Ferris_101007 - Functional Magnetic Resonance Imaging...

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Functional Magnetic Resonance Imaging Bridging the Science Between Animal and Human Research Craig Ferris, Ph.D. Director Center for Comparative Neuroimaging Department of Psychiatry University of Massachusetts Medical School
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Center For Comparative Neuroimaging mouse rat marmoset rhesus University Massachusetts Medical School
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Magnetic Resonance Spectrometer (4.7 T) RF Probes Computer Console Passive Shielding
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Magnetic Resonance Imaging “Then & Now” Damadian et al., Science 194:1431,’76 CCNI, 9.4T Kramer et al., Neuroradiology 21:239 ’81 - Lauterbur
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High Resolution Magnetic Resonance Image Of Marmoset Monkey Brain
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Superconducting Magnets ¾ Generate External Magnetic Field - B 0 ¾ Field Strength Between 1.5 – 11.7 Tesla (T) ¾ Operate Near Absolute Zero Temperature
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Manipulating Hydrogen Atoms ¾ MRI is non-invasive and uses the protons from mobil hydrogen in water and fat to generate signals ¾ The hydrogen nucleus spins creating a local magnetic field causing the charged nucleus to act like little magnet aligning in B O . ¾ Over time (2-3 sec) protons come to equilibrium or net magnetization M O
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Hydrogen Protons “Wobble” ¾ Not only does the nucleus of the hydrogen atom spin like a top but it also precesses or “wobbles.” ¾ The precessional frequency is defined by the Larmor Equation ω = γ B O γ = 42.6 MHz/T for hydrogen ¾ When the field strength increases so does the precessional frequency
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Flipping Hydrogen Protons To Get MR Signal ¾ An RF pulse with the same precessional frequency can “flip” the proton into the transverse plane ¾ Protons precess around the transverse plane giving off an oscillating signal ¾ Protons are initially in phase but rapdily dephase and signal decays in 20 to 30 msec.
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