What Are the Different Types of Motion Detectors?

X-ray detector (X-ray detector) is the core of CT imaging. It converts "X-rays" that are invisible to the naked eye into "digital signals" that can be finally converted into images.

An X-ray detector is a type of X-ray energy that can be recorded

Energy-charge coefficient

The ratio of the average charge (N) and the lost energy (E) obtained by X-rays in the dielectric material is called the energy-charge conversion coefficient. Because the energy-charge conversion is statistical, it is generally expressed as an average.

Energy resolution

The most important system parameter in an X-ray detector is the energy resolution, which reflects the energy resolution of the detector for different types of incident particles. A smaller energy resolution indicates that the detector can distinguish smaller energy differences. Usually we divide energy resolution into two types: absolute and relative resolution. The full-width at half maximum (FWHM) of the energy Gaussian distribution is called absolute resolution; the relative resolution is expressed by the ratio of absolute resolution to peak position.

The energy resolution of the detector is affected by many factors, such as the effective detection area of the detector, the type of detection components, the identification and counter capabilities, and the time constant of the subsequent processing circuit. The time constant usually refers to the time taken by the pulse processor, that is, the time required for the radiation to measure and process energy after it enters the detector. There is a clear correlation between the resolution of the detector and its time constant, area, and analysis efficiency, that is: the size of the area is inversely proportional to the resolution; when the area is constant, the time constant and the accuracy of the photon measurement increase at the same time. The better the discrimination effect [5]. It is not difficult to see that time constant is an important factor affecting analysis efficiency and energy resolution, but the two are not the same. Therefore, from the practical level of the instrument, resolution and sensitivity must be taken into consideration.

Output stability

The sensitivity of the detector energy-charge conversion coefficient to relevant conditions such as the ambient temperature t and the supply voltage V is often referred to as its output stability.

Detection efficiency

Detection efficiency is often defined as the ratio of the number of pulses recorded to the quantum number of incident X-ray light. Because the effects of X-rays and matter are not continuous, and the phosphorescence or ionization generated by the interaction of X-ray light with matter is not absolute, the detection efficiency of X-ray detectors will not be greater than 1. Generally, we divide the detection efficiency into two categories according to different characteristics: absolute efficiency and intrinsic efficiency. The ratio of the total number of incident X-rays to the quantum number emitted by the radiation source is called absolute efficiency. Usually, the sensing area of the detector is only a small range relative to the emitted light quantum, and the radiation source is uniform light emission. In this way, the detector can receive limited radiation photons, so the absolute detection efficiency rate is affected by the detector. The influence of Bunsen characteristics is also related to the appearance design of the detector system. The intrinsic efficiency refers to the ratio of the number of pulses recorded by the system to the quantum number of light incident on the sensing area of the detector.

Time-resolved

The time resolution capability of the detector is mainly determined by the rise time of the signal output from the detector system and the acquisition time of the data signal acquisition [6]. Of course, it is also related to the photosensitive area, detector material, and ambient temperature of the detector ^[4]

Increase the z-axis coverage width

From a development point of view, it is hoped that the X-ray tube can get more layers after one rotation, and it can complete the scan of an organ and achieve the so-called volume scan. For this reason, it is necessary to increase the coverage width of the detection z-axis. To extend the coverage width of the z-axis, it is not only dependent on increasing the number of detectors. It is also important to establish more data acquisition channels, so as to ensure the Z-axis coverage. The coverage width does not reduce the spatial resolution. Due to the development of semiconductor technology, data processing chips have the ability to process massive amounts of data, greatly improving the acquisition speed, and smaller in size. ^[2]

Increase sensitivity

With the development of technology, the quality of CT images has improved significantly, and the resolution has also been greatly improved, but this is mostly at the cost of increasing X-ray energy. Obtaining high-quality images and making patients receive as little X-ray radiation as possible should be one of the key points of the next CT reform. Therefore, it is necessary to improve the sensitivity of the detector and improve the image quality without increasing or even reducing the radiation dose. ^[2]

Dual detector system

In 2005, Siemens first used two x-ray sources and two detectors on the new SOMATOM Definition product for the first time. It was also the world's first dual-source CT system. Because it uses two X-ray sources and two detectors at the same time, the current CT system uses only one ray source and detector, so the dual detector system is more efficient than any existing CT technology. ^[2]