Why is it important to maintain consistent EI/S numbers across serial DR exams?

• A. To store patient names.
• B. To adjust histograms automatically.
• C. To calibrate display monitors.
• D. To ensure technique comparability and dose tracking.

Answer: (D)

In digital radiography, keepingEI/S numbers consistent across serial exams gives a stable reference for comparing exposure, image quality, and patient dose over time. The Exposure Indicator (EI) reflects how much exposure the detector received, and the S-number (or system sensitivity) shows how the detector responds to that exposure. When these values stay within an expected range for the same anatomy and technique, you can attribute changes in image appearance to factors like patient size, positioning, or technique adjustments rather than to a different dose level. This consistency is essential for dose tracking—you can monitor and document how much radiation a patient has received across visits and ensure techniques remain within safe limits (ALARA). It isn’t about storing patient names, automatically adjusting histograms, or calibrating display monitors, which are separate concerns.