* Digital radiography (DR)
* Principle of imaging: DR and CR both convert analog information into digital information, and the difference between the two lies mainly in the difference in the way the X-rays are acquired and the images are converted.
CR is a kind of X-ray indirect conversion technology, which utilizes IP as the X-ray medium, and records the intensity change of X-ray in the form of latent image after IP is irradiated by X-ray. The intensity of the latent image signal decreases with time. The laser scanner generates a red laser or near infrared laser, when the laser beam gradually scans the surface of the IP, the latent image signal is converted into visible light by the laser (photofluorescence effect), the fluorescence from each point on the IP, through a special optical system coupled to a photomultiplier tube, photomultiplier tubes at each point of the different intensities of the light signal into an electrical signal, the signal is amplified and sampling, to the quantization of analog-to-digital converter, and then to the computer imaging. The signal is amplified and sampled, quantized by an analog-to-digital converter, and sent to a computer for imaging.
DR using flat panel detector or fluorescent plate CCD camera directly to the X-ray photons into digital signals, the conversion link less, reducing the generation of noise; so that the loss of X-ray photon signals to a minimum, image quality is high.
Image quality: DR has a higher resolution than CR, a larger dynamic range, and a higher signal-to-noise ratio
Exposure dose: DR is about 2/3 of that of CR
Efficiency: DR works more efficiently than CR
System compatibility: CR can be compatible with the original X-ray machine, and DR is not compatible with the original X-ray machine.
Dynamic images: Flat panel detectors have been able to output dynamic images for fluoroscopic acquisition, expanding their range of application.
For its clinical applications, DR can completely replace CR, which is the transition from traditional X-ray equipment to digital X-ray equipment.
CR system is mainly used IP detector, commonly known as IP plate, this is the acquisition of recorded image information carrier. CR imaging principle, that is, the IP plate has a light-excited fluorophore, in the x-ray irradiation to the above, can absorb and store x-ray energy. The captured energy is then released under the excitation of additional laser energy of the appropriate wavelength. The process of release is such that a specialized CR reader is required. The released energy, by the photomultiplier tube will be converted from the optical signal into a voltage, the voltage through the increase, input analog / digital converter into digital, through the sampling and quantization, it is stored in the computer. Finally, after the image is read, the data on the IP board is eliminated by applying strong light irradiation so that it can be reused.
DR generally refers to digital photography based on charge-coupled device (CCD) technology, where cesium iodide crystals are commonly used as the most common detector material. Cesium iodide crystals are irradiated by x-rays, which can directly convert x-ray photons into visible light, and the visible light excites the photodiode below the cesium iodide layer, which generates an electric current in the photodiode, which is then stored in the diode's own capacitance. The electrical signal is then read out by the reading circuit and quantized into a digital signal. Finally, it is transmitted to the image processor through the communication interface and stored in the computer.
Then in practice, it is probably like this
CR: first take a blank IP board, enter the relevant information on the computer, photography, read the image with a reader, the computer to view.
DR: computer to enter the relevant information, photography, computer to view.
Obviously, DR is much more convenient. If there are a lot of patients, it is necessary to prepare a certain number of blank IP boards in the department, otherwise I will have to read and erase every patient after the photo, in order to carry out the next patient's photography. Second, if a patient's image does not meet the diagnostic requirements, the CR cannot be detected on the computer until I read it with a reader, whereas the DR can be seen on the computer directly after the exposure is completed.
To use a poor analogy, CR is like the old cameras that required film and had to go to a studio to develop the image, whereas DR is like today's digital cameras, where you press the shutter and see the image on the display.