Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
PRI-Unit 3
Exposure Technique
| Question | Answer |
|---|---|
| Formula for mAs: | mA X S= mAs |
| Reciprocity Law Formula: | mA S = mA S |
| 15% Rule Formula: | (To Increase) kVp X 1.15= (To Decrease) kVp X 0.85= |
| Explain the 15% rule: | -a 15% increase in kVp equals roughly a double in mAs -a 15% decrease in kVp equals roughly a 1/2 in the mAs |
| Inverse Square Law Formula: | |
| Distance Maintenance Formula: | |
| Which factors of the beam does kVp affect: | Quality & Quantity |
| Which factors of the beam does mAs affect: | Quantity (intensity) only |
| In film screen kVp controls which factors: | -Primary controlling factor for contrast -Influences density |
| In film screen mAs is the controlling factor of what: | Density |
| Milliampere (mA) is: | The measure of x-ray tube current |
| What does mA control and how: | -Controls the amount of radiation by heating the filament causing thermionic emission and produces the number of electrons |
| What type of relationship does mA and the number of x-rays produced have: | It is directly proportional -If mA is doubled the quantity of x-rays doubles -If mA is reduced by half the quantity of x-rays is reduced by half |
| Time is directly proportional to: | The number of electrons crossing the tube & the number of x-rays produced |
| mAs is a product of: | mA & Time, so it is a product of the x-ray tube current and exposure time |
| Law of Reciprocity: | As long as mAs remain constant, and conbination of mA & time values will create the same x-ray intensity (quantity) |
| mAs indicates the: | Intensity of the x-ray beam |
| If mAs is increased what will happen to x-ray exposure: | It will increase directly proportional |
| To accomodate involuntary movement what can be done to mAs: | The shortest exposure time should be selected |
| Increasing mA (Tube current) does what: | -Increases amount of electrons flowing -Increases amount of radiation (intensity) -Increases density on film |
| To see a visible difference on film, what percentage of mAs change is reqired: | 25%-30% |
| If a radiograph is too light (insufficient density) what factor should be changed and how much: | mAs should be doubled |
| If a radiograph is too dark (too much density) what factor should be changed and how: | mAs should be decreased by half |
| Not enough mAs means: | Underexposed |
| Too much mAs means: | Overexposed |
| If insufficient mAs is used in digital imaging how will it effect the overall image: | -The EI will be out of range -Correct brightness -Quantum noise |
| If too much mAs reaches the IR in digital imaging how will it effect the overall image: | -EI will be out of range -Correct brightness -Patient (overexposed) will have received too much radiation |
| Longer wavelengths= | Weaker energy |
| Shorter wavelengths= | Stronger energy |
| Increasing the kV to the tube will increase what: | Exposure rate & percentage of higher energy photons (short wavelength/higher frequency) |
| What is kVp: | -Measure of max. electrical potential across an x-ray tube -expressed in kilovolts -Controls the speed of the electrons in the tube current |
| What does kVp affect: | -Potential difference that moves the electrons in tube -Beam energy (quality) -Penetration of body part -Controls scale of contrast |
| Long-scale contrast is achieved by: | Higher kVp ranges |
| Short-scale contrast is achieved by: | Lower kVp ranges |
| Long-scale contrast: | -Lots of grays -low contrast -High kVp |
| Short-scale contrast: | -Black & white -High contrast -Lower kVp |
| For more contrast in an image what should be adjusted & how: | Lower kVp |
| For less contrast in an image what should be adjusted & how: | Higher kVp |
| Why does increased kVp results in more x-ray production: | It increases the efficiency (quality) of x-ray production |
| The penetrating power of an x-ray beam is called: | x-ray quality |
| Why should kVp not be used to control density: | Because changing kVp will result in a change in contrast |
| kV controls energy and strength of the beam, therefore, a change in the kV alters the ________ of the beam when all other factors remain constant: | Intensity or (quantity) |
| What type of relationship does kVp and density share: | Direct relationship, but it is not directly proportional -Increasing kVp increases IR exposure & the density on the film image -Changes are not equal throughout the range of kVp (greater change is needed for higher kVp ranges 90+ than lower kVp -70) |
| An increase of ____% will cause a doubling of density on a film: | 15% |
| Small changes in kVp will result in _________ changes in radiographic density: | Large (especially in lower kVp ranges) |
| Techs can use the 15% rule to manipulate what: | The contrast |
| To compensate for the change in kVp what must be done to the mAs to maintain a constant density: | The mAs should should be adjusted by factors of 2 (Multiplied by 2 to double/increase density or Divided by 2 to half/reduce density) |
| kVp controls what: | The quality (penetrability) of the beam |
| kVp effects what: | The quantity of the x-ray photons produced |
| kVp is the controlling factor for what: | Contrast |
| Which quantitative factors affect the quantity of x-ray photons for each exposure: | mAs & kVp |
| If one increases kVp (quality) and reduces the mAs (quanity) the amount of radiation exposure to the patient is ___________: | Reduced |
| A good balance of kVp will demonstrate what: | Enough kVp to penetrate the body part, but provide quality image with as little patient exposure as possible |
| kVp affects the __________ as well as the ________ of radiation reaching the IR: | Strength & Amount |
| What affects the quality or penetrating ability of the x-ray beam: | kVp |
| Increasing kVp increase the number of __________ __________, which increases scatter & reduces contrast: | Compton Interactions |
| Changing kVp changes the __________ & __________ interactions: | Absorption & transmission (beam attentuation) |
| As long as the kVp chosen is sufficient enough to penetrate the body part...: | Contrast can be adjusted in the computer by choosing a different set of algorithms |
| Secondary factors are: | SID & OID |
| SID: | -Source to image recptor distance -Directly affects the density on film or the EI & image quality on digital -Inverse Square law |
| Inverse Square Law: | The intensity of radiation at a given distance from a point source in inversely proportional to the square of the distance |
| As SID changes what else changes: | density |
| Why is the inverse square law important: | It measures exposure rates |
| What does a change in SID result in: | A change in density |
| What is the influencing factor of SID: | X-ray photons diverge, therefore the width of the beam increases as the distance from the target increases |
| Exposure rate _________ as the distance increases: | Decreases |
| As distance increases, intensity ____________: | Decreases |
| How does an increased distance affect a film image: | Density decreases |
| How does an increase in distance affect a digital image: | Image quality decreases, quantum noise increases & EI is more out of range |
| How does SID affect radiation quality: | It has NO effect |
| SID determines the ___________ of the x-ray beam: | Intensity |
| What does OID stand for: | Object to IR distance |
| OID causes what: | Reduction in the quantity of radiation, which results in less density in film & EI and quantum noise may be affected in digital |
Created by:
akhernandez19