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Abdominal CT: Windows basics

Changing the window settings

Many practitioners regularly review radiology images but are unfamiliar with the basic tools that allow them to extract the most information from the images.

One of the most important tools to learn when using a PACS viewer is changing the window settings. These settings can be adjusted, allowing you to see all of the important structures that have been captured in the image.

Each window setting is defined by specific numbers in Hounsfield units. Put simply, each radiology image has more information than can be shown in a single grey scale image. Changing the window settings allows you to shift the grey scale range so you can completely evaluate all important structures in an image. You can think of this as viewing the same image through different lenses, where each lens allows you to see different structures in better detail.

Changing the window settings is more than just adjusting the brightness of the image. It changes what structures you see the best. Below, the soft tissue, bone, and lung windows have been applied to the same axial CT image.

Abdominal CT window settings basic

Soft tissue window

The most common window setting you will use is the soft tissue setting. The soft tissue window is best used when reviewing the solid organs and vasculature. In the following images, we can see the heart, liver, aorta, and major vessels.

Abdominal CT. Soft tissue window. Axial, coronal, Sagittal
Abdominal CT. Soft tissue window. Axial, Coronal, Sagittal views

However, there are two major structures that we cannot see well with this setting

  • We cannot see the lungs at all, and we only see a little bit of the pulmonary vasculature.
  • Also, it is hard to evaluate the bones because they are too bright.
Abdominal CT soft tissue window poor for lung and bone
Abdominal CT. Soft tissue window – poor for lung and bone

Lung window

Changing the window setting alters the grey scale values. In the image below on the left, we have the soft tissue window. On the right, we’ve changed our lens to allow us to see the lungs. Notice how the lung window allows us to see the lung tissue, but we can no longer see the detail of the heart as well as all structures outside of the lungs, which appear white and blended together.

Abdominal CT lung window

Bone window

Similarly, in the soft tissue window, bone is too bright to evaluate. When we change our lens to the bone window, we can see the bone structure and anatomy of the spine in more detail, but now the non-bone structures appear washed out compared to the soft tissue window.

Abdominal CT bone window

Each window setting has trade-offs when it comes to which structures you can see the best, but all combined they provide a complete picture of the patient’s anatomy to help you make the diagnosis.


This is an edited excerpt from the Medmastery course Abdominal CT Essentials by Michael P. Hartung, MD. Acknowledgement and attribution to Medmastery for providing course transcripts.

References

Radiology Library: Abdominal CT Basics

Abdominal CT interpretation

Assistant Professor of Abdominal Imaging and Intervention at the University of Wisconsin Madison School of Medicine and Public Health. Interests include resident and medical student education, incorporating the latest technology for teaching radiology. I am also active as a volunteer teleradiologist for hospitals in Peru and Kenya. | Medmastery | Radiopaedia | Website | Twitter | LinkedIn | Scopus 

Dr Adam Brown LITFL Author

MBChB (hons), BMedSci - University of Edinburgh. Living the good life in emergency medicine down under. Interested in medical imaging and physiology. Love hiking, cycling and the great outdoors.

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