Nuclear Magnetism and MRI Flashcards
Regarding nuclear magnetism and MRI (true or false):
The nucleus of a hydrogen isotope has an equal number of protons and neutrons
False. Hydrogen has a single proton in its nucleus.
Regarding nuclear magnetism and MRI (true or false):
Nuclear magnetism is the combination of positive electric charge and spin
True
Regarding nuclear magnetism and MRI (true or false):
Most hydrogen nuclei will orientate with a strong magnetic field
True
Regarding nuclear magnetism and MRI (true or false):
Most hydrogen nuclei will orientate with a strong magnetic field
True
Regarding nuclear magnetism and MRI (true or false):
The Larmor frequency defines the magnetic field strength
False. The Larmor frequency defines the precessional frequency.
Regarding nuclear magnetism and MRI (true or false):
Magnetic field strength is inversely proportional to precessional frequency
False. Magnetic field strength is directly proportional to the precessional frequency.
Regarding relaxation (true or false):
Relaxation describes the loss of energy to the surrounding tissue when the RF energy is switched off and net magnetization returns to equilibrium
True
Regarding relaxation (true or false):
T1 relaxation is the time taken for the loss of phase coherence of the net magnetization, following the rotation of the net magnetization
False. T1: time taken for the rotated net magnetization to realign with the main magnetic field.
Regarding relaxation (true or false):
T2 relaxation is the time taken for the rotated net magnetization to realign with the main magnetic field
False. T2: time taken for the loss of phase coherence of the net magnetization, following the rotation of the net magnetization.
Regarding relaxation (true or false):
Free induction decay is the loss of the MR signal due to T1 relaxation
False. FID: loss of the MR signal due to T2 relaxation.
Consider two tissues with different T1 relaxation times, one longer than the other.
Decide which statement describes the proportion of tissues returning to equilibrium (realigned with the main mag
netic field), if TR is long (in the order of 2000 ms).
A. Strong likelihood that a large proportion of both tissues will have returned to equilibrium
B. Strong likelihood that only a small proportion of both tissues will have returned to equilibrium
C. Strong likelihood that there will be a difference between the two tissues, with one having largely returned to equilibrium and the other having only slightly returned to equilibrium
A. If TR is long (ie around 2000ms) then T1 relaxation times of most tissues will be exceeded, allowing tissues time to realign with the magnetic field.
Considering two tissues with different T1 relaxation times, decide what proportion of the tissues returned to equilibrium if the TR was short (in the order of 500 ms).
A. Strong likelihood that a large proportion of both tissues will have returned to equilibrium
B. Strong likelihood that only a small proportion of both tissues will have returned to equilibrium
C. Strong likelihood that there will be a difference between the two tissues, with one having largely returned to equilibrium and the other having only slightly returned to equilibrium
C. At a TR of 500ms, T1 relaxation time of the tissue is longer than the TR. Therefore, the proportion of each tissue to have returned to equilibrium will be quite different between the two tissues.
If T1 weighting is obtained using a pulse sequence with a short TR and a short TE, what would eradicate T1 information from such a pulse sequence?
Select one or more options from the list below.
Possible answers:
A. Short TR, short TE
B. Short TR, long TE
C. Long TR, short TE
D. Long TR, long TE
C. & D. Lengthening the TR eradicates any T1 information, whereas lengthening TE only diminishes it without eradicating it.
Why does hydrogen possess the property of nuclear magnetism?
A. It has a single neutron within its nucleus
B. It has a single proton within its nucleus
C. It has a single orbiting electron
The imbalance between the number of protons and the number of neutrons in the nucleus of an atom provides an isotope with the property of nuclear magnetism.
Precessional frequency of a nuclear magnetic isotope is directly proportional to:
Select one or more options from the list below.
A. Gyromagnetic ratio
B. Inherent energy
C. Magnetic field strength
D. Net magnetization
E. Positive electric charge
A & C.
As expressed in the Larmor equation: ω ∝ γ Β0
ω = precessional frequency
γ = gyromagnetic ratio
Β0 = magnetic field strength
Why is hydrogen the isotope used in clinical MR imaging?
Select one or more options from the list below.
A. It is abundant in the body Correct answer
B. It is the only isotope that can be imaged
C. It is the only isotope that has nuclear magnetism
D. It provides a good MR signal
A & D.
Compared to other isotopes, hydrogen provides the strongest MR signal of all isotopes. Its abundance in differing body tissues is a fortunate coincidence.
Regarding RF pulses (true or false):
An RF pulse, applied at the precessional frequency, results in the net magnetization of tissue rotating away from the main magnetic field
True. The longer the RF pulse is applied, the further the net magnetization rotates.
Regarding RF pulses (true or false):
Relaxation occurs when the RF pulse is applied
False. Relaxation begins as soon the RF pulse is switched off.
Regarding RF pulses (true or false):
T1 and T2 relaxation times are unique for different tissues
True. Although there is a fair degree of overlap.
Regarding RF pulses (true or false):
T1 relaxation times vary with magnetic field strength
True. The higher the field strength, the longer the T1 relaxation time.
Regarding RF pulses (true or false):
T2 relaxation times vary with field strength
False. Effectively, there is no real difference.
An MR pulse sequence is:
A. The name given to T1 relaxation measurements
B. The time between the excitation of a slice of tissue with RF pulses
C. A number of specifically-timed RF pulses applied to a slice of tissue
D. A loss of phase of individual magnetic moments
C
RF pulse sequences are set up with the scanning parameters manipulated to maximize contrast within an image. Clinicians refer to the images produced as:
A. T1 time
B. T1-weighted
C. T2 time
D. T2-weighted
B & D.
These are the commonest scanning sequences used. It is possible to calculate relaxation times for different tissues but, in general, the pulse sequences have been developed to maximize the differences (contrast) in the relaxation times of different tissues.
In a T1-weighted image, order the following from shortest to longest in terms of relaxation times:
A. Bone appearing white
B. CSF appearing black
C. Brain tissue appearing grey
A -> C -> B
In a T2-weighted image, order the following from shortest to longest in terms of relaxation times:
A. Grey matter appearing light grey
B. CSF appearing white
C. White matter appearing dark grey
C -> A -> B
