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Advanced Imaging Techniques: Image Reproduction and fMRI Mechanism

Explore the processes of Image Reproduction and Functional MRI mechanism, including Filtered Back Projection and Phase Encoding methods. Learn about brain activity, blood flow, and oxygen consumption using Magnetic Resonance Imaging techniques.

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Advanced Imaging Techniques: Image Reproduction and fMRI Mechanism

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  1. Image reproduction +fMRI

  2. Filtered Back Projection

  3. Filtered Back Projection

  4. Filtered backprojection • Filter the measured projection data at different projection • angles with a special function. • Backproject the filtered projection data to form the • reconstructed image. • Filtering can be implemented in 2 ways, in the spatial domain, the filter operation is • equivalent to to convolving the measured projection data using a special convolving • function h(t) • More efficient multiplication will be in the spatial frequency domain. • FFT the measured projection data into the frequency domain: • p(,)=FT {p(t, ) • Multiply the the fourier transform projections with the special function. • Inverse Fourier transform the product p’(,).

  5. Phase Encoding

  6. Phase encoding

  7. K space

  8. K Space

  9. Partial K space reconstruction

  10. Partial K space reconstruction

  11. Partial K space reconstruction

  12. Zero padding

  13. Conjugate symmetry

  14. Conjugate symmetry

  15. Homodyne reconstruction

  16. Homodyne reconstruction

  17. Homodyne reconstruction

  18. Homodyne reconstruction

  19. Mechanism of BOLD Functional MRI Brain activity Oxygen consumption Cerebral blood flow Oxyhemoglobin Deoxyhemoglobin Magnetic susceptibility T2* MRI signal intesity

  20. Magnetic Properties of Oxyhemoglobin and Deoxyhemoglobin Deoxyhemoglobin: paramagnetic (c > 0) paramagnetic with respect to the surrounding tissue Oxyhemoglobin: diamagnetic (c < 0) isomagnetic with respect to the surrounding tissue

  21. T2* Effect in fMRI action MR signal (S) rest TE t reception excitation

  22. Time Series and Activation Maps Signal Intensity Off On Off On Off On Off On Scan Number

  23. Temporal resolution Impulse-response function 12s 5s 2s t

  24. Temporal components (sd, % variance explained) 1 105.7, 77.8% 2 26.1, 4.8% Component 3 15.8, 1.7% 4 14.8, 1.5% 0 20 40 60 80 100 120 Frame Spatial components 1 2 Component 3 4 0 2 4 6 8 10 Slice PCA_IMAGE: PCA of time  space: 1: exclude first frames 2: drift 3: long-range correlation or anatomical effect: remove by converting to % of brain 4: signal?

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