Midterm Review Flashcards
What happens when mAs is increased on an x-ray emission spectrum?
-increase in amplitude
What happens when kVp is increased on the x-ray emission spectrum ?
- increase in amplitude
- increase average energy
- increased peak energy (end point on curve)
What happens with a higher atomic number of target material on the x-ray emission spectrum?
- increased amplitude
- increased average energy
- different characteristic spectrum
What happens with a higher voltage waveform on the x-ray emission spectrum?
- increase amplitude
- increase average energy
What happens to the x-ray emission spectrum when filtration is added?
- decreased amplitude
- increased average energy
Describe characteristic radiation
When the projectile electron interacts with an inner shell electron and removes it from the atom. An outer shell electron then replaces the empty spot, and energy is given off in the form of characteristic radiation
Which characteristic x-rays of tungsten are useful for imaging?
K-characteristic. The characteristic x-rays produced from other inner shells are at an energy level that is too low for diagnostic purposes
What is another name for the characteristic spectrum?
The discrete emission spectrum
What type of x-rays form a continuous emission spectrum?
Bremsstrahlung x-rays
How does bremsstrahlung radiation occur?
The projectile electron interacts with the nuclear field of an atom, and when it changes direction, it loses kinetic energy in the form of radiation
How does adding filtration affect patient dose?
It reduces it, because the low energy x-rays that are absorbed by the patient are removed from the x-ray beam
What effect do Compton interactions have on image quality?
It produces scatter, which degrades the image quality and reduces image contrast. Any time that more scatter is produced, image quality is decreased
How does body habitus affect radiographic density?
The larger the patient, the less radiographic density will be on the image due to exponential attenuation
What effect do Compton interactions have on radiographic density?
Scatter contributes to the radiographic density on the image, as it is additional photons that make it onto the image
When kVp is increased:
⬆️ radiographic density
⬆️ scatter
⬇️ patient dose
When mAs is increased:
⬆️ radiographic density
scatter: no change
⬆️ patient dose
When x-ray energy is increased:
⬆️ Total interactions
⬆️ compton interactions
⬇️ PE interactions
When OID is increased:
⬇️ radiographic density
⬇️ scatter
patient dose: no change
When atomic number is increased:
compton interactions: no change
⬆️ PE interactions
⬇️ transmission
When SID is increased:
⬇️ radiographic density
scatter: no change
When focal spot size is increased:
Radiographic density: no change
Scatter: no change
Patient dose: no change
When collimating is decreased: (larger light field)
⬆️ radiographic density
⬆️ scatter
⬆️ patient dose
What is the minimum change in mAs required in order to produce a visible effect on the image?
30%
An x-ray tube with a stationary anode: A) incorporates the line-focus principle B) limits leakage radiation C) provide for greater heat dissipation D) usually has a very small focal spot
A! Incorporates the line focus principle
Why does the anode heel effect occur?
It is a consequence of the line focus principle, x-ray photons produced on the anode side must transverse a greater thickness of target material than the x-rays on the cathode side
the main reason for using the line-focus principle is
To decrease the size of the actual focal spot
What happens when a two step exposure button is pressed?
- during the first step, the rotor accelerates and the filament is heated (forming electron cloud)
- during the second step, the kVp is applied and electrons travel to the anode where x-rays are created
What type of charge is placed on the focusing cup and why?
Focusing cup is negatively charged, so that it can “focus” the electrons beam to a small area on the anode. Its negative charge pushes the electrons closer together
X-rays are emitted through an opening in the glass envelope called a port (true/false)
False! There isn’t an actual opening, just a thinned out area
The smaller the anode angle, the _______ the heel effect
The larger the heel effect
The smaller the IR, the _______ heel effect
The smaller the heel effect
The longer the SID, the ______ the heel effect
The smaller the heel effect
What is the auto transformer sometimes referred to as and why?
Can be referred to as the kVp selector as it directly impacts the voltage being supplied to the primary side of the step up transformer. When the kVp is selected on the console, it controls the auto transformer
What type of current does the step up transformer require?
Alternating current (AC)
What type of current does the x-ray tube require, and why?
Direct current (DC), as the electron flow must go in one direction (cathode to anode)
What is the purpose of a rectifier?
Allows current to flow only in one direction, so depending on how rectifiers are aligned in a circuit, can control the direction of current flow. “One way valves”
Why is a high frequency generator more efficient at x-ray production as compared to a single phase generator?
Single phase generators have 100% ripple, meaning that the voltage fluctuates from 0 to max. X-rays are only produced near the peak voltage, so x-rays are not being produced during the entire voltage waveform. High frequency generators have 1% ripple, so the voltage only fluctuates between 99% and max, meaning x-ray production is happening the entire time of exposure
what are the three types of beam restrictors?
Aperature diaphragm, cones/cylinders, and variable aperature collimator
If a cone cylinder is not aligned with the x-ray source and interferes with the x-ray beam what is it referred to?
Cone cutting
Which type of collimator is most effective at reducing image blur caused by off focus radiation?
Variable aperature collimator
Does the use of PBL replace manual collimation?
No, it only adjusts the collimator to match the size of the IR. The tech will still need to adjust the collimation to restrict it to only the area of interest
Which x-rays are transmitted through a grid?
Those that travel in the direction of the interspace. X-ray photons that scatter at a different angle through the interspace will be absorbed by the lead strips
Grid lines will be more apparent with
Low grid frequency
How is grid performance measured?
With the k factor (contrast improvement factor). Must be higher than 1 to indicate contrast improvement has occurred
A synonym for grid factor is
Bucky factor
True or false: grid cut off will always occur with parallel grids
TRUE
Which grid error(s) will result in the image appearing underexposed, decreased density across the image?
- off level
- off center
