I. Principle of imaging
1. DR is a direct X-ray conversion technology, which uses a flat panel detector to receive X-rays, the flat panel detector has a CCD, amorphous silicon, amorphous selenium and other types of amorphous selenium, there is a detector covered with crystal circuits to convert the X-ray photon directly into a digitized current.
2. CR is an indirect conversion of X-rays, which uses an image plate as an X-ray detector, the image plate is irradiated by X-rays and immediately emits fluorescence, in the process of X-ray energy loss of nearly half, and in the form of a latent image stored in the spatial image of the residual changes in the intensity of X-rays. The latent image signal decays with time. When the scanner scans the image wrench, the latent image signal is converted to visible light by the laser and sent to the computer for imaging through the optoelectronic system.
3. X-ray film imaging technology is X-ray irradiation to the emulsion layer of the film, the emulsion layer of silver halide crystals in the chemical reaction, and with the neighboring X-ray irradiation of silver halide crystals are also polymerized with each other, deposited on the film, leaving an image. The more light the emulsion layer receives, the more crystals agglomerate together, and the less light there is, the less the crystals change and agglomerate. The less light there is, the less variation and agglomeration of crystals. There is no variation or agglomeration of crystals on the emulsion where no light falls. This results in a different image.
II. Image quality
1. Image resolution
- CR system due to its own structure, when subjected to X-ray irradiation, the phosphorus particles in the image wrench so that there is scattering of X-rays, causing latent image blurring, the more serious is that in the process of reading out the image, the scanner's excitation of the light, in the penetration of the image wrench in the deep part of the scattering, the formation of excited fluorescence along the path of the image blurring, reducing the resolution of the image.
- DR systems do not have optical blurring, and their clarity is determined primarily by pixel size. High spatial resolution, wide dynamic adjustable range, and abundant image post-processing functions allow for satisfactory diagnostic results.
- Film imaging The size of silver iodide particles in high-quality film can be up to a dozen micrometers or even smaller, so the film can achieve very high resolution.
2. Exposure Tolerance
Relative to the X-ray film imaging technology, CR and DR due to the use of digital technology, a wide dynamic range, both have a wide tolerance, but the DR system allows for technical errors in the photographic, even in some of the conditions are difficult to master the occasion can also obtain a very good image.
3. Noise
There are many sources of noise in a CR system, including structural noise in the image wrench, fluctuations introduced in the conversion and detection of X-ray photons, laser power drift, drift in the position of the laser beam, fluctuations in the laser beam laser image wrench emitted by the probability of fluctuations, and noise in the electronic chain.
The noise in a DR system is mainly structural noise, but because DR can automatically recover the detector array before the image is directly received, the structural noise is greatly reduced, and the signal-to-noise ratio of DR is much higher than that of CR in comparison.
Three, exposure dose
DR systems can directly acquire digital image data, while CR systems use the residual latent image to generate an image, and with the passage of time, there is signal attenuation, so compared with DR and X-ray film imaging technology, CR's X-ray quantum conversion rate (DQE) is relatively low, and the exposure dose requirements are high.
Four, workflow comparison
1) CR system to produce an image needs to be
IP board exposure, and then get the scanner to read out, the whole process requires a number of steps, the time is longer.
2) In the DR system, the image can be obtained within 40
seconds after the end of the exposure, and the detector can be fixed in the equipment, the technician does not need to move the detector, which reduces the labor intensity, saves time, and improves work efficiency.
3) There are three stages of image formation in film imaging: developing → fixing → visible image formation, which can be accomplished by manual hand washing, or by a film washer.
V. Network Integration
CR and DR systems, the acquisition of digital images, can be networked. However, DR is a direct conversion technology, integrated DICOM3.0 standard protocols to make DR network integration features stronger. DR technology has revolutionized conventional projected X-ray imaging and is superior to CR and X-ray film imaging in many ways.
Sixth, image storage
Traditional film preservation, management, query requires a lot of manpower, material resources and time, in addition to the film will be stored with the increase in time and gradual deterioration, so that the quality of the image degradation. CR and DR digital images, you can use the computer's mass storage, digital electronic management, will no longer need to be huge and difficult to keep the library of negatives.
VII, defects in judgment
Film imaging technology depends on the evaluation of film assessors, this method is simple, but labor-intensive, subjective, poor consistency. At present, the vast majority of weld defects inspection, including film imaging and digital imaging are using manual judgment, the use of automatic identification technology with general defect detection is not mature enough. But in the PCB board, aluminum wheel, lithium batteries and other industries, defects in the automatic judgment system to improve product consistency and quality assurance.
Eight, equipment costs
For large enterprises, in the purchase of digital imaging system at a higher cost, but in two years or even a year to save the cost of film and digital imaging system is comparable to the cost of digital imaging in the long run, the use of digital imaging costs much lower than the cost of film.
Nine, environmental protection
CR and DR are eliminated in the film development of industrial heavy metal pollution and harmful wastewater production, in favor of environmental protection.
X. Conclusion
From the adaptation of the environment, film imaging is greatly superior to digital imaging. From the imaging speed, film imaging technology has been far from meeting the needs of modern production processes. With the continuous development of high-tech development, digital imaging technology in many areas to gradually replace the film imaging technology.