As the name suggests, Medical Color Presets consist of predefined sets of values experimentally determined to visualize specific tissues and organs in CT and MRI Images. Many of the presets are named according to the regions of the human body that they are defined to visualize.

A good start to get a general view of your dataset would be the CT-AAA or MRI-Default presets. Select either from the dropdown menu for a quick volume render. CT-AAA has been applied in the example below.

The 'Preset Adjustment Widget' will appear at the top-left of the Canvas once a Preset is applied. The widget lists each value in the Preset, and the corresponding color and opacity applied to that value. In the example above, at value -1024 (air), a color of black is applied with an opacity of 0 (transparent). You can adjust the color and opacity at each of the values in the Preset, to visually control the final appearance of the volume render.

Customization

To customize the color applied at a specific value, click on the adjacent square color box. A color picker will appear, from which you can pick any new color. The layout of this color picker depends on your browser. Pick a color, and it will be applied to the volume giving you immediate feedback.

To customize the opacity applied at a specific value, drag the handle of the adjacent slider right to increase or left to decrease the opacity. Once you release the handle, the new opacity will be applied to the volume giving you visual feedback.

In the example above, the CT-Cardiac preset is applied. To the left is the immediate result, using the preset's default values. To the right, is a render of the heart with more clarity. This is a result of a couple of small adjustments made to the preset.

Observe the 'Preset Adjustment Widget' above each volume. At value 95 the opacity is reduced to 0, and the color is changed to a dark red shade. At value 179 the opacity remains the same, however the color is changed once again, this time to a lighter shade of bright red. With these two simple adjustments, the structure of the heart from this CT-Scan becomes immediately more clear.

Advantages & Disadvantages

The ability to adjust the color and opacity values gives the Medical Color Presets some versatility. However, the main advantage of the Presets over the Scientific Colormaps in volume visualization, is speed. The Presets are best suited for quick visualization, where you don't want to spend too much time working on refining a volume render.

The main disadvantage of the Medical Color Presets is that due to their values being pre-defined, if any values in your CT or MRI dataset significantly deviate from the norm, the resulting render may not come out as expected. This is where the Scientific Colormaps shine. As the colormap is applied dynamically to any dataset, of any range of values, it is flexible and can be controlled to produce a great result irrespective of the data.