What technique is used to remove noise within transmission scans and separate images with similar densities?

The technique used to remove noise within transmission scans and separate images with similar densities is spatial filtering. This method enhances the quality of images by improving the signal-to-noise ratio, thus facilitating better visualization and analysis of the data obtained during a PET scan.

Spatial filtering works by applying a filter to the image data that averages or otherwise processes neighboring pixel values to reduce randomness and fluctuations that contribute to noise. This is particularly important in medical imaging, where visual clarity is crucial for accurate diagnosis and interpretation.

Image segmentation, while important in distinguishing different regions of interest within an image, does not primarily focus on noise reduction within transmission scans. Instead, it involves partitioning an image into segments that represent different objects or features. Texture analysis and histogram equalization also serve different purposes in image processing; texture analysis examines surface properties while histogram equalization enhances contrast. Thus, spatial filtering stands out as the appropriate choice for removing noise in this context.