Flashcards in Basic CT Principles Deck (156)
Imaging modality that produces 2D images
-superimposition of all structures
-difficult to distinguish slight density changes of tissues
-difficult to identify precise location of abnormalities
-x-ray tube and film move simultaneously and in opposite directions
-imaging modality that brings into focus only the anatomical structure lying in a plane of interest, while structures on either side of that plane are blurred
-immediate goal us to eliminate structures above and below the focused section or focal plane. This is difficult to achieve
-limitations: persistent image blurring that cannot be completely removed, degradation of image contrast because of scatter, fail to demonstrate slight differences in subject contrast (tissue), contrast cannot be adjusted after it has been recorded on film
-focal plane (aka section thickness)
▪️blur ⬆️ as distance from the focal plane ⬆️
▪️fulcrum: imaginary pivot point about which the x-ray tube and the image recpetor move
-⬆️ tomographic angle = ⬇️ section thickness
-imaginary pivot point about which the x-ray tube and the image receptor move
Advantages of tomography vs general radiography
⬆️ radiographic contrast
⬆️ subject contrast
Disadvantages of tomography vs general radiography
⬆️ patient dose
What is a shortcoming of radiography?
Superimposition of structures
What is an example of a negative contrast agent?
How would a contrast agent with a high Z (atomic #) affect a radiographic image?
Increased image contrast, due to increased absorption
If an object is slightly less dense than water, what would be the expected HU measurement?
The gantry houses all of the following except A) 3 phase generator B) beam collimators C) collimators D) DAS
A) 3 phase generator
_____ interactions produce scatter, which degrades image quality and image _____. Anytime more of these types of interactions occur image quality is _____
COMPTON interactions produce scatter, which degrades image quality and image CONTRAST. Anytime more of these types of interactions occur image quality is DECREASED
True or false: two essential components of a digital image processing system are the ADC and the DAC
What is another name for density values?
Increasing _______ reduces patient dose, because the ____ energy photons that could be absorbed by the patient are removed from the x-ray beam
Filtration, low energy photons
Data acquisition in CT refers to
Getting data from the patient through a systematic motion of the x-ray tube and detectors
What is not a common anatomical landmark in CT?
Give an example of a low attenuation structure
Trachea (air filled)
What does not produce a transverse axial sectional image?
An image of a hyposthenic will have _____ than an image of an asthenic patient?
Decreased radiographic density, due to exponential attenuation
What happens to the emission spectrum when a higher voltage waveform is utilized?
Increased amplitude; increased average energy
True or false: area closest to the fulcrum has less blur
Farther away from fulcrum = more blur
True or false: fulcrum is dead centre on image
True or false: big angle on the tube = smaller slice
-image blurring (poor image contrast outside of focal plane)
-GOOD for curved structures
True or false: The isocenter of a gantry is not an important consideration for patient positioning
What is a universal limitation, and what is a common concern in x-ray imaging?
Heat production; motion
True or false: decreasing the tomographic angle increases slice thickness
In CT, a high kilo-voltage technique is generally used for which reason?
Decrease the dependence of attenuation coefficients on photon energy