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Summary functional imaging methods

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2023/2024

Description: This comprehensive text delves into the workings of MRI scanners, elucidating the principles behind neuroimaging techniques such as the application of strong magnetic fields, radiofrequency pulses, and gradient coils. It discusses the behavior of protons under magnetic fields and the role of RF pulses in disrupting their alignment, leading to the generation of MRI signals. The text further explores the intricate processes of spatial encoding using gradient coils and Fourier transform, alongside the creation of tissue contrast through pulse sequences like T1 and T2 contrasts. Additionally, it elaborates on the fascinating realm of BOLD fMRI, highlighting its reliance on changes in local blood flow and oxygenation to detect neural activity. It elucidates concepts like the Hemodynamic Response Function (HRF) and the characteristics of noise in fMRI data. Furthermore, it provides insights into preprocessing steps aimed at enhancing the quality of MRI data for statistical analysis. Moreover, the text extends into MEG and EEG, delineating their biophysical basis and resolutions. It discusses the forward and inverse problems in neuroimaging, along with solutions like dipole fitting and beamforming. Furthermore, it explores Event-Related Potentials (ERPs), categorizing them into endogenous and exogenous components and elucidating their role in cognitive processes through experimental paradigms like the oddball paradigm and semantic processing. In essence, this text serves as a comprehensive guide to understanding the intricate workings of MRI scanners, BOLD fMRI, MEG, EEG, and ERPs, offering valuable insights into the techniques and principles underlying neuroimaging and cognitive neuroscience research. MRI scanner, neuroimaging techniques, radiofrequency pulse, gradient coils, protons, static magnetic field, RF pulse, excitation phase, reception, gradients, Fourier transform, slice selection gradient, frequency encoding gradient, phase encoding gradient, k-space, tissue contrast, pulse sequences, BOLD fMRI, HRF, temporal lag, noise, SNR, preprocessing, slice acquisition time correction, head motion correction, coregistration, normalization, spatial and temporal filtering, MEG, EEG, forward problem, inverse problem, ERPs, endogenous ERPs, exogenous ERPs, oddball paradigm, face processing, semantic processing, P1 component, N1 component, MMN.

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Subido en
2 de febrero de 2024
Número de páginas
34
Escrito en
2023/2024
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Resumen

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MRI physics

,MRI scanner: how does it work?
• MRI scanners use strong magnetic fields and radio waves to generate very
detailed images of the brain.
• Different components
1. Main magnetic field (B0) to align the hydrogen protons with the magnetic fi
2. Radiofrequency pulse (B1) to temporarily disrupt the alignment of the proto
3. Gradient coils to encode spatial information

,Properties of protons
• When a strong magnetic field is applied protons:
1. align themselves with the main magnetic field. This alignment is often rega
as the ‘phase’ of the protons
2. ‘’spin’ or ‘precess’ around the direction of the main magnetic field at a freq
called Larmor frequency

, Static magnetic field (B0) and RF pulse
• A strong static magnetic field is applied to align hydrogen protons. However,
B0 is not responsible for the image formation.
• Following the B0, an RF pulse is applied. This pulse will resonate at the same
frequency as the Larmor Frequency of the hydrogen protons.
 This pulse temporarily disrupts the alignment of the protons ‘knocking them out of place’. T
called the excitation phase, as protons absorb the energy from the pulse.
 When the RF pulse is turned off, the protons go back to alignment. As they do so, they relea
the energy that was absorbed during the excitation.
 The released energy gets detected by the RF coils during a process called reception. This cr
the MRI signal
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