Spin Echo Pulse Sequences
Use a 90 degree RF pulse followed by one 180 degree exication pulse
What is Conventional Spin Echo
GRE sequences are said to be flow sensitive because?
In GRE all nuclei are rephased by the gradients, meaning we can obtain signal from blood without need Gad
What does > TR do to SNR
What does < TR do to SNR
<TR < SNR
What the difference between CNR and resolution
CNR is the ability to tell the difference between two structures.
Resolution is just how clear the image is.
Basic scan time equation for CSE.
What is TR*NEX*Phase
TR 550 ms
TE 25
What Weighting is this?
T1W
Weakness of GRE include
Lower SNR
Unable to compensate for inhomogeneities and metal artifact
Louder noise
What does > NEX do to the SNR?
What the consequence?
If NEX is increased from 1 to 3 what will this cause the SNR to do (what the percent improvement of SNR?)
Square root of 3 is 1.7 so the SNR increase by a factor of 1.7 or 170%.
What does fat sat technique require
A good field homogeneity. B/c any metal artifact will create a bad shim, and prevent good saturation
FSE scan time equation
What is (TR*NEX*Phase) / ETL
Two echoes are generated per TR but the PE is only active once per TR.
What pulse sequence does this statement refer to?
What is Dual Spin Echo
FA ranges from _ in GRE
Does increasing RBW increase or decrease SNR
WHY?
Increasing RBW decrease SNR because the sampling widow bigger allowing for more noise to be sampled.
What does increasing resolution due to resolution
Does a fine matrix increase or decrease resolution
What the opposite of fine matrix
Increasing Res will always decrease SNR
Fine matrix increase the number of pixels leads to high resolution low SNR
Opposite of fine matrix is coarse
3D scan time equation
What is TR*NEX*Phase*Slice thickness
There are more than 2 echos per TR what are the 2 spin echo pulse sequences that this could be.
Single Shot Fast Spin Echo and Fast Spin Echo
What does a spoiler gradient do vs a rewind gradient
Which one is used for FID + echo
Which one is used for echo + RTM
Spoiler Gradients dephase nuclei by turning on and exposing nuclei to a linear range of different magnetic field strengths. Used for FID + echo
Rephased gradients rephase nuclei by using the opposite slope compared to the spoiler (dephasing) gradient. Used for echo + RTM
What a dixon technique
Designed to generate uniform fat saturation. Less affected by artifacts such as metal artifact. Provides images with and without fat suppression from a single acquisition. In-phase vs out of phase
What happens to scan time if you double the Echo Train Length (ETL)?
The scan time will be cut in half
What the biggest advantage to CSE and the biggest disadvantage?
What the actual TE vs effective TE in reverse-echo sequences
What different about the relationship between TR and TE and what does this allow
Actual TE: time from peak of echo to next excitation pulse
Effective TE: time from peak of echo to the excitation pulse that generated it.
Only sequence where TE > TR allow for more proper T2W
How does: Increase slice thickness, Increased Image matrix, and Increase FOV affect SNR
•Increase slice thickness increase SNR
•Increased Image matrix decrease SNR
•Increase FOV Increase SNR
The largest difference in chemical shift of hydrogen is between fat and water:
At 1, 1.5, and 3 Tesla field strength what the difference in Hz
1-Tesla field strength: 147Hz
1.5-Tesla field strength: 220Hz
3-Tesla field strength: 440 Hz
In a 3D sequence the:
TR = 1000 ms
Matrix = 300*200
Slice encode step = 70
ETL = 10
Nex = 2
What is the scan time in minutes
4 min and 39.6 seconds