5 keys for Digital Radiography

dose-creep
Table of contents

By: CE4RT

Computed Radiography (CR) and Direct Radiography (DR) are now the standard imaging technologies in many hospitals and imaging centers. These digital systems mark a significant evolution in the field of medical imaging. X-ray technicians must grasp several critical concepts to effectively utilize these technologies. Familiarity with the functionalities, advantages, and specific operational aspects of both CR and DR systems is essential for maximizing image quality and ensuring patient safety. Each system has unique applications and demands specific skills and knowledge for effective management. Learn more about the capabilities and applications of digital radiography systems here.

 

1. Digital Vs. Film, Know the Difference

While film radiography has evolved significantly over the years with advancements such as high-speed film and rare earth screens, digital radiography systems, including Computed Radiography (CR) and Direct Radiography (DR), have become the standard in modern medical imaging. CR utilizes digital cassettes that are portable and capable of holding a latent image, whereas DR captures images directly onto a plate and facilitates immediate image transfer.

The shift to digital x-ray systems offers numerous radiation protection benefits compared to traditional film. Notably, modern digital receptors are more sensitive than their film counterparts, which allows for reduced mAs settings on technique charts, thereby decreasing patient exposure. Additionally, the enhanced imaging capabilities and processing speed of digital systems significantly reduce the likelihood of needing repeat exams, further minimizing patient exposure to radiation.

  • The images produced by digital radiography systems are generally of higher clarity and quality than those produced by traditional film radiography. This enhanced image quality is crucial for accurate diagnosis and improved patient outcomes.
  • Digital images offer significant advantages in terms of post-processing capabilities. They can be easily edited and enhanced using various viewing tools such as inversion, zooming, and other adjustments that allow medical professionals to examine the subject from multiple angles and perspectives based on a single exposure. Importantly, these enhancements can be applied without altering the original diagnostic integrity of the image, ensuring that all modifications are reversible and the base image remains unchanged for accurate review and comparison.
  • One of the major advantages of digital imaging systems is the reliability of data storage. When properly archived, digital images can be preserved indefinitely without degradation, ensuring they remain accessible whenever they are needed. This permanence is particularly beneficial in healthcare settings, as it guarantees that patient images are available for review or comparison, regardless of whether the patient is currently admitted to the hospital or has been discharged, thereby supporting ongoing and future medical care.
  • The processing and delivery of digital images are significantly faster compared to traditional film-based methods. This expedited workflow not only streamlines clinical operations but also facilitates quicker diagnoses. The ability to promptly diagnose conditions is critical, as it can greatly enhance the effectiveness of treatment and improve patient outcomes. Early detection made possible by the speed of digital imaging can be pivotal in the management and resolution of health issues.
  • Film-based radiography can be fraught with mechanical and chemical processing issues. Processor rollers are prone to breaking, leading to films getting stuck, and the chemical baths used for developing film can suffer from inconsistent temperatures and concentrations if not maintained correctly. In contrast, digital radiography systems typically experience fewer technical issues, as most problems that do arise are due to human error rather than mechanical failure. This reliability enhances workflow efficiency and image quality.
  • Many digital radiography systems are equipped with automatic exposure controls. These controls help to mitigate the risk of incorrect exposure settings, ensuring optimal image quality and reducing the likelihood of needing repeat exposures. This feature not only improves patient safety by minimizing unnecessary radiation exposure but also enhances the diagnostic accuracy of the radiographic assessments.
  • As technology has progressed, the advantages of using film in radiography have significantly diminished. One of the few remaining benefits of film is its independence from electricity—once developed, film can be viewed in any setting without the need for power. This feature becomes particularly valuable in remote locations or during power outages where electronic devices might be inoperable. However, even this advantage can be mitigated in digital systems if there is forethought and preparation; digital images can be preemptively printed onto film, ensuring availability regardless of electricity access.
  • While digital radiography systems present cost advantages for large-scale imaging centers over the long term, the initial costs and maintenance of a film-based system may still be more economical for facilities with low imaging volumes. This is because the investment in staff and the infrastructure required to support and maintain the computer systems necessary for digital radiography can be substantial. In the past, another barrier to adopting digital systems was the learning curve associated with mastering the required computer software for physicians and support staff. However, this concern has diminished significantly in recent years, as most individuals now possess basic computer skills, making the transition to digital systems smoother and more feasible across a wider range of healthcare settings.
  • Many experienced professionals argue that the most skilled digital radiographers are those who originally trained using analog systems. This perspective suggests that techs trained on analog systems tend to develop a strong foundation in radiographic techniques, as they must rely less on the advanced capabilities of equipment and more on their own expertise and precision. As a result, they often transition effectively to digital systems, bringing a high level of skill and attention to detail that enhances image quality. Conversely, the newer generation of radiologic technologists, who are trained exclusively on digital equipment, might miss experiencing certain traditional aspects of the field, such as the distinctive smell of developer in a darkroom.
  • 2. Follow the CR / DR Checklist

