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brain-scan-MRI-500x282 - Coggle Diagram
TE (ECHO Time)
As TE is increased: ↑T2 CONTRAST, ↓SNR, ↓PD, ↑T2
CONTRAST, ↓# SLICES, ↑MAGNETIC SUSCEPTIBILITY And as TE is decreased: ↓T2 CONTRAST, ↑SNR, ↑PD, ↓T2
CONTRAST, ↑# SLICES, ↓MAGNETIC SUSCEPTIBILITY
Patient
Scan Time
The time required to collect all data needed to generate the programmed images
Contrast Media (e.g. Gadolinium)
TR (Repetition Time)
As TR is increased:↑SNR, ↓T1 CONTRAST, ↑# SLICES, ↑TIME, ↑PD, ,↑MOTION ARTIFACTS, ↑FLIP ANGLE. And as TR is decreased: ↓SNR, ↑T1 CONTRAST, ↓#SLICES, ↓TIME, ↓PD, ↓MOTION ARTIFACTS, ↓FLIP ANGLE
IR (Inversion Recovery)
Pulse sequence for MRI wherein the net magnetization is inverted and relaxes to equilibrium with the emission of an MR signal after a 90° RF pulse; a method similar to spin echo but each excitation is preceded by an inversion pulse time T1.
Flip Angle
As Flip Angle is increased: ↑T1 CONTRAST, ↓T2
, ↑SNR, ↑Spins onto Transverse plane. And as Flip Angle is decreased: ↓T1 CONTRAST, ↑T2
, ↓SNR, ↓Spins onto X & Y plane
FOV (Field of View)
As FOV is increased: ↑IMAGED AREA, ↑SNR/VOXEL,↓SR, ↓ALIASING, ↑ARTIFACTS. And as FOV is decreased: ↓IMAGED AREA,↓SNR/VOXEL, ↑SR, ↑ALIASING, ↓ARTIFACTS
Slice Thickness
As Slice Thickness increases: ↑SNR, ↑AREA IMAGED, ↓SR, ↑PARTIAL VOLUME AFFECT. And as Slice Thickness is decreased: ↓SNR, ↓AREA IMAGED, ↑SR,↓PARTIAL VOLUME AFFECT
Bandwidth
As Bandwidth is increased: ↓SNR, ↓Q (quality), ↓MINIMUM TE, ↓CHEMICAL SHIFT, ↑SNR SLICE THICKNESS. And as Bandwidth is decreased: ↑SNR, ↑Q, ↑MINIMUM TE, ↑CHEMICAL SHIFT, ↓SLICE THICKNESS
Magnet Strength
An increase in field strength requires a decrease in TR, and a decrease in field strength requires an increase in TR.
Artifacts (e.g. Chemical Shift &Partial Volume)
As Chemical Shift Artifact increases: ↑W/NARROW (low) Receiver BW. And as Chemical Shift Artifact decreases:↓W/WIDER (higher) W/- with Receiver BW
As Partial Volume Artifact Increases: ↑W/ SLICE THICKNESS, ↑VOXELS, ↓SR, ↑ SNR . And as Partial Volume Artifact decreases: ↓W/ SLICE THICKNESS, ↓VOXELS, ↑SR, ↓SNR
SNR (Signal to Noise Ratio)
As the Ratio is increased: ↑SNR, ↓IR, & ↑IT. And as the Ratio is decreased: ↓SNR,↑IR, & ↓IT
Magnetic Susceptibility
Measure of the ability of a substance to become magnetized
Voxel Size
Volume element; or 3-D analog of a pixel
Spatial Resolution (SR) and Contrast (CR)
CR- It is the ability of an imaging system to distinguish between multiple densities in the radiographic image. And SR- the ability of an imaging system to differentiate between two near-by objects.
NEX (Number of Excitations), FAT/SAT (FAT Saturation)
As NEX is increased: ↑TIME & ↑SNR (√²). And as NEX is decreased: ↓TIME & ↓SNR (√²)
Echo Train Length
As ETL is increased: ↓SNR, ↓TIME, ↓# SLICES, ↑CONTRAST MIX, ↑BLURRING. And as ETL decreases: ↑SNR, ↑TIME, ↑# SLICES, ↓CONTRAST MIX, ↓BLURRING
Coil Size/Location
As Coil Size is increased: ↑FOV, ↑ARTIFACTS, ↑AREA IMAGED, ↓SNR. And as Coil Size is decreased: ↓FOV, ↓ARTIFACTS, ↓AREA IMAGED,↑SNR
FID (Free Induction Decay)
As FID is increased: ↓FID & ↓MOTION ARTIFACTS. And as FID is decreased: ↑FID & ↑MOTION ARTIFACTS
Amplitude
As Amplitude is increased:↑# SLICES, ↓SLICE THICKNESS, ↓FOV, ↓TE, ↓SCAN TIME. And as Amplitude is decreased: ↓# SLICES, ↑SLICE THICKNESS, ↑FOV, ↑TE, ↑SCAN TIME
IT (Inversion Time)
The time between the 180° inverting pulse and the 90°-pulse
3 Principle Parameters
PD (Proton Density)
A long TR and short TE
TR: >1000
TE: <30
flip angle: 90°
The image looks like:
fluid (e.g. joint fluid, CSF): high signal intensity (white)
muscle: intermediate signal intensity (grey)
fat: high signal intensity (white)
hyaline cartilage: intermediate signal intensity (grey)
fibrocartilage: low signal intensity (black)
T2 (Spin-Spin Relaxation Time)
A long TR and long TE
TR: >2000
TE: >80
flip angle: 90°
The image looks like:
fluid (e.g. urine, CSF): high signal intensity (white)
muscle: intermediate signal intensity (grey)
fat: high signal intensity (white)
brain: grey matter: intermediate signal intensity (grey). And white matter: hypointense compared to grey matter (dark-ish).
T1 (Spin-Lattice Relaxation Time)
A short TR and short TE
TR: <800
TE: <30
flip angle: 90°
The image looks like:
fluid (e.g. urine, CSF): low signal intensity (black)
muscle: intermediate signal intensity (grey)
fat: high signal intensity (white)
brain: grey matter: intermediate signal intensity (grey) And white matter: hyperintense compared to grey matter (white-ish)
Number Of Slices
Paramagnetic Materials
Type of substance with a small but positive magnetic susceptibility; the addition of a small amount of paramagnetic substance may greatly reduce the relaxation times of a tissue; used as contrast agents
Motion
Matrix
As Matrix size is increased: ↑SNR (√²), ↑SNR/VOXEL, ↑SR, ↑CR, ↑TIME, ↓TRUNCATION. And as Matrix size is decreased: ↓SNR (√²), ↓SNR/VOXEL, ↓SR, ↓CR, ↓TIME, ↑TRUNCATION.
Partial Saturation
Excitation technique applying repeated RF pulses in times comparable to or shorter than T1. Incomplete T1 relaxation leads to reduction of the signal amplitude;; there is the possibility of generating images with increased contrast between regions with different relaxation times.
