Published on 04-Apr-2024

Digital Radiography Testing in NDT

Digital Radiography Testing in NDT

Table of Content

Digital radiography, also known as direct digital radiography (DR), has revolutionized NDT with its filmless precision and real-time capabilities. In a world that once relied on traditional film-based radiography, DR is the equivalent of switching from old film cameras to modern digital ones. This advanced technology provides immediate image acquisition, editing, and transfer to computer systems, enabling technicians to optimize inspections efficiently. Moreover, DR boasts remarkable dose efficiency and is rapidly becoming the preferred choice for NDT Professionals.

This article will explore the various aspects of Digital Radiography, from understanding the technology and its two primary types, Computed Radiography and Direct Radiography (DR), to the inner workings of digital radiography, Computed Radiography vs Digital Radiography, the multiple benefits it offers, and its extensive applications in diverse fields. Before delving deeper into Digital radiography here’s a background about the use of radiography in NDT.

Digital Radiography Testing 

Digital Radiographic Testing, an innovative and transformative approach to radiography, has emerged as a cornerstone technology across many fields, including Non-destructive Testing, healthcare, aerospace, and Welding. Digital radiography (DR) which is an advanced form of x-ray radiography produces an instant digital radiographic image on a computer. This cutting-edge method harnesses the power of X-ray-sensitive plates to capture crucial data, replacing traditional Film-based Radiography. The captured data during inspection, is instantly transferred to a computer without using an intermediate cassette. One of the defining features of digital radiography is its seamless immediacy.

In direct radiography, since the captured data is swiftly and directly transferred to a computer system, it eliminates the need for cumbersome intermediaries like discs or cassettes. This real-time digital transfer capability enables images and information to become available for analysis within mere seconds, enhancing the speed and accuracy of diagnostics.

Computed Radiography, another facet of digital radiography, employs advanced photo-simulated screens within digital radiography cassettes, as opposed to conventional X-ray Films. This modern approach eliminates the time-consuming and costly aspects of traditional film processing. Subsequently, a reader efficiently converts the data from these cassettes into a digital format. The use of flexible and durable digital radiography imaging plates further simplifies the process by eliminating the need for rigid holders.

How does Digital Radiography work?


Digital Radiography employs flat panel detectors, also known as Digital Detector Arrays (DDA). These flat detectors complete a direct or indirect conversion process to transform X-ray or gamma-ray radiation into an electronic signal. Transistor sensors interpret the electric charge and convert it into digital information. Here are the various components and processes used in digital radiography.

1. Image Acquisition and Processing

Digital Radiography relies on the conversion of absorbed X-ray energy into electrical charge, which is then digitally represented in grayscale images. Digital image processing software plays a crucial role in creating the final radiographic image. The primary objectives of image processing are to enhance image quality by minimizing noise, eliminating artifacts, and, if necessary, adjusting contrast.

  • Image Storage and Retrieval


After the acquisition of radiographic data, the final images are stored digitally on various storage media. These images are accessible through computer systems, where they can be viewed, analyzed, and manipulated. This includes the ability to zoom in, measure distances and angles, pan across the image, and adjust the window settings for optimal visualization. Moreover, the digital nature of these images facilitates remote viewing on other computers and integration with digital record systems for efficient retrieval and diagnosis.

2. Flat Panel Detectors

Flat Panel Detectors are a critical component of digital radiography systems. There are two primary types of flat panel detectors - direct and indirect conversion detectors. They are designed to cover the entire imaging field efficiently.

> Indirect Conversion Flat Panel Detectors

Indirect conversion Flat Panel Detectors consist of three layers. The top layer contains scintillators, such as cesium or gadolinium, which convert incident X-rays into visible light. The middle layer consists of amorphous silicon photodiode detectors, while the final layer is made up of thin-film transistor (TFT) arrays. The TFT arrays are as large as the imaging field. They amplify the electrical signal produced by the light conversion from photodiodes and store it as an electrical charge. When a high potential difference is applied to the TFT, it releases the charge, and the rows of detectors indicate the originating pixel based on timing. This process, which converts light to charge, is why they are called indirect conversion detectors.

> Direct Conversion Flat Panel Detectors

Direct conversion Flat Panel Detectors use a light-conductive material, often selenium, that is coated onto a thin-film transistor (TFT) array. This material accumulates and stores electrical charge. The outermost layer of the detector is composed of electrodes with a high voltage bias. These detectors offer improved spatial resolution and lower radiation dosage compared to conventional X-rays. They are less sensitive to underexposure or overexposure, which can be crucial for image quality.

