Prime Factors (Ch 12) Flashcards
What are the three principle factors that affect x-ray quality and quantity?
- Milliamperage per second (mAs)
- kilovoltage (kVp)
- Distance.
The three principle factors are under the __________ ____________ of the radiographer.
Direct control
What is “quantity” the measure of?
Measure of the number of x-ray photons of the useful beam. A.k.a. the output, intensity, or exposure.
What is the unit of measure for quantity?
Roentgen (R)
What is the prime controller of quantity?
mAs
Quantity is also affected by _______, _________, & _____________.
kVp, distance and filtration
What does quality measure?
Measure of the penetrating ability of the x-ray beam or distance it travels in matter.
Quality is numerically represented by ________________.
Half value layer (HVL)
The greater the HVL the _____________ the quality.
Greater
What is the prime controller of quality?
kVp
Quality is also directly affected by _____________.
Filtration
Milliamperage (mAs) per second is the measure of x-ray tube ______________.
Current
mA and time are both ________ proportional with the number of electrons crossing tube.
Directly
As mA increases, so does the number of _____________.
Electrons
As time increases so does the ___________.
Number of electrons
Exposure index (EI)
Numeric exposure value of IR exposure assessed
True or false
exposure index does not indicate patient dose
True
True or false
Index range and values vary from vendor to vendor
True
What is the prime controller of image receptor exposure?
mAs
As long as mAs is constant, any combo of _____ and ______ will create the same exposure.
mA & time
Increasing kVp will cause an _____________ in the speed and ___________ of electrons applied across the tube.
Increase and energy
What is the 15% rule?
15% increase in kVp is equal to double the number of photons
15% decrease in kVp is equal to half the number of photons
Doubling the kVp
The number of photons increase about four times
Doubling the kVp
The number of photons increase about four times
As kVp increases, so does the energy of each ___________.
Electron (quality)
Greater photon energy=
More penetrability
kVp affects both _____________ and _______________ of the x-ray beam
Quality, quantity
An increase in kVp causes a(n) ____________ in penetrability and a ____________ in image contrast.
Increase, decrease
Define contrast (IR)
Visibility of detail or differences between an IR exposure level; it is a characteristic of image quality
Define Contrast
The ability to distinguish the differences in adjacent tissues or structures
A primary beam with __________________ kV results in overall ___________ in penetration through all tissues, therefore resulting in a _____________ contrast radiograph or ___________ scale of contrast
Greater, rise, lower, longer
High kVp= __________ contrast= __________ scale
Low, long
Low kVp= _____________ contrast= __________ scale
High, short
True or false
kVp should be used to control IR exposure
False. kVp is usually preset by vendor to yield optimal contrast
At lower kVp, ___________ radiation is absorbed by the patient
More
In general, higher kVp and ____________ mAs will reduce patient dose, but at the expense of contrast
Lower
Inverse square law
Doubling of distance increases the area four times which decreasing the intensity by 1/4
Quantity remains unchanged; but distribution decreases within a given area (involves distance)
Increasing distance causes a ______________ of exposure
Decrease
Why do we use the direct square law?
To compensate for IR exposure changes when distance changes must be made
Direct square law
