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Computed Tomography questions with accurate answers.
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Computed Tomography questions withaccurate answers.
What is windowing? ANS - A method in which the CT image gray scale can be manipulated in order to
enhance different structures of varying tissues
What are the 2 windowing mechanisms? ANS - - Window width
- Window level
What is Window Width (WW)? ANS - - The range of the CT numbers in the image
- Determines the maximum number of shades of gray that can be displayed on the CT monitor
- Effects contrast
What is Window Level (WL)? ANS - - The center or midpoint of the range of CT numbers
- Effects brightness
Wide window widths (400 to 2000 HU) are necessary for ____? ANS - Varying body tissues
Narrow window widths (50 to 350 HU) are necessary for ____? ANS - Different tissues of similar
densities
What are the effects of WW on image contrast? ANS - - As the WW increases, the contrast decreases
- As the WW decreases, the contrast increases
What are the effects of WL on image brightness? ANS - - Moving the WL toward the higher CT numbers
results in a darker image
- Moving the WL toward the lower CT numbers results in a brighter image
,What is a multi-slice scanner (MSCT)? ANS - - CT system equipped with a multiple-row detector array to
simultaneously collect data at different slice locations
- Can scan up to 64 slices
In CT, the attenuated image-forming radiation is detected by what? ANS - A solid state image receptor
What is Helical CT? ANS - - Continuous gantry rotation + continuous table feed
- Scan data traces a helical path or spiral around patient
What is Isotropic Imaging? ANS - 2D pixel in a CT image represents a 3D voxel
Name the 3 types of Data acquisition systems? ANS - - Conventional
- Helical single slice (spiral)
- Multi-slice
What is a Linear Attenuation coefficient? ANS - Characterizes how easily a volume of material can be
penetrated by the x-rays
What is a bowtie filter? ANS - Used to allow a uniform beam to reach detectors
What occurs with CT filtration? ANS - - Removes long wavelength x-rays which contributes to patient
dose
- Shapes the energy distribution across the radiation beam to produce uniform beam hardening when x-
rays pass through the filter and the object causing beam hardening artifacts
What is pitch? What is the formula? ANS - Relationship between the patient couch movement and the
x-ray beam collimation and is expressed as a ratio
Pitch = Couch movement each 360 degrees / Slice Thickness
, How do different structures appear on CT? ANS - - Bone and high density structures, such as radiopaque
contrast media, appear white
- Air and other low density structures appear black
- Fat and organs appear in varying shades of gray
What are two types of brain tumours? ANS - - Primary brain tumour: grows originally in the brain
- Secondary brain tumour: A tumour that has spread to the brain from a different site in the body such
as lungs, bowel
What is hydrocephalus? How does it appear on a CT scan? ANS - - Congenital disease where a child is
unable to drain excess CSF
- Can also be acquired as an adult
- Ventricles appear enlarged and very black
Multi-phasic imaging is frequently used for what studies? ANS - Specialized studies of the pancreas,
liver, and kidney as well as in many abdominal CTA protocols
For most protocols of the abdomen or pelvis, patients are scanned in what position? ANS - The supine
position with the arms elevated
Patients are asked to suspend respiration during image acquisition to reduce ____ and decrease
artifact? ANS - Movement
What are 2 common pathologies seen in the liver with CT? ANS - - Fatty infiltrates
- Cavernous hemangioma
The liver is most often scanned during what contrast phase? ANS - The portal venous phase
Measurements from a CT image of the abdomen show the liver density is 35 HU whereas the density of
the spleen is 65 HU. Which is a likely diagnosis?
a. Metastatic disease of the liver
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