Another type of detector used in direct Digital Radiography is the Charge-Coupled Device (CCD) which are light-sensitive sensors, similar to those used in cameras. They are typically combined with a phosphor to convert X-rays into light, which is then focused on the CCD for conversion into electrical charge. The resulting data passes to a TFT array for readout.

Types of Digital Radiography 

There are two primary types of digital radiography: Computed Radiography and Direct Radiography. These methods represent significant advancements in medical and industrial imaging, offering distinct benefits in capturing and processing radiographic data. 

1. Computed Radiography (CR)

Computed Radiography is a digital radiographic technique that closely emulates the process of traditional film-based radiography, making it a convenient transition for many healthcare and industrial settings. Here's how CR works:

Imaging Plate: Instead of Traditional X-ray Film, CR employs a special imaging plate coated with phosphors. These phosphors capture and store X-ray energy when exposed to radiation.

Image Capture: When the imaging plate is exposed to X-rays, the phosphors store the energy in a latent image.

Laser Scanning: To read the stored information, a laser scans the imaging plate, stimulating the phosphors to release the stored energy as light.

Digital Conversion: A photosensitive detector then converts this emitted light into a digital signal, creating an electronic image that can be displayed and stored on a computer.

Computed Radiography offers flexibility in image processing and manipulation. It allows for post-exposure adjustments in image contrast, brightness, and magnification. This technology is widely used in medical radiography for its adaptability to existing X-ray systems.

2. Direct Radiography (DR)

Direct Radiography is a more contemporary and streamlined approach to digital radiography, offering real-time image acquisition without the need for intermediate steps. Here's how DR works:

Digital Detector Arrays (DDA): In DR, X-ray-sensitive detectors known as Digital Detector Arrays (DDA) are directly exposed to radiation during the imaging process.

Immediate Data Transfer: The DDA immediately converts the incoming X-ray data into digital information and transfers it to a computer system for real-time viewing and analysis.

DR eliminates the need for imaging plates or cassettes and the associated processing steps, offering rapid and seamless radiographic imaging. Both Computed Radiography and Direct Radiography have their advantages, with CR being a practical choice for facilities transitioning from traditional Film Radiographic, and DR offering the benefits of real-time digital imaging.

The choice between the two often depends on factors like the existing Equipment, workflow, and specific imaging needs of the application, whether it's in the medical field, aerospace, or Industrial Inspection. In the field of Non-destructive Evaluation, Direct Radiography is considered the best choice due to its real-time imaging, high image quality, and efficiency, as it eliminates the need for intermediate steps involving imaging plates or cassettes.

Computed Radiography vs. Direct Digital Radiography

Computed Radiography (CR) and Direct Digital Radiography (DR) are two prominent techniques in the realm of digital radiography, both offering substantial advantages over traditional Film-based Radiography. Here's a comparison between the two:

1. Image Acquisition

CR employs an imaging plate coated with phosphors to capture X-ray energy. After exposure, the plate is scanned with a laser to release the stored energy as light, which is then converted into a digital signal. Digital Radiography uses Digital Detector Arrays (DDA) to directly convert X-ray energy into a digital signal in real-time. There is no intermediate step involving imaging plates or cassettes.

2. Speed and Efficiency

In Computed Radiography, the process of scanning imaging plates and converting them into digital images takes longer compared to DR. It may require several minutes to obtain an image, whereas Digital Radiography offers immediate image acquisition. Data is converted into digital format and available for viewing within seconds, significantly reducing the time of examination.

3. Workflow and Convenience

Computed Radiography is a more straightforward transition from traditional Film Radiographic, as it uses similar imaging plates and readers. However, it still involves the manual handling of cassettes. Digital Radiography simplifies workflow by eliminating the need for imaging plates and cassettes. It is well-suited for applications requiring real-time image acquisition and immediate results.

4. Image Quality

Computed Radiography offers good image quality and is adaptable to existing X-ray systems. It allows for post-exposure adjustments in image contrast and brightness. Digital Radiography provides high-quality images in real-time, often with better spatial resolution. It offers immediate image enhancement and manipulation capabilities.

4. Dose Efficiency

Computed Radiography may require a higher X-ray dose compared to DR to achieve the same image quality. Digital Radiography typically offers better dose efficiency, requiring lower X-ray doses for comparable image quality. While both Computed Radiography (CR) and Digital Radiography (DR) represent significant advancements in radiography, DR stands out for its speed, efficiency, immediate results, and often superior image quality.

