chapter26 Image receptor exposure

Typical OD range

0.25-2.5

Changes in MAs required

Minimum 30% for visible density change

Quantum noise

A lack of sufficient incoming data to process an image

System noise

Noise caused by electronic components in the imaging receptor

Ambient noise

Background radiation

Single phase wave

Form has significantly lower average photon energy than a high- frequency wave form

Results from high mA selection

Is an increase in the focal spot size at increased tube current

Cathode side of the beam

IR exposure up to 45% greater

Proper positions can take advantage

Inverse square law

The intensity is inversely proportional to the distance from the source

Increase in SID

decrease IR exposure

Decreased patient dose

Increase OID

decrease IR exposure

Filtration

Increase _____ will decrease IR exposure

Increase ______ will increase average energy of beam but reduces intensity of the beam (quantity)

Less ESE

More transmission

Less pt. Dose

More penetration

Increase in part thickness/ Z# causes a decrease in IR exposure

If there is no corresponding change in technique between IR exposure and part thickness/ tissue density

Additive pathology

• is radiopaque

• Decreases density

• Decreases IR exposure

Destructive pathology

• is radiolucent

• Increases density

• Increases IR exposure

Part thickness variation with large tube angles

-increases pt exposure

• less IR exposure

Grids

• eliminate scatter

• Decreases IR exposure

• Increases patient dose

No grid

1

5:1

2

6:1

3

8:1

4

10:1/12:1

5

16:1

6

Increase in speed

Decreases pt dose