CT REGISTRY (excluding anatomy) Exam with accurate detailed
|| || || || || || || ||
solutions
how do you reduce beam hardening - correct answer✔✔1. Increase dose
|| || || || || || || || || ||
2. Reduce collimation--Reduce slice thickness
|| || || ||
3. Increase window width
|| || ||
At what level does the abdominal aortal bifurcate? - correct answer✔✔L4
|| || || || || || || || || ||
What is the typical scan delay after injection of contrast media for studies of the liver? -
|| || || || || || || || || || || || || || || || ||
correct answer✔✔30-45 seconds || ||
What window settings provide the best tissue differentiation within the liver? - correct
|| || || || || || || || || || || || ||
answer✔✔window width= 140, level= 60 || || || ||
What is the window settings that provide the best bone window for the pelvis? - correct
|| || || || || || || || || || || || || || || ||
answer✔✔window width=2000, window level=350 || || ||
What mAs is typically used in routine CT exams of the abdomen? - correct answer✔✔200-
|| || || || || || || || || || || || || ||
300 mAs ||
What is the result of the bifurcation of the abdominal aorta? - correct answer✔✔The right
|| || || || || || || || || || || || || || ||
and left common iliac arteries
|| || || ||
What is the anode target angle? - correct answer✔✔12 degrees
|| || || || || || || || ||
,At what level do the common carotids bifurcate into the internal and external carotid
|| || || || || || || || || || || || || ||
arteries? - correct answer✔✔C3-C4 || || ||
The floor of the orbit is formed by the __________ bones. - correct answer✔✔maxillary and
|| || || || || || || || || || || || || ||
zygomatic
||
The lateral wall of the orbit is formed by the ___________ bones. - correct
|| || || || || || || || || || || || || ||
answer✔✔zygomatic and sphenoid || ||
The medial wall of the orbit is formed by the _________ bones. - correct answer✔✔ethmoid
|| || || || || || || || || || || || || ||
and lacrimal bones
|| || ||
how do you calculate effective mAs? - correct answer✔✔mAs/pitch
|| || || || || || || ||
define window level and window width - correct 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|| ||
Black = <0
|| ||
Level 100, Width 150
|| || ||
White = >+175|| ||
Black = <25
|| ||
factors that affect spatial and contrast resolution - correct 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 - correct answer✔✔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 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 - correct answer✔✔Calibration error or defective detector cause consistently
|| || || || || || || || || || ||
erroneous reading at each angular position, resulting in a circular artifact
|| || || || || || || || || ||
|| || || || || || || ||
solutions
how do you reduce beam hardening - correct answer✔✔1. Increase dose
|| || || || || || || || || ||
2. Reduce collimation--Reduce slice thickness
|| || || ||
3. Increase window width
|| || ||
At what level does the abdominal aortal bifurcate? - correct answer✔✔L4
|| || || || || || || || || ||
What is the typical scan delay after injection of contrast media for studies of the liver? -
|| || || || || || || || || || || || || || || || ||
correct answer✔✔30-45 seconds || ||
What window settings provide the best tissue differentiation within the liver? - correct
|| || || || || || || || || || || || ||
answer✔✔window width= 140, level= 60 || || || ||
What is the window settings that provide the best bone window for the pelvis? - correct
|| || || || || || || || || || || || || || || ||
answer✔✔window width=2000, window level=350 || || ||
What mAs is typically used in routine CT exams of the abdomen? - correct answer✔✔200-
|| || || || || || || || || || || || || ||
300 mAs ||
What is the result of the bifurcation of the abdominal aorta? - correct answer✔✔The right
|| || || || || || || || || || || || || || ||
and left common iliac arteries
|| || || ||
What is the anode target angle? - correct answer✔✔12 degrees
|| || || || || || || || ||
,At what level do the common carotids bifurcate into the internal and external carotid
|| || || || || || || || || || || || || ||
arteries? - correct answer✔✔C3-C4 || || ||
The floor of the orbit is formed by the __________ bones. - correct answer✔✔maxillary and
|| || || || || || || || || || || || || ||
zygomatic
||
The lateral wall of the orbit is formed by the ___________ bones. - correct
|| || || || || || || || || || || || || ||
answer✔✔zygomatic and sphenoid || ||
The medial wall of the orbit is formed by the _________ bones. - correct answer✔✔ethmoid
|| || || || || || || || || || || || || ||
and lacrimal bones
|| || ||
how do you calculate effective mAs? - correct answer✔✔mAs/pitch
|| || || || || || || ||
define window level and window width - correct 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|| ||
Black = <0
|| ||
Level 100, Width 150
|| || ||
White = >+175|| ||
Black = <25
|| ||
factors that affect spatial and contrast resolution - correct 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 - correct answer✔✔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 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 - correct answer✔✔Calibration error or defective detector cause consistently
|| || || || || || || || || || ||
erroneous reading at each angular position, resulting in a circular artifact
|| || || || || || || || || ||
