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14 Cards in this Set
- Front
- Back
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What are the main advantages of CT & MRI over digital radiography?
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-better contrast resolution
-tomographic: imaging in slices (eliminates anatomic superimposition) -MR provides for physiologic imaging: primarily looking at water |
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Order the following from best spatial resolution to worst spatial resolution: radiography, CT, MRI.
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radiography
CT MRI |
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Order the following from best contrast resolution to worst contrast resolution: radiography, CT, MRI.
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MRI
CT radiography |
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Order the following from best detail to worst detail: radiography, CT, MRI.
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radiography
CT MRI |
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What is the basic principle of CT image formation?
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based on quantification of x-ray absorption: similar to radiography, but in slices
image generated by computer after measuring x-ray attenuation |
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What are characteristics of generic CT scanners?
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-x-ray beam used to image slices of patient
-thickness of slice can be varied from 1-10 mm -each slice takes ~1 s. -table moves after each slice |
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What are characteristics of modern CT scanners?
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-table moves continuously
-acquire > 1 image slice per tube resolution (4, 16, or 64) -scan patient in a few seconds -provides high quality data for exquisite images (allows valuable 3-D images to be made) |
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How can contrast medium be used w/ CT?
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used to look for BBB leaks (helpful when looking for brain tumors), vascular leaks, & hypervascularity
contrast medium is iodinated & thus increase x-ray absorption: appears white on CT |
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On what does the image appearance depend in MRI?
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image appearance depends on chemical composition: free water, tissue water, fat
-we are primarily imaging hydrogen protons (i.e. water) -water creates a high signal in some MR image types -most lesions have ↑ water, so we commonly look for signs of ↑ water |
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What are some advantages of MRI over CT?
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much greater contrast resolution
image can be made in any plane provides physiologic imaging |
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What are the basics principles of MRI?
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-very strong magnetism
-magnet causes protons in patient to align w/ magnetic field -radio wave (RF) knocks protons out of alignment into X-Y plane *shielding used to keep outside radio waves from interfering -misaligned protons create signal in receiving coil -signal strength converted to gray scale in image *high signal = white *low signal = black -safety concerns d/t very strong magnetism (1.5 Tesla) |
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What is the appearance of the following in T1 MRI?
a. fat b. free water c. tissue water d. bone |
a. white
b. black c. gray d. black |
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What is the appearance of the following in T2 MRI?
a. fat b. free water c. tissue water d. bone |
a. white
b. white c. gray d. black |
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How can contrast medium be used w/ MRI?
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can be used in T1 images to look for areas of BBB breakdown, vascular leakage, & hypervascularity
contrast medium is magnetic & influences proton behavior |
