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CT REGISTRY- STUDY THIS AND YOU-LL PASS!!.
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CT REGISTRY- STUDY THIS ANDYOU'LL PASS!!
how do you reduce beam hardening - answer-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? - answer-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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answer-30-45 seconds
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What window settings provide the best tissue differentiation within the liver? - answer-
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window width= 140, level= 60
b b b b
What is the window settings that provide the best bone window for the pelvis? - answer-
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window width=2000, window level=350
b b b
What mAs is typically used in routine CT exams of the abdomen? - answer-200-300
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mAs
b
What is the result of the bifurcation of the abdominal aorta? - answer-The right and left
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common iliac arteries
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What is the anode target angle? - answer-12 degrees
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At what level do the common carotids bifurcate into the internal and external carotid
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arteries? - answer-C3-C4
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The floor of the orbit is formed by the __________ bones. - answer-maxillary and
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zygomatic
b
The lateral wall of the orbit is formed by the ___________ bones. - answer-zygomatic
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and sphenoid
b b
The medial wall of the orbit is formed by the _________ bones. - answer-ethmoid and
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lacrimal bones
b b
how do you calculate effective mAs? - answer-mAs/pitch
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,define window level and window width - answer-LEVEL: a chosen midpoint in the
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grayscale
b b
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 300b b b
White = >+250 b b
Black = <-50 b b
Level 100, Width 200b b b
White = >+200 b b
Black = <0 b b
Level 100, Width 150b b b
White = >+175 b b
Black = <25 b b
factors that affect spatial and contrast resolution - answer-Spatial resolution:
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1) focal spot
b b
2) detector width (aperture)
b b b
3) reconstruction algorithm - bone>soft tissue
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4) slice thickness - thinner is better
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5) pixel/FOV/matrix
b
6) pitch - decreased pitch means no gaps
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7) nyquist limitations
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Contrast resolution: CNR b b
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 - answer-Brain: W80,L+40
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Lung: W1500, L-400 b b
Abdomen: W400, L+50 b b
Bone: W1600, L+500 b b
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? - answer-1) as the X-ray beam passes through an
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object, lower energy photons are removed (like filtration!) leaving a "harder beam" of
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high 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
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of the beam 360 degrees around the object. happens in the head
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3) Streak: these are dark bands that occur in between two dense objects - nearly all the
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photons are removed in a line between the two objects
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4) fixes:
b
A) Filtration: pre-hardening the beam to remove low energy photons
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B) Calibration: using a phantom to set a compensated mA/kVp
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C) Correct software: iterative reconstruction may help
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D) Avoidance: tilting the gantry of positioning the patient to avoid areas that may cause
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hardening.
b
ring artifact - answer-Calibration error or defective detector cause consistently
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berroneous reading at each angular position, resulting in a circular artifact
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is the focal spot large or small? - answer-large 0.6-1.2 - so as not to overheat the anode
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bfrom such a high mA b b b b
Which of the following will result in an increased voxel size: B increased slice thickness
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- answer-A)decreased reconstruction FOV B) increased slice thickness C) increased
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matrix D) none of these
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If a tissue with a CT number of +300 appears white on the image, which of the following
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bare the window width and window level selected: A)window level =0, window width
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b=500 B)window level= +300, window width= 500 C)window level =+100, window width
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b=1000 D)none of these - answer-A) window level =0, window width =500
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What is the volume of a voxel if a slice thickness of 3 mm, a 512x512 matrix & a
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reconstruction field of view of 25.6cm are used A) 0.75mm³ B)1.5mm³ C) 6.0mm³
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D)none of these - answer-A. Solve this by finding the pixel size first FOV/matrix size ...
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that is 0.5 ... now square that 0.25 .... multiply that by slice thickness and you get 0.75
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Which of the following parameters is responsible for partial volume averaging: A) matrix
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size B) kVp C)slice thickness D) patient dose - answer-C
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Voxel equation - answer-pixel area x section thickness
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What is interpolation? - answer-Mathematical method for taking SPIRAL data and
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viewing it as AXIAL images
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, Bone windows - answer-2000-4000 WW
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200-400 WL b
Lung windows - answer-1400-1600 WW
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(-)400-600 WL b
Modular Transfer Function? - answer-graphical representation of SPATIAL
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RESOLUTION measured in lp/cm, tells how small you can scan without blurring
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Decrease partial volume averaging? - answer-Reduce slice thickness
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Which portion of the pancreas is the most common site for tumors?; and where located?
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- answer-The head of the pancreas. It is located approximately at T12
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LUNG WINDOW b
(-) IS AIR - answer-2000 WW and -200 WL =
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The Hounsfield unit that is -1000 most likely represents which of the following? -
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answer-Air
b
Relative to CT topography, slice thickness is best represented by which of the following
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axes? - answer-Z axis
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What unit is the basis for exposure based on ionization in air? - answer-mR or C/kg
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What radiation unit considers the biological effectiveness of radiation exposure? -
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answer-mrem or mSv
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"Fan" beam technology first historically came on the scene with which acquisition
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bgeometries? - answer-Second b b
"Rotate-rotate" applies to which of the following geometries? - answer-Thirdb b b b b b b b b
In CT what imaging plane is the pituitary best visualized? - answer-coronal
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The third ventricle of the brain communicates with the fourth ventricle through the -
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answer-Cerebral aqueduct
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refers to an excessive Amount of nitrogenous materials in the blood and is a symptom
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bof renal failure. - answer-Azotemia
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Which paranasal sinus is usually the last to fully develop? - answer-Frontal
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What is the average annual radiation dose? - answer-2 rem
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10 rem converted to Sieverts is what? - answer-0.1 Sv
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