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21 Cards in this Set
- Front
- Back
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What are the four factors in assessing the quality of MRI images? |
1. SNR 3. spatial resolution 4. scan time |
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The volume of tissue in a patient is determined by these three factors. |
1. slice thickness 2. matrix size 3. FOV |
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What is the TI for STIR, FLAIR and T1 IR? |
STIR = 100-175 FLAIR = 1700-2500 T1 IR = 200-800 |
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What are two disadvantages of decreasing bandwidth? |
- increased chemical shift - increased motion artifact |
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What are three things related to the use of RF coils that can help improve SNR? |
- coil selection - size of coil appropriate for area - coil positioned perpendicular to Bo |
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How could you reduce your scan time? |
- decrease TR - decrease phase matrix - decrease NEX - decrease slice number - increase ETL |
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What are the effects of increasing your ETL? |
- blurriness - decreased signal - decreased magnetic susceptibility - decreased scan time |
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What do isotropic pixels mean? |
The pixels are the same dimension in all planes. |
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What is the term for the artifact that is caused when two different frequencies with the same peak are placed in the same voxel? |
Wrap-around (aliasing) |
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The artifact appear as multiple rings or bands of regular periodicity or duplication at transitions between high and low signal intensities. |
Truncation (Gibbs) |
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What sequence is good for the differentiation between white and grey matter? |
IR T1 |
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An ADC map will show areas of restricted diffusion as... |
Dark |
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In this imaging technique, an image volume is repeatedly subjected to RF pulses that flip the longitudinal magnetization into the transverse plane thus decreasing the tissue's signal. |
TOF |
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What are the advantages of a 2D TOF MRA? |
- sensitive to slow moving vessels - larger coverage - faster |
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T2 time is the time it takes ____% of the total magnetization to be lost in the transverse plane via _________ interaction. |
63% via spin-spin |
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An ETL is the number of ______________ per TR. |
180 degree rephasing pulses |
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How can CNR be improved? |
- saturation sequences - T2 sequences - contrast agents - TOF sequences |
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What are intrinsic contrast parameters that determine image weighting? |
- proton density - T1 and T2 values - flow |
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What are two strengths of PD weighted images? |
- meniscal pathology - anatomical detail |
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What are the two most common artifacts seen in the cervical spine and how can you resolve them? |
- motion (swap phase and frequency, sat band) - flow (sat band) |
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What are two artifacts seen in the T and L spine and how can you resolve them? |
- motion (sat band) - wrap-around (over-sampling) |