CR has its merits, particularly in scenarios where a transition from traditional Film-based Radiography is more practical, but DR is increasingly becoming the preferred choice in various applications, including medical and industrial imaging, where real-time results and dose efficiency are paramount.

Applications of Digital Radiography

Digital Radiography has a wide array of applications, particularly in industries like aerospace, Oil and Gas Industry, manufacturing, and construction. In all these industries, NDT has a prominent role in assessing the structural integrity of components and DR is one of the commonly employed NDT techniques. 

1. Digital Radiography in Non-destructive Testing

Digital Radiography is used to inspect critical components, welds, and materials for structural integrity, detecting defects, cracks, and material anomalies. Its real-time imaging, high-quality results, and efficiency make it invaluable for assessing the quality and safety of welded joints, pipelines, aircraft components, and various structures without damaging them. It enhances the accuracy and reliability of NDT inspections, contributing to improved product quality and safety in diverse industrial sectors.

Corrosion is one of the major areas of concern for NDT Inspectors. What makes them extremely dangerous is the fact that some defects due to corrosion are not easily visible. Unseen corrosion, such as that occurring inside the pipe or beneath the insulation, might go unnoticed for months or years before they appear as leaks or spills. Nondestructive digital radiography techniques such as Computed Radiography give inspectors a precise, safe, and nondamaging examination of the interior of the Pipeline. Shadow projections are evaluated during corrosion examinations using digital radiography. Since the X-rays can penetrate through the wall of a pipeline, digital radiography can reveal pipe wall thicknesses. Inspectors can discover early indicators of metal loss and sites of weakness by studying variations in wall thickness, which may be associated with corrosion degradation.

2. Corrosion Under Insulation Detection

Corrosion Under Insulation is a severe type of external decay often found on insulated carbon, stainless steel, and low-alloy steel equipment operating at specific temperatures, typically within the petrochemical, offshore, refining, and marine industries. If left undetected, it can lead to safety risks, prolonged downtime, equipment failures, and environmental concerns. Digital radiography is an effective tool for detecting and addressing this issue promptly.

3. Flow-Accelerated Corrosion Detection

Digital radiography is also instrumental in identifying flow-accelerated corrosion, a type of electrochemical degradation in systems involving water and steam. This Corrosion results from the uncontrolled dissolution and transfer of iron oxides in the system cycle. It includes different forms of corrosion such as single-phase, dual-phase, and liquid droplet impingement corrosion. Digital radiography can aid in the detection and assessment of these corrosion types, helping to prevent equipment degradation and failure.

  • Industrial Applications 

1. Oil and Gas Industry:

Digital radiography plays a vital role in detecting corrosion, weld quality, and Pipeline Integrity in the petrochemical and oil and gas sectors.

2. Manufacturing:

Quality control in manufacturing relies on digital radiography to identify defects in products, materials, and assemblies.

3. Casting and Forging:

The casting and forging industry employs digital radiography to detect defects in metal parts, ensuring structural integrity.

4. Aerospace Products Examination:

Aerospace product examination is critical for ensuring the safety and reliability of aircraft.

Even minor errors or undetected complications can pose serious risks to pilots, crew, and passengers.

Digital radiography plays a pivotal role in inspecting, outfitting, and maintaining aircraft.

It is also invaluable during the design and development of new aircraft, enhancing their quality and safety.

  • Digital Radiography in Medical Diagnoses

Digital radiography is an essential tool in medical diagnosis, enabling healthcare professionals to visualize and assess internal structures and conditions within the human body.

It provides high-quality X-ray images with minimal radiation exposure, aiding in the detection and diagnosis of various medical issues, including fractures, tumors, infections, and bone-related conditions.

Its efficiency and digital nature allow for quick image acquisition and analysis, contributing to accurate and timely medical diagnoses.

  • Research and Academic Applications of Digital Radiography

1. Material Science:

Researchers use digital radiography to study the internal structures of materials, such as composites, metals, and polymers, aiding in material development and characterization.

2. Archaeology:

Digital radiography is employed to non-invasively explore historical artifacts and fossils, revealing hidden details without damaging them.

3. Art Conservation:

Art conservators use digital radiography to examine the internal structure of paintings and sculptures to detect hidden layers, repairs, and alterations.

4. Paleontology:

Paleontologists employ digital radiography to study fossils and ancient specimens, shedding light on prehistoric life.

5. Veterinary Medicine:

In veterinary medicine, digital radiography supports the diagnosis and treatment of animals, from companion pets to livestock and wildlife.

6. Soil and Environmental Studies:

Researchers use digital radiography to investigate soil structure and root systems, aiding in environmental and agricultural studies.

