Yes, a couple of hundred thousand of them. Any doctor, radiologist or not, who uses a PACS system does this on most images a couple of times every day. They don't call it "manipulating" the image; it's called "improving window and level settings". The image actually is not changed since all DICOM images have this information and capability built into the image format. Only the "display" of the image is changed.
Of course, at a higher level, there are inumerable filters and segmentation algorithms that are used to "manipulate" images in order to extract more or optimized information from the images. This field is called "image processing" and you can even get a PhD in it. Thousands of people spend their entire academic or scientific life working on image processing. Even those cute little computer programs that you use to correct "red-eyes" in pictures you shot with your camera; there is a whole science behind the algorithms that do this job with the press of a button.