X-ray machines are used more and more in the medical industry. Yueshen Medical, as a manufacturer of domestic and foreign high-end medical equipment, X-ray machines often meet the requirements of our customers to install equipment, but everyone uses X-rays in daily life. When I was on the phone, I encountered a lot of confusion and problems. This article will explain the following professional knowledge of X-ray machines:
1. Basic knowledge and types of X-ray machines
2. What foreign objects can the X-ray machine detect?
3. What factors can affect the sensitivity of X-ray machines
1. Basic knowledge and types of X-ray machines
a: X-ray knowledge
Let me talk about X-rays first. On November 8, 1895, a German physicist Professor Roentgen discovered X-rays when he used cathode rays in his daily experiments. At the time, the physicist didn't know what these rays were, so he named them "X-rays."
X-rays are actually very powerful rays. Compared with light waves, X-rays have much higher energy and stronger penetrating power. X-rays can pass through materials that ordinary light waves cannot penetrate. Such as wood, glass, bones, skin, clothing, etc. In addition, X-rays can also penetrate many other non-metallic materials and some relatively thin metal materials.
In addition to the use of X-ray machines in the medical industry, X-ray inspection equipment is used in other industries (such as airport baggage security inspection machines and some food inspections). These application scenarios are basically the same in principle.
b: Composition of X-ray machine
The X-ray machine is mainly composed of the following three important components:
X-ray generator: Generates and emits X-rays.
X-ray detectors: X-ray detectors are made of scintillator materials that convert X-rays into visible light. The scintillator body material is a row of photodiodes positioned opposite the X-ray generator.
Control system: The control system will analyze the X-ray image formed on the detector of the detected object, and compare the image with the software preset standard through the proprietary control system software, so as to watch and compare.
The relationship between the X-ray detector and the X-ray generator is like the relationship between the photosensitive element of the camera and the light.
c: X-ray machine imaging principle
To put it bluntly, the X-ray system is a scanning device. When the X-ray beam passes through the object, the system will take an image of the entire object. According to the size of the detector diode, the X-ray divides the object into many small blocks for scanning to form the image data of each small block. For example: using a detector diode with a size of 0.8 mm, a new line of image data is acquired every time the object moves 0.8 mm along the moving direction. All image data is represented using grayscale values ranging from 0 (completely black) to 255 (completely white).
Substances of different densities in the composition of objects have different amounts of absorption of X-rays, resulting in different gray values. The thicker or denser the product, the more X-rays it absorbs, the less the detector senses the rays, and the darker the imaging gray value.
d: X-ray machine type
According to the number of X-ray generators, X-ray machines can be divided into three types: single beam, double beam and combined multi-beam. Generally, the more beams, the more capable and expensive the equipment is.
Type 1: Single Beam System
According to the beam irradiation position, X-ray machines are divided into three types: vertical irradiation, horizontal irradiation and overlooking beam.
Single beam vertical irradiation is the most commonly used detection method, which can detect most objects.
Single beam horizontal irradiation. Suitable for low-density packaging forms are upright objects.
Single beam top view beam irradiation. Applicable to the product industry, some objects packaged in glass containers.
The second type: double beam system
Dual Beams emit X-ray beams from two angles, pointing at two detectors. Images of the ray passing through the object are shown from two different angles, which can increase the chance of detection.
The third type, combined beam system
This combined beam system has both vertical and horizontal beams. This combined beam will significantly improve the foreign object detection rate of some special objects. For example, for products packaged in glass and metal cans or products in large packages, the combined beam can increase the detection area and foreign object detection rate of the can body and the bottom of the can.
2. What kinds of foreign objects can X-ray machines detect?
As mentioned above, the X-ray machine mainly scans objects with X-rays. Substances of different densities in the objects will form images of different gray values on the sensor, and foreign objects can be identified and observed according to the difference in gray values.
The biggest factor affecting the gray value is the density of the object, so the foreign matter that can be detected by the X-ray machine needs to have a large difference in density between the detected foreign matter and the object itself to be easily detected. For example, when doing human body testing, the difference between bones and flesh can be clearly distinguished.
3. Factors affecting the detection sensitivity of X-ray machines
There are five main factors affecting the sensitivity of X-ray machines to detect foreign objects:
The object itself
Foreign body type and size
Foreign body location
The outer clothing of an object
The accuracy of the equipment itself
The object itself is mainly the object to be tested, and the density and thickness of the object and the uniformity of the texture of the object will affect the detection sensitivity.
First, about the influence of object density and thickness. The amount of X-ray absorption is proportional to the density and thickness of the object through which the rays pass. That is to say, the denser the object is, the thicker the thickness is, the more X-rays are absorbed, so for the same foreign matter mixed in, the thicker the object is, the contrast between the image gray value of the detected foreign matter (such as metal or glass) will be reduced, thus will reduce sensitivity. In order to better illustrate the influence of the thickness of the object on the sensitivity, we give an example of the sensitivity of the same steel ball foreign matter in different thicknesses of cheese.
Scenario 1: Steel balls (density about 8) in the case of 10 layers of cheese (density about 1), the amount of X-rays absorbed by normal cheese is calculated as: 10 layers*1=10, and the amount of X-rays containing steel balls The absorption is calculated as: 10 layers*1+8=18, which is 8 higher than normal cheese. The X-ray absorption of steel balls is 80% higher than that of normal products. The steel ball is easy to detect like this.
