Final answer:
To achieve the darkest image with the highest contrast in a CT-guided biopsy, the window level should be decreased and the window width should be narrowed, which enhances the contrast and darkness of the image.
Step-by-step explanation:
The radiologist is requesting changes to the brightness and contrast of images for a CT-guided biopsy in the pelvis. To achieve the darkest image with the highest contrast, the radiologist would need to adjust the windowing of the CT image appropriately. In CT imaging, windowing refers to the process of adjusting the range of Hounsfield units displayed in the images. By narrowing the window width and decreasing the window level, a radiologist can increase contrast and produce a darker image. Specifically, the window level (the center of the window width) can be set lower than the tissue of interest, and the window width (the range of Hounsfield units) can be made narrower to increase the contrast. A high-contrast window setting enhances the visibility of structures with higher and lower densities than the surrounding tissues, making it suitable to identify specific anatomical features or pathologies during procedures like biopsies.