Functional Brain Signal Processing: EEG & fMRI Lesson 10 Kaushik Majumdar Indian Statistical Institute Bangalore Center M.Tech. (CS), Semester III, Course B50

K Space Mezrich, 1995 K space in MR imaging Localization in terms of spatial frequency. Wave number K space is named after the wave number k. ialFrequency.html

3D Magnetic Gradient X Y Z B(x) = B 0 + G.x B(y) = B 0 + G.y B(z) = B 0 + G.z B(x) = B 0 - G.x B(y) = B 0 - G.y B(z) = B 0 - G.z

Slice Location: Location Along Z axis For Hydrogen gyromagnetic ratio is 42.6 MHz/T. For a 2.5 T gradient magnetic field strength (say in a 3 T scanner) the RF pulse should be in a band ± δ MHz. Kandel et al., 2000 Pooley, 2005

Frequency Encoding: Location Along X Axis Buxton, 2009

Phase Encoding: Location Along Y Axis Buxton, 2009

Magnetic Pulses Along X, Y and Z Axes Buxton, 2009

MR Signal Representation in K Space ƒ(x) is the variable magnetic field Mezrich, 1995

Trade Off Challenge in MR Imaging Simultaneous achieving of (1) high spatial resolution, (2) high temporal resolution, and (3) high SNR.

Talairach Coordinate System

Talairach Coordinate (cont.) Talairach origin is at the intersection of posterior and superior margins of the anterior commissure (AC) on the midhemispheric plane.

Cerebral Dimension of Brain Templates Lancaster et al., 2007

References R. Mezrich, A perspective on K space, RSNA, 195: 297 – 315, 1995, available online at MIA/reading/fourier.kspace.mezrich.1995.pdf MIA/reading/fourier.kspace.mezrich.1995.pdf R. B. Buxton, Introduction to Functional Magnetic Resonance Imaging, 2e, Cambridge University Press, Cambridge, UK, 2009.

References (cont.) J. L. Lancaster et al., Bias between MNI and Talairach coordinates analyzed using ICBM- 152 brain template, Hum. Brain Mapp., 28: 1194 – 1205, 2007.

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