FINAL STUDYGUIDES Flashcards
Which pulse sequence timing parameter combination will result in T1 weighted images when performing a spin echo pulse sequence?
short TR/short TE
Which pulse sequence timing parameter combination will result in Spin Density weighted images when performing a spin echo pulse sequence?
long TR/short TE
Which pulse sequence timing parameter combination will result in T2 weighted images when performing a spin echo pulse sequence?
long TR/long TE
When is a tissue vector considered to be partially saturated?
when it flips >90 degrees but <180
When is a tissue vector considered to be fully saturated?
when it reaches 180 degrees from equilibrium, it is positioned along the –z axis
A technologist sets up a pulse sequence as follows: type of pulse sequence: fast spin echo, TR = 3500 ms, TE = 20ms, matrix 256x192, NSA 3. What is the resulting image weighting?
Proton density
Explain the term homogeneity, as it applies to MRI.
Homogeneity is the even-ness or uniformity of the static field
State the source of T2’ decay.
T2’ decay is caused by inhomogeneities (uneven-ness) of the static field
Which imaging parameter(s) control(s) the amount of T1 weighting present in images obtained by performing a gradient echo pulse sequence?
Flip angle and TR
Which imaging parameter(s) control(s) the amount of T2 weighting present in images obtained by performing a gradient echo pulse sequence?
TE
Name the component of the MR system that induces parallel or anti-parallel alignment of the magnetic moments in a sample of tissue
the static magnetic field
Which gradient is simultaneously activated each time that RF is transmitted?
slice select
Which gradient is applied, as the slice select gradient, when obtaining coronal images of the brain?
the Y gradient
When the MR system applies a greater current amplitude to the activated gradient coils, what is the impact on the slope of the gradient?
the slope becomes steeper
What is the impact on the speed of precession along a gradient?
spins in the area where the magnetic field becomes stronger precess faster, spins in the area where the magnetic field becomes weaker precess slower
What is the impact on the phase position of the spins along the gradient?
The slope of the PE gradient determines the amount of phase shift present in the image; steep gradient has large phase shift and shallow gradient has small phase shift
What is the impact on the direction of the gradient when the polarity of the current in the gradient coils is changed by the MR system?
when the polarity of the current applied to the gradient coil switches, the direction of the magnetic field gradient also switches
Name the 3 processes that make up spatial encoding.
Slice selection, phase encoding, frequency encoding
What two things does the MR system adjust when the technologist selects a slice thickness value?
the transmitted bandwidth and the slope of the slice select gradient
If a technologist makes an adjustment to the bandwidth parameter, which is being adjusted:
receive bandwidth
What is another name for the frequency encoding gradient?
the readout gradient
Along which axis is the phase encoding gradient typically applied?
the short axis of the patient’s anatomy
In what area of k-space is contrast data stored?
the center
In what area of k-space is spatial resolution data stored?
the periphery or the edges
What determines how many lines of data will be acquired along the phase axis of k-space?
the phase matrix
What determines whether a positive or negative line of data will be acquired and stored in k-space?
the polarity of the phase encoding gradient applied by the system
What determines whether the data acquired will be mapped into the center or periphery of k-space?
the amplitude or steepness of the phase encoding gradient applied by the system
Name 3 methods of acquiring data in k-space.
sequential, 2-D volumetric, 3-D volumetric
What type of domain is k-space?
a spatial frequency domain
Where is k-space physically located?
in the array processor
What are the two axes of k-space?
phase and frequency
What happens once k-space is filled?
the pulse sequence is complete
What user-selected parameter determines how many data points will be acquired for each line of k-space?
the frequency matrix
Signal is:
reproducible & occurs at the TE time
Noise is:
random & fluctuating
What is the impact of an increase of B0 on SNR?
SNR increases as B0 increases
Name the 3 parameters that impact voxel volume and therefore in-plane resolution.
FOV, matrix, slice thickness
Describe the relationship between voxel volume and SNR.
direct, as voxel volume increases, SNR increases and vice versa
A technologist changes the Number of Signals Averaged (NSA) of the scan protocol from 1NSA to 4NSA. What is the impact (increase or decrease) & the quantity of the impact on SNR?
SNR increases, it doubles
A technologist adjusts the receive bandwidth from +/-32kHz to +/- 16kHz. State the impact on SNR and minimum TE
SNR increases by 40%, minimum TE increases
What impact will an increase in TR have on SNR?
increasing TR, increases SNR and vice versa
Which family of pulse sequences should be chosen to optimize the SNR of MR images?
spin echo
A technologist uses a surface coil with a diameter of 5 inches. How deep will adequate signal from the patient’s tissues be generated?
2.5 inches
