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Missed and SNR
Missed MRIQuiz Mock exam qs and parameters to increase SNR
| Question | Answer |
|---|---|
| Increase TR | increase SNR |
| decrease TE | increase SNR |
| increase NEX | increase snr, more slices being sampled = increase signal |
| decrease ETL | increase SNR |
| reducing matrix/increase pixel size | Large pixel = more snr |
| Increased FOV | increase SNR bc more pixels |
| reduce rBW | increase snr = less noise being sampled |
| increase slice thickness | increase snr bc more protons being sampled |
| decrease parallel imaging | increase SNR (parallel imaging also known as Grappa) |
| increase mag field strength | increase snr bc increase mag field equals increase NMV |
| Half-fourier definition (half-scan) | technique of acquiring a little more than half of phase k-space data and using inherent conjugate summary to calculate the rest |
| Partial or fractional echo | is when only half views of k-space are filled in the frequency axis when is used to shorten TR and TE |
| Increasing phase encodings from 256 to 512 does what to SNR | decreases SNR (pixels are smaller) |
| Steep slice select gradient or narrow tBW have what affect on slice thickness | thinner slices |
| A narrow rBw disadvantage | increase susceptibility artifact |
| All the following comprise the biliary tree besides | splenic duct, comprised of common hepatic common bile, l and r hepatic, and pancreatic |
| a disadvantage of TOF MRA is high signal from background tissues, to minimize this signal the TE should be selected so background fat and water are | out of phase |
| Phase contrast MRA techniques produce images in which the signal intensity within the vessel is dependent upon the... | velocity of the flowing blood |
| Active Shielding can be defined as | Superconducting windings within the scanner reducing the fringe mag field |
| ----can be used to line the walls and/or floors of the mri mag room to reduce the fringe field and is known as ---- shielding | steel, passive |
| A technique that is reduce scan time but requires array coils | Parallel imaging |
| if the TR in a gradient echo sequence is less than T2 (or T2*) the resulting condition is known as | steady state bc it is creating residual transverse mag |
| Chemical fat suppression techniques suppress fat signal based on the | precessional frequency of fat |
| IN TOF MRA, signal from specific vessels (i.e veins) can be eliminated by | Spatial pre-saturation |
| Reducing TE yields images with what change in image contrast | decreases t2 info |
| In order to generate thin slices: | Steep SS gradient, high amplitude SS, and narrow TRANSMIT bandwidth |
| The receiver bandwidth (rBw) affects | SNR and chem shift only |
| Shimming can be performed by all the following except | turning the shim on and off rapidly |
| Which of the following flip and TR combo would create a T2 gradient echo | 450 TR, 30 flip (long tr, short flip) |
| Reducing the FOV by a factor of 2 will reduce the voxel volume by | 4 |
| T1 Contrast: TR range | 350-700 ms |
| T1 Contrast: TE Range | 10-30 ms |
| T2 contrast: TR Range | 2000-6000 ms |
| T2 contrast: TE Range | 80-120 ms |
| PD TR range | 1600-4000 ms |
| PD TE range | 10-30 ms |
| Dynamic MRA sequences of the mesenteric arteries are performed using... | incoherent gradient echo |
| In a fast spin echo, the k-space filled for each TR period would be... | 2 lines |
| Which of the following field strengths would require the SHORTEST TI time to suppress signal from fat when performing a STIR sequence? | 0.5T bc the T1 relax time of fat is field strength dependent and is shorter at lower field strengths |
| To null signal from a specific tissue using an inversion recovery sequence, the TI selected should be _______% of the t1 relaxation time of that tissue | 69% |
| On the sagittal t2 image of the cervical spine, you notice lines mimicking a syrinx, known as Gibbs truncation artifact. How do you fix this? | increase the number of phase encodings (doing this adds more data and makes the edges of the image more defined which reduces or eliminates the artifact) |
| Which of the following is not a fomite in the MRI environment (coil, keyboard, mr table, syringe) | Syringe (bc it is sterile, one time use) |
| As TR increases, what occurs? | t1 decreases, Increase in slices, increase in SNR |
| Utilizing a higher matrix and thin slices will do what to resolution? | increase spatial res (high matrix = small pixel, thin slices = less noise) |
| Reducing FOV will result in? | decreases signal to noise, increase spatial res |
| Instrinsic Factors Are? | T1, T2, PD, ADC, FLOW |
| Extrinsic Factors | TR, TE, TI, Flip Angle, ETL |
| Way to remember Extrinsic vs Instrinsic | EXtrensic - external - can be touched/manipulated |
Created by:
emjohnson4