E3505-25 Is Here
A Smarter Standard for CT Image Quality Assessment
In this article:
- ASTM E3505-25 Sets New Benchmark for CT Imaging: The newly released ASTM E3505-25 standard introduces a unified approach to CT image quality assessment by combining visual and numerical metrics, including Detail Detection Sensitivity (DDS), Modulation Transfer Function (MTF), and Contrast Discrimination Function (CDF)
- Disk-Shaped IQIs Enable Consistent Evaluation: Standardized Image Quality Indicators (IQIs) with embedded micro-holes allow precise measurement of CT system performance, enabling reliable detection of features as small as 63 µm and supporting consistent cross-system comparison
- Waygate Technologies Automates Compliance: Waygate’s RAD systems are already aligned with E3505-25, offering automated image quality checks and integrated MTF/CDF evaluations in a single scan—streamlining workflows and enhancing decision-making in industrial and medical CT applications
ASTM International Releases New CT Imaging Standard: E3505-25
In July 2025, ASTM International published E3505-25, a new standard practice focused on enhancing the quantitative assessment of image quality in X-ray Computed Tomography (CT). This standard provides a systematic method for determining the Detail Detection Sensitivity (DDS) and calculating the Numerical Detection Limit (DDSLimit) within CT image slices.
The standard introduces the use of Image Quality Indicators (IQIs)—specifically, disk-shaped IQIs (flat right circular cylinders) embedded with precisely sized round or square holes. These IQIs serve as reference objects to evaluate how well fine details can be detected in CT scans.
To support a comprehensive image quality evaluation, E3505-25 also outlines procedures for measuring:
- Modulation Transfer Function (MTF) – which quantifies the system’s ability to reproduce varying levels of detail (spatial resolution),
- Contrast Discrimination Function (CDF) – which assesses the system’s ability to distinguish between objects of different densities,
- Contrast-Detail Diagram (CDD) – which visualizes the relationship between object contrast and size for detectability.
These measurements are all derived from the same CT scan, ensuring consistency and enabling the accurate calculation of the numerical detection limit, a key metric for non-destructive testing (NDT), industrial CT, and medical imaging applications.
Detail Detection Sensitivity - DDS
This image shows a cross-sectional slice from a CT scan of a disk-shaped Image Quality Indicator (IQI). The IQI has rows of tiny holes arranged in a star-like pattern. Each row contains 9 holes, each with a different diameter. The smallest hole size where all 9 holes can still be clearly seen is 63 micrometers (µm). This means the Detail Detection Sensitivity of the scan is 63 µm — in other words, the scan can reliably detect features as small as 63 µm.
MTF, CDF, CDD, and DDS Limit
In an ideal case the size of the visibility holes is predicted by the CDD which is the ratio of CDF and MTF. We explain more details in: How to describe image quality in CT images?
The CDD shows which relative contrast a hole needs to provide in the object to be recognized by the human eye under the scan conditions. The relative contrast provided by an empty hole in the object is 100%. Hence, the feature size at which CDD reaches 100% at the size of the smallest hole that is expected to be seen, the DDSLimit.
An important detail reveals in this diagram. Both MTF and CDF contribute Detail Dection Sensitivity, i.e., the same DDSLimit can be achieved for different combinations of CDF and MTF. In other words, to a certain extend, a good Contrast to Noise Ratio (CNR) can compensate for a moderate resolution and vice versa.
Expert’s Insights
“E3505-25 marks a significant step forward in standardizing CT image quality. By combining visual and numerical methods, it empowers users to make more informed decisions about system performance and image reliability.”
Holger Roth, Senior Sales Manager, Technical Sales
Waygate Technologies’ RAD systems are already well-aligned with the principles of E3505-25. The automation capabilities in our CT platforms allow for seamless integration of visual DDS, MTF, and CDF measurements—all in one scan. This means our customers can benefit from the new standard without changing workflows, while gaining deeper insights into system performance.
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