Radiographic Equipment and Image Production
Radiographic Equipment and Image Production
This domain tests the chain from generator to receptor: tube design, exposure factor effects, beam restriction, grids, and digital capture. Expect questions that connect a change in technique to image appearance and dose.
Core rules
- mA and exposure time set quantity (mAs); kVp sets beam quality and penetration. Increasing kVp raises receptor exposure and lowers contrast; increasing mAs raises exposure without changing contrast.
- SID affects magnification and receptor exposure by inverse square. OID increases magnification and blur; a small focal spot reduces geometric unsharpness but limits mA.
- Grids remove scatter and improve contrast at the cost of dose; grid ratio, frequency, and cut-off matter. Collimation limits field size and scatter. AEC terminates exposure at the receptor.
- Digital systems separate acquisition from display; the exposure indicator is not a dose measurement and must be interpreted against the vendor range.
Worked example
A non-grid knee at 70 kVp and 10 mAs is converted to 80.5 kVp, about a 15% increase. The 15% rule predicts doubled receptor exposure, so halve mAs to 5 to maintain exposure. Reasoning: higher kVp gives more penetration and a longer grayscale, while lower mAs controls dose.
Traps
Do not say higher kVp always improves quality; it lowers contrast. Do not treat EI as patient dose. Do not compensate for a grid error with mAs alone. Focal-spot blur is not fixed by increasing mAs.
Key takeaways
Link every factor change to exposure, contrast, and dose.