chapter 26- image receptor exposure

What are the two photographic properties that allow details to be seen on radiographic images?

IR exposure and contrast

Brightness is:

1. A setting on the monitor

2. Window level (controls brigtness of the image)

Exposure indicator (EI):

Number is used as a reference to determine the amount of IR exposure

Exposure indicators are ______ Specific

Manufacturer

Exposure indicator

• What is deviation index (DI)

Standardize method to evaluate exposure

If underexposed: Potentially what happens

Not all details will be recorded on the image

What happens during under exposure?

Insufficient signal reaches the IR ——> insufficient signal to noise ratio (SNR) ——→ Quantum mottle/noise is visible

If overexposed: The patient____

Was exposed to more ionizing radiation than necessary

What can compensate for most IR overexposures

Digital processing

• If this is the case, the EI is the only indicator for over exposure

If over exposure is extreme, ____ Of image receptor can occur

Saturation

What is the controlling factor for IR exposure?

mAs

What are the factors affecting IR exposure?

mAs, kVp, generator configuration, anode heel effect, distance, filtration, beam restriction, anatomical part, grids, image receptors (relative speed)

What is the rule of thumb when adjusting mAs to adjust IR exposure?

a minimum of 30% change in mAs is needed

What is the general rule when changing mAs and IR exposure if not using AEC?

If not using AEC and IR exposure needs adjusted, the radiographer should make changes to mAs by doubling or halving it

Doubling the mAs (cna be via mA or time) does what to the spectrum curve?

raises the xray spectrum curve twice as high at every point

IR exposure is best controlled using what?

is best contrlled using the AEC and technique charts (or pre-programmed techniques in the console)

kVp is considered an ____ but not the controlling factor when thinking of IR exposure

“influencing factor”