01
The three relationships to remember
Start with the technical factor that changes the outcome you are trying to control.
Penetration and contrast
Higher kVp increases beam energy and penetration. It also tends to produce a longer scale of contrast when other conditions are unchanged.
Photon quantity
mAs primarily controls the number of photons. Doubling mAs approximately doubles receptor exposure.
Geometry
Increase SID and minimize OID to reduce magnification and improve recorded detail when the projection allows.
02
Read the image before repeating it
Use visible clues to identify the most likely correction.
| Image clue | Likely cause | First check |
|---|---|---|
| General quantum mottle | Too few photons reached the receptor | Technique, patient size, and detector placement |
| Loss of sharpness | Motion or poor geometry | Immobilization, exposure time, OID, and SID |
| Cutoff anatomy | Centering or collimation error | Landmarks, IR placement, and field borders |
| Asymmetric anatomy | Rotation | Compare paired structures and positioning landmarks |
03
Before-you-expose checklist
A repeatable sequence protects the patient and improves consistency.
- IdentifyUse two approved patient identifiers and match the imaging order.
- ConfirmVerify examination, body part, laterality, and relevant precautions.
- PositionAlign the patient, anatomy, central ray, and image receptor.
- CollimateRestrict the field to the anatomy of interest and shield according to current policy.
- CommunicateExplain breathing and motion instructions before making the exposure.
04
Quick knowledge check
Open each answer only after choosing your response.
01Which factor primarily controls X-ray beam penetration?
kVp. Increasing kVp increases the beam's average energy and penetrating ability.
02If mAs is doubled while other factors remain constant, what happens to receptor exposure?
Receptor exposure approximately doubles. mAs controls the quantity of X-ray photons produced.
03What is the most direct way to reduce magnification?
Decrease object-to-image distance and, when practical, increase source-to-image distance.
04What should happen before every exposure?
Verify the patient with approved identifiers, confirm the examination and laterality, remove artifacts, collimate, and communicate clearly.
05A rotated PA chest often shows what clue?
The medial clavicular ends are not equidistant from the thoracic spine.
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