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MRI test 3


what combination of technique give more slices Long TR short TE
if the matrix is adjusted from 256x256 to 128x256, what effect will this have on the image? will decrease SNR, increase spatial, and cut image time down
flair sequences are used for what? to null CSF- you can see pathology
STIR can be used with gadolinium at all field strength
Stir surpreses all tissues with the same T1 value
Laminar flow is predictable flow
flow phenomenon occurs because stationary tissue has a higher signal later in a slice, flow has bright signal in the beginning of the slice
when using regulaar spin echo signal from flow is null because of belocity
to better visualize flow, you should use presaturation pulse and use gre sequence
chemical shift occurs fat and water are close to anatomy
when spins are together and give a lot of signal they are.. in phase/ coherent
when you use 3 or more RF pules to produce an echo this will be a what? stimulated echo
in a steady state sequence TR must be significantly shorter than T2
in steady state a long t2 restores transverse magnetation, the tails of FID and spin echos will merge, a signal of amplitude is produced
the first gradient applied in gradient echo sequence is applied in a negative direction (in order to rephrase them)
GRE sequences are best done to.. on scanners with good homogeneity
things that affect SNR are proton density area under examination, voxel volume, NEX
when you decrease the size of the voxel SNR decreases
A course matrix has a low number of frequency encoding
if you half the number of phase encodings SNR is halved
Boxel wolume is determined by slice thickness and pixel area
proton density weighting the pelvis has high signal
the applitude of signal in the area bing examined is determined by T2
wich scan has more signal spin echo
the most protent factor that affects SNR angle
as the received bandwidth increases SNR decreases
increasing minimum bandwidth ?
SNR is increased by Long TR- also short TE gives you more SNR, less flip angle gives less SNR less saturation
contrast to noise ratio if affected by voxel volume
only signal from what can be visualized free protons
reducing slice thickness reduces partial boluming increases spatial resolution
the matrix determines scan time, fov, resolution
To optimize image quality we can do this by smaller FOV, thin slices, fine matrix
to optimize spatial resolution you select a steep in phase encoding- info will go outside of k-space (that means spatial resolution)
If you have a steep gradient this will affect fewer slices
TR is affected by Number of slices and fov
large coils cause increase area of signal
increasing fov increases anatomy coverage
increasisng the slice thickness will increase SNR
volume imaging allows for increased SNR, isotropic volumes, no gap
what is this sequence TE 20 TR 2000 128x128 NEX 2 proton density because of the short te and also a spin echo
using an echo train it allows us to fill more than one line of k space at a time, have faster scans, have various weighting
with a long echo train we get more echos with shallow phase encoding near the effected TE
some benefits of t2 fast spin echo are less artifact from metal implants
long turbo factors cause too much t2 weighting fro t1 proton density weighting images
short turbo factor gives more slices per TR
the weighting of an inversion recovery sequence is dependent on a TI
in inversion recovery the TR is time between each 180
inversion recovery is used to produce produce t1 for pathology
a TI of 300 ms is used to null signal for muscle
when using contrast with inversion recovery always use SPUR
Flair is used to null csf, used to better differentiate pathology from CSFm means fluid attenuation inversion recovery
the flip angle in conjuntion with the Tr determines saturation true or false true
to prevent saturation the flip angle should be large and TR long true or false false
to minimize t2*, te should be short true or false false- we use 180 to control t2*
in GRE, the GR controls the number of slices that can be excited during the aquisition true or false true
steady state is a condition where TR is longer than the T1 and T2 of the tissue true or false false
the flip angle in tr maintains steady state true or false true
steady state uses two fid's to acuire a spin echo known as a stimulated echo true or false true
incoherent swquences use a rewinder to achieve rephasing true or false false it's a spoiler
coherent gradient echo pulse swquences produce inmages that are t2 true or false false
coherent pulse sequences produce dard fluid true or false false
rewinding is achieced by reversing the slope of the phase encoding gradient after read out true or false true
disadvantages of coherent sequences are poor SNR, 2D and loud noise true or false true
incoherent pulse sequences use gradient rephaseing to produce and echo true or false true
digitized RF can only be transmitted at a specific frequency true or false true
RF spoiled sequences demonstrate good T2 anatomy true or false false
in GRE vessels are generally bright true or false true gre is good for flow
when doing an exam that requires sat pulses you should always place them superior to flow true or false false
when doing a coronal biew of the shoulder you should place your sat band medially to the anatomy true or false true
if nuclei are out of phase at 40 ms they will be in phase 40 ms later true or false true
aliasing is produced by atoming outside fov true or false true
presat is transmitted in the same frequency and evenly to the whole fov so that dense areas of fat receive the same energy as areas with less dense fat true or false true
pre saturation pulses make flowing nuclei bright true or false false
pre sats can be used to null fat or water true or false true
pre stats have no effect on patients SAR true or false false
istinguishing between fatty and nonfatty components of tumor does not require sat pulse true or false false
pre saturation pulses are only usefull is they are applied to tissue true or false true
in fat hydrogen is linked to carbon and in water is linked to oxygen true or false true
it is very important to separate fat frequencies from water to saturated well true or false true
presaturation is generall used in either t2 or proton density weighting true or false false
pulse of flow is not constant so that gradient moment rephasing if often more effective on venous rather than arterial flow true or false true
entry slice phenomenon effects giving different signal intensities to stationary nuclei true or false true
nuclei flowing in the opposite direction to slice excitation is called co current flow true or false false
entry slice phenomenon increases when using short TR true or false false
flow related enhancement increases as the TE Decreases true or false false
entry slice phenomenon happns because of nuclei that have not been previously excited enter the slice fresh and have not been saturated true or false true
time of flight phenomenon takes place in spin echo because flowing nuclei only recieves one excitation pulse before exciting the slice true or false true
stangnet flow behaves as startionary tissue true or false true
TE has not effect on time of flight effect true or false false
as the velocity flow increases the time of flight decreases true or false false
laminar flow is considered second order flow true or false false
laminar flow is flow that is at a different but constant velocities across the vessel true or false true
for t1 breathhold your best sequence would be 2D incoherent gradient echo true or false true
Epi is faster due to how k space is filled true or false True
there are no adverse effects from EPI because you dont' use numerous RF pulses true or false false
in an epi sequence the TR are short true or false False
Created by: 1145508893