Explain detector lag and its potential impact on follow-up imaging.

• A. Lag is residual signal from prior exposure; it can ghost into subsequent images, potentially mimicking pathology; mitigated by calibration and proper sequencing.
• B. Lag is the delay in image processing; causes longer study times; mitigated by faster CPU.
• C. Lag refers to patient movement; mitigated by immobilization.
• D. Lag is the time between exposure and display; not affecting interpretation.

Answer: (C)

Detector lag is the residual signal from a prior exposure that remains in the detector and can appear on the next image as a ghost of previous anatomy or devices. This lingering signal can be mistaken for new pathology or can obscure real findings in follow-up imaging because the same structures may seem brighter or in a slightly different pattern than they actually are in the current exposure. The effect fades over time as the stored signal decays, and it can be influenced by how much dose was used previously and by the detector technology in use. Mitigation focuses on calibration and proper sequencing: performing routine calibrations (such as dark-frame and flat-field corrections) to account for fixed-pattern lag, planning the imaging order to minimize carrying over signal, and using clearing or erasing steps between exposures in CR systems to reset the detector. In modern direct detectors, lag is reduced through processing and design, but awareness and interpretation should still consider the possibility of ghosting when evaluating follow-up studies.