7. Water Quality:

In environmental science, digital radiography assists in the analysis of water quality, particularly in sediment and contaminant studies.

Digital radiography's adaptability and versatility have made it an indispensable tool across these diverse fields, enhancing imaging precision, reducing radiation exposure, and improving diagnostic capabilities.

Its applications continue to expand as technology advances, offering new opportunities for research, healthcare, industry, and more.

Benefits of Digital Radiography 

Digital radiography has transformed the way we capture and interpret X-ray images, offering a host of benefits that improve efficiency, image quality, and overall environmental impact in NDT

1. Quality Care:

One of the foremost benefits of digital radiography is its potential to enhance patient care. In the realm of medical diagnostics, patients are increasingly concerned about potential side effects from radiation exposure.

Digital radiography employs significantly lower doses of radiation, making it a safer and more patient-friendly form of radiology.

Furthermore, it delivers high accuracy, reducing the need for retakes and ensuring precise diagnostic results.

2. Processing Times:

Traditional X-ray film processing was a time-consuming and expensive affair, involving the chemical development of films in darkroom. Digital radiography, on the other hand, provides real-time imaging. This rapid availability of images streamlines consultations enhances overall processing times, and significantly boosts productivity for both medical professionals and industrial clients.

3. Ease of Use:

Digital radiography is marked by its user-friendly nature. Minimal training is required, making it accessible to a wide range of healthcare and aerospace professionals. The process is streamlined and straightforward compared to traditional Radiography Methods.

4. Imaging Quality:

Image quality is paramount in both medical and non-medical applications, where clear and reliable images are essential for tests and projects. Digital radiography excels in this regard, delivering higher-quality images compared to traditional imaging techniques. This enhanced image quality is achieved through specialized software that electronically manipulates images to improve definition, allowing for more precise analysis.

5. Image Sharing and Storage:

Digital radiography simplifies image sharing and storage. Rapid electronic transfer of images is more efficient than manual or physical transportation of X-ray films, expediting professionals' ability to complete projects. Storage is equally streamlined, reducing the risk of misplaced or lost images. Digital radiography results can be securely stored on a hard drive with controlled access, ensuring image retrieval as needed.

6. Resource Efficiency:

Digital radiography eliminates the need for chemical developers or film processors, significantly reducing environmental impact. A one-time installation investment is followed by routine maintenance, keeping the machinery running smoothly. The efficiency of digital radiography also contributes to labor cost savings, as digital X-rays do not require lengthy development times.

In the medical field, digital radiography excels in real-time applications, offering shorter exposure times, enhanced detail detection, and improved linearity. Beyond healthcare, the benefits extend to non-medical applications, where digital radiography offers advantages such as an improved signal-to-noise ratio, portability, an enhanced dynamic range with multiple thicknesses, immediate feedback, efficient electronic data transfers, reduced downtime, and increased productivity.

It also allows for image enlargement and enhancement for a more detailed view. Moreover, it's environmentally friendly, as it eliminates the need for processing chemicals.Digital radiography is a transformative technology that not only enhances Non-destructive Testing and the NDT inspector’s efficiency but also finds extensive use in various other fields, where the benefits of rapid, high-quality imaging, streamlined processes, and reduced environmental impact are highly valued.

Key Takeaways

  • Digital Radiography Revolution: DR is the modern equivalent of switching from film cameras to digital ones. It offers immediate image acquisition, editing, and transfer to computers, revolutionizing NDT and medical diagnostics.
  • Understanding Digital Radiography Testing: DR uses X-ray-sensitive plates for precise imaging, with real-time data transfer, making it efficient for inspections across various industries.
  • Types of Digital Radiography: CR and DR are the two primary types. CR emulates traditional film processing, while DR offers real-time imaging with Digital Detector Arrays (DDA).
  • How Digital Radiography Works: DR uses flat panel detectors, converting X-rays to electronic signals in real-time, allowing for immediate image viewing and analysis.
  • Benefits of Digital Radiography: Digital radiography offers quality care with reduced radiation exposure, faster processing times, ease of use, superior imaging quality, streamlined image sharing and storage, and resource efficiency.
  • Applications of Digital Radiography: DR finds extensive use in aerospace, corrosion detection, flow-accelerated corrosion, healthcare, industrial settings, research, academic applications, art conservation, and veterinary medicine.


1. Arise Global

2. Climax Inspection Services

3. Durr NDT

4. TWI Global

5. Velosi Asset Integrity, Engineering,

Tree PNG back


Tree PNG back




Tree PNG back


Application Notes