MRI Physics Questions and Answers 2023
Gyromatic Ratio
The ratio of the magnetic moment to the moment of inertia.
Larmor Frequency
In a static homogenous magnetic field, all protons in a nucleus of a given type of element will rotate with exactly the same frequency.
Proton/spin den...
MRI Physics Questions and Answers 2023
Gyromatic Ratio - answer The ratio of the magnetic moment to the moment of inertia.
Larmor Frequency - answer In a static homogenous magnetic field, all protons in a nucleus of a given type of element will rotate with exactly the same frequency.
Proton/spin density - answer Quantity of spins in tissue relative to proton density of water.
Repetition Time (TR) - answer The time period between repetitions of the excited pulse.
Echo Time (TE) - answer The time period between excitation and sampling of the induced signal.
Inversion Time (TI) - answer The time period between the 180 degree inversion pulse and the 90 degree excitation pulse in IF sequence.
Spin-lattice relaxation time (T1) - answer time it takes 63% of Mo to realign itself with
Bo after RF excitation has been removed.
--longitudinal recovery
--increases as strength of Bo increases.
Spin-spin relaxation time (T2) - answer The time it takes for spins angled to the Bo to
lose 63% of their coherence. --transverse decay
--spin-spin interactions
--varies dependent on tissue type
Gradient Magnetic Field - answer Magnetic field that increases or decreases (slopes)
over distance.
-main purpose of field: is to provide or encode spatial info in the received MR signals.
Z gradient - answer head to foot; slice selection
Y gradient - answer anterior to posterior direction of the patient; phase encoding gradient
X gradient - answer right to left direction; frequency encoding agent.
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