1. A semiautomatic method of processing intravascular Optical Coherence Tomography (OCT) images, comprising: receiving in a computer a primary cross-sectional OCT image visualising a section of a blood vessel having a lumen and a vessel wall; pre-processing the primary image by the computer, wherein the pre-processing step comprises segmenting a guide wire in the lumen and excluding the guide wire from the primary image to obtain a pre-processed image; determining whether the lumen is closed; if the lumen is determined to be closed, performing a first automatic lumen segmentation procedure on the pre-processed image to define a perimeter line of the lumen, corresponding to the inner edge of the vessel wall, and determine a centroid C L of the lumen area; if the lumen is determined not to be closed, sequentially performing an automatic lumen closing procedure on the pre-processed image, and a second automatic lumen segmentation procedure, to define a perimeter line of the lumen, corresponding to the inner edge of the vessel wall, and determine a centroid C L of the lumen area; automatically finding an outer edge of the vessel wall and defining a first region of interest ROI 1 between the inner edge and the outer edge of the lumen; automatically segmenting a fibrous plaque in the first region of interest ROI 1 , thereby defining a second region of interest ROI 2 that contains the fibrous plaque, and segmenting a hyporeflective plaque, contained in a radial region that falls within ROI 1 and is external to ROI 2 .