Scenario 2: If the same steel ball is in 100 layers of cheese, the amount of X-ray absorption by normal cheese is calculated as: 100 layers*1=100, and the absorption amount containing steel balls is calculated as: 100 layers*1+8= 108, the absorption of steel balls is also 8% higher than that of normal products, but the ratio is only increased by 8%. The steel ball is then more difficult to be detected like this.
From the above case, we know that the thicker the object, the less likely the foreign matter will be detected, and the thinner the object, the easier the foreign matter will be detected.
The sensitivity of object density to detection is similar to the principle of object thickness. The smaller the object density and the greater the density difference with metal foreign objects, the easier it is to be detected. The sensitivity of object density to detection is similar to the principle of object thickness. The smaller the object density and the greater the density difference with metal foreign objects, the easier it is to be detected. For example, glassy foreign bodies are easier to detect in a loaf of low-density bread than in dense, hard cheese.
Secondly, the uniformity of the object affects the sensitivity.
The better the uniformity of the object, the smaller the change in the absorption of radiation by the object itself, so the change in the absorption of foreign objects will be more easily detected.
The more uniform the object, the less it will affect the sensitivity. The more inhomogeneous the object, the more affected the sensitivity.
Foreign body type and size
The accuracy of the foreign matter detected by the metal detector is related to the material and size of the foreign matter itself.
The larger and denser the foreign matter, the easier it is to detect. The smaller the foreign matter and the lower the density, the more difficult it is to be detected.
Let’s take 10 layers of cheese mixed with metal steel balls and glass balls of different sizes as an example. The schematic diagram is as follows:
Normal product: Assuming that the density of cheese is 1, the normal product density is 10 layers*1=10
Scenario 1 - Mixing steel balls: The first situation is that a steel ball is mixed into the product. If the size of the steel ball just occupies the position of a layer of cheese, then there are 9 layers of cheese and a layer of steel balls with a density of 8. Add them together The density of is 9+8=17.
Scenario 2 - Mixing small glass balls: The second case is that a glass ball of the same size as a steel ball is mixed into the product, so that the glass density is 3, occupying one layer, plus 9 layers of cheese, the combined density is 9+ 3=12. If the normal detection limit of the X-ray machine is set to 14, no small glass balls will be detected.
Scenario 3--Mixed with a large glass ball: If a large glass ball is mixed (accounting for 3 layers), the density becomes 7 layers of cheese * 1 + 3 layers of glass balls * density 3 =16. This is greater than the detection limit of 14, and the large glass ball can be detected.
This is usually the reason why the glass ball of the verification module is larger than the steel ball because the density of glass is lower than that of stainless steel in the verification module of our X-ray machine.
Foreign body location
The distance between the foreign matter and the X-ray emitter will affect the detection sensitivity. When the foreign matter is close to the source of the emitter, the effective area projected by the detector (X-ray shadow) will be enlarged, and it will be easier to be detected. For dense foreign matter, the foreign matter on the upper left side is easier to detect than the foreign matter on the lower right side. The same foreign matter is located near the center line of the product. Compared with the two sides of the conveyor belt, because it is closer to the transmitter and the radiation loss is smaller, it is easier to detect the foreign matter in the center.
The outer clothing of an object
The outer clothing material of different objects has a great influence on the detection sensitivity. Therefore, when we generally conduct tests in hospitals, we need to take off most of our clothes, which is to make our tests more accurate.
The device itself
The hardware and software of the device itself will affect the sensitivity, mainly due to the following factors:
(1) Emitter X-ray tube intensity. The most commonly used type is the glass window X-ray tube because of its penetrating capabilities for a variety of applications. Beryllium window X-ray tubes can be used instead of glass window X-ray tubes if the objects to be inspected are of low density and small thickness (typically less than 30 mm). Detection levels are also higher when suitable for detection of moderately dense contaminants such as glass, ore, and calcified bone. Such as detection of bones in poultry meat production.
(1) Emitter X-ray tube intensity. The most commonly used type is the glass window X-ray tube because of its penetrating capabilities for a variety of applications. Beryllium window X-ray tubes can be used instead of glass window X-ray tubes if the product to be inspected is of low density and thickness (typically below 30mm). Detection levels are also higher when suitable for detection of moderately dense contaminants such as glass, ore, and calcified bone. Such as detection of bones in poultry meat production.
(2) Dimensions of the detector diode. Diode sizes range from typically 0.4 mm to 1.6 mm pitch, the smaller the size, usually the better the accuracy, but also requires a stronger emitter. A balance of both emitter and detector needs to be maintained.
(3) The speed and cleanliness of the conveyor belt. The X-ray beam passes through the product and the conveyor belt. Conveyor belts absorb small amounts of X-rays. The higher the density of the conveyor belt, the lower the detection sensitivity. And the thickness and density of the conveyor belt must be consistent. Differences can also lead to false rejections if there is a high absorption signal. The speed of the conveyor affects the image quality, the faster the speed, the lower the image quality. Finally, the static electricity on the conveyor belt may affect the electronic components of the X-ray machine, thus affecting the sensitivity.
(4) Calibration analysis software. The monitoring system of the X-ray machine will restore the normal state of the system when no product passes through, and the analysis software will perform different analyzes on the imaging, thereby reducing the false rejection rate. This module is very reflective of the technical level of Jinxuan.
The above is the basic knowledge about the X-ray machine, I hope it can help you to answer the confusion you encountered in the use of the X-ray machine.
