Functional MR Mapping of Activated Cortical Areas

Summary

Magnetic resonance imaging (MRI) has recently been demonstrated to be sensitive to changes in neuronal activity of cortical areas. We report our initial experiences with functional MR brain mapping at high spatial resolution using a conventional whole-body MR system. A total of 10 visual and motor cortex activation studies were carried out on 8 healthy volunteers. In each examination, a time course series of 15 strongly T2*-weighted FLASH images was measured from three adjacent slices. The image analysis revealed a subtle but highly significant signal increase in cortical layers of gray matter in primary and associative visual as well as sensorimotoric cortex regions during periods of excessive brain activity provoked by photic stimuli or motoric tasks, respectively. To correlate brain structure and brain function, the computed MR brain activation maps were directly superimposed on T1-weighted anatomic spin-echo images. With this advance into the area of functional neuroimaging, MRI is moving into an established domain of positron emission tomography (PET). We, therefore, discuss the advantages and limitations of the MR method in comparison to PET as far as this can be done at present.

Zusammenfassung

Wie kürzlich gezeigt wurde, ist die Magnet-Resonanz-Tomographie (MRT) empfindlich gegenüber Veränderungen in der neuronalen Aktivität kortikaler Hirn-areale. Wir berichten über unsere Erfahrungen mit der funktionellen MR-Bild-gebung an einem konventionellen Ganzkörper-MR-Tomographen zur räumlich hochaufgelösten Abbildung stimulierter Kortexareale. Bei 8 Probanden wurden insgesamt 10 Untersuchungen zur Aktivierung des visuellen und des motorischen Kortex durchgeführt. Bei jeder Studie wurde der Zeitverlauf von 15 stark T2*-gewichteten FLASH-Aufnahmen in drei Schichten gemessen. Die Analyse der Bilder ergab einen subtilen, aber hoch signifikanten Anstieg des MR-Signals in der grauen Hirnsubstanz des visuellen und sensomotorischen Kortex während der Phasen exzessiver visueller bzw. taktiler Stimulation. Um eine direkte Korrelation von Hirnfunktion und -struktur zu ermöglichen, wurden die berechneten MR-Aktivierungskarten direkt auf T1-gewichtete anatomische Spinecho-Bilder überlagert. Mit der Entwicklung funktioneller Bildgebungstechniken stößt die MRT in eine klassische Domäne der Positronen-Emissions-Tomographie (PET) vor; aus diesem Grund diskutieren wir die Möglichkeiten und Limitationen der MR-Technik im Vergleich zur PET, soweit dies zur Zeit möglich ist.

Key words

Functional brain mapping - cortex activation - magnetic resonance imaging (MRI) - positron emission tomography (PET)

Schlüsselwörter

Funktionelle Hirnkartierung - Kortexaktivierung - Magnet-Resonanz-Tomographie (MRT) - Positronen-Emissions-Tomographie (PET)

