With digital imaging, brightness and contrast are no longer controlled solely by exposure factors. Modern systems post-process images to deliver consistent density and contrast, even when exposure factors vary. While this provides greater latitude, it also means a radiographer can’t rely on image appearance alone to judge whether an exposure was too high or too low.
That’s where exposure indicators come in. These values provide feedback on the amount of radiation delivered to the image receptor — but their meaning depends on the manufacturer and the type of indicator used.
Definition: Numeric value representing the exposure received by the receptor.
Relationship to Dose: Inverse — a higher S-value means lower exposure, and a lower S-value means higher exposure.
Interpretation:
Above target range → Underexposed
Below target range → Overexposed
Limitations: Does not indicate how far over or under you are.
Definition: A linearly proportional estimate of radiation exposure to the detector.
Relationship to Dose: Direct — over means over, under means under.
Practical Tip: If your EI is half the target, you need to double your dose to meet it.
Definition: Quantifies the difference between the actual EI and the target EI, placing it on a scale.
Interpretation:
DI = 0 → Perfect match to target exposure.
Positive DI → Overexposure (amount over is indicated by the value).
Negative DI → Underexposure (amount under is indicated by the value).
Advantage: Makes it easy to see how far above or below target you are and adjust accordingly.
Target exposure indicator values are site-specific and should be set with guidance from:
Your physicist
Radiologist
Applications specialist
Exposure indicators — whether S-value, EI, or DI — are valuable tools for maintaining image quality and optimizing patient dose. Understanding how your system’s indicator works allows you to make precise adjustments and maintain consistency across exams.
Need help configuring your system’s exposure targets? Visit our website or call 1-800-701-XRAY for expert support.
