Diagnostic Imaging
Diagnostic imaging items test radiation safety, positioning, technique, and recognition of common artifacts. You do not need to be a radiologist, but you must produce a diagnostic image and protect the team.
Core rules
- ALARA: use the smallest exposure that gives a diagnostic image; collimate to the area of interest; wear lead gloves, apron, and thyroid shield when holding.
- Take orthogonal views (at least two perpendicular planes) for most lesions.
- kVp controls contrast; mAs controls density/blackening. mAs = mA × seconds.
- Grids reduce scatter for thicker body parts; they require higher mAs and correct focal distance.
- Ultrasound uses high-frequency sound; gel is needed for contact, and image quality depends on probe frequency and patient preparation.
Worked example
A technique chart lists 300 mA and 0.05 s for a lateral thorax. mAs = 300 × 0.05 = 15 mAs. If you increase time to 0.08 s, mAs = 300 × 0.08 = 24 mAs. Reasoning: changing time changes mAs proportionally; do not change kVp and time together without a reason.
Traps
- Holding a patient without PPE because "it is just one shot."
- Positioning only one view and missing a displaced fracture.
- Using a grid without adjusting mAs, causing an underexposed image.
- Leaving ultrasound gel out of the contact area or using too high a frequency for deep tissue.