Imaging Equipment and Quality Control
Equipment components
Know the x-ray tube (anode, cathode, focal spot, heel effect), generator types (single-phase, three-phase, high-frequency), and the collimator and filtration assembly. Understand detector systems for radiography (CR plates, DR flat panels) and how each converts x-rays to signal. For CT, know the gantry, detector arrays, and the distinction between axial and helical acquisition. For fluoroscopy, understand image intensifiers and flat-panel detectors plus automatic brightness control.
Quality control and acceptance testing
Understand the purpose of QC: verify performance, detect drift, and ensure dose efficiency. Know common tests-kVp accuracy, mAs linearity, timer accuracy, focal spot size, collimation and alignment, half-value layer, and detector uniformity and dead pixels. For CT, know CT number accuracy, noise, slice thickness, and dose index metrics. Understand that QC frequency and tolerances come from standards and institutional protocols.
Traps to watch
Questions often confuse the heel effect direction (thinner anode side has higher intensity toward the cathode side) or test whether a test measures beam quality versus quantity. Watch for items on why flat-panel detectors need gain and offset calibration and why dead-pixel maps matter. Another trap is assuming higher kVp always improves image quality rather than trading contrast for penetration.
Worked example / rule of thumb
mAs linearity: doubling mAs should double output within tolerance (commonly a few percent). If output rises from 100 to 190 units when mAs doubles, the deviation is (190-200)/200 = -5%, which may exceed a tight tolerance. Rule of thumb: check linearity across the clinical range, not just one setting.
Study guidance
Practice matching each QC test to the parameter it verifies and the failure mode it detects.