I work at a hospital. I saw a technician doing a chest x ray the other day. He placed the x ray machine at least 5 feet about the patients chest. Wouldn’t this cause the radiation to scatter? How does it only put the lungs in focus then?
In: Engineering
X-rays come from a tiny pont in the machine. The image is produced as a “shadow” where bones block the beam and the rest of the body only slightly blocks it allowing some rays through.
If the x-ray source was placed close, then the direction of the beam going to the left shoulder would be different to the direction of the beam going through the heart.
The different angles of the diverging beam result in the image being magnified. The closer an object is to the x-ray source the more it is magnified. This means that the anatomy closer to the x-ray source is more magnified than the anatomy close to the detector.
In a standard chest x-ray that means that the spine and back ribs are magnified compared to the sternum and front ribs (which are next to the detector). The closer the x-ray source to the anatomy, the more this magnification difference occurs. By placing the x-ray source 5 feet away, this effect is reduced and the magnification is reasonably even, which allows rough measurements to be taken from the image.
It’s not just the beam direction being different, the length is different – it’s longer to the shoulder because of the angle and x-ray beam strength is very sensitive to length (inverse square law). This would result in an uneven exposure, too many x-rays at the centre of the image, and not enough at the corners. By placing the x-ray source as far away as practical, this effect is reduced and a reasonably even exposure can be achieved.
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