Data Acquisition and Processing Flashcards
What are the 5 basic steps to a pulse sequence
alignment excitation slice selection phase encoding rephasing slice selection frequency encoding
What hardware performs alignment in a pulse sequence
main magnet
What hardware performs excitation slice selection in a pulse sequence
RF coil and gradients
What hardware performs phase encoding in a pulse sequence
phase encoding gradient
What hardware performs rephasing slice selection in a pulse sequence
RF coil (for SE) gradients (for GE)
What hardware performs frequency encoding in a pulse sequence
frequency encoding gradient
What are the 2 types of pulse sequences
spin echo and gradient echo
Which pulse sequence uses a 90° excitation pulse followed by one or more 180° rephasing pulses in order to generate one or more spin echos
spin echo
What are the 3 types of spin echos
conventional spin echo (CSE)
fast spin echo (FSE)
inversion recovery (IR)
This type of spin echo uses a 90 alpha pulse and a singe 180 rephasing pulse per TR
conventional spin echo
How many lines of K space are filled per TR during a conventional spin echo
one (resulting in longer scan times, so CSEs are usually only T1 weighted)
What are the advantages of a conventional spin echo
excellent image quality
“true” image weighting (since there is no signal averageing of multiple echos)
What are the disadvantages of a conventional spin echo
long scan times (only 1 line of K space is filled per TR)
What are the TR and TE parameters for a T1 weighted CSE
TR = 300-700 ms TE = 10-30ms
What are the TR and TE parameters for a T2 weighted CSE
TR = 2000ms+ TE = 80ms+
What are the TR and TE parameters for a PD weighted CSE
TR = 2000ms+ TE = 20ms
Fast spin echoes (FSE) are also referred to as what
Turbo spin echoes (TSE)
Which pulse sequences use a 90ﾟ alpha pulse and multiple 180ﾟ rephrasing pulses per TR
Fast spin echoes (FSE) aka Turbo spin echoes (TSE)
What parameter is averaged during a fast spin echo
TE is averaged and creates an “effective TE”
Is it possible to acquire true image weighting during FSE sequences
no because the TEs for each echo are averaged
What are the advantages of an FSE sequence
Shorter scan times (multiple lines of K space are filled per TR)
decreased magnetic susceptibility artifacts
What are the 4 disadvantages of an FSE sequence
Increased motion artifact (sinse signal during motion is acquired multiple times)
increased image blurring (from signal averaging of long echo trains)
decreased SNR
decrease of ability to detect small hemorrhages (because of the reduction in magnetic susceptibility artifacts)
Which spin echo sequence combines FSE with a Partial Fourier technique in order to fill all lines of K space during a single TR period
Single shot fast spin echo (SS-FSE)
What are the advantages of a single shot fast spin echo (SS-FSE) sequence
Dramatic reduction in scan time
What are the disadvantages of single shot fast spin echo (SS-FSE) techniques
Increased tissue heating
increased SAR (due to the extra RF rephasing pulses)
What does the acronym DRIVE stand for
Driven Equilibrium Fourier Transform
Which pulse sequence uses a reverse flip angle excitation pulse after the echo train (90-180-180-90), thus driving any residual transverse magnetization into the longitude plane so that it cannot be further excited at the beginning of the next TR cycle
Driven Equilibrium Fourier Transform (DRIVE)
Which pulse sequence yields a hyper intense fluid signal when compared to standard FSE pulse sequences
Driven Equilibrium Fourier Transform (DRIVE)
What are the TR and TE parameters for a T1 weighted FSE
TR = 300-700 ms
effective TE = minimum
What are the TR and TE parameters for a T2 weighted FSE
TR = 3000-10000 ms
effective TE = 80-140ms
What are the TR and TE parameters for a PD weighted FSE
TR = 3000-10000 ms
effective TE = minimum
A pulse sequence that begins with a 180ﾟ inverting pulse followed by a conventional spin echo (CSE) or fast spin echo (FSE) pulse sequence.
