Principles of magnetic resonance imaging
A.O. Rodríguez
Centro de Investigación en Imagenología e Instrumentación Médica, Universidad Autónoma Metropolitana Iztapalapa, Av. San Rafael Atlixco 186, México, D. F., 09340. México, Telephone No.: 85 02 45 69, Fax No.: (5255) 5804-4631, E-mail:arog@xanum.uam.mx
Recibido el 25 de agosto de 2003; ]]> Aceptado el 8 de diciembre de 2003.
Abstract
The concepts of magnetic resonance imaging are reviewed and its application to medical and biological systems is described. The magnetic resonance phenomenon can be described by both classical and quantum mechanical approaches. Magnetic resonance imaging is based on the techniques of nuclear magnetic resonance. The scanner first aligns the nuclear spins of hydrogen atoms in the patient and starts rotating them in a perfect concert. The nuclei emit maximum-strength electromagnetic waves at the start, but over time the rotating spins get out of synch, simply due to small differences in local magnetic fields. The unsynchronized spins cause the combined electromagnetic signal to decay with time, a phenomenon called relaxation. A slice is selected applying a gradient in a particular direction (X, Y or Z). Magnetic resonance signals are then formed by means of the application of magnetic field gradients along three different directions. Finally, the signals are acquired and Fourier transformed to form a two-dimensional or three-dimensional image. Important parameters determining the image quality such as signal-to-noise ratio, contrast and resolution are discussed too. A review of the most widely utilised imaging techniques is given including ultra-fast sequences.
Keywords: Magnetic resonance imaging; pulse sequences; ultra-fast imaging.
Resumen
Los conceptos de la imagenología por resonancia magnética son revisados y se describen algunas de sus aplicaciones a sistemas biológicos y médicos. El fenómeno de resonancia magnética puede describirse tanto con un enfoque mecánico cuántico como clásico. El escaner primero alinea los núcleos de los espines de los átomos de hidrógeno que se encuentran dentro del paciente, y luego comienza a rotarlos de acuerdo a un concierto perfecto. Los núcleos emiten ondas electromagnéticas al inicio, pero a medida que transcurre el tiempo los espines pierden la sincronización, debido simplemente a un decaimiento que representa el denominado fenómeno de relajación. Posteriormente se selecciona una rebanada por medio de la aplicación de un gradiente de campo magnético en un dirección particular (X, Y o Z). A las señales de resonancia magnética que se generan se les aplica la transformada de Fourier para formar una imagen bidimensional o tridimensional. También se estudian los parámetros que determinan la calidad de la imagen como el cociente señal a ruido, el contraste y la resolución. Además, se presenta un breve resumen de las secuencias imagenológicas más usadas incluyendo las secuencias ultra rápidas.
Descriptores: Imagenología por resonancia magnética; secuencias de pulsos; imagenología ultra rápida.
]]> PACS: 42.30.Va; 76.60.Lz; 76.60.Pc; 87.57.-s; 87.61.-c; 87.61.Cd; 87.63.-d
DESCARGAR ARTÍCULO EN FORMATO PDF
References
1. F. Bloch, W.W. Hansen, and M.E. Packard, Phys. Rev. 69 (1946) 127. [ Links ]
2. F. Bloch, Phys. Rev. 70 (1946) 460. [ Links ]
3. F. Bloch, W.W. Hansen, and M.E. Packard, Phys. Rev. 70 (1946) 474. [ Links ]
4. E.M. Purcell, H.C. Torrey, and R.V. Pound, Phys. Rev. 69 (1946) 37. [ Links ]
