CT fundamentals & principles Flashcards
attenuation is
the degree to which an x-ray beam is reduced by an object
To differentiate adjacent objects on a CT image, there must be:
a density difference between the two objects.
Hounsfield units quantify:
the degree that a structure attenuates an x-ray beam.
volume averaging is:
The process in CT by which different tissue attenuation values are averaged to produce one less accurate pixel reading is called
Heat capacity vs heat dissipation. What impact do they have on the ability to scan?
The ability of the tube to withstand the resultant heat is called its heat capacity, whereas its ability to rid itself of the heat is its heat dissipation. The length and frequency of scans can be determined in part by the tube’s heat capacity and dissipation rate.
The CT process can be broken down into three main segments:
- Data Acquisition (Get Data)
- Image Reconstruction (Use Data)
- Image Display? (Display Data)
In a CT system, what is the function of the digital-to-analog converter?
Converts a digital signal from a computer into electrical signals for a display monitor
What controls the size of a beam used in SDCT scans?
Collimation
A CT examination of the lumbar spine reveals a herniated disc at the level of L2-L3. Which reformatted imaging plane would best demonstrate a posterior compression of the disc material onto the spinal cord?
Sagittal
Which structure would appear with the most blur, if a focal plane measured 4mm?
A) 6mm from the fulcrum
B) 3mm from the fulcrum
C) 2mm from the focal plane
D) 5mm from the focal plane
D) 5mm from focal plane
Which imaging plane is parallel to the foot’s plantar surface?
Axial
What will significantly increase patient dose in CT?
A) Not isocentering the patient prior to scan acquisition
B) Reconstructing images in a DFOV equal to the SFOV size
C) Filtering the x-ray beam
D) Reformatting axial images into a coronal imaging plane
A) Not isocentering the patient prior to scan acquisition
What describes linear tomography?
A) Increasing tomographic angle increases the focal plane size
B) Objects positioned outside the level of the fulcrum will appear blurred
C) Tube and IR move simultaneously in opposite directions
D) Increasing tube motion decreases tomographic angle
C) Tube and IR move simultaneously in opposite directions
A CT scan for ethmoid sinuses was taken on a 25 year old male patient with limited mobility of the head and neck. How was the patient most likely positioned for this axial image?
Supine
What describes the Z-axis?
Slice thickness
What is the pitch of a 16-slice MDCT, using 0.5mm slice thickness, and table movement of 12mm per rotation?
1.5
What are some shortcomings of planar imaging?
Superimposition of structures
Lower subject contrast
Lower radiographic contrast
What is the pitch of a 32-slice MDCT, using 0.2mm slice thickness, and a 8mm table movement per tube rotation?
1.3
Which of the following combinations of mA and scan time would be the best choice for a cardiac scan?
A) mA = 300; scan time = 0.4 seconds
B) mA = 200; scan time = 2 seconds
C) mA = 700; scan time = 1/2 second
D) mA = 350; scan time = 1 second
mA = 300; scan time = 0.4 seconds
What can a technologist do that would lead to a misdiagnosis in CT?
a) Improperly centering the patient in the “x” and “y” b) directions
b) Inaccurately identifying patient position during acquisition
c) Incorrectly select the systems spatial resolution
d) Post-processing the raw data inappropriately
b) Inaccurately identifying patient position during acquisition
CT can produce images that are not cross-sectional T/F
True
