Provided are an apparatus and method for processing a medical image of a body lumen. The apparatus includes: - an image analysis unit arranged to extract from the medical image brightness intensities of a first body lumen region of the medical image and brightness intensities of a second body lumen region of the medical image, and - a measuring unit arranged to calculate a first body lumen value and a second body lumen value, each value being calculated as a predetermined linear combination of the brightness intensities of the corresponding region, and to compare the first body lumen value with the second body lumen value. The apparatus and method allow an accurate measurement of the degree of stenosis of a stenosis blood vessel region.
