X-Ray

Transparency and Energy in X-Rays

You always need some time to find out the best exposure values for a photo. Same idea holds in X-Ray imaging.

Today I did an x-ray series with my biggest Nautilus shell on a conventional radiography sensor, not a film. Starting from the lowest possible value 40kV an increment of 10 kV up to 70 kV can be seen in the images:

40kV 10mAs

Black regions in the image a transparent, white are opaque. The center of the Nautilus has a loss of structure.

With 50 kV the structure in the center of the Nautilus is better depicted wheras the edge gets more transparent:

50kV 2mAs

Same effect for the center and the edge can be seen with 60 kV:

60kV 2mAs

With 70 kV it’s an exaggeration for the edge and best depiction for the center:

70kV 10mAs

Higher kV means more transparency for denser structures but a loss of structure in transparent areas. 

At fixed energy, X-Ray imaging behaves like a shadow related to visible light. When photographing, there is not chance to look through an opaque object. With higher energies, x-rays go through opaque objects and can be collected on a sensor. 

Composing the images obtained at different energies is an X-Ray HDR image:

Nautilus X-Ray Energy HDR © Julian Köpke

The representation of an X-Ray with white on black is a reminiscence of the film era. Radiologists just looked at the negatives ! Inverting black and white shows the positive image, like a print. Here I show the same image as positive, but rotated and flipped horizontally. Look how ethereal it appears now:

Nautilus X-Ray Energy Compressed © Julian Köpke

I like to make things visible the naked eye isn't able to see. That's part of my profession as a radiologist, too.

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