• Literatur

• 1 Bandettini PA, Wong EC, Hinks RS, Tikofsky RS, Hyde JS. Time course EP[ of human brain function during task activation. Magn Reson Med 1992; 25: 390-97.
• 2 Belliveau JW, Kennedy DN, McKinstry RC. et al. Functional mapping of the human visual cortex by magnetic resonance. Science 1991; 254: 716-19.
• 3 Blamire AM, Ogawa S, Ugurbil K. et al. Dynamic mapping of human visual cortex by high-speed MRI. Proc Natl Acad USA 1992; 89: 11069-73.
• 4 Brix G. Grundlagen der MRT und MRS, speziell S.57-8. In: Magnetresonanztomographie. Reiser M, Semmler W. (Hrsg). Berlin, Heidelberg, New York: Springer Verlag; 1992
• 5 Buxton RB, Frank LR. A physiological model for the quantitative interpretation of functional MR brain activation studies. New York: Society of Magnetic Resonance in Medicine: Book of abstracts; 1993: 4.
• 6 Connelly A, Jackson GD, Frackowiak RSJ. et al. Functional mapping of activated human primary cortex with a clinical MR imaging system. Radiology 1993; 188: 125-30.
• 7 Constable RT, Mc Carthy G, Allison T, Anderson AW, Gore JC. Functional brain imaging at 1.5 T using conventional gradient echo MR imaging techniques. Magn Reson Imaging 1993; 11: 451-9.
• 8 Fox PT, Raichle ME. Focal physiological uncoupling of cerebral blood flow and oxidative metabolism during somatosensory stimulation in human subjects. Proc Natl Acad Sci USA 1986; 83: 1140-4.
• 9 Fox PT, Raichle ME, Mintun MA, Dence C. Nonoxidative glucose consumption during focal physiologic neural activity. Science 1988; 241: 462-4.
• 10 Frackowiak RSJ. Functional imaging: Issues in cognitive neuroscience. New York: Society of Magnetic Resonance in Medicine: Book of abstract; 1993: 1.
• 11 Frahm J, Merboldt KD, Hanicke W. Functional MRI of human brain activation at high spatial resolution. Magn Reson Med 1993; 29: 139-44.
• 12 Friston KL, Frith CD, Liddle PF, Frackowiak RSJ. Comparing functional (PET) images: The assessment of significant change. J Cereb Blood Flow Metab 1991; II: 690-9.
• 13 Greenberg JH, Reivich M, Alavi A. et al. Metabolic mapping of functional activity in human subjects with the [^l8F]fluorodeoxyglucose technique. Science 1981; 212: 678-80.
• 14 Guyton AC. Textbook of medical physiology, Chapter 57. Philadelphia: W. B. Saunders; 1991
• 15 Guyton AC. Textbook of medical physiology. Capter61. Philadelphia: W. B. Saunders; 1991
• 16 Haase A, Frahm J, Matthaei D, Hanicke W, Merboldt KD. FLASH imaging: rapid NMR imaging using low flip-angle pulses. J Magn Reson 1986; 67: 258-66.
• 17 Jonides J, Smith EE, Koeppe RA. et al. Spatial working memory in humans as revealed by PET. Nature 1993; 363: 623-5.
• 18 Kim SG, Ashe J, Hendrich K. et al. Functional magnetic resonance imaging of motor cortex: hemisphere asymmetry and handedness. Science 1993; 261: 615-7.
• 19 Kwong KK, Belliveau JW, Chesler DA. et al. Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation. Proc Natl Acad Sci USA 1992; 89: 5675-9.
• 20 Merboldt KD, Bruhn H, Hanicke W, Michaelis T, Frahm J. Decrease of glucose in the human visual cortex during photic stimulation. Magn Reson Med 1992; 25: 187-94.
• 21 Ogawa S, Lee TM, Nayak AS, Glynn P. Oxyge-nation-sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields. Magn Reson Med 1990; 14: 68-78.
• 22 Ogawa S, Menon RS, Tank DW. et al. Functional brain mapping by blood oxygenation level-dependent contrast magnetic resonance imaging. Biophys J 1993; 64: 803-12.
• 23 Ogawa S, Tank DW, Menon R. et al. Intrinsic signal changes accompanying sensory stimulation: functional brain mapping with magnetic resonance imaging. Proc Natl Acad Sci USA 1992; 89: 5951-5.
• 24 Pardo JV, Fox PT, Raichle ME. Localization of a human system for sustained attention by positron emission tomography. Nature 1991; 349: 61-4.
• 25 Petersen SE, Fox PT, Posner MI, Mintum M, Raichle ME. Positron emission tomography studies of the cortical anatomy of single-word processing. Nature 1988; 585-9.
• 26 Petrides M, Alivisatos B, Meyer E, Evans AC. Functional activation of the human frontal cortex during the performance of verbal working memory tasks. Proc Natl Acad Sci USA 1993; 90: 878-82.
• 27 Phelps ME, Kuhl DE, Mazziotta JC. Metabolic mapping of the brain’s response to visual stimulation: study in humans. Science 1981; 211: 1445-8.
• 28 Press WH, Flannery BP, Teukolsky SA, Vetter-ling WT. Numerical recipes: the art of scientific computing. Chapter 13. Cambridge: Cambridge University Press; 1992
• 29 Prichard J, Rothman D, Novotny E. et al. Lactate rise detected by ‘H NMR in human visual cortex during physiologic stimulation. Proc Natl Acad Sci USA 1991; 88: 5829-31.
• 30 Reivich M, Gur R, Alavi A. Positron emission tomographic studies of sensory stimuli, cognitive processes and anxiety. Hum Neurobiol 1983; 2: 25-33.
• 31 Schad LR, Trost U, Knopp MV, Müller E, Lorenz WJ. Motor cortex Stimulation measured by magnetic resonance imaging on a standard 1.5 T clinical scanner. Magn Reson Imaging 1993; 11: 461-4.
• 32 Talbot JD, Marrett S, Evans AC. et al. Multiple representations of pain in human cerebral cortex. Science 1991; 251: 1355-8.
• 33 Thulborn KR, Waterton JC, Matthews PM, Rad-da GK. Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high fields. Biochim Biophys Acta 1982; 714: 265-70.
• 34 Turner R, Jezzard P, Wen H. et al. Functional mapping of the human visual cortex at 4 and 1.5 Tesla using deoxygenation contrast EPI. Magn Reson Med 1991; 29: 277-9.
• 35 Turner R, Le Bihan D, Moonen CTW, Despres D, Frank J. Echo-planar time course MRI of cat brain oxygenation changes. Magn Reson Med 1991; 22: 159-66.
• 36 Willard FH. Medical neuroanatomy. Philadelphia: J. B. Lippincott; 1993
• 37 Yang TT, Gallen CC, Schwartz BJ, Bloom FE. Noninvasive somatosensory homunculus mapping in humans by using a large-array bio-magnetometer. Proc Natl Acad Sci USA 1991; 90: 3098-102.
• 38 Zatorre RJ, Jones-Gotman M, Evans AC, Meyer E. Functional localization and lateralization of human olfactory cortex. Nature 1992; 360: 339-40.