Fundamentals of MRI Flashcards
Precessional frequency is measured in :
MHZ
The ratio of a magnetic moment to its angular momentum
Gyromagnetic Ratio
Gyromagnetic ratio is measured in
MHz/T
Processional frequency of hydrogen is
42.5 MHz/t (1T scanner) 63.8 MHz/T (1.5 scanner)
The circular track that wobbling nuclei follow around the external magnetic field
Precessional path
Occurs when a nucleus is exposed to an oscillation that has a frequency close to its own
Resonance
in order for resonance to occur the frequency of transmitted RF must be the same as the precessional frequency of the atoms with which the RF interacts
What occurs during resonance?
Spins flip into the transverse plane
Spins precess in-phase with eachother
Spins absorb energy from the transmitted RF pulse
What is another term for “in-phase”
Coherent
Spin up/ parallel protons are in which state
Low energy state
Spin down/ anti parallel protons are in which state
High energy state
When a hydrogen spin moves into the opposing energy state after the application of an RF pulse that is oscillating at the precessional frequency of hydrogen
Energy state transition
What is the natural decay of the net magnetization vector directly after the application of an RF pulse?
Free Induction Decay (FID)
Inherent characteristics
T1 Relaxation
T2 Decay
Proton Density
T2* Decay
Diffusion
Flow
Perfusion
Which occurs faster or slower, T1 or T2 relaxation
T1 is slower relaxation than T2
T2* weighting is a result of dephasing due to
Both T2 decay and magnetic field inhomogeneities
What tissue characteristic represents the relative number of hydrogen protons per unit volume?
Proton Density
Only Nuclei with a _______ mass number contain a magnetic moment
Odd
What is another name for the XY plane?
Transverse plane
Traditional closed-bore scanners have a _________ XY plane, whereas open-bore scanners have a _________ XY plane
Vertical / Horizontal
What Axis is oriented in the same direction as the magnetic field?
Z Axis - also known as the longitudinal axis
Traditional closed-bore scanners have a _________ Z plane, whereas open-bore scanners have a _________ Z plane
Horizontal / Vertical
What planes belong to which physical gradient?
Axial - Z Gradient
Sagittal - X Gradient
Coronal- Y Gradient
Obliques- multiple sets of physical gradients
The _________ usually spatially encodes the signal sampled along the short axis of anatomy
Phase Encoding Gradient
The phase encoding gradient is switched on after the application of the ______ and before the application of the________.
Alpha Pulse / RF rephasing pulse
