CT REGISTRY-
how do you reduce beam hardening - Answer: 1. Increase dose
2. Reduce collimation--Reduce slice thickness
3. Increase window width
At what level does the abdominal aortal bifurcate? - Answer: L4
What is the typical scan delay after injection of contrast media for studies of the liver? - Answer:
30-45 seconds
What window settings provide the best tissue differentiation within the liver? - Answer: window
width= 140, level= 60
What is the window settings that provide the best bone window for the pelvis? - Answer:
window width=2000, window level=350
What mAs is typically used in routine CT exams of the abdomen? - Answer: 200-300 mAs
What is the result of the bifurcation of the abdominal aorta? - Answer: The right and left
common iliac arteries
What is the anode target angle? - Answer: 12 degrees
At what level do the common carotids bifurcate into the internal and external carotid arteries? -
Answer: C3-C4
The floor of the orbit is formed by the __________ bones. - Answer: maxillary and zygomatic
,CT REGISTRY-
The lateral wall of the orbit is formed by the ___________ bones. - Answer: zygomatic and
sphenoid
The medial wall of the orbit is formed by the _________ bones. - Answer: ethmoid and lacrimal
bones
how do you calculate effective mAs? - Answer: mAs/pitch
define window level and window width - Answer: 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
,CT REGISTRY-
Black = <0
Level 100, Width 150
White = >+175
Black = <25
factors that affect spatial and contrast resolution - Answer: 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 - Answer: Brain: W80,L+40
Lung: W1500, L-400
Abdomen: W400, L+50
, CT REGISTRY-
Bone: W1600, L+500
What is beam hardening?
what are the two types of beam hardening artifact?
how do you compensate for it? - Answer: 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 - Answer: 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? - Answer: large 0.6-1.2 - so as not to overheat the anode from
such a high mA
how do you reduce beam hardening - Answer: 1. Increase dose
2. Reduce collimation--Reduce slice thickness
3. Increase window width
At what level does the abdominal aortal bifurcate? - Answer: L4
What is the typical scan delay after injection of contrast media for studies of the liver? - Answer:
30-45 seconds
What window settings provide the best tissue differentiation within the liver? - Answer: window
width= 140, level= 60
What is the window settings that provide the best bone window for the pelvis? - Answer:
window width=2000, window level=350
What mAs is typically used in routine CT exams of the abdomen? - Answer: 200-300 mAs
What is the result of the bifurcation of the abdominal aorta? - Answer: The right and left
common iliac arteries
What is the anode target angle? - Answer: 12 degrees
At what level do the common carotids bifurcate into the internal and external carotid arteries? -
Answer: C3-C4
The floor of the orbit is formed by the __________ bones. - Answer: maxillary and zygomatic
,CT REGISTRY-
The lateral wall of the orbit is formed by the ___________ bones. - Answer: zygomatic and
sphenoid
The medial wall of the orbit is formed by the _________ bones. - Answer: ethmoid and lacrimal
bones
how do you calculate effective mAs? - Answer: mAs/pitch
define window level and window width - Answer: 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
,CT REGISTRY-
Black = <0
Level 100, Width 150
White = >+175
Black = <25
factors that affect spatial and contrast resolution - Answer: 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 - Answer: Brain: W80,L+40
Lung: W1500, L-400
Abdomen: W400, L+50
, CT REGISTRY-
Bone: W1600, L+500
What is beam hardening?
what are the two types of beam hardening artifact?
how do you compensate for it? - Answer: 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 - Answer: 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? - Answer: large 0.6-1.2 - so as not to overheat the anode from
such a high mA
