X-Rays

Here’s what happens step-by-step:

 

1. The Filament:

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A small wire made of tungsten (a metal chosen because it can withstand very high temperatures without melting) is heated. This process is called thermionic emission, which means the filament gives off electrons when it becomes hot.

 

2. Electron Acceleration:

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A strong electrical field is established by the high voltage supply between the strongly negative cathode (tungsten filament) and positive anode (target). This electrical field exerts an electrical force on the electrons released by the cathode within the glass vacuum tube from the cathode to the anode. This force accelerates the electrons toward the tungsten target disk (anode). Because the electrons are accelerating in a vacuum tube in the absence of air friction, they achieve very high speeds before they impact the anode.

 

3. X-ray Generation:

 

When these high-velocity electrons hit the metal target, their energy is converted into two things: X-rays and heat. The X-rays are released in all directions from the site of impact of  the electron with the target. The oil circulating around the glass tube absorbs the heat, ensuring that the tube does not overheat.

 

4. Shaping the Beam:
 

1. The X-rays produced by the impact of the electron and the target anode travel in all directions, similar to light from a bulb. The lead encasing around the glass tube absorbs X-rays that are not travelling towards its small opening. X-rays that travel through its small opening are further filtered using collimators (metal filters) that absorb X-rays that are not travelling in a plane of motion in line with the intended target body part.

 

5. Patient:

 

The X-rays that pass through the collimator are directed toward the specific body part being examined. As they travel through the body, different tissues absorb or allow the X-rays to pass through them to varying degrees. Dense tissues like bone absorb a large portion of the X-rays due to their high atomic number and density. Soft tissues such as muscle and fat absorb less, allowing more X-rays to pass through. Air-filled spaces, like the lungs, absorb very little, allowing most of the X-rays to continue through the body. This selective absorption is a key principle in how X-rays interact with the human body.

 

6. Detection:

 

After passing through the body, the remaining X-rays reach a detector plate positioned on the opposite side of the patient. This detector captures the X-rays that were not absorbed by the body’s tissues. The detector is made of materials that convert the incoming X-ray energy into electrical signals. These signals are then processed by a computer and translated into a digital image. The varying amounts of X-rays received by different areas of the detector correspond to differences in tissue absorption, allowing the system to reconstruct an internal view of the body’s structures in a digital format.

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• Dense structures like bones absorb most of the X-rays, meaning fewer X-rays reach the detector behind them. These areas register as bright or white on the digital image.

• Soft tissues, such as muscle or fat, absorb less radiation, allowing more X-rays to reach the detector; these areas appear in shades of gray.

• Air-filled spaces, like the lungs, absorb very little X-ray radiation, so a large amount reaches the detector, producing dark or black regions on the image.

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This variation in absorption is what creates the contrast that allows us to visualize internal anatomy on an X-ray.
 

Historical Point: In the past, the detector was a sheet of film that had to be chemically developed. Today, it's usually a digital plate that instantly turns the X-rays into an image displayed on a screen. This transition from film to digital has made X-rays faster, safer, and easier to store or share.