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CT REGISTRY- STUDY THIS AND YOU-LL PASS!! (excluding anatomy) QUESTIONS & ANSWERS RATED 100%
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CT REGISTRY- STUDY THIS AND YOU-LL PASS!! (excluding anatomy) QUESTIONS & ANSWERS RATED 100%
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CT REGISTRY- STUDY THIS ANDYOU'LL PASS!! (excluding anatomy)
QUESTIONS & ANSWERS RATED 100%
how do you reduce beam hardening - ANS-1. Increase dose
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2. Reduce collimation--Reduce slice thickness
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3. Increase window width
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At what level does the abdominal aortal bifurcate? - ANS-L4
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What is the typical scan delay after injection of contrast media for studies of the liver? -
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n ANS-30-45 seconds n
What window settings provide the best tissue differentiation within the liver? - ANS-
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window width= 140, level= 60
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What is the window settings that provide the best bone window for the pelvis? - ANS-
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window width=2000, window level=350
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What mAs is typically used in routine CT exams of the abdomen? - ANS-200-300 mAs
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,What is the result of the bifurcation of the abdominal aorta? - ANS-The right and left
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n common iliac arteries n n
What is the anode target angle? - ANS-12 degrees
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At what level do the common carotids bifurcate into the internal and external carotid
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n arteries? - ANS-C3-C4 n n
The floor of the orbit is formed by the __________ bones. - ANS-maxillary and zygomatic
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The lateral wall of the orbit is formed by the ___________ bones. - ANS-zygomatic and
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n sphenoid
The medial wall of the orbit is formed by the _________ bones. - ANS-ethmoid and lacrimal
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n bones
how do you calculate effective mAs? - ANS-mAs/pitch
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define window level and window width - ANS-LEVEL: a chosen midpoint in the grayscale
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WIDTH: number of grayscale values above and below the level.
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- The width is DIVIDED in HALF and distributed above and below the level.
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- Anything above the window is white
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,- Anything below the window is black
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The wider the window the more grayscale values, the lower the contrast!
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example:
Level 100, Width 300
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White = >+250 n n
Black = <-50 n n
Level 100, Width 200
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White = >+200 n n
Black = <0 n n
Level 100, Width 150
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White = >+175 n n
Black = <25 n n
factors that affect spatial and contrast resolution - ANS-Spatial resolution:
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1) focal spot
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2) detector width (aperture)
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3) reconstruction algorithm - bone>soft tissue
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4) slice thickness - thinner is better
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5) pixel/FOV/matrix
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, 6) pitch - decreased pitch means no gaps
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7) nyquist limitations
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Contrast resolution: CNR n n
1) energy of X-rays - kVp - ↑ kVp ↓ contrast
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2) number of X-rays - mA - ↑ mA ↓ mottle
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3) slice thickness - thicker is better
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4) reconstruction method - iterative > filtered
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5) reconstruction algorthith - soft tissue>bone
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Give window levels for brain, lung, abdomen, bone - ANS-Brain: W80,L+40
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Lung: W1500, L-400 n n
Abdomen: W400, L+50 n n
Bone: W1600, L+500 n n
What is beam hardening?
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what are the two types of beam hardening artifact?
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how do you compensate for it? - ANS-1) as the X-ray beam passes through an object,
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n lower energy photons are removed (like filtration!) leaving a "harder beam" of high
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n energy photons. This causes two artifacts:
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2) Cupping: the center of a round object is darker than the periphery due to hardening of
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n the beam 360 degrees around the object. happens in the head
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