CT Assignment Flashcards
Which generation of CT detectors use a “translate-rotate” tube and detector assembly motion
1st and 2nd
which CT scanners use a fanned x-ray beam?
2nd and 3rd
True or false: slip ring technology improve temporal resolution
true
which artifact result from beam hardening in CT?
Cupping
what is the relationship between patient dose and pitch?
if pitch increases, patient dose decreases
A technologist wishes to image 40cm of tissue with a beam width of 8mm in 25 sec. If the gantry rotation time is 1.5s, what is the required pitch?
3:1
do pre-detector grids in CT scanners increase or decrease contrast?
increase
what do sharpening filters do?
- accentuate image noise
- increase spatial resolution
- decrease blurring
In CT systems with the capability of gantry angulation, what is the typical maximum degree of angulation possible?
± 30 degrees
Solid state scintillation detectors in the latest 3rd generation CT scanners are made of?
Cadmium Tungstate
The “filter” in filtered back-projection refers to the?
mathematical function applied to the attenuation profile to reduce blurring
A virtual non-contrast image may be generated using data from which dual-energy CT acquisition techniques?
- temporal sequential scanning
- rapid kVp switching
- multilayer detectors
- dual x-ray source
For the first time, sub-second imaging was possible with which generation of CT scanners?
3rd
True or false: Mild differences in attenuation in the brain requires the use of a sharp filter to accentuate these differences during image reconstruction using filtered back projection technique.
False
Image reconstruction times in CT are primarily dependent on the?
RAM
Before a CT image can be reconstructed by the computer, the signal produced by the photodiode must be converted into numeric/binary information by which of the following?
Analog-to-digital converter
True or false: CT has a higher scatter to primary beam ratio than general radiography.
True
The type of filter used between the x-ray tube and the patient in a CT scanner is called a?
bowtie filter
Which of the following is not controlled/manipulated by the CT operator when planning image acquisition?
Pitch
What would decrease the total scan time for a given volume of tissue in CT?
increasing the number of detector rows during image acquisition and increasing pitch
What pitch ratio produce contiguous image slices in CT?
1:1
The average CT number (Hounsfield unit) of blood is approximately:
+30 HU
Changing Kernels in filtered back-projection results in?
- a trade-off between image shapes and noise
True of False: The primary advantage of iterative reconstruction techniques in CT over back projection techniques is faster reconstruction times.
False
The technique that involves the estimation of an unknown value from known values on either side of it is termed?
interpolation
What is the approximate Hounsfield unit (CT number) of water?
0
A disadvantage of 3rd generation CT scanner design compared to previous generations is?
the possibility of ring artifacts
True or False: Bowtie filters in 3rd generation CT reduce the intensity of the peripheral x-ray beam to a much greater degree than the central beam.
True
The term ____________ describes the ability of the CT scanner to differentiate objects with minimal differences in attenuation coefficients.
contrast resolution
When a patient is placed supine on the CT table, the X-axis of the patient…
runs in the right to left direction
In dual-energy CT scanners, what is the biggest challenge during temporally sequential scans?
patient motion
