measurement of beam quality but it does affect beam quantity (intensity) to a lesser extent.
kVp is
quantity
mAs affects
electrons move faster, creates x-ray that are stronger and can get through the patient easear
When kVp is raised
quality
mAs does not affect
mAs
Primary controlling factor for beam quantity
because it changes quality and quantity and we don’t want that
kVp is not primary controlling factor of density
is the minimum amount of kVp required to penetrate the patient
Optimum kVp
gray
To much kVp makes image
mAs reduces by 50%
If we increase the kVp 15%
mAs doubles
If we reduce the kVp 15%
no amount of mAs can compensate for a lack of adequate kVp
Classic phrase
cuts the dose 2/3
Increase of kVp 15% and reduction of mAs 50% ,what happens to dose?
5%
How much increase in kVp is required to see visible increase in density?
30%
5% increase in kVp decreases mAs
reduce patient dose; for example if pregnant
15% increase in kVp and 50% decrease in mAs can be done to
increases the dose to a patient but it protects the film
Using the grid
absorb the scatter exiting the patient and increase contrast
Grids…
increase kVp 15% and reduce mAs 50% or reduce kVp 15% and double the mAs
To maintain density we can
double the density
Increasing kVp 15% without compensation will do what to density?
reduce the density 50%
Decreasing kVp 15% without compensation will do what to density?
Fluid in the stomach
Ascites
50% increase in mAs or 7.5% increase in kVp (Ascites, Paget’s disease, Pleural Effusion)
Additive Diseases require
double the mAs AND increase kVp by 15%
For Wet plaster:
double the mAs OR increase the kVp by 15%
For Dry plaster:
increase mAs by 30% or increase kVp by 5% (kvp better)
For Fiberglass: (most common)
increase mAs by 50% or increase kVp by 7.5%
For Plaster/Fiberglass:
average
Sthenic
above average
Hypersthenic
below average
Hyposthenic
anorexive
Asthenic
determined by the atomic number of the cells that make up the anatomy of interest
Tissue Opacity
30% decrease in mAs OR 5% decrease in kVp (Emphasyma or COPD, Osteoperosis, Pneumothorax)
Destructive disease requires
Thermionic Emm
is the process of producing electrons in front of the fillament
Thermoinic Emission
low energy x-ray, saves the patient dose
Filtration removes
produce more x-ray, density goes up because there is more beam intensity
Bigger generators
