Direct digital radiography（DDR）refers to the technology, which use one-dimensional or two-dimensional x-ray detectors to directly turn x-ray image information into a digital signal under the control of a computer with image processing functions.
Direct digital photography is more leading technology of the digital X-ray photography. Compared with the indirect method of storage digital photography, it contains four characteristics: (1) smaller dosages to patients; (2) higher dynamic range and quantum detection efficiency; (3) cover a larger range of contrast, images are richer; (4)increase image resolution and faster, more efficient of work.
Digital Radiography(DR), which is consist of the electronic magazine, scanning controller, system controller, video monitor display device etc., It is used to convert x-ray photon directly into digital images by the electronic magazine, and a broad sense, direct digital X-ray photography. The narrow sense of direct digital radiography usually refers to using the image of direct conversion flat panel detector to directly convert into digital radiography of technology. It is the real direct digital X-ray imaging system and the current trend .It will help to enhance medical diagnosis quality, and promote the hospital management level modernization.
Technical terms for the DR, to determine its image quality is not only flat panel detector type used, as well as plate DQE and MTF, acquisition matrix, collecting gray scale, spatial resolution, the smallest pixel size and other important factors.
Indirect digital photography (IDR): flat panel detector is base on amorphous silicon photodiode array as the core of the medical x ray image detector.
Imaging process: x line -visible light -electric charge image -digital image.
The basic structure of amorphous silicon flat panel detector:
1. Cesium iodide scintillator (x line - the process of visible light).
2. Amorphous silicon photodiode array (visible - the image of the process of charge)
3. Line drive circuit.
4. Image signal read circuit.
Imaging principle: firstly, at the top of the cesium iodide detector scintillation crystal turn the incident x-ray into visible light. Then amorphous silicon photodiode array, under the visible light layer of cesium iodide, make the photodiode produce current, which will transform visible light into electrical signals, forming their own storage charge in the photodiode capacitance. Changes in the charge of each pixel and the intensity is proportional to the incident x-ray, while the array will be the continuous x-ray image is converted to a number of rows and columns form the total array of images. The density matrix decides the the image spatial resolution. Under the unity control of central timing controller, the line driver circuit living in the line direction and the signal living out the direction read out the charge circui line by line, which will be transformed to a serial pulse sequence, and quantize quantify the digital signal. the digital signal form the x-ray digital Image after being send to the image processor through interface circuit.

本文由广州佳誉医疗器械有限公司编辑