Inversion recovery
What 2 things are used to null the signal from certain tissues such as fat or fluid in an inversion recovery sequence
A 180ﾟinverting pulse
Time of inversion (TI)
What are the 2 types of IR sequences
STIR
FLAIR
The time between the 180ﾟ inverting pulse and the 90 alpha pulse is called what
Time of inversion (TI)
What is occurring during the TI interval
longitudinal recovery - allowing more T1 relaxation between tissues (decreasing T1 contrast since more tissues relax to the longitudinal axis)
Longitudinal recovery during an IR sequence does what to T1 contrast
Decreases it - since more tissues relax to the longitudinal axis
When the 90ﾟ RF pulse is applied during an IR sequence, what happens to tissues nearest the transverse plane
They will flip an additional 90ﾟ- moving past the transverse plane into full saturation thus becoming nulled out
What happens to tissues that were able to relax nearer the longitudinal plane when the 90ﾟ RF pulse is applied during and IR sequence
they will be flipped 90ﾟ into the transverse plane where they will contribute to image signal
The TI interval that is selected represents what
What tissues will be nulled
What determines image weighting during an IR sequence
The TR and TE - just like all other sequences
What does STIR stand for
Short TI inversion recovery
or
Short TAU inversion recovery
An inversion recovery pulse sequence that uses a short TI of approximately 100-175ms
STIR
Which inversion recovery sequence is used to null fat
STIR
What is the TI for a STIR sequence
100-175ms
How will CSF and fat appear on a STIR
CSF will be bright
fat will be dark
Which inversion recovery pulse sequence uses a long TI of 1700 - 2200ms
FLAIR
What does FLAIR stand for
Fluid attenuating inversion recovery
How does fat and CSF appear on a FLAIR
Fat is bright
CSF is dark
What weighting does a STIR have
T1
What weighting does a FLAIR have
T2
What is the TI for a FLAIR
1700 - 2200ms
What does GRE stand for
Gradient recall Echo
What are the 2 acronyms for gradient pulse sequences
GRE (Gradient recall Echo)
GE (Gradient echo)
What sequence uses an alpha pulse with a variable flip angle, as well as the frequency encoding gradient - instead of a 180ﾟ RF pulse - for rephrasing
Gradient echo
What does a gradient echo use to rephrase spins
The frequency encoding gradient
What do spin echoes use to rephase spins
A 180ﾟ RF pulse
Can gradients compensate for magnetic field inhomogeneities
no
Due to the inability of gradients to compensate for magnetic field inhomogeneities, all gradient images have some extent of what type of contrast
T2*
Are gradient pulse sequences sensitive to flow
yes
Are gradient echo pulse sequences fast or slow
Fast (commonly used for breath hold sequences)
What are the 5 types of gradient echoes
Conventional gradient echo (CGE)
Steady state (SS)
Fast gradient echo (FGE)
Balanced gradient echo (BGE)
Echo planar imaging (EPI)
How many lines of K space are filled per TR during a conventional gradient echo
only 1
What type of gradient echo pulse sequence uses 2 excitation pulses, with variable flip angles, at TR time intervals less than the T1 and T2 times of the body’s tissues in order to maintain residual transverse magnetization for the creation of a stimulated echo
Steady state sequences
If a steady state sequence uses 2 90ﾟ excitation pulses, the echo created by the application of the 2nd pulse is referred to as a
Hann echo
How many times is the frequency encoding gradient used for rephasing during a steady state sequence
once
Steady state sequences are called as such because they maintain partial longitudinal and transverse magnetization at all times, never allowing the NMV to return to the longitudinal axis. T/F
true
What type of steady state pulse sequence uses 2 alpha pulses with variable flip angles, as well as subsequent gradient rephasing where only the gradient echo (FID) is sampled
Incoherent (spoiled) gradient echo
How many types of steady state sequences are there
3
Name the 3 types of steady state sequences
Incoherent (spoiled) gradient echo
Coherent gradient
Steady state free precession
This type of steady state pulse sequence prevents the stimulated echo from contributing to image contrast by spoiling (dephasing) it through the use of RF spoiling or gradient spoiling (application of all 3 gradients
Incoherent (spoiled) gradient echo
Incoherent gradient echo sequences are typically used for what type of weighting
T1, sometimes PD
What are the advantages to using an incoherent (spoiled) gradient echo
Very fast (making breath holds possible)
very sensitive to flow (good for angiography)
What are the disadvantages to using an incoherent (spoiled) gradient ago
Increased magnetic susceptibility artifacts
Produce loud gradient noise
What is the flip angle used for incoherent gradient echoes
30-45ﾟ
What TR is used for an incoherent gradient echo
20-50ms
What TE is used for an incoherent gradient echo
5-10ms
