At which point should the window level be set?

Setting the window level is an essential aspect of image processing in computed tomography (CT) that allows for optimal visualization of the specific tissues of interest. The window level specifically refers to the midpoint of the range of attenuation values that will be displayed in the resulting image.

Choosing the average attenuation number of the tissue of interest as the window level is crucial because it helps to enhance the contrast and improve the visibility of structures within that specific tissue. Each type of tissue in the body has a characteristic attenuation value, and by setting the window level at this average value, the CT technologist ensures that the most diagnostic information is seen. This setting allows for the most significant number of gray shades to represent the variations in attenuation within that tissue, which helps in identifying pathologies or abnormalities.

Other approaches, such as trying to set the window level at the maximum attenuation number of the body part or at an arbitrary value, may not provide the clarity needed for accurate interpretation, as they could obscure important details or make lesions harder to detect. Similarly, setting it at the average attenuation of the room does not relate to the anatomical structures being examined and would not optimize the display for diagnostic purposes.