I am a surgeon when I take pictures of muscle or

The Fuji S2 sensor is noted for this red sensitivity. Here's a few different approaches to getting the shot with the S2, all of which require some experimentation.

1. Set the "Color" and "Tone" Function options to "ORG". Underexpose the shot. Progressively change the exposure compensation downward until when checking the histogram, the red channel does not show saturation at the high end. Advantages: this is the simplest approach to getting the picture. Disadvantages: the S2 already had a fairly limited dynamic range, and this will make things worse for the parts of the photo that are not red. For the surgical setting and use of a ringflash, this may not be much of a disadvantage, since a lot of the stuff of interest will be red, and ringflash illumination generally is of lower contrast than directional lighting.

2. Set the "Color" and "Tone" Function options to "ORG". Use a custom white balance. The idea here is to have the camera adjust the red channel sensitivity itself, and leave the blue and green channels alone. To do this, start with several sheets of white paper and a red or pink marker or highlighter. Scribble with the marker across a sheet, then use that to set a custom white balance. Take a test shot of the red stuff that has been problematic, and see whether the histogram for the red channel shows that there is no saturation at the high end. Repeat this with progressively more red or pink on each sheet used to set the custom white balance until you find the custom white balance that takes enough of the edge off the red channel response. Alternative: I just tried out making a gradient across an 8.5x11" sheet of paper going from white to about 30% red saturation. I can set more or less red adjustment in a custom white balance just by pointing the camera at different parts of the page. This seems to work OK for me. Advantage: can allow the full dynamic range of the sensor to be used. Disadvantages: the experimentation period is likely to take a while to get the best results, and the final images are unlikely to look completely natural.

3. Set the "Color" Function option to "B/W". Use a green or cyan filter on the lens to cut the amount that the red color channel contributes to the final image. Advantages: this is fairly simple as an approach. A similar post-processing technique can be applied to the photos that you already have, by nulling out the red channel contribution and desaturating the blue and green channels to produce a grayscale image. Disadvantages: you lose the color information entirely. Since much of what you want information about is colored red anyway, the organs are likely to appear quite dark when only taking the blue and green channel contributions to the image.