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T2* revision

T2* revision. Vector coherence. Schering. Dephasing. Spins will precess at slightly different frequencies due to variations in the local magnetic field. Time. It is often easier to understand this dephasing is a frame of reference that is rotating at the average frequency of spins.

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T2* revision

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  1. T2* revision

  2. Vector coherence Schering

  3. Dephasing Spins will precess at slightly different frequencies due to variations in the local magnetic field Time It is often easier to understand this dephasing is a frame of reference that is rotating at the average frequency of spins Time

  4. T2* artefacts Good(ish) shim Phantom with coin near it Bad shim

  5. Glucose and O2 Arteriole Venule Capillary Bed Glucose and O2 Resting cortex Blood cells containing deoxy- and oxy- haemoglobin

  6. Active cortex Blood flow Blood volume Blood oxygenation Glucose and O2 Arteriole Venule Capillary Bed Glucose and O2

  7. Assumed monoexponential: Decay rate is R2* M xy M o Active Rest 0.5 x Time after pulse z -0.5

  8. BOLD effect due to T2* effects around blood vessels

  9. 1 March 2009 Nature How do people maintain an active representation of what they have just seen moments ago? The visual areas of the cerebral cortex that are the first to receive visual information are exquisitely tuned to process incoming visual signals, but not to store them. On the other hand brain areas responsible for memory lack visual sensitivity, but somehow people are able to remember a visual pattern with remarkable precision for many seconds, actually, for as long as they keep thinking about that pattern.

  10. 1 March 2009 Nature Our question was, where is this precise information being stored in the brain? "Using a new technique to analyze fMRI data, we've found that the fine-scale activity patterns in early visual areas reveal a trace or something like an echo of the stimulus that the person is actively retaining, even though the overall activity in these areas is really weak after the stimulus is removed,”.

  11. Phospholipid structures

  12. Blood brain barrier

  13. Central sulcus departments.weber.edu/chfam/2570/Neurology.html

  14. Sensory areas of the brain From FMRIB, Oxford

  15. Magnetic forces Positive susceptibility: object attracted Ferromagnetic Paramagnetic Diamagnetic -1 0 Susceptibility  Negative: repelled Positive: attracted

  16. Magnetic forces Negative susceptibility: object repelled or levitated Ferromagnetic Paramagnetic Diamagnetic -1 0 Susceptibility  Negative: repelled Positive: attracted

  17. Magnetic forces Superconductors -1 Permanent magnets 106 Deoxyg. Blood -6.52 10-6 Water -910-6 Air (oxygen) +0.36 10-6 Ferromagnetic Paramagnetic Diamagnetic -1 0 Susceptibility  Negative: repelled Positive: attracted

  18. Red blood cells

  19. Special dissociation curves CO stop haemoglobin giving up oxygen Fetal blood preferentially takes up oxygen in placenta

  20. Effect of [dHb] on relaxation times

  21. Assumed monoexponential: Decay rate is R2* M xy M o Low dHb High dHb 0.5 x Time after pulse z -0.5

  22. a b

  23. 1/T2* against % dHb for blood at 7T

  24. Glucose and O2 Arteriole Venule Capillary Bed Glucose and O2 Resting cortex Blood cells containing deoxy- and oxy- haemoglobin

  25. Active cortex Blood flow Blood volume Blood oxygenation Glucose and O2 Arteriole Venule Capillary Bed Glucose and O2

  26. Spins will precess at slightly different frequencies due to variations in the local magnetic field Time It is often easier to understand this dephasing is a frame of reference that is rotating at the average frequency of spins Time

  27. Lights on Lights on Lights on a 60 30 0 Bold signal b Time (s)

  28. Heamodynamic response function Bold signal Stimulus Time (s) 8 s Initial dip Post stimulus undershoot

  29. Heamodynamic response function (effect of adding CA)

  30. Effect of echo time 7 T TE 18 25 34 43

  31. B C stimulus BOLD timecourses Time course of signal change at optimum TE for each field strength averaged over subjects Cycle average for each field strength. Rising edge of response intersects base-line earlier at higher field.

  32. Minimize the sum of squared differences between images

  33. Squared Error Rigid body transformations parameterised by: Translations Pitch Roll Yaw Image registration (From Welcome Functional Imaging Lab)

  34. Image registration (From Welcome Functional Imaging Lab) • Minimising mean-squared difference works for intra-modal registration (realignment) • Simple relationship between intensities in one image, versus those in the other • Assumes normally distributed differences

  35. Image registration (From Welcome Functional Imaging Lab)

  36. Statistical analysis(From Welcome Functional Imaging Lab)

  37. Convolution of paradigm with HRF

  38. Cross Correlation From MNI

  39. Dont forget to Fill IN thE National Student survey

  40. Somatotopic mapping

  41. Post Central Gyrus Area 1 Dystonia Normals Centre of activation separation Normals(6) 11  2 mm Dystonics (5) 4.4  0.9 mm p=0.00048 Little Finger Index Finger Both Fingers

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