    Computed Radiography (CR) and Direct Radiography (DR) are now pivotal in general medical radiography, a significant contributor to man-made background radiation. Radiologic technologists are instrumental in safeguarding public health by adhering to best practices during digital radiography exams. Below is a checklist of these best practices for performing CR and DR exams, inspired by the Image Wisely campaign. For those still utilizing film technology, it’s important to adapt this checklist to include specific practices related to film, such as film selection, development, and processor maintenance.

    As you greet the patient

    • Confirm the patient’s identity to ensure that the correct individual is receiving the radiographic
      examination.
    • Verify that the imaging order is appropriate and corresponds accurately with the patient’s reported symptoms and medical complaints.
    • Ensure that the examination procedure has been thoroughly explained to the patient and, if applicable, to their parent or guardian.
    • For female patients, confirm the reproductive status to ensure appropriate precautions are taken to protect reproductive health during the imaging process.

    Before you begin

    • Is the exam information acquired from a modality work list?
    • Have all unnecessary persons been cleared from the room prior to exposure?
    • Is there alignment of the beam and body part and image receptor?
    • Is the signal to image distance (SID) correct?
    • Is a grid needed and appropriately placed?
    • Is the beam properly angled and collimated?
    • Have markers been placed?
    • Is shielding necessary and placed correctly?
    • Have the correct technical factors been selected?
    • Have positioning and breathing instructions been given and understood?

    During the exam

    • Are images processed correctly in the reader?
    • Does the correct exam information appear on the images?
    • Is the exposure index correct for the exam?
    • Is the image masked correctly?
    • Are any digital annotations needed?
    • Is the image processed correctly?
    • Have any necessary notes regarding the exam such as medications been charted?
    • Are all images visible and correct in the diagnostic viewing system?

    3. Watch Exposure Indicators

    When operating Computed Radiography (CR) or Direct Radiography (DR) systems, it is crucial to monitor the exposure indicators. These indicators provide essential feedback by displaying the relative exposure levels received at the image receptor. The displayed values are a direct reflection of the digital receptor’s efficiency and sensitivity, playing a critical role in assessing the quality of the radiographic technique and ensuring patient safety.

    .

    Without an exposure indicator, it is impossible to verify whether the appropriate exposure factors have been selected, which is essential for producing high-quality images while ensuring patient safety. Additionally, there is a learning curve associated with digital radiography for technologists. Understanding the nuances of digital image acquisition, processing, and display requires training and experience, as these components are critical to maximizing the benefits of digital imaging technologies.

    A significant challenge in digital radiography arises from the fact that manufacturers of this equipment employ varied methods for determining and reporting exposure indicators. These differences can include variations in terminology, units, mathematical formulas, and calibration conditions. Such inconsistencies can lead to confusion among technologists, radiologists, and physicists, particularly when they need to operate systems from multiple vendors. The situation is further complicated when adequate training on the specific unit in use is not provided, increasing the potential for errors and discrepancies in radiographic outcomes.

    Fuji of Japan utilizes a sensitivity number (S), designed to reflect the “speed class” concept, which is familiar to technologists who have experience with film-screen radiography. This approach helps bridge the gap between older and newer technologies by providing a measure that feels familiar yet applies to digital contexts. In contrast, Carestream, based in New York, uses an “exposure index” to denote its exposure indicator, reflecting the average pixel value observed within the clinical region of interest. This provides a direct measure of the radiation that has interacted with the detector. Similarly, Agfa of Belgium employs a CR exposure indicator known as lgM, which calculates the logarithm of the median exposure value, focusing on a specific region of interest to assess exposure levels. Despite these advancements, many manufacturers of Direct Radiography (DR) systems were initially slow to develop comprehensive exposure indices, which are crucial for assessing image quality and ensuring patient safety at the image receptor level.

