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Functional Brain Signal Processing: fMRI and EEG Techniques

Explore T1, T2, and T2* relaxation times in brain imaging with a focus on fast fMRI methods for improved data acquisition. Learn about EPI, SAR, and safety issues in EPI technology. Visit http://www.isibang.ac.in/~kaushik for more info.

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Functional Brain Signal Processing: fMRI and EEG Techniques

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  1. M.Tech. (CS), Semester III, Course B50 Functional Brain Signal Processing: EEG & fMRILesson 11 Kaushik Majumdar Indian Statistical Institute Bangalore Center kmajumdar@isibang.ac.in

  2. Buxton, 2009 T1 and T2 Relaxation Time Clearly, T2 << T1. Let T2* be partly due to T2 of homogeneous magnetic property of the tissue and partly due to inhomogeneous magnetic property of the same. So where T’2 is time delay due to pure inhomogeneity. So T2* < T2 << T1. Buxton, 2009, p. 148

  3. Buxton, 2009 Free Induction Decay (FID) About one million oscillations during the T2*.

  4. Buxton, 2009 Repetition Time (TR)

  5. Buxton, 2009 Spin Echo and Echo Time (TE)

  6. Fast fMRI In conventional phase encoding if TR = 2 s and 256 lines are to be drawn, it will take 8 minutes 32 seconds for generating one image. If we reduce the number of lines to 64 the time required is 2 minutes 8 seconds. Our ultimate goal is to get as much information from fMRI as possible from LFP. One way to address the problem is to go for ‘fast’ fMRI, at least, as fast as we can. EPI is one paradigm for fast fMRI.

  7. Mezrich, 1995 Fast Spin Echo Technique

  8. Deichmann et al., 2010 Echo Planar Imaging (EPI) K space in EPI

  9. Deichmann et al., 2010 EPI (cont)

  10. Buxton, 2009, p. 249 Safety Issues in EPI • Specific absorption rate (SAR). • Up to 130 dB acoustic noise due to rapid switching (about 1000 Hz) of gradient magnetic field. (A major issue in EPI.) • Nerve stimulation. Y gradient is generally not used for frequency encoding in EPI. (A major issue in EPI.) • Generation of heat in body tissues due to RF pulses is always there in MR imaging including in EPI.

  11. References • R. B. Buxton, Introduction to Functional Magnetic Resonance Imaging, 2e, Cambridge University Press, Cambridge, UK, 2009.

  12. THANK YOUThis lecture is available at http://www.isibang.ac.in/~kaushik

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