ISO 18939:2013

Overview

ISO 18939:2013 - Imaging materials - Digital hard copy for medical imaging - Methods of measuring permanence defines laboratory test methods to evaluate the permanence and image stability of greyscale digital hard‑copy films used in medical imaging. It applies to thermally processed materials (photothermography, thermography, microcapsule) and greyscale inkjet prints on polyester (PET) safety film supports. The standard is focused on transmission‑mode medical records (radiographs, mammograms) and specifies tests to quantify changes caused by heat, light and mechanical interactions.

Note: ISO 18939:2013 does not cover wet‑processed silver halide films, black‑and‑white paper, medical colour images, colour inkjet/D2T2 prints, reflective referral prints, or filmless systems such as PACS.

Key topics and technical requirements

• Scope and definitions for thermally processed, photothermographic, microcapsule and inkjet technologies, and terms such as jnd (just noticeable difference) and jnd‑contrast.
• Physical test methods (adhesion, binder stability, blocking and image interaction) to assess mechanical and layer integrity.
• Image stability tests:
  • Thermal‑ageing (dark stability) - accelerated temperature exposure to evaluate thermal degradation.
  • Light chamber (light stability) - controlled exposure with specified illuminance, temperature and humidity to simulate viewing/storage light ageing.
  • Image spread - evaluation of image diffusion or bleed under stress.
• Measurement and evaluation tools: transmittance density, CIE colour coordinates (Δa*, Δb*), and jnd‑based perceived contrast metrics; annexes provide JND evaluation, CIE parameters and conversion guidance.
• Endpoints and extrapolation: the standard requires the selection of “illustrative end points” for colour and contrast changes and allows Arrhenius‑type extrapolation (see ISO 18924). It warns that extrapolations based on these endpoints do not have proven diagnostic/clinical relevance without radiologist scoring.

Applications - who uses this standard

• Manufacturers of medical dry hard‑copy films and printers for product development and quality control.
• Independent testing laboratories and standards labs performing permanence and accelerated ageing tests.
• Hospital radiology departments, archivists and records managers specifying acceptance criteria for medical film procurement and long‑term storage.
• Regulatory and standards bodies aligning test protocols for medical imaging hard copy permanence.

Related standards

• ISO 18924 - Arrhenius‑type prediction methods for imaging materials
• ISO 5‑2 / ISO 5‑3 - Density measurement methods
• ISO 18902, ISO 18911 - Storage and preservation of imaging materials
• ISO 18907 - Wedge test for brittleness

Keywords: ISO 18939:2013, imaging materials, digital hard copy, medical imaging, permanence, image stability, thermally processed, inkjet, thermal‑ageing, light chamber test, jnd contrast.