Digital Radiography in NDT: Pros, Cons & Use Cases

Digital Radiography Overview

Digital radiography (DR) is an evolution of conventional radiographic testing that uses digital detectors—such as flat panel detectors or computed imaging plates—to directly capture x-ray images and convert them into electronic data (instead of using film). 

Because DR does not require chemical development, images are available almost instantly, can be enhanced digitally, and are easier to store, share, and analyze. 

In the world of weld inspection and industrial NDT, ISO 17636-2 defines practices and quality criteria for digital radiographic testing of fusion-welded joints.  Meanwhile, ISO 17636-1 defines film-based radiographic techniques, which still matter as a comparative baseline. 

Digital radiography can be subdivided into:

• Computed Radiography (CR) — using imaging plates (photostimulable phosphor plates) that are scanned to digitize the image

• Digital Radiography (DDR / DR with digital detectors) — uses flat or flexible panel detectors that convert x-ray photons directly into electronic signals

How DR Works (Technical Flow)

1. X-ray / Gamma Source
   
   A radiation source emits x-rays or gamma rays at controlled energy levels.
   
   
2. Detector / Imaging Device
   
   
   • In CR, an imaging plate captures the exposure; then it’s scanned by a reader to convert latent image to digital.
     
     
   • In DR, a flat panel detector (often with scintillator + photodiode array) captures and converts x-ray attenuation to an electronic image.
     
     
3. Signal Processing
   
   The raw digital image is processed by software (contrast/brightness adjustment, filtering, enhancement) to improve defect visibility.
   
   
4. Display & Analysis
   
   The image is displayed on a workstation; operators can zoom, pan, annotate, compare with standards, and archive.
   
   
5. Archiving & Sharing
   
   Digital images can be stored, backed up, transmitted, or compared across sites with ease.
   
   

Because DR removes the need for film handling and darkrooms, the workflow is faster and safer, especially in field use.  

Advantages of DR vs Film Radiography

One case: moving from film to computed radiography in piping functions has cut inspection time by ~50 % and reduced lifecycle costs by about 25 %. 

However, DR systems typically have a higher upfront cost (detectors, software, hardware) compared to film-based systems. 

Challenges / Limitations & Considerations

While DR offers many benefits, it comes with trade-offs and constraints:

• • Detector Cost & Durability
    Flat panel detectors are expensive and sensitive. Dropping or mishandling them can damage panels.

• • Spatial Resolution vs Film
    In some applications, film can offer higher resolution or sharper grain under certain conditions.

• • Dynamic Range Saturation / Overexposure
    If exposure is too high, digital detectors may saturate and lose contrast detail.

• • Detector Size & Geometry Limitations
    Detectors may not conform to tight or curved geometries (though CR plates are more flexible).

• • Software & Calibration Needs
    Proper calibration, correction algorithms, and software versioning are critical. Standards like ISO 17636-2 lay out guidance.

• • Image Artifacts & Noise
    Digital noise, scatter, beam hardening artifacts, and stitching artifacts can degrade interpretability if not managed.

• • Radiation Safety & Regulation
    Even though DR may reduce total dose, radiation hazards remain. Regulatory compliance (shielding, licensing, safety zones) is mandatory.

• • Legacy & Standards Mismatch
    Older inspection programs or specifications may mandate film or reference prior film-based baselines, complicating adoption.