chap 3 Flashcards
decides what line of K-space each echo is going to fill
the phase gradient
what reduces FSE by acquiring all lines of k-space at once? half the lines are acquired in one TR & the other half are transposed
Single-Shot TSE
IR prep sequence that nulls blood, useful in looking at morphology of the heart & great vessels
double IR prep
IR prep sequence that nulls fat & blood together, useful in determining fatty infiltrates of the heart walls
triple IR prep
what pulse sequence applies a reverse flip angle excitation RF pulse at the end of the echo train so that transverse magnetization is available for excitation at the beginning of the next TR period?
- produces increased signal intensity in fluid based structures (CSF) using a shorter TR than normal TSE
DRIVE
advantage of spin echo
good quality , true T2 contrast
disadvantage of spin echo
long scan times
what are the two fast inversion recovery sequences that we often use ?
STIR - nulls the signal from fat
FLAIR - nulls the signal from water
determines amount of T1 & time from one RF excitation pulse to next RF pulse.
TR
determines the amount of T2 , time from RF pulse to the peak of signal induced in the coil
TE
the equation to calculate scan time of a FSE?
Scan Time = (TR x P x NSA) / ETL
spin echo , eliminates T2*
180-degree rephasing pulse
spin echo, causes magnetic moments to dephase or “fan out” in the transverse plane
T2*
spin echo, flips the NVM into the transverse plane
90-degree RF excitation pulse
the time elapsed between the preparatory 180 degree pulse and 90 degree excitation(slice selection) RF pulse
TI, time to inversion
T/F: using a long echo train decreases the SAR (amount of power deposited in certain tissue mass)
false
controls the point at which longitudinal magnetization is nulled
TI
determines number of k-space filled every TR. Controls how many rephasing pulses are applied every TR and how many times the phase-encoding is applied to the different amplitudes every TR
ETL/TF
phase encoding gradients with a steep slope
low signal amplitude (applied to the outer zones of k-space)
phase encoding gradients with a shallow slope
high signal amplitude (applied to the center zones of k-space)
all fat is dark or nulled and the water is heavily weighted
STIR
weighting in fast spin echo because echos are generated at different TE times
effective TE weighting
FLAIR stands for
Fluid Attenuation Inversion Recovery
T/F: gadolinium should be used with STIR images
false
which pulse sequence is the gold standard ?
spin echo
represents suppressed CSF
FLAIR
used for MSK, spine, thorax - fat suppression technique
STIR
what is the string of 180s called in FSE
echo train or turbo factor
