Parameters and Tradeoffs Flashcards
SNR
signal to noise ratio
The amount of voltage induced in the coil at the time the echo is collected
signal
The frequencies of RF energy that exist randomly in time and space
noise
Describe low SNR
grainy
noisy
Coil position for maximum signal
transverse plane, perpendicular to B0
The parameter controls the number of echos stored per line of k-space
number of signal averages (NSA or NEX)
A range of frequencies
bandwidth
The smallest unite of a digital image
pixel
3D unit of volume
voxel
Find voxel volume
pixel area x slice thickness
Find pixel area
FOV/Matrix
Name the 2 dimensions of the pixel
phase matrix
frequency matrix
Which matrix will always be the smaller number?
phase matrix
Scan Time equation
TR x Phase Matrix x NEX
What’s known as under sampling and over sampling?
Rectangular FOV
Does Rec FOV affect voxel size?
no, doesn’t change resolution
What increases number of echoes but doesn’t add any dimension to the image?
oversampling
Oversampling Benefits
avoid aliasing
increase SNR
increase scan time
no change to resolution
TR increased
increase SNR
increase number of slices
increase scan time
decreases T1 weighting
TR decreased
decrease scan time
decrease SNR
decrease number of slices
increase T1 weighting
TE increased
decrease SNR
increase T2 weighting
TE decreased
increase SNR
decrease T2-weighting
NEX increased
increase SNR
increase in scan time
increase signal averaging
NEX decreased
decrease SNR
decrease signal averaging
decrease in scan time
Slice thickness increased
increases SNR
increase coverage of anatomy
increase partial voluming
decrease spatial resolution
Slice thickness decreased
increase spatial resolution
decrease partial voluming
decrease SNR
decrease coverage
FOV increased
increase SNR
increase coverage of anatomy
decrease potential of aliasing
decrease spatial resolution
Matrix increased
increase spatial resolution
increase scan time
decrease SNR if pixel small
Matrix decreased
decrease scan time
decrease spatial resolution
increase SNR if pixel large
Receive bandwidth increased
decrease in chemical shift
decrease in min TE
decrease SNR
Receive bandwidth decreased
increase in SNR
increase in chemical shift
increase in min TE
Find best spatial resolution?
smaller voxel size
smallest FOV
Find best SNR
increase voxel volume
increase slice thickness
increase NEX
increase FOV
increase TR
decrease TE
decrease coils
decrease bandwidth
decrease matrix
What happens when B0 increases,
SNR increases
How to change an image from low resolution to better resolution?
decrease FOV
decrease slice thickness
decrease matrix
increase NEX
Increased multi slice leads to:
increase scan time
decrease T1 weighting
Factors affecting SNR
TR
TE
flip Angle
bandwidth
proton Density
voxel volume
Find new SNR
original SNR x square root of new factor of increase
Benefits of GRE
scan time
Under sampling Benefits
decrease scan time
decrease SNR
aliasing
If an image looks too fuzzy/blurry,
increase matrix
decrease slice thickness
decrease FOV
Get better T1 contrast,
decrease TR
