Computed Tomography- Exam 3 Questions
with Accurate Answers
3D Shaded Surface Display (SSD) correct answer -reconstructs images of the
surfaces of anatomical structures
-utilized for surgical planning and radiation therapy
Aliasing Artifacts correct answer -appear as streaks and are a result of insufficient
projection or view sampling
-to minimize aliasing, increase the number of views or ray samples per view
Artifact correct answer - a distortion or error in an image that is unrelated to the
subject being studied
-CT image artifact is any discrepancy between the reconstructed CT numbers in
the image and true attenuation coefficients of the object
-artifacts degrade image quality and can cause misdiagnosis
-classified according to appearance & cause
Attenuation correct answer -CT/Hounsfield numbers
-represents the attenuating properties or density of each tissue
, -baseline reference numbers:
*water equal to 0
*bone equal to 300 to 1000
*air equal to -800 to -1000
*fat -80
*soft tissues 30 to 80
*calcifications 100 and up
-Water is used as the reference tissue and is given a value of zero.
-Any CT number greater than zero will represent tissue that is denser than water
and will appear to become progressively lighter shades of gray to white.
-Tissues with a negative number will appear to become progressively darker
shades of gray to black.
-CT Number Calibration Test
*Performed on a daily basis using a water phantom
*CT number of water must measure between -3 and +3
Beam Hardening Artifact correct answer -creates an artifact because the beam is
not uniform. There is less beam hardening at the edges of an object than the
center which is reflected by the CT numbers assigned
with Accurate Answers
3D Shaded Surface Display (SSD) correct answer -reconstructs images of the
surfaces of anatomical structures
-utilized for surgical planning and radiation therapy
Aliasing Artifacts correct answer -appear as streaks and are a result of insufficient
projection or view sampling
-to minimize aliasing, increase the number of views or ray samples per view
Artifact correct answer - a distortion or error in an image that is unrelated to the
subject being studied
-CT image artifact is any discrepancy between the reconstructed CT numbers in
the image and true attenuation coefficients of the object
-artifacts degrade image quality and can cause misdiagnosis
-classified according to appearance & cause
Attenuation correct answer -CT/Hounsfield numbers
-represents the attenuating properties or density of each tissue
, -baseline reference numbers:
*water equal to 0
*bone equal to 300 to 1000
*air equal to -800 to -1000
*fat -80
*soft tissues 30 to 80
*calcifications 100 and up
-Water is used as the reference tissue and is given a value of zero.
-Any CT number greater than zero will represent tissue that is denser than water
and will appear to become progressively lighter shades of gray to white.
-Tissues with a negative number will appear to become progressively darker
shades of gray to black.
-CT Number Calibration Test
*Performed on a daily basis using a water phantom
*CT number of water must measure between -3 and +3
Beam Hardening Artifact correct answer -creates an artifact because the beam is
not uniform. There is less beam hardening at the edges of an object than the
center which is reflected by the CT numbers assigned
