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3.2.2 Magnetic Field in general direction Larmor frequencies: Hamiltonian: In matrix representation
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Rewriting the Hamiltonian: Characteristic equation:
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Eigenstates: Spin Flip: or Initial state Time evolved state z B
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z BProbability of a spin flip
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Sinceand Rabi Formula t z B
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t (a) (b) t (c) z B z B B z
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The most general initial state: In matrix formalism 0 T T
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Probability for measuring the spin projection along the z-axis: Probability for measuring the spin projection along the x-axis:
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3.4 Magnetic Resonance Magnetic Resonance Image showing a vertical cross section through a human head. Modern 3 tesla clinical MRI scanner. Magnetic Resonance Imaging (MRI) http://en.wikipedia.org/wiki/Magnetic_resonance_imaging
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Uniform magnetic field: Additional rotating magnetic field: Total magnetic field: Time dependent Hamiltonian: x y z
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Matrix representation of the Hamiltonian: Schrödinger Equation :
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State vector as viewed from the rotation frame: Schrödinger Equation becomes:
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where In the rotating frame the Hamiltonian is time independent!!
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Rabi Formula When Rabi Formula with
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Rabi flopping equation where Generalized Rabi frequency When (resonance condition), Rabi frequency.
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Amplitude of the spin flip probability: Lorentzian curve Magnetic resonance curve FWHM emissionabsorptionemission absorption t Time dependent spin flip probability:
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