ISO 15708-4:2025

Overview

ISO 15708-4:2025 - Non-destructive testing (NDT) - Radiation methods for computed tomography - Part 4: Qualification - provides guidance for qualifying the performance of an industrial computed tomography (CT) system for specific testing tasks. It is limited to industrial computed tomography (non-medical) and defines consistent CT performance parameters and their relationship to CT system specifications. The document does not apply to other tomography techniques such as translational tomography or tomosynthesis.

Key topics and requirements

• Scope of qualification: Guidance for both defect testing and dimensional testing, identifying when a task-specific qualification of a CT system is required.
• Performance parameters: Definitions of spatial resolution, contrast (density) resolution, CT grey-value dynamic range and the link between these parameters and system specifications.
• Test planning information: Required knowledge about the test object (dimensions, weight, materials, X‑ray path length) and target features (type, position, size, distribution).
• Feature detectability: Methods to specify and verify limiting defect/feature size and how feature detectability drives system specification and cost.
• Verification procedures: Use of reference objects (natural or synthetic defects), cross-checks (including destructive checks where applicable), and default sensitivity approaches when reference specs are unavailable.
• Consistency checks and documentation: Post-scan checks for reconstruction artefacts, CT data scaling, sinogram issues; mandatory documentation of qualification results and system parameterisation.
• System component checks: Clause-level guidance for verifying manipulation systems, image scale, beam-axis perpendicularity, tube focal spot and stability, detector performance, reconstruction and visualization.
• Resolution evaluation methods: Examples for CT system resolution assessment, acquisition parameters, recommended reference objects and density resolution measurement approaches.

Applications

ISO 15708-4:2025 is directly applicable to industrial NDT tasks where CT is used to:

• Detect and size pores, cracks, inclusions, contaminants and internal assemblies.
• Perform dimensional inspection and metrology of complex or internal geometries.
• Verify manufacturing processes (additive manufacturing, castings, bonded assemblies), product qualification, and failure analysis. The standard helps ensure traceable, task-specific CT performance for quality assurance, supplier qualification, and regulatory compliance.

Who should use this standard

• NDT engineers and CT operators
• Quality managers and inspection laboratories
• Manufacturers using industrial CT for inspection (aerospace, automotive, tooling, electronics, additive manufacturing)
• Technical decision-makers specifying CT system sensitivity and testing protocols

Related standards

• ISO 15708-1 (Vocabulary) - normative reference for terms and definitions
• ISO 15708-3:2025 (Operation and interpretation) - referenced for CT system set-up and image quality parameters

Keywords: ISO 15708-4:2025, industrial computed tomography, CT system qualification, non-destructive testing, feature detectability, CT performance parameters, defect testing, dimensional testing.