    Fuji
    corporation S Number 
     Agfa corporation IgM  Kodak/Carestream – Exposure Index   Detector Exposure – Estimate (mR) Action
    > 1000 < 1.45 < 1250 < 0.20 Underexposed: repeat
    601-1000 1.45-1.74 1250-1549 0.2-0.3 Underexposed: QC
    301-600 1.75-2.04 1550-1849 0.3-0.7 Underexposed: Review
     150-300  2.05-2.35 1850-2150 0.7-1.3  Acceptable range
     75-149  2.36-2.65  2151-2450  1.3-2.7  Overexposed: Review
     50-74 2.66-2.95  2451-2750 2.7-4.0 Overexposed: QC
     < 50  > 2.95  >2750  > 4.0  Overexposed: repeat if
    necessary

    Source Image Gently: Using Exposure Indicators To Improve Pediatric Digital Radiography – Abbreviation: QC = quality control.

    4. Avoid Dose Creep

    Dose creep refers to the gradual, unintentional increase in radiation exposure that can occur with digital radiography systems. These systems possess the ability to process a wide range of exposures into clear images, which can inadvertently lead to higher doses being used than are actually necessary. In contrast, traditional analog screen-film radiography involves a fixed film speed and consistent processor controls, which require precise exposure settings. Any deviation in these settings could result in images that are either too light, indicating underexposure, or too dark, indicating overexposure. It is crucial for technologists to monitor and adjust their practices to prevent dose creep in order to maintain both image quality and patient safety.

    In digital imaging, the immediate feedback that alerts technologists to incorrect exposures is often absent. Both DR (Direct Radiography) and CR (Computed Radiography) systems are highly effective at compensating for suboptimal technique, which can inadvertently lead to a problematic issue known as ‘dose creep’. This occurs particularly in CR systems that lack automatic exposure controls, where the flexibility of digital processing can mask exposure errors, resulting in gradually increasing radiation doses without noticeable degradation in image quality. This underscores the importance of vigilance and strict adherence to established exposure guidelines to prevent unnecessary radiation exposure to patients.

    This issue arises because digital detector systems possess the capability to produce high-quality radiographic images even in instances of significant overexposure or underexposure. The digital technology’s advanced processing abilities enable it to optimize images for display on soft copy monitors or hard copy film, maintaining excellent image quality across a wide range of exposure levels. Estimates suggest that digital image processing can effectively compensate for underexposures by up to 100% and for overexposures by more than 500%. This robust flexibility, while beneficial in ensuring image clarity, can also inadvertently encourage less precise exposure practices, known as dose creep, if not carefully monitored.

    Unfortunately, in scenarios where dose creep occurs, patients may be subjected to unnecessary radiation exposure without the awareness of the medical professionals involved in either acquiring or interpreting the images. It is not uncommon for patients to receive radiation doses that are three to five times higher than necessary, without detection or complaint from clinical staff. This highlights the critical need for stringent monitoring and regulation of exposure levels to ensure patient safety while maintaining the diagnostic integrity of medical imaging.

    Dose creep often results from the fact that while underexposed images may appear poor or unusable, overexposed images can still look acceptable or even flawless, inadvertently encouraging technologists to err on the side of overexposure. This tendency poses a risk of unnecessary radiation exposure to patients. The objective in medical imaging should always be to obtain the clearest and most diagnostically useful image while minimizing the radiation dose to the lowest possible level. Striking this balance is essential to ensure patient safety without compromising the quality of diagnostic information.

    To assist technologists in achieving optimal image quality with minimal radiation exposure, most digital detector systems are equipped with an “exposure indicator.” This tool offers crucial feedback by indicating the relative exposure received by the detector. It does this by analyzing the intensity of the raw image data and the scaling adjustments necessary to achieve an image with suitable brightness and contrast levels. Such feedback is instrumental in guiding technologists to make more informed decisions about exposure settings, thereby helping to prevent overexposure and minimize radiation risks.

    5. Collimate

    It is fundamental, though worth emphasizing, that radiographers must meticulously employ collimation to the specific anatomical area of interest during examinations. Proper collimation is crucial not only for minimizing patient exposure to radiation but also for ensuring accurate processing of the digital image data. Careful collimation helps to reduce scatter radiation and enhance image quality, which in turn aids in accurate diagnosis while safeguarding patient health by limiting unnecessary radiation exposure.

