Ch. 6 and 7
5
the longitudinal magnetization, Mz, reaches equilibrium after approximately ___ T1 relaxation times
XY
the net magnetization must have a component in the __ plane to produce an MR signal
1
the regrowth of Mz is the T__ process and represents the spins return to equilibrium
high
voxels with (high/low) hydrogen concentration or proton density appear bright
C
A disadvantage of gradient echo imaging is that _______________. A:it is very slow B: it requires a high flip angle C: there is a lot of susceptibility artifact D: it is difficult to see blood with it
B
As compared with healthy tissue, diseased tissue usually has _______________. A: a shorter T1 B: a longer T1 C: a shorter T2 D: a longer T2
A
Contrast agents in MRI typically work by doing what? A:shortening T1 time B: shortening T2 time C: lengthening T1 time D: lengthening T2 time
A
In a T1-weighted image, what type of tissue would appear bright? A:material with a short T1 B: material with a short T2 C: material with a long T1 D: material with a long T2
D
In a T2-weighted image, which type of tissue would appear bright? A: material with a short T1 B: material with a short T2 C: material with a long T1 D: material with a long T2
B
MRI signal intensity is proportional to _______________ A: spin state B: proton density C: T1 D: T2
B
MRI signals from tightly bound H atoms will _______________. A:be very strong B: decay quickly C: decay slowly D: rotate very fast
63
One T1 relaxation time results in relaxation to __% of Mo
Mz
T1 relaxation describes the growth and decay of __
XY
T2 relaxation represents a loss of net __ magnetization, it represents the loss of phase coherence in a plane transverse or perpendicular to Mo
shorter
T2* is much (longer/shorter) than T2
B
The time between a 180° pulse and a 90° pulse in an inversion recovery scan is the _______________. A:TE B: TI C: TR
C
There must be net magnetization in which plane to detect a signal in MRI? A:XZ plane B: YZ plane C: XY plane D: Z plane
A
To maximize T1 contrast in spin echo imaging, TR time must be _______________, and TE time must be _______________. A: short; short B: short; long C: long; long D: long; short
B
To maximize T2 contrast in spin echo imaging, TR time must be _______________, and TE time must be _______________. A:short; short B: long; long C: short; long D: long; short
C
What causes spins to rephase and form a spin echo? A: a 90° pulse B: an inversion pulse C: a 180° pulse D: the T1 time
D
What does the T1 relaxation time represent? A: The time it takes for Mz to decay by 37%. B: The time it takes for Mz to decay by 63% C: The time it takes for Mz to regrow by 37%. D: The time it takes for Mz to regrow by 63%.
A
What does the T2 relaxation time represent? A:The time it takes for Mxy to decay by 37%. B: The time it takes for Mxy to decay by 63%. C: The time it takes for Mxy to regrow by 37%. D: The time it takes for Mxy to regrow by 63%.
B
What is one reason that it is difficult to image the lungs with MRI? A:tightly bound H atoms B: low PD C: high T1 D: High T2
A
Which is an example of a material that contains a lot of tightly bound H atoms? A: bone B: fat C: water D: white matter
B
Which of the following is a synonym for T1 relaxation time? A: spin-spin relaxation B: spin-lattice relaxation C: T2 relaxation D: proton density
D
Which of the following is not a tissue property related to MRI? A: PD B: T1 relaxation times C: T2 relaxation times D: TE
D
Which of the following parameters of MRI does not control image contrast? A:TR B: TE C: TI D: Bandwidth
proton density
___ __ is the measure of concentration of mobile hydrogen nuclei available to produce an MRI signal
T2, T1
___ relaxation never exceeds ___ relaxation time for any given tissue
Mxy
before equilibrium is reached, ___ will relax to zero
faster
the further Mz is from Mo, the (slower/faster) it approaches Mo
black
cortical bone appears ___ on MRI
mobile
loosely bound hydrogen are where the typical MR signal originates from, these are called __ hydrogen
higher
the (higher/lower) the concentration of mobile hydrogen nuclei, the stonger the magnetization at equilibrium (Mo) and the more intense the signal