5. N. Bloembergen, E.M. Purcell, and R.V. Pound, Phys. Rev. 73 (1948) 679. [ Links ]
6. P.C. Lauterbur, Nature 242 (1973) 190. [ Links ]
7. P. Mansfield, P.K. Grannell, J. Phys. C 6 (1973) L422. [ Links ]
8. E.L.Hahn, Phys. Rev. 80 (1950) 580. [ Links ]
9. J.B. Weaver, Y. Xu, D.M. Healy, and J.R. Driscoll, Magen. Re-son. Med. 24 (1992) 275. [ Links ]
10. P. Mansfield, PG. Morris, NMR Imaging in Biomedicine, Supplement 2 in Advances in Magnetic Resonance (Waugh, J.S., Editor), Academic Press, New York, 1982. [ Links ]
11 . R. Damadian, M. Goldsmith, L. Minkoff, Physiol. Chem. Phys. 10 (1978)285. [ Links ]
12. W.S. Hinshaw, Phys. Lett. A 48 (1974) 87. [ Links ]
13. A. Kumar, D. Welti, R.R. Ernst, J. Magn. Reson. 18 (1975) 69. [ Links ]
14. W.A. Edelstein, J.M.S. Hutchinson, G. Johnson, and T. Redpath, Phys. Med. Biol. 25 (1980) 751. [ Links ]
15. N.S. Cohen and R.M. Weisskoff, Magn. Reson. Imaging 9 (1991) 1. [ Links ]
16. H. Fischer, F. Schmitt, H. Barfuss, H. Bruder, 7th Ann. Meet. Soc. Mag. Res., San Francisco, 1988. [ Links ]
17. C.H. Oh, S.K. Hilal, J.B. Ra, Z.H. Cho, Books of Abstracts, 6th Ann. Meet. Soc. Mag. Res., New York, 1987. [ Links ]
18. L.E. Crooks, M. Arakawa, J.D. Hale, J.C. Hoenninger, J.C. Watts, L. Kaufman, D.A. Feinberg, Books of Abstratcs, 5th Ann. Meet. Soc. Mag. Res., Quebec, 1986. [ Links ]
19. Haase, A., Frahm, J., Matthaei, D., Hanicke, W., Merboldt, K. D., J. Magn. Reson. 67 (1986) 258. [ Links ]
20. P.V.D. Meulen, J.P. Groen, and A. M. C. Tinus Brutink, Magn. Reson. Imag. 6 (1988) 335. [ Links ]
21. P. Mansfield, J. Phys. C: Solid State Phys. 10 (1977) L55. [ Links ]
22. R. Ordidge, Ph D Thesis, University of Nottingham, 1981.
23. S. Ljunggren, J. Magn. Reson. 54 (1983) 338. [ Links ]
]]>24. A.M. Howseman et al., Brit. J. Rad. 61 (1988) 822. [ Links ]
25. B. Chapman et al., Magn. Reson. Med. 5 (1987) 246. [ Links ]
26. M.K. Stehling, R.J. Ordidge, R. Coxon, P. Mansfield, Magn. Reson. Med. 13 (1990) 514. [ Links ]
27. I.L. Pykett and R.R. Rzedizan, Magn. Reson. Med. 5 (1987) 563. [ Links ]
28. P. Mansfield, R.J. Ordidge, R. Coxon, J. Phys. E: Sci. Instrum. 21 (1988) 275. [ Links ]
]]> 29. A.M. Blamire, Ph D Thesis, University of Nottingham, 1990.30. K.P. Pruessman, M. Weiger, M.B. Scheidegger, and P. Boesiger, Magn. Reson. Med. 42 (1999) 952. [ Links ]
31. D.K. Sodickson and W.J. Manning, Magn. Reson. Med. 38 (1997) 591. [ Links ]
32. A. Abragam, Principles of Nuclear Magnetism (Clarendon Press, Oxford, 1989). [ Links ]
33. C.P. Slichter, Principles of Magnetic Resonance, 3rd Edition, (Springer-Verlag, Berlin, 1992). [ Links ]
34. D.G. Gadian, Nuclear Magnetic Resonance and Its Applications to Living Systems. 2nd Ed., (Oxford, University Press, 1995). [ Links ]
35. P.G.Morris, Nuclear Magnetic Resonance Imagingin Medicine and Biology (Clarendon Press, Oxford, 1986). [ Links ]
36. C.N. Chen, D.I. Hoult, Biomedical Magnetic Resonance Technology(Adam Hilger, IOP Publishing, Britain, 1989). [ Links ]
37. M.A. Foster, J.M.S. Hutchinson, (Editors), Practical NMR Imaging, (IRL Press, Oxford, 1987). [ Links ]
38. E.M. Haacke, R.W. Brown, M.R. Thompson, R. Venkatsen, Magnetic Resonance Imaging, Physical Principles and Sequence Design, (Wiley-Liss, New York, 1999). [ Links ]
39. Z.P. Liang, P.C. Lauterbur, Principles of Magnetic Resonance Imaging, A signal processing perspective, (IEEE Press, New York, 2000). [ Links ]
]]>