Why Is Your Image Quality Indicator Lying to You?

Background

Radiographic image quality is often reduced to one reassuring observation: the required image quality indicator (IQI) is visible. That observation matters, but it does not fully demonstrate that an image can reveal the discontinuities the inspection is intended to find.

An IQI provides evidence that a defined feature can be resolved under the specific conditions represented at its location. However, it does not independently characterize image quality across every thickness transition, geometric feature, or critical region of the part. A radiograph may satisfy the required IQI visual sensitivity while the region of interest remains compromised by unsharpness, scatter, weak contrast, noise, saturation, artifacts, or uneven detector response.

The IQI did its job. The mistake was asking it to answer a question it was never designed to answer.