A flat-panel detector room shows a faint uniform vertical line on all images at different kVp settings, plus subtle nonuniform background density on flood images after a power outage and recalibration delay. Which detector calibration and uniformity test sequence best identifies and corrects this artifact?

A persistent faint vertical line on every image regardless of kVp with nonuniform flood background after a power outage indicates detector fixed-pattern gain and dark-current drift rather than exposure, positioning or beam factors, so flat-field flood acquisition with SNR uniformity analysis localizes both the column defect and global variation, fresh gain-offset calibration rebuilds per-pixel gain correction and new dark offset, and repeat flood verification confirms uniform response before clinical use. The defective-pixel mapping sequence properly addresses column defects with interpolation routinely used for dead lines, but fails by concept because interpolation masks isolated pixels without correcting the broad sensitivity variation causing background nonuniformity. The gain calibration with stored offset sequence properly uses floods and uniformity metrics for routine drift, but fails by concept because dark signal resets after power loss, so old offset data cannot remove current fixed-pattern noise. The no-verification sequence performs the right calibration but fails by concept because without a repeat flood and SNR uniformity check there is no proof that the line and background nonuniformity were corrected. An exam caveat is that artifacts changing with kVp, mAs or positioning favor tube, grid or scatter sources, whereas uniform kVp-independent lines persisting on floods favor detector calibration. A practical check is to save pre- and post-calibration flood images with SNR profiles, kVp, exposure index and date for trending and service documentation, and if a column line persists on the repeat flood, update the defective-pixel map or call service.