
    Heilmaier C, Theysohn JM, Maderwald S et al (2011) A large-scale study on subjective perception of discomfort during 7 and 1.5 T MRI examinations. Bioelectromagnetics 32:610–619PubMedCrossRefGoogle Scholar
  57. 57.
    Nagel AM, Schmitter S, Bock M et al (2009) Parameter optimization for 7 T 23Na-MRI. In: Proc of the international society for magnetic resonance in medicine. ISMRM, Honolulu, p 2465Google Scholar
  58. 58.
    Noebauer-Huhmann IM, Szomolanyi P, Juras V et al (2010) Gadolinium-based magnetic resonance contrast agents at 7 Tesla: in vitro T1 relaxivities in human blood plasma. Invest Radiol 45:554–558PubMedCrossRefGoogle Scholar
  59. 59.
    Hardy CJ, Cline HE (1989) Broadband nuclear magnetic resonance pulses with two-dimensional spatial selectivity. J Appl Phys 66:1513–1516CrossRefGoogle Scholar
  60. 60.
    Pauly JM, Nishimura DG, Macovski A (1989) A k-space analysis of small-tip-angle excitation. J Magn Reson 81:43–56Google Scholar
  61. 61.
    Meyer CH, Pauly JM, Macovski A, Nishimura DG (1990) Simultaneous spatial and spectral selective excitation. Magn Reson Med 15:287-304PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Erwin L. Hahn Institute for Magnetic Resonance Imaging, Institut für Diagnostische und Interventionelle Radiologie und NeuroradiologieUniversität Duisburg-Essen, Universitätsklinikum EssenEssenDeutschland
  2. 2.Abt. Radiologie – Medizin PhysikUniversitätsklinikum Freiburg FreiburgDeutschland

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