4. Image-based methods of stiffness computation
Image-based stiffness computation involves three stages: 1) segmentation
of the lumen and IMC 2) estimation of lumen diameter (LD) and IMT, and
3) computation of Young’s modulus (or β-stiffness and Peterson’s
modulus). Algorithms used for segmentation of lumen and IMC are of two
types: boundary-based and region-based. Boundary-based (edge-based)
approaches include methods that applied Hough transform [88], snake
algorithm [89], active contours [90], and level-sets [91].
However, information about the intensity and curvature of the artery is
required before initialisation of contour and energy functions [92].
Region-based methods involve split-and-merge algorithms that include
watershed [93], region splitting, region merging [94] and
graph-based approaches [95]. Concisely, based on operator
intervention splitting, these algorithms are either semi-automatic or
automatic. Moreover, a few techniques process multi-frame while others
process a single frame. After segmentation of the ROI, estimation of LD
and IMT is done using distance measurement techniques such as
mean-absolute distance or polyline distance. The final stage of
stiffness computation includes the application of Eq. 1 or Eq. 2.