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What Is Lung Opacity

How to understand and analyze transparency in lung x-ray images

3-Minute Read


References What are lung opacities?

This post is a continuation of the Covid-19 Xray lung detection, because when processing the pre-sample data, we need to be able to know more clearly how the medical field processes and analyzes these x-ray maps so that we can better design our own deep neural network architecture.

Let’s first look at a lung x-ray of our normal person and determine if there is a lesion in the lung by the black, white and gray in the image.

  • black -> air

  • White -> skeleton

  • Gray -> soft tissue or fluid

Transparency can be understood in this way, the black part is like an alpha channel in the image, where it is filled with air is, the skeleton will present white equivalent to this area is not transparent, the gray area is equivalent to a transparency, the higher the transparency, it means that the black occupies more and more air here, when the gray is slowly approaching white, it means that there is a certain density of material accumulated in this one area.

Comparing the radiographs of patients with symptoms of lesions, one can see a blurred transparency shadow at the markers in the figure, indicating the presence of lesions here.

The change in transparency shows the point that when the lung is infected, where there should have been air, it is filled with some other material, such as fluid, bacteria, and antibodies, so that where there should have been a blackish area, a fuzzy gray color is seen in the radiograph.

By the change in transparency, we can go and determine where the disease appears in the lungs.

On the left is a normal lung, and on the right is a lung with pneumonia. You can see that the area marked in the diagram has a clear hairy glass blur, and the transparency is significantly reduced, indicating that the area of the lung that should be filled with air is filled with some other material.

Why we can analyze the health status of the lungs by discerning transparency, the following image can give us the solution to this puzzle.

When we inhale air, the alveoli attached to the bronchi in our lungs are used to exchange gases, expel carbon dioxide from the body, and import oxygen into the bloodstream. When inflammation occurs in the alveoli, the cells in the alveoli become infested with bacteria or viruses, and the alveoli, where there was a lot of air, now have a lot of fluid and other substances in the alveoli, resulting in less space to store air in the alveoli, and this is what we can read in the x-rays, and the gray areas will occupy those areas of the lungs where lesions occur like a state of hairy glass.

For more information on the classification of transparency see the specialized book [Felson’s Principles of Chest Roentgenology](https://www.amazon.com/Felsons-Principles-Roentgenology-Programmed- Goodman/dp/1455774839?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-ffab-20&linkCode=xm2&camp=2025&creative=165953& creativeASIN=1455774839)

The following figure shows two lesions Consolidation and Ground Glass.

After understanding the above, we can analyze and process the pre-radiographic data more carefully and prepare for the automatic image segmentation to find the lesion area later.

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