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How to Choose an X-ray Tube?

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Do you often worry that you might make a big mistake in choosing a suitable X-ray tube for your X-ray imaging system?

The X-ray tube is a critical part of any X-ray imaging system and can differentiate between a fantastic X-ray imaging system and a substandard one. Choosing a suitable X-ray tube requires carefully considering specific parameters that are central to achieving the best X-ray inspection result. The image produced during an X-ray inspection is essential to the accuracy of the result and choosing the right X-ray tube is half the work required. 

This guide gives you all the parameters you should carefully consider before putting money down for an X-ray tube. So, if you’d like to know more, then let’s dive in together.


I. Key Parameters of the X-ray Tube 

Many parameters apply to the X-ray tube when setting the X-ray machine to achieve optimum utilization and a high-quality image and high result accuracy. However, key parameters of the X-ray tube ensure these outcomes are possible. At the same time, these parameters also point to the essential factors you should consider when picking an X-ray tube. These parameters are highlighted below. 


  • kV and mA Power 

When choosing a suitable X-ray tube for a specific X-ray inspection requirement, the kV and mA power rating is critical. The reason is that the kV is a measure of the voltage, and the mA is the amperage that relates to the current. The combination of both parameters constitutes the capacity of the X-ray tube to release electrons and X-rays to penetrate test samples efficiently. Also, these parameters determine the heat released within the X-ray tube since heat is part of the component of the electrons generated in the X-ray tube. 

The more the mA and kV, the more the heat is released. Estimating the heat generated helps to ascertain an optimum setting that ensures that the X-ray tube does not overheat during operation, helping to sustain and elongate the lifespan of the X-ray tube. 

  • Tube Current and Tube Power 

In an X-ray tube, the flow of electrons between both anode and cathode constitutes the tube current, and it is measured in mA, as seen previously. It is regulated by controlling the low voltage applied to the cathode. However, it is important here to note that the rate of heat generation within an X-ray tube is equal to the electric power given by the X-ray tube and are usually related to the formula given as 

Power (watts) = w x kVp x mA. Where w is the waveform factor determined by the waveform of the voltage, kVp peak voltage, and mA is the amperage or current in the X-ray tube.

The tube current increases the temperature of the filament in the X-ray tube, and the higher the temperature, the greater the number of electrons leaving the cathode to the anode. Reducing the mA (milliampere) setting on the console lowers the filament temperature, which correlates to the strength of the X-ray production.


  • Target Current and Target Power 

The target current signifies the amperage reaching the anode disc during the production of an X-ray beam. The target power combines the voltage and the current supplied to the target. The target current and the power are essential parameters. They determine the effectiveness of rotation of the target disc, which is responsible for efficiently projecting the X-ray beams through the X-ray tube window to the test sample. The more power that gets to the rotating target disc, the more efficiently it projects the X-ray beam to the test sample and the more accurate the inspection result will be. Therefore, it is crucial to carefully select the X-ray tube with a target current and power suitable for the required X-ray inspection. An inefficient projection of the X-ray beam by the target disc can lead to overheating, which can negatively impact the lifespan of the target and the X-ray tube. 


  • Target Angle 

The target, also known as the anode angle, is the angle made by the rotating anode disc with the horizontal plane where the electrons from the cathode hit on reaching the anode so that it can be efficiently channeled through the window to the test sample. The target angle is a critical parameter because of the relationship it has with the focal spot on the anode disc. The target angle ties the focal spot width, projected spot size, and the focal spot heat capacity together. 

The target angle is inversely proportional to focal spot width and focal spot heat size and ranges between 7° and 20°. This point means that the higher the target angle, the lower the focal spot’s size and heat capacity and vice versa. However, there is a limited area of reach for the X-ray beam with a smaller target angle. Hence, this parameter is vital, especially when purchasing an X-ray tube, so that a balance can be reached between focal spot size and the expected area of X-ray beam coverage. 


