PS 2 Flashcards
a “single shot” or “snap shot” F/TSE sequence is when the ________ equals the ________.
when the ETL equals the PHASE ENCODING STEPS REQUIRED.
What are the main differences between echo imaging (GRE) vs Spin Echo (SE)?
Short TR’s
Gradient-induced echoes
<90° Slice excitation pulses.
What is the main characteristic of Inversion Recovery (IR) vs Spin Echo (SE)?
IR Starts with a 180°-90°-180° RF slice excitaion order.
A tissue that is “saturated” will yield a high or low SNR?
Low SNR.
What is Echo Spacing?
The time between each echo in the echo train
What is the gradient used to generate an echo in a GRE?
Gx
True or False:
IR is a pulse sequence used only for T1 weighting.
False.
True or False:
Magnetic Susceptibility effects can both degrade & improve diagnostic imaging quality.
True
In GRE, what is used to eliminate residual transverse magnetization?
“Spoiler” pulses.
What is the signal characteristic of a tissue at the null point?
(high or low SNR?)
Low SNR
The calculation for scan time in a F/TSE is the same as SE except for:
Dividing the result by the ETL.
In a SE sequence, if 120 phase encoding steps are selected, the TR is repeated _______ times.
120
The ability of a tissue to become magnetized is:
Magnetic Susceptibility
STIR is an IR sequence used to produce __________
Robust fat suppression
A parameter used in IR that is not used in SE is:
TI (inversion time)
In IR, the first 180° slice excitation pulse places the LMZ into the:
-z axis
What is an effective method for reducing echo spacing?
Decrease frequency encoding steps
increase the receive bandwidth
Signal dephasing due to local inhomogeneities is referred to as what?
T2’ (prime)
When the TR is shorter than a tissue’s T2 decay time, the “leftover” transverse magnetization of that tissue is referred to as what?
Residual Transverse Magnetization
Another characteristic of IR is that it always requires a _________ than SE.
Longer TR
Tissues become saturated due to _____ flip angles and very ______ TR’s.
High Flip angles
Very short TR’s
What happens when there is a great variance of T2 Decay in the ETL?
F/TSE blurring
What is the point at which the LMV crosses from the -z axis to the +z axis known as?
Null Point
What is the best T1 time for STIR imaging at 1.5T
160 msec
______ is described as the ability of a substance to attract iron, cobalt, and nickel.
Magnetism
What is a pulse sequence?
a series of events that include radio frequency transmissions & detections & various magnetic gradient fields timed to achieve an image with a particular SNR, spatial resolution, and contrast.
Gradient echos are ________ at correcting for dephasing caused by inhomogenities while 180° radio frequency echoes are _________.
ineffective
effective.
In IR, the time between the 180° & the first 90° RF pulse is called T1 as well as:
Tau
In fast/turbo spin echo (F/TSE), if the echo train is 8 and the number of phase encoding selected is 256, what is the number of TR’s that are repeated?
32
In a T2W flair sequence of the brain, what is suppressed in order to make long T2 pathologies moer conspicuous?
(such as edema, inflammation, and certain tumors)
CSF
in Fast/turbo spin echo (F/TSE) , what is the echo train made up of?
a series of 180° RF Pulses
In the IR pulse sequence known as a FLAIR, what is suppressed?
Fluid
