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Questions and Answers
Which effect does the spin echo recover dephasing due to?
Which effect does the spin echo recover dephasing due to?
- Spin-spin interactions
- Spin-flip interactions
- Spin-lattice interactions (correct)
- Spin-echo interactions
What happens to the protons after a 90° RF pulse?
What happens to the protons after a 90° RF pulse?
- They continue to dephase (correct)
- They stay in phase
- They rotate over to the opposite axis
- They begin to rephase
What effect does the 180° RF pulse have on the spins?
What effect does the 180° RF pulse have on the spins?
- It causes them to rotate over to the opposite axis
- It causes them to dephase further
- It causes them to rephase (correct)
- It causes them to stay in phase
What is the purpose of the spin echo?
What is the purpose of the spin echo?
What effect does the spin echo have on the spins?
What effect does the spin echo have on the spins?
Which effect does the spin echo recover dephasing due to?
Which effect does the spin echo recover dephasing due to?
What causes the protons to dephase in the transverse plane after a 90° RF pulse?
What causes the protons to dephase in the transverse plane after a 90° RF pulse?
What happens to the spins after a certain amount of time and a 180° RF pulse is applied?
What happens to the spins after a certain amount of time and a 180° RF pulse is applied?
What is the purpose of the spin echo?
What is the purpose of the spin echo?
What effect does a 180° RF pulse have on the spins?
What effect does a 180° RF pulse have on the spins?
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Study Notes
Magnetic Resonance Imaging (MRI)
- A spin echo recovers dephasing due to magnetic field inhomogeneities and spin-spin interactions.
Proton Behavior after RF Pulses
- After a 90° RF pulse, protons are aligned in the transverse plane, causing them to precess at the Larmor frequency.
- A 180° RF pulse reverses the direction of the spins, causing them to rephase.
Purpose and Effect of Spin Echo
- The purpose of the spin echo is to refocus the magnetization of protons, allowing for the creation of an MR signal.
- The spin echo has a rephasing effect on the spins, allowing them to re-align in the transverse plane.
Dephasing of Protons
- Protons dephase in the transverse plane after a 90° RF pulse due to differences in their Larmor frequencies caused by magnetic field inhomogeneities.
- A 180° RF pulse can rephase the protons, allowing them to realign in the transverse plane after a certain amount of time.
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