CT REGISTRY- STUDY THIS AND YOU'LL PASS!! (excluding anatomy) 100% CORRECT ANSWERS!!
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Course
CT REGISTRY
Institution
CT REGISTRY
how do you reduce beam hardening correct answers 1. Increase dose
2. Reduce collimation--Reduce slice thickness
3. Increase window width
At what level does the abdominal aortal bifurcate? correct answers L4
What is the typical scan delay after injection of contrast media for studies of the ...
CT REGISTRY- STUDY THIS AND YOU'LL PASS!!
(excluding anatomy) 100% CORRECT ANSWERS!!
how do you reduce beam hardening correct answers 1. Increase dose
2. Reduce collimation--Reduce slice thickness
3. Increase window width
At what level does the abdominal aortal bifurcate? correct answers L4
What is the typical scan delay after injection of contrast media for studies of the liver? correct
answers 30-45 seconds
What window settings provide the best tissue differentiation within the liver? correct answers
window width= 140, level= 60
What is the window settings that provide the best bone window for the pelvis? correct
answers window width=2000, window level=350
What mAs is typically used in routine CT exams of the abdomen? correct answers 200-300
mAs
What is the result of the bifurcation of the abdominal aorta? correct answers The right and
left common iliac arteries
What is the anode target angle? correct answers 12 degrees
At what level do the common carotids bifurcate into the internal and external carotid arteries?
correct answers C3-C4
The floor of the orbit is formed by the __________ bones. correct answers maxillary and
zygomatic
The lateral wall of the orbit is formed by the ___________ bones. correct answers zygomatic
and sphenoid
The medial wall of the orbit is formed by the _________ bones. correct answers ethmoid and
lacrimal bones
how do you calculate effective mAs? correct answers mAs/pitch
define window level and window width correct answers LEVEL: a chosen midpoint in the
grayscale
WIDTH: number of grayscale values above and below the level.
- The width is DIVIDED in HALF and distributed above and below the level.
- Anything above the window is white
- Anything below the window is black
The wider the window the more grayscale values, the lower the contrast!
,example:
Level 100, Width 300
White = >+250
Black = <-50
Level 100, Width 200
White = >+200
Black = <0
Level 100, Width 150
White = >+175
Black = <25
factors that affect spatial and contrast resolution correct answers Spatial resolution:
1) focal spot
2) detector width (aperture)
3) reconstruction algorithm - bone>soft tissue
4) slice thickness - thinner is better
5) pixel/FOV/matrix
6) pitch - decreased pitch means no gaps
7) nyquist limitations
Contrast resolution: CNR
1) energy of X-rays - kVp - ↑ kVp ↓ contrast
2) number of X-rays - mA - ↑ mA ↓ mottle
3) slice thickness - thicker is better
4) reconstruction method - iterative > filtered
5) reconstruction algorthith - soft tissue>bone
Give window levels for brain, lung, abdomen, bone correct answers Brain: W80,L+40
Lung: W1500, L-400
Abdomen: W400, L+50
Bone: W1600, L+500
What is beam hardening?
what are the two types of beam hardening artifact?
how do you compensate for it? correct answers 1) as the X-ray beam passes through an
object, lower energy photons are removed (like filtration!) leaving a "harder beam" of high
energy photons. This causes two artifacts:
2) Cupping: the center of a round object is darker than the periphery due to hardening of the
beam 360 degrees around the object. happens in the head
3) Streak: these are dark bands that occur in between two dense objects - nearly all the
photons are removed in a line between the two objects
4) fixes:
A) Filtration: pre-hardening the beam to remove low energy photons
B) Calibration: using a phantom to set a compensated mA/kVp
,C) Correct software: iterative reconstruction may help
D) Avoidance: tilting the gantry of positioning the patient to avoid areas that may cause
hardening.
ring artifact correct answers Calibration error or defective detector cause consistently
erroneous reading at each angular position, resulting in a circular artifact
is the focal spot large or small? correct answers large 0.6-1.2 - so as not to overheat the anode
from such a high mA
Which of the following will result in an increased voxel size: B increased slice thickness
correct answers A)decreased reconstruction FOV B) increased slice thickness C) increased
matrix D) none of these
If a tissue with a CT number of +300 appears white on the image, which of the following are
the window width and window level selected: A)window level =0, window width =500
B)window level= +300, window width= 500 C)window level =+100, window width =1000
D)none of these correct answers A) window level =0, window width =500
What is the volume of a voxel if a slice thickness of 3 mm, a 512x512 matrix & a
reconstruction field of view of 25.6cm are used A) 0.75mm³ B)1.5mm³ C) 6.0mm³ D)none of
these correct answers A. Solve this by finding the pixel size first FOV/matrix size ... that is
0.5 ... now square that 0.25 .... multiply that by slice thickness and you get 0.75
Which of the following parameters is responsible for partial volume averaging: A) matrix
size B) kVp C)slice thickness D) patient dose correct answers C
Voxel equation correct answers pixel area x section thickness
What is interpolation? correct answers Mathematical method for taking SPIRAL data and
viewing it as AXIAL images
Bone windows correct answers 2000-4000 WW
200-400 WL
Lung windows correct answers 1400-1600 WW
(-)400-600 WL
Modular Transfer Function? correct answers graphical representation of SPATIAL
RESOLUTION measured in lp/cm, tells how small you can scan without blurring
Which portion of the pancreas is the most common site for tumors?; and where located?
correct answers The head of the pancreas. It is located approximately at T12
LUNG WINDOW
(-) IS AIR correct answers 2000 WW and -200 WL =
, The Hounsfield unit that is -1000 most likely represents which of the following? correct
answers Air
Relative to CT topography, slice thickness is best represented by which of the following
axes? correct answers Z axis
What unit is the basis for exposure based on ionization in air? correct answers mR or C/kg
What radiation unit considers the biological effectiveness of radiation exposure? correct
answers mrem or mSv
"Fan" beam technology first historically came on the scene with which acquisition
geometries? correct answers Second
"Rotate-rotate" applies to which of the following geometries? correct answers Third
In CT what imaging plane is the pituitary best visualized? correct answers coronal
The third ventricle of the brain communicates with the fourth ventricle through the correct
answers Cerebral aqueduct
refers to an excessive Amount of nitrogenous materials in the blood and is a symptom of
renal failure. correct answers Azotemia
Which paranasal sinus is usually the last to fully develop? correct answers Frontal
What is the average annual radiation dose? correct answers 2 rem
10 rem converted to Sieverts is what? correct answers 0.1 Sv
annual limit of occupational lens dose correct answers 0.15 Sv
annual limit of shallow dose equivalent to skin/extremities correct answers 0.5 Sv
occupational exposure to embryo/fetus during pregnancy correct answers 0.5 mSv
total effective dose equivalent to public
--also average background radiation correct answers 1 mSv
Mild reactions to iodinated intravenous contrast media include correct answers nausea,
vomiting, mild urticaria, and a warm flushed sensation
Moderate reactions? correct answers Dyspnea, Hives (urticarial); wheezing (mild
bronchospasm); change in pulse; facial edema; vasovagal response; hypo- or hypertension
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