Imaging parameters Flashcards
The difference in SNR between 2 adjacent pixels
Contrast to noise ratio (CNR)
CNR and SNR are controlled by the _______ parameters in the ________ way.
Same/Same
What parameter influences SNR the greatest?
FOV
The ability of the imaging system to detect two points in a pixel as separate structures (distinguish)
Spatial Resolution
Square pixels provide ________ resolution than rectangular pixels
Better
Which techniques providers square pixels?
Square FOV and a square matrix
Rectangular FOV and a rectangular matrix
What factor has an affect on 3D image acquisition time, but has no effect on 2D image acquisition time?
Slice numbers
Conventional Pulse sequence acquisition time formula
TR x NEX(NSA) x Phase encodings = scan time
Fast spin echo pulse sequence scan time formula
TR X NEX X Phase encodings / ETL =
Scan time
Formula for scan time during 3D image acquisition
TR x NEX x Phase encodings x Slice#
= Scan time
What parameter predominantly controls T2* weighting?
Echo time (long TR and Long TE)
What is another name for T2* Decay
Susceptibility Decay
T2* image weighting depends on
T2 decay, magnetic field inhomogeneities
T2 decay, T2 prime
Transverse relaxation, T2 prime
The dephasing of precessing spins due to magnetic field inhomogeneities is referred to as
T2 prime
What is the abbreviation for T2 prime
T2’
What parameter is described as the time between the alpha pulse and the peak of the echo?
TE (echo time) - measured in milliseconds
The time of inversion takes place between
The 180 degree inversion pulse and the excitation pulse during Inversion recovery sequences
NSA/NEX determines how many times signal is encoded within each line of k-space by controling the amplitude and the slope of which gradient
Phase encoding gradient
Flip angle is controlled by
The amplitude and duration of incoming RF pulse
To obtain THIN slices a ___________ slice-select gradient slope and a ________ bandwidth is used
Steep/Narrow
Opposite for thick slices
Shallow/broad
In order to reduce artifacts, it is recommended to use atleast a gap space of atleast _____% of the slice thickness
30%
During FSE sequences, the echos that are closer to the effective TE value, get placed in the ________ of k-space as _________ data.
Center / Contrast
During FSE sequences, the echos that are further from the effective TE value, get placed in the ________ of k-space as _________ data.
Periphery / Spatial Resolution
Transmit bandwidth is selected by the system automatically when _________ is selected
Slice thickness
If Receive bandwidth is doubled, approx. ______ of SNR is _______.
40% / Lost
If Receive Bandwidth is halved, approx. _______ of SNR is ________.
40% / Gained
What parameter directly controls the number of acquisitions performed within a pulse sequence
Concatenations
Increasing concatenations usually allows the use of _______ TR if one is not obtainable due to the MRI’s system SAR limitations
Shorter