  • Focal Spot Size 

A careful selection of an X-ray tube with a suitable focal spot size for the intended X-ray inspection is critical as the focal spot size significantly contributes to the intensity of the X-ray beam projection. The focal spot size deals with measuring the spatial resolution presented by a specific X-ray tube. To get a good image resolution, it is often required to use a small focal spot size since the smaller focal spot size, the better the resolution. However, the focal spot size is also affected by the amperage of the X-ray tube, the voltage, duty cycle, target angle, and the required beam coverage. The voltage and amperage relationship is especially vital to the focal spot size as lower voltage and amperage are needed to achieve a small focal spot size. However, the repercussion of low voltage is the lower intensity of the electron beams projected on the test sample, reducing the sample’s penetration effect.


  • Spatial Resolution 

Another important parameter for selecting a suitable X-ray tube for a specific X-ray inspection requirement is the spatial resolution of an X-ray tube. An X-ray image system can identify the distinct unique features of two different but close images. The spatial resolution is a pixel function that makes up a digital image. Consequently, a substantial pixel size will be incapable of resolving two close structures compared to smaller pixel sizes. The unit of measurement of spatial resolution in line pairs per millimeters. 

Nonetheless, spatial resolution and contrast resolution determine an image resolution. Still, unlike a spatial resolution, an image’s contrast resolution is the X-ray tube’s ability to differentiate between various densities in the picture. The contrast resolution depends on the image system’s bit-depth for a digital image. 


  • Detail Detectability

The detail detectability of an X-ray tube depends on a lot of factors, including the ones previously including X-ray tube voltage, current, focal spot size, target current, spatial resolution, and magnification. The voltage determines the capacity of the X-ray tube to produce electron beams, and it also determines the intensity of the electron beams. The higher the voltage of the X-ray tube, the more electrons are created and the higher the intensity of the X-ray beams, which ensures that dense test samples can be effectively penetrated to reveal hidden details. 

However, the magnification ability of an X-ray tube significantly determines its detail detection ability. The more the magnification capacity, the more detail it can reveal. An X-ray tube with a 4x magnification has a lower detail detection ability than one with 16x magnification. Spatial resolution and contrast resolution are two other important parameters that contribute immensely to the ability of an X-ray tube to detect details.


➤ Related Article: X-Ray Tube Type

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➤ Related Article: X-Ray Tube Working Principle And Its Construction


Considerations for Choosing an X-ray Tube

The X-ray tube is a critical component of the X-ray system as the main X-ray generating components reside within the X-ray tube. Therefore, careful consideration to get a suitable X-ray will serve the specific X-ray inspection objectives. Clearly, many factors need to be considered, including the parameters previously mentioned. 

But wait, there’s more.

One essential consideration is the choice of a radiation source. This factor is necessary to determine the penetration ability of the X-ray tube for the desired X-ray inspection before purchasing it. It is crucial to ascertain lower limits and upper limits for the material thickness expected because using a higher voltage than is required to penetrate a particular thickness will decrease the radiographic contrast.

Another important consideration is the window type of the X-ray tube, as the material used for the window significantly affects the radiation of the electrons. For instance, in situations where very minimal radiation energy is needed to achieve higher image contrast, a beryllium window material will allow for effective transmission of the low radiation. However, a glass window may be more effective for voltage above 150kVp.

Focal spot size is yet another consideration you should have before choosing an X-ray that will be suitable for your peculiar X-ray inspection needs. The area of the anode disc that projects the electron beams to the sample is called the focal spot size, and it is critical to achieving a high quality that is central to an accurate result. 

Lastly, installed protective devices make an excellent addition to the list of factors to consider before choosing an X-ray tube. These devices ensure that the X-ray tube enjoys a long working life while remaining safe for users. Protective devices can include an overload circuit breaker, an overcurrent fuse used to regulate filament current supply, and an overheating thermostat. 


How to Choose an X-ray Tube



To wrap up, considering the correct X-ray tube parameters while making your selection helps solve half of the challenges of achieving a high-quality image that makes achieving an accurate inspection result possible. Some critical parameters include special resolution, X-ray tube voltage, current, and detail detection ability. Also, a protective device like overheating thermostat, overload circuit breaker, and over-current fuses that help increase the lifespan of your X-ray tube are necessary considerations that you should have before choosing your X-ray tube.

The benefits of these parameters are numerous and help you achieve your inspection objectives with high-cost effectiveness. 

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