Digital x-ray imaging for dental programme changes (2)

In conventional x-ray systems, each component signals recession consumes more than 60% of the original x-ray signal energy.

Therefore, only less than 40% of the original image information can be used to generate the image. By digital x-ray imaging to add digital detector, captured more than 80% of the original image information and use various tools to further improve the picture quality post-processing becomes possible. Digital x-ray imaging will provide diagnostic radiology what change? this article will introduce to you. Indirect conversion for indirect conversion, CCD output needs to be correlated double sampler (CDS). Signal level of reduction of voltage and image signal level through the analog front end (AFE) into digital data. AFE's sampling rate from CCD array of pixels and a frame rate decision. In addition, the AFE will calibration sensor error, such as an undercurrent correction, offset voltage and defective pixels. Programmable gain amplifier (PGA) of existence, the PGA of linearity and gain range available is also very important, depending on the signal level. In the digital process, the digits will decide the contrast of the image. Usually, you need to set the initial data for accuracy than the ultimate digital image required digits high 2 to 4 bits of data. Therefore, if you need an 8-bit data of the final image, you first should be a 10-bit digitization to allow image processing rounding errors occur. The main image quality metrics is a "quantum detection efficiency" (DQE), it combines contrast and SNR (signal to noise ratio), a percentage represents. Contrast ratio is higher and the lower the noise, the higher the DQE. Contrast is the order of grayscale, it depends on the output resolution ADC; typically, 14-bit or 16-bit comparison suitable applications. SNR directs not only originate from ADC's SNR, and is the system of SNR, which is protected by x-ray dose, pixel size and impact of all electronic components. You can increase the x-ray dose and increase the photodiode spacing and electrical noise reduction to improve the SNR. Increased x-ray dose will have on patients or operator. Increase the photodiode space does not work, because doing so would decrease the spatial resolution. Decrease from the noise in the system for electronic devices will be the main challenges. System total noise is: all the noise on the signal chain of the square root of the composition (assumptions these noise component does not have an associated). This means including ADC, operational amplifier and benchmarks, all the parts must have a very low noise or severe filtering (if applicable). Temperature stability is another major challenge. The power consumption of the internal temperature rise may offset gray levels and make the image distortion, dynamic acquisition process. Therefore, the ADC, operational amplifier and benchmarks should have high temperature stability.