The flashcards below were created by user
acmolt
on FreezingBlue Flashcards.
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What is the TI time?
time from 180 degree pulse to 90 degree pulse
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What exhibits the longest T1 relaxation time?
CSF
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What controls spatial localization?
slice select, phase and frequency
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T/F: increasing TR increase SNR?
True
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T/F: Increasing slice thickness will increase spatial resolution?
False: Decreasing slice thickness will increase spatial resolution
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What has a long TR and short TE?
PD weighted images
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What has a Short TR and Short TE?
T1 weighted images
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What will be dark in a T1 SE pulse sequence?
CSF
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What will CSF be in a T2 SE pulse sequence?
Bright White
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What are T2* characteristics contributed from?
magnetic inhomogeneities, varying magnetic susceptibilities, fat and water cycling
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What is the benefit of fat saturation?
is that it nulls fat to better visualize surrounding anatomy
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What is Free water protons resonance frequency separation?
3.5 ppm
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What is the pulse sequence know as when refocusing is provided by a 180 degree RF pulse?
Spin echo pulse sequence
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T/F: in proton magnetic resonance spectrum the water shifted down field from TMS is 4.7 ppm?
true
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What sequence is the preparatory pulse a pulse that is applied prior to the gradient echo?
Turbo
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T/F: EPI can be dangerous because of the extremely high magnetic field which can produce
True
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What are the types of GRE image sequence?
"steady state" and "spoiled"
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what and the k-space of the EPI be filled to?
1 RF pulse
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what is a principle hardware characteristic needed in order for EPI to work?
Shielded gradient
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what is the frequency in which images are recorded?
temporal resolution
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what is an array of numbers usually arranged in two dimensions
matrix
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What is the TE in which the operator wishes to weight the image?
Effective echo time
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What is a pulse sequence that closely follows gradient echo imaging. It is acquired when a preparatory pulse is applied followed by several variable flip angles.
Turbo
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What is a hybrid pulse sequence that combines gradient echo and fast spin echo pulse sequences?
GRASE
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What is a pulse sequence that produces a train of gradient echoes by continuously switching the read gradient rapidly inside the envelope of the FID or Spin echo.. it usually fills the k-space with RF pulse.
Echo Planar
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When the _________ gradient is turned off, all of the spins precess with he same frequency but now have different phase.
phase-encoding
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The phase encoding gradient has to be energized for the number of phase encoding steps which is equal to_______.
Matrix size
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_______ is a technique used to alter tissues contrast in MRI.
Magnetization transfer
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What are the 3 principle MRI parameters:
T1, T2, PD
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what uses a large flip angle and has a short TR and short TE?
T1
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what uses a small flip angle has a long TR and short TE?
PD
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what uses a small flip angle and has a long TR with a long TE?
T2
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What makes chemical shift artifact become worse?
narrow bandwidth and when magnetic field strength increases
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What are the parameters of spatial criteria
size, shape, and position
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what is a pulse sequence that starts with a 180 degree RF pulse, followed by another 180 degree RF pulse.
Inversion recovery
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How does IR images produce higher contrast images?
and the expense of longer imaging times
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T/F: during basic SE pulse sequence, the Slice Select gradient (Bss) is always turned on when RFt is turned off?
false: during basic SE pulse sequence, the Slice Select gradient (Bss) is always turned on when RFt is turned ON
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what occurs when there is no transverse magnetization and no signal?
null point
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Fo a t2 weighted pulse sequence the operator should choose a TR of what AND a TE of what?
TR 500, TE 20
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if you increase TR what else will it effect?
increase SNR
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Long TR and Long TE=
T2 weighted images
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What is the most commonly employed MR pulse sequence?
Spin Echo
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In turbo imaging, low spatial frequencies, which contain the patient's course structures, follow a ______ phase-encoding gradient.
Weak
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In turbo imaging, high spatial frequencies which contains patient's fine structures, follow a _______phase-encoding gradient
Strong
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An alpha pulse, represents _________in regards to MRI
flip angle less than 90 degrees
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Faster imaging times will improve ________.
Temporal resolution
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A_______ field is used to rephase spins during GRE imaging.
Gradient Magnetic
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In regards to filling k-space in an EPI sequence, the "blip" is referred to as _______
Phase Gradient
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The fundamental idea of EPI is __________.
Filling k-space in a single RF pulse
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Describe null point in inversion recovery and a pulse sequence we use it in?
there is a value of T1 where Mz equals zero. Application of a 90 degree RF pulse at this point results in no signal because there is no Z magnetization to rotate onto the XY plane
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Describe the appearance of the chemical shift artifact and along which gradient it appears?
Chemical Shift artifacts are always in the frequency encoding direction and appear as black and bright border
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what are 3 ways to optimize MRI images?
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List 3 fast acquisition pulse sequences
Turbo, GRASE, EPI
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What is the benefit of MRI gating?
Gating: a segmentation step that improves turbo imaging. It's purpose is to allow quick images without motion
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State the 2 fundamental characteristics in how Gradient Echo differs from spin echo
In gradient echoes, spins are refoccused with a gradient magnetic field, rather than a 180 degree RF pulse. SE is a long TR, FRE is shorter TR.
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Describe effective TE in detail?
the time interval between the middle of the excitation pulse and the middle of the echo signal that is observed.
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Why are STIR and FLAIR pulse sequences used to image musceoskeletal system and central nervous system respectively
STIR: short time inversion recovery used to image fat. For tissue with a short T1 relaxation time, such as fat, a short T1 allows elimination of the high signal from fat.
- FLAIR: fluid attenuated inversion recovery; used to image the CNS; fluid has a relatively long T1 and TI's of about 2 sec. are necessary to minimize the signal from fluid
- structures.
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how is k-space filled differently in fast spin echo vs. conventional spin echo and how is the phase gradients involved in both of these processes
conventional epin-echo: k-space is filled line by line in sequential order from bottom to top. Starts with large, negative phase encoding gradient amplitudes, through the zero phase encoding, then to a large, positive phase encoding amplitude.
fast spin echo: more than 1 line is filled per TR
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describe the difference between steady state and spoiled gradient echo?
Steady state echo: the condition of constant longitudinal magnetization after repeated alpha pulses
Spoiled gradient echo: assuming that Mxy is dephased before each alpha pulse
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