Pulse Sequences Flashcards
an inversion recovery spin echo sequence begins with a
180 RF pulse
a typical SE sequence uses pulses
90, 180
a typinca inversion recovery spn echo sequence uses pulses
180, 90, 180
T2 weighted fluid attenuated inversion recovery (FLAIR) sequences are typically used for the evaluation of
periventricular white matter disease
typical gradient echo sequence begins with a
alpha pulse that varies with desired image contrast
short tau inversion recovery (STIR) sequences are typically used for the evaluation of all of the following
musculoskeletal contusoins
fat suppression
lesions within the retro orbital fat
STIR sequences can supress the signal from all of the following
fat within bone marrow
gadolinium enhancing lesions
retro orbital fat
to produce the echo a gradient echo pulse sequence uses a
gradient magnetic firled
RF pulse
the 180 pulse taht follows the initial 90 pulse in a spin echo sequence will cause the NMR signal to reappear while correcting for
slight magnetic field inhomogenieties
chimical shift
slight magnetic susceptibility effects
the gradient that is on during the production of the echo is called the
frequency encoding gradient
readout gradient
if the TR of a gradient echo pulse sequence is considerably less than the T2 (and T2*) the condition that will exist is known as
steady state
phase encoding is performed
prior to frequency encoding
the gradient taht is on during the production of the echo is the
frequency
the readout gradient is also known as the
frequency gradient
if a phase resolution of 256 is desired, then the TR must be repeated (for one NSA)
256 times
in the multi echo spin echo sequence shown in figure C 1, the number of SHORT TE images created with a 20 slice sequence will be
20
in the multi echo spin echo sequence shown in figure C 1, the number of LONG TE images created with a 20 slice sequence will be
20
in the multi echo spin echo sequence shown in figure C 1 the number of images PER SLICE LOCATION created will be
2
in the multi echo spin echo sequence shown in figure C 1 the TOTAL number of images wiht a 20 clice sequence will be
40
in the multi echo spin echo sequence shown in figure C 1 images will be acquired with varying amounts of
T2 information
if the pulse sequence shown in figure C 1 were a fast spin echo sequence the number of lines of K space filled during each TR period would be
2
if a given conventional spin echo sequence takes 12 minutes to acquire a fast spin echo sequence using an ETL of 6 with all other factors that affect scan time remaining the same, will take
2 minutes
in a FSE sequence the effective TE is the echo that is perfomred with the
low amplitude phae encoding gradients
in a FSE sequence spatial resolution is associated with the
high amplitude phase encoding gradients
in a FSE sequence acquired with a short effective TE, (T1 or PD weighted images) blurring can be reduced by the selection of
shorter ETL
in a FSE sequence acqwuired with a long effective TE (T2 images) scan time can be reduced by the selection of
longer ETL
a gradient echo sequence in which any residual transverse magnetization is removed prior to the next excitation pulse is known as
incoherent/spoiled
when a gradient echo sequence is acquired for dynamic contrast enhanced imaging of the liver _________is performed
spoiling
gradient echo sequences acquired for high signal from fluid are known as all of the following
coherent gradient echoes
steady state gradietn echoes
T2* gradietn echoes
dynamic enhanced MRA sequences of the renal arteries are performed with the use of
incoherent gradient echoes
gradient echo sequences can yeild either T1 or T2* characteristics
true/false
true
gradient echo sequences can yeild either T1 or T2* characteristics with influencs cause by all of the followng
susceptibility
inhomongeniety
chemical shift
gradient echo sequences acquired for the evaluation of hemorrhagic lesions rely on
susceptibility
sequence is utilized to supress the signal from fluid
FLAIR
which of the following field strenghts would require the shortest (lowest) T1 time to supress/null the signal from fat when acquiring a STIR sequence in an MR exam of the knee
0.35 T
if one desires to null the signal from a specific tissue using an inversino recovery sequence, one should select an inversion time that is______of the T1 relaxation tim eof that tissue
69%
which of the followoing best describes an EPI sequence
a train of gradient echoes
which of the following best describes a FSE sequence
a train of spin echoes
which of the folloiwng best describes an IR sequence
180 pulse followed by a 90/180 combination
which of the following best describes an SE sequence
90 pulse followed by a 180
in which of the following EPI sequences would one expect there to be the least susceptibility distortion artifacts
multishot (4shot) SE-EPI, 256x256 matrix
when acquireing an fMRI series to map out the visual cortex which of the followoing sequences would be utilized in order to maximize sensitivity to the BOLD effect
gradient echo EPI
in which of the folloiwng sequences would MS plaques appear hyperintense relative to both CSF and normal white matter
T2 FLAIR
in a balanced GRE acquisition the contrast weighting is
weighted for the ratio of T2/T1
in an image acquired with a blamace GRE sequence (fig C 2) all of the following have high (bright) signal
blood in the left ventricle
CSF
IVC
parallel imaging techniques are also known as all of the follwoing
SENSE
SMASH
GRAPPA
when parallel imaging techniques are performed a low resolution ______scan is acqiured pror to the acquisition
calibration
when doing an MRA of the IVC a saturation band should be placed _________to the axial slices
superior
when doing an MRA of the carotid arteries a saturation band should be places _______to the axial slices
superior
when doing an MRA of the circle of willis, a saturation band should be placed _____to the axial slices
superior
when doing an MRA of the superior sagittal sinus a saturation band should be places ______to the axial slices
inferior
scan time for 2D IR pulse sequences can be calculated by
TR x #PEs x NSA
scan time for 2D GRE pulse sequences can be calculated by
TR x #PEs x NSA
scan time for EPI pulse sequences can be calculated by
TR x #shots x NSA
scan time for 2D FSE puilse sequences can be calculated by
TR x #PEs X NSA/ETL
scan time for a volume acquisition can be calculated by
TR x #PEs x NSA x #slices
in a FSE sequence if the echo trail length is increased by a factor of rour, the scan will be
four times as fast
in a volume acquisition the scan time is
TR x NSA X number of phase encodings X number of slices
the number of shots is calculated by
PEs/ETL
a signle shot FSE sequence is acquired when
PEs = 256 and ETL =256
a multi shot FSE sequence is acquired with four shots shen
PEs =256 and ETL = 64
to keep a scan time a minimum diffusion imaging is typically performed with
single shot EPI acquisition
