Non-Destructive Testing Radiography Glossary 

A glossary for film radiography, digital radiography (CR & DDA), and computed radiography (CR) focused on the BS EN ISO 17636-1:2022, BS EN ISO 17636-2:2022, and BS EN ISO 16371-2:2017 standards.

Area of Interest (AoI) – Minimum area evaluated on the radiograph containing the weld, heat affected zone (HAZ) on both sides, and all markers, lead letters and IQIs. 

Aliasing – Image artefacts occurring when the spatial frequency of the object exceeds the detector’s sampling capability, typically appearing as jagged edges or moiré patterns.

Basic Spatial Resolution (SRᵦ) – Half of the measured image or detector unsharpness, representing the smallest geometrical detail that can be resolved.

• SRᵦ detector: measured with duplex wire IQI directly on detector
• SRᵦ image: measured with duplex wire IQI on the object (source side)

Bad Pixel – Underperforming detector element of a digital detector array (DDA).

Computed Radiography (CR) – Digital radiography technique using storage phosphor imaging plates instead of film. 

Contrast to Noise Ratio (CNR) – Ratio between the difference in mean signal of two image areas and the noise level; a key component of digital image quality.

Normalized Contrast to Noise Ratio (CNRₙ) – CNR normalized to basic spatial resolution, enabling comparison of detection sensitivity across systems.

Digital Detector Array (DDA) – Electronic detector converting incident radiation into a digital image via discrete detector elements (pixels).

Double Wall Double Image (DWDI) – Radiographic technique where both walls of a component are penetrated and both wall images are evaluated. 

Double Wall Single Image (DWSI) – Radiographic technique where both walls are penetrated but only the wall adjacent to the detector is evaluated.

Geometric Magnification (v) – Ratio of source to detector distance (SDD) to source to object distance (SOD). 

Geometric Unsharpness (uᴳ) – Image blur caused by finite source size and inspection geometry. 

Grey Value (GV) – Numeric value representing pixel intensity in a digital radiographic image. 

Linearized Grey Value – Grey value directly proportional to radiation dose, required for quantitative image evaluation (SNR, CNR).

Heat Affected Zone (HAZ) – Material region adjacent to the weld affected by the welding thermal cycle; minimum width considered is weld width or at least 10 mm.

Image Quality Indicator (IQI) – Device (wire, step hole, duplex wire) used to verify radiographic image quality and sensitivity. 

Imaging Plate (IP) – Photostimulable phosphor plate used in computed radiography to store a latent radiographic image.

Nominal Thickness (t) – Thickness of the parent material, excluding manufacturing tolerances.

Penetrated Thickness (w) – Total material thickness in the direction of the radiation beam, accounting for all penetrated walls.

Region of Interest (RoI) – Defined group of pixels used for measurement of SNR, CNR or other image metrics.

Signal to Noise Ratio (SNR) – Ratio of mean signal level to noise level in a selected region of a digital image. 

Normalized Signal to Noise Ratio (SNRₙ) – SNR normalized to basic spatial resolution, used as a primary acceptance metric in digital radiography. 

Source to Detector Distance (SDD) – Distance between radiation source and detector; equivalent to SFD in film radiography

Source to Object Distance (SOD) – Distance between radiation source and the surface of the test object. 

Source Size (d) – Effective size of the radiation source or focal spot, influencing geometric unsharpness.