The PET/CT sat idle overnight, and the CT tube has been off since yesterday's last attenuation-correction scan. The manufacturer's protocol requires a tube warm-up after this shutdown. The department runs calibration and image-quality checks on a weekly cycle, so only the steps that address the idle period are due now. The first patient is on the table for a routine whole-body study. Which CT tube preparation step is required before the first patient exposure?

The stem states that the manufacturer’s protocol requires a tube warm-up after this shutdown, so you must complete that prescribed routine before the first patient exposure. Warm-up sequences and the conditions that trigger them vary by system; follow the manufacturer’s instructions rather than assuming every overnight idle period requires the same sequence. An empty-table air calibration updates detector calibration data, but it does not substitute for a prescribed tube warm-up. Scanning the water phantom and comparing its reconstructed CT numbers with the weekly acceptance baseline is a periodic image-quality check, which is not due now under the stated schedule. The console’s automatic function check verifies detector and gantry readiness, but it does not warm the tube. A useful exam caveat is that the need for warm-up depends on the system’s specified shutdown conditions, not simply on the fact that the scanner was idle overnight. Before exposing the patient, check the applicable manufacturer procedure and confirm that the required warm-up has completed; do not use patient exposures as warm-up shots.