    By effectively limiting the area exposed to radiation through precise collimation, radiographers can significantly reduce the amount of the patient’s tissue that is exposed. This practice not only decreases the patient’s overall radiation dose but also minimizes the amount of scatter radiation that reaches the patient. Moreover, collimation plays a critical role in enhancing the quality of radiographic images. Proper collimation helps to reduce excess scatter radiation that can strike the receptor, which is crucial for maintaining high image contrast and ensuring diagnostic clarity.

    Digital radiography systems are equipped with software that enables electronic masking, or collimation, which functions by recognizing the borders of the exposed area on the image receptor. Radiographers may sometimes need to manually adjust this electronic masking to ensure it precisely aligns with the exposure field. However, it’s important to note that while electronic masking, shuttering, or cropping can refine the image after exposure, these methods should not be used as substitutes for the beam restriction provided by physical collimation of the x-ray field size. Proper physical collimation is essential for directly controlling the radiation dose and minimizing the exposure to non-targeted areas, thereby ensuring both patient safety and image quality.

    Masking should never be employed to obscure any part of the anatomy that was within the exposure field at the time of image acquisition. This practice is strongly discouraged due to legal and radiation safety concerns. It is essential to maintain the integrity of the original radiographic image as captured, ensuring that all anatomical areas exposed during the procedure are visible for accurate diagnosis and compliance with medical imaging standards.

    In digital radiography systems, mathematical algorithms play a crucial role in adjusting image brightness and contrast. However, excessive white space within an image can disrupt these calculations, potentially leading to inaccurate image rendition. Therefore, a best practice in radiography is to precisely collimate the x-ray beam to cover only the anatomic area relevant to the diagnostic procedure. When electronic masking is employed to enhance image viewing conditions, it should be utilized in such a way that clearly shows the actual edges of the exposure field. This practice is important for documenting proper collimation and ensuring that the entire area exposed during the procedure is visible. Importantly, masking should never be used to cover any part of the anatomy that was within the exposure field at the time of image acquisition, as doing so could obscure critical diagnostic information.

     

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    FAQs

    1. What is the main difference between Computed Radiography (CR) and Digital Radiography (DR)?

    The main difference between Computed Radiography (CR) and Digital Radiography (DR) lies in how they capture and process images. CR uses photostimulable phosphor plates that need to be processed in a CR reader to convert the image into a digital format, whereas DR uses flat-panel detectors that directly capture and digitize the image, allowing for immediate viewing and faster workflow.

    2. How does a CR system work in capturing X-ray images?

    In a CR system, an X-ray image is captured on a photostimulable phosphor plate. After exposure, the plate is inserted into a CR reader, where it is scanned with a laser. The laser stimulates the phosphor, causing it to emit light proportional to the X-ray exposure. This light is then converted into a digital image by a photomultiplier and processed for viewing and analysis.

    3. What are the advantages of using Digital Radiography (DR) over Computed Radiography (CR)?

    Digital Radiography (DR) offers several advantages over Computed Radiography (CR), including:

    • Faster image acquisition and processing, leading to improved workflow efficiency.
    • Higher image quality with better spatial resolution and contrast.
    • Immediate image availability, reducing patient wait times and allowing for quicker diagnosis and treatment decisions.
    • Reduced radiation exposure to patients due to more sensitive detectors.
    • Elimination of the need for physical processing and handling of imaging plates.

    4. What are the common artifacts seen in CR and how can they be minimized?

    Common artifacts in CR include:

    • Plate reader artifacts: Caused by issues with the CR reader, such as dirt or debris on the rollers. Regular maintenance and cleaning can minimize these artifacts.
    • Phosphor plate artifacts: Scratches, dust, or damage to the phosphor plate can create artifacts. Handling plates carefully and storing them properly can reduce these occurrences.
    • Image processing artifacts: Arising from incorrect image processing parameters. Proper calibration and using appropriate processing algorithms can help minimize these artifacts.

    5. How can radiologic technologists ensure optimal image quality in DR systems?

    To ensure optimal image quality in DR systems, radiologic technologists should:

    • Regularly calibrate and maintain DR equipment to ensure it is functioning correctly.
    • Use appropriate exposure settings to achieve the best balance between image quality and patient dose.
    • Employ proper positioning and technique to minimize motion artifacts and ensure clear images.
    • Stay updated with training and best practices in DR technology to fully utilize the system’s capabilities.
    • Conduct regular quality control checks to identify and address any issues promptly.