mAs

mAs, which determines the QUANTITY of x-rays being produced, is calculated by multiplying the mA x time (in seconds).  When you see a question that has mA and time separated, you must calculate mAs before going any further in the question.  For instance:


 Density Maintenance

(Old mAs/New mAs) = (Old Distance Squared/New Distance Squared)

The most common mistake we tend to make is confusing this with the Inverse Square Law and having the numbers on the distance side of the equation backwards.  For density maintenance, make sure you have (old/new)=(old/new).  The second most common mistake is forgetting to SQUARE the distances. 

For example: If a radiograph was taken using 400 mA, 200ms at 72", what would your new mAs have to be in order to maintain radiographic density at a distance of 40"?