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The secret of the flat-panel detector: How does the magic of capturing images happen in an instant?
In the medical field, innovations in digital radiology have completely changed the way we capture and analyze images of the inside of the human body. Digital radiology technology uses X-ray-sensitive flat panels to capture images directly, and its ability to instantly transmit images to a computer system shows extraordinary efficiency compared to traditional methods. Intermediate film processing is no longer required, which not only reduces time but also reduces radiation dose while maintaining image quality.
Digital radiology imaging technology provides greater convenience for radiologists through real-time image preview and transmission.
Types of detectors
In digital radiology imaging, detectors play a key role. The most common are Flat Panel Detectors (FPDs), which can be further divided into two categories:
Indirect flat panel detector
Indirect FPDs are usually made of ammonia silicon (a-Si) combined with a flash material (such as sodium iodide CsI or ammonium zirconium oxide Gd2O2S) to convert X-rays into light. This light is converted into a digital output signal by an a-Si photodiode layer and then read by thin-film transistors (TFTs) or fiber-coupled CCDs. This design makes the indirect imaging device more flexible in terms of image quality.
Direct flat panel detector
Direct flat-panel detectors are made of ammonia selenium (a-Se), which can directly convert X-ray photons into electrical charges. In this design, the outer layer of the detector usually contains a high-voltage bias electrode. X-ray photons form electron-hole pairs in the ammonia selenium, and the movement of the holes depends on the potential of the bias voltage, and the resulting charge pattern is ultimately read out in the TFT array.
Direct detectors are gradually replacing traditional X-ray cassettes because of their instant response and high resolution capabilities.
Other direct digital detectors
In addition to FPDs, detectors based on CMOS and charge-coupled devices (CCDs) have also been developed, but these devices have not been widely used due to their bulky design and poor image quality. In addition, high-density scanning solid-state detectors have also been developed. These detectors use lithium-doped phosphor materials that can store and release energy during X-ray exposure to generate images.
Phosphor plate radiography technology
Phosphor plate radiation technology is similar to the older analog systems, consisting essentially of a light-sensitive film sandwiched between two X-ray-sensitive screens. It differs in that the analog film is replaced by an imaging plate containing photostimulable phosphors (PSP) that can be read by an image reader and transmit the image to a picture archiving and communication system (PACS). This technique is called computed radiography, although it is not the same as computed tomography (CT).
The advantage of phosphor-emission technology is that it can be seamlessly integrated into existing equipment without requiring modifications.
Industrial Uses
Safety Testing
Digital radiography has been used in security screening for more than 20 years. In the field of safety and non-destructive testing (NDT), it is gradually replacing the traditional use of film. Digital technology provides the inspection industry with excellent image quality, high detection probability, portability and environmental protection, and can achieve real-time image display.
Material Testing
In fields such as aviation and electronics, non-destructive testing of materials is crucial because the integrity of the materials directly affects safety and cost. Digital technology is becoming increasingly common in these industries due to its ability to provide instant results.
History and Future Outlook
The development of digital radiographic imaging technology has changed our understanding of image capture. With the advancement of technology and the reduction of costs, more and more medical institutions and industrial units are beginning to adopt these digital detection technologies. Looking ahead, we can imagine that with the further integration of artificial intelligence and machine learning, the accuracy of image analysis will reach new heights.
What untapped potential and opportunities are there for the future of digital radiology technology?
