Technology evolution
For a long time, screen-film systems remained the standard. They provided high spatial resolution but had a narrow exposure latitude (frequent retakes) and lacked flexible post-processing capabilities. Diagnostic radiology departments gradually transitioned to a digital environment integrated with Picture Archiving and Communication Systems (PACS).
This transition is based on two main technologies:
- Computed radiography (CR). Uses photostimulable phosphor receptor plates. The method was introduced over thirty years ago but remains relevant today due to compatibility with legacy X-ray equipment. It is especially in demand for mobile (bedside) radiography.
- Direct digital radiography (DR). Has virtually replaced CR. Here, X-ray photons are converted into an electrical signal. Conversion can be direct (photoconductors in detectors, e.g., amorphous selenium) or indirect (cesium iodide scintillator plus CCD or flat-panel detector).
Pros and pitfalls of flat-panel detectors (FD)
The transition to DR with flat-panel detectors (flat-panel detector) has dramatically improved the visualization process. Main advantages of the technology:
- Efficient conversion of radiation into an image.
- Wide photographic latitude (dynamic range), minimizing the number of repeat examinations.
- Ability to visualize bones and soft tissues on a single image through post-processing.
- Reduced radiation dose with proper settings.
- Convenient storage and instant transmission across the clinic network.
Risk of overexposure: When working with digital radiography, there is a serious risk of inadvertently increasing the radiation dose (overexposure). Unlike film, where overexposure results in a black, unreadable frame, a digital system corrects the brightness via hardware. The operator sees a high-quality image and may not realize that the patient received an unjustifiably high dose.
Digital tomosynthesis
Digital tomosynthesis (Digital Tomosynthesis) is a method that resolves the issue of anatomical structure overlap characteristic of 2D radiography.
The tube makes a single vertical movement over a stationary detector, capturing a series of projections at angles from -17.5° to +17.5°. As a result, up to 60 coronal slices are generated at the desired depth.
- Pros: In-plane resolution is higher than in CT. Radiation dose is significantly lower than in computed tomography. An excellent alternative to CT for monitoring cystic fibrosis or pulmonary nodules.
- Cons: Scanning takes about 10 seconds, requiring a breath hold. The method is not suitable for small children. The radiation dose is 3 times higher than that of a standard PA chest radiograph. Depth resolution is limited due to the small imaging angle.
Due to the active development of low-dose and ultra-low-dose CT, tomosynthesis is not yet widespread.
Pediatric imaging features
Although the digital environment has greatly simplified work, pediatrics still faces a shortage of specialized pediatric equipment.
Manufacturers strive to reduce the radiation dose, but the ultimate responsibility always lies with the doctors and radiologic technologists. They are obliged to manually adapt "adult" protocols and settings for children, as the pediatric body is more radiosensitive.
Class and exam questions
How does CR differ from DR?
CR uses phosphor plates that are read by a special scanner. In DR, the signal is read directly by a flat-panel detector (with direct or indirect photon conversion) and immediately transmitted to the system.
Why is it easy to miss patient overexposure in DR?
Digital algorithms correct image brightness via hardware. Even with a greatly excessive dose, the image on the screen will look normal, unlike overexposed analog film.
In what cases is laterography used?
A lateral decubitus radiograph (horizontal beam) is needed to detect pleural effusion not visible in the standing position, to assess fluid shifting, or to confirm questionable opacities on the frontal projection.
What else to study on this topic
- Modern approaches to chest CT (MSCT, DECT, iterative reconstruction)
- Application of PET-CT in oncology practice
- Digital technologies in mammography (DBT, CESM) and MRI screening
- Imaging methods for soft tissue tumors of the musculoskeletal system
- Ultrasound diagnostics and elastography in the radiologist's practice
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