Flat panel detector is a core component of medical DR equipment, and its performance largely determines the image quality. Nowadays, there are many brands and models of flat panel detectors on the market, and what parameters should you pay attention to when selecting a dr flat panel detector? The following are the main parameters of the dr flat panel detector, is what you should know.
First, the first parameter to focus on is the pixel size, which refers to the ratio of the length of the imaging effective area to the number of pixels, or expressed as the distance between the centers of adjacent pixels. Pixel size in turn includes the following subdivisions:
(1) Resolution: the ability to resolve the minimum distance between two neighboring details.
(2) System resolution: in the absence of the inspected workpiece, when the transmissive geometric magnification is close to 1, the ability of the detection system to resolve the smallest distance between two neighboring details per unit length. Reflects the characteristics of the detection system itself, also known as the basic spatial resolution of the system.
(3) Image resolution: the detection system can distinguish the minimum distance between two neighboring details per unit length in the image of the inspected workpiece, also known as the spatial resolution.
(4) Limit resolution: the maximum resolution of the inspection system under the condition of no physical (geometric) magnification.
Pixel size is too small, will increase the image noise; pixel size is too large, will reduce the image resolution. So when choosing the detector pixel size should be selected according to the specific needs of the detection, can not be overly pursued small pixel size detector.
Currently on the market there is a model PLX8600 flat panel dynamic DR, which is equipped with a 17″ × 34″ large size flat panel detector. Compared with multiple shots and then software splicing DR equipment, PLX8600 solves the problems of uneven density of spliced images, image alignment and magnification effect at the splicing place, and brings the clinic a real large field of view image solution with high-definition image quality, accurate imaging without distortion, and one-time coverage of the whole spine or double lower extremity images.
In addition, PLX8600 plate dynamic DR photography speed, and a single photographic radiation dose is conventional multi-photography and then software splicing DR 1/2 or 1/3, low dose to patients more care.
Second, the second to clarify the type of scintillator dr flat panel detector, the current industry common amorphous silicon scintillator coating materials are two cesium iodide, gadolinium sulphoxide.
Cesium iodide will convert X-ray into visible light than gadolinium thiouxide but the cost is relatively high; cesium iodide will be processed into a columnar structure, which can further improve the ability to capture X-ray and reduce scattered light. Detectors using gadolinium thiouxide as a coating have fast imaging speed, stable performance and lower cost, but the conversion efficiency is not as high as cesium iodide coating.
Third, then the dynamic range of the dr flat panel detector, which refers to the range in which the detector can accurately measure the intensity of the rays.
Dynamic range formula: D = Vs/Vn Dynamic range expressed in decibels formula: D = 20lg (Vs/Vn) D detector dynamic range Vs detector output maximum signal Vn electronic noise The greater the dynamic range, indicating that in the case of large differences in the thickness of the detected workpiece can still be obtained in good contrast sensitivity.
Fourth, the sensitivity: the detector output can be detected when the minimum input signal strength required.
Amorphous silicon detector sensitivity is determined by four factors: X-ray absorption, X-ray – visible light conversion factor, fill factor and photodiode visible light – electronic conversion factor. It is usually expressed in terms of the X-ray sensitivity S. For example, the X-ray sensitivity S of a detector can be labeled as: S ~ 1000e-/nGy/pel DN-5 Beam indicating that the detector produces 1000 charges per nGy on a single pixel under standard DN-5 X-rays. As the X-ray sensitivity S and line quality is usually given at the same time line quality standards such as: DN-5 Beam detector sensitivity accuracy the higher the better, a good detector sensitivity can reach 1 photon.
Fifth, the modulation transfer function MTF: for the detector contrast spatial frequency transfer function, usually used to indicate the detector for the resolution of image details.
Theoretically speaking, the higher the detector MTF the more real image information, the perfect detector MTF should be independent of the spatial frequency of the horizontal straight line, but in practice, due to the existence of sampling effects, this view is not entirely correct, which will be reflected in the analysis of detector artifacts and noise. It can be seen that the MTF value of the detector is not the higher the better, how to choose the appropriate MTF distribution is a problem that needs to be carefully considered in the detector analysis.
Sixth, the quantum detection efficiency DQE: defined as the ratio of the square of the output signal-to-noise ratio to the square of the input signal-to-noise ratio is usually expressed as a percentage.
Detector DQE is defined as follows: DQE = (Sout/Nout) / (Sin/Nin) Roughly, it can be thought of as follows: when the system DQE is higher, the same image quality can be obtained with a lower dose; or the same dose to obtain a higher image quality. With the development of digital image post-processing technology, it has been possible to improve the contrast and edge sharpness of the image through appropriate algorithms, so as to achieve the purpose of improving the image effect. However, it cannot improve the other two factors that limit the image quality: noise (especially the noise entering the frequency domain of the image signal) and artifacts. These two are more dependent on the image system detector itself.
Noise: An output signal that is not caused by the input signal. The main sources of noise: electronic noise of the detector, ray image quantum noise.
Signal-to-noise ratio: the detector to obtain the average of the image signal and the standard deviation of the image signal ratio, expressed as SNR. The higher the SNR, the better the image quality.
Normalized SNR: Comparison of the SNR of different detectors must be carried out under the same detector unit size. Calculation formula: SNRn=SNRm×88.6/P SNRn normalized signal-to-noise ratio, SNRm measured signal-to-noise ratio, P detector pixel size (um).
Linearity:is the ability of the detector to produce a signal that is proportional to the incident intensity over the range of maximum dose ray intensities.
Stability: is the ability of the detector to process the signal to produce consistency as the operating time increases, linearity and stability directly affect the detector accuracy.
Response time: is the detector from receiving ray photons to obtain a stable detector signal time required, it is the rate of independent sampling and data quality of the key. By the detector preparation time, exposure waiting time, exposure window, image readout time consists of four parts.
Memory effect: the parameter that indicates the image residual, usually with two parameters to indicate the change of the residual factor. One exposure after 20S detector short-term memory effect (Short-term memory effect 20s) such as: 0.1% One exposure after 60S detector short-term memory effect (Short-term memory effect 60s) such as: 0.02%.
