MRI in Practice Notes Flashcards
MR active nuclei are __
nuclei with odd number / atomic weight
Protons consists of __ quarks - __ spin up & __ spin down
3; 2; 1
protium
hydrogen isotope
k-space
array of numbers representing spatial frequency in x & y axis of MR image; fourier transform of MR image
The individual points (kx,ky) in k-space __ one-to-one with individual pixels (x,y) in the image
do not correspond
each k-space contains ___ about every pixel in final image
spatial frequency & phase information
Time of Echo
time between middle of 1st RF to peak of spin echo
what is the purpose of the 180 degree pulse in spin echo
refocuses non-moving spins whose phases have been scattered by constant field distortions & inhomogeneities
what does the 180 degree pulse not correct for
T1 or true T2 effects due to random processes at atomic/molecular level
the amplitude of each echo in multi-echo spin echo progressively decreases due to __
T2 decay
fast spin echo
multiple 180 degree pulses & echoes follow each 90 degree pulse
fast spin echo utilizes __
different phase encoding gradients with each 180 degree pulse
The liquid helium used to cool the magnetics’ coil has a temperature of __
-452 degrees fahrenheit
Maximum SNR is achieved when the NMV is at _______ to a receiver coil.
90 degrees
How many 90 RF pulses are used in 1 TR of a Fast Spin Echo sequence?
1
How many pairs of gradients are there?
3
The flip angle that produces a spin‐echo is _______.
180 degrees
The difference in signal intensity between tissues is called _______.
contrast
T1 is the time taken for the transverse NMV to return to equilibrium at B0.
True or False
False
T2 is the time for the transverse NMV to decay to its original value.
True or False
False
How many RF pulses are needed to produce a single spin echo?
2
Coils are orientated at what angle to the NMV?
parallel / orthogonal / perpendicular
Patients are at risk of cardiac stimulations during MRI.
True or False
False
For a Time of Flight MRA of the carotids ARTERIES, the saturation pulse is placed _______ to the slices/slab
superior
When in the equilibrium state, protons precess _______.
at larmor frequency
Components of the Larmor equations are: Precessional frequency, Gyromagnetic ratio, and _______.
field strength
Why does air not give signal on MR images?
lack of H+
Slice thickness is determined by the _______?
Bandwidth of the Excitation pulse
At equilibrium, the spins are precessing in phase, about the main magnetic field B0.
True or False
False
The process of tissues giving off energy to the _______ is called _______?
lattice;T1
Another name for proton density is _______?
hydrogen & spin density
Another name for T1 relaxation is _______?
Longitudinal Relaxation
The RF pulses used in MR imaging are considered to be
Non‐ionizing and low energy
The gyromagnetic ratio of hydrogen is measured in _______?
MHz
In a Spin Echo sequence, to get a T1w image, the TE is ___
twice the time between 90 and 180 pulse
An Inversion Recovery sequence (eg STIR or FLAIR) sequence starts off with a _______pulse .
180 degrees
A spin-echo sequence …
May not produce T2* weighted images
An excitation pulse will flip the longitudinal NMV into the _______ if the RF pulse has the same _______ as the slice.
x/y; precessional frequency
What tissue has a Long T1 and Long T2?
CSF / water
Another name for T2 relaxation is _______?
transverse relaxation
To produce a gradient echo, the sequence lacks a _______.
180 degrees refocusing pulse
Which one of the following will Fourier transform be applied to?
K-space
Turning on the frequency encode gradients, will change __
both the frequency and phase of the spins
In a T1 weighted image, which choice is correct for brightest to darkest tissue
Fat, muscle, water
The magnetic moment possessed by a hydrogen proton comes from the proton having _______.
spins
When a conductor loses electrical resistance at low temperatures, it means it is a _______?
superconductor
Noise is present in all electronic equipment.
True or False
True
Which best describes a surface coil?
Used to selectively increase signal from a region
Fat Saturation may be achieved by utilising the fact that fat and water
have different precessional frequencies & T1 timings
How many RF pulses are needed to produce an FID echo?
1
Hydrogen density is determined by _______.
Number of protons in a tissue
The result of the excitation pulse is _______.
Protons precess in phase
Magnetic susceptibility is what?
A tissue’s ability to be magnetized
Signal in a coil is _______ through _______.
generated, induction
The inherent body coil is a _______ coil.
Transmit/Receive
Flip Angle is determined by :
How long the B1 field is applied
A vector has what two properties?
Amplitude / Magnitude and Direction
In a T2 weighted image, which choice is correct for darkest to brightest tissue
Muscle, fat, water
A gradient echo can be PD, T1 or T2* weighted depending on the
TR, TE and Flip Angle
Fat Saturation is typically applied
Before excitation
In Diffusion weighted imaging (DWI), the desired contrast depends on
water movement between the cells
The B₁ Field is produced by the _______.
RF Transmission Coil
The distribution or concentration of hydrogen spins describes what?
PD
In a hydrogen density weighted image, the short TE will decrease the _______ and a long TR will decrease the _______.
T2, T1
As the TE is increased, what can be said about the image contrast?
more T2 weighted
There are three magnetic states of material. Ferrous, Diamagnetic, and _______
Paramagnetic
Which RF pulse imparts the largest amount of transverse net magnetization?
60, 80, 180, 45
80 degrees
A gradient echo sequence is affected by __
spin-spin, susceptibility, inhomogeneity
Which RF pulse imparts the largest amount of energy into a tissue?
180°
in acute haemorrhage (1-2 days), blood appears
Dark on T2*
what factors decrease such that spatial resolution increases
FOV / Matrix / Voxel Size
thinner slices
when phase encoding steps __, spatial resolution increases
increases
when receiver bandwidth __, SNR increases
decreases
