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MRI test 3
test
| Question | Answer |
|---|---|
| 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 |
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