Method of deriving a quantitative measure of the instability of calcific deposits of a blood vessel
A computer-implemented method of processing an image of at least part of a blood vessel to derive a measure indicative of the instability of calcific deposits in the blood vessel, said blood vessel containing at least one calcific deposit, comprises locating and annotating one or more calcific deposits. Using information derived from the annotation of said calcific deposits, the method further comprises calculating a measure reflecting either one or both of a) the aggregate of the deviations from roundness of individual calcific deposits, and b) up to at least a threshold value, the extent to which the separate calcific deposits are spaced from one another.
1 . A computer-implemented method of processing an image of at least part of a blood vessel to derive a measure indicative of the instability of calcific deposits in the blood vessel, said blood vessel containing at least one calcific deposit, which method comprises:
locating and annotating one or more calcific deposits;
using information derived from the annotation of said calcific deposits to calculate a measure reflecting either one or both of a) the aggregate of the deviations from roundness of individual calcific deposits, and b) up to at least a threshold value, the extent to which the separate calcific deposits are spaced from one another.
2 . A method as claimed in claim 1 , wherein locating and annotating the one or more calcific deposits comprises locating and annotating the boundary of each said calcific deposit and calculating a measure reflecting a combination of a) and b) is obtained by:
calculating the area occupied by the calcific deposits;
expanding the boundary of each said calcific deposit outwards by a distance x corresponding to between 4 mm and 20 mm of a life-size image;
calculating the area occupied by the expanded calcific deposits; and
calculating a comparative index by comparing the area of expanded calcific deposits with the area of unexpanded calcific deposits to derive said measure.
3 . A method as claimed in claim 2 , wherein the step of expanding the boundary of each said calcific deposit outwards comprises dilating the boundary of each calcific deposit.
4 . A method as claimed in claim 3 , further comprising dilating the boundary of each said calcific deposit using a circle of radius x.
5 . A method as claimed in claim 2 , further comprising counting the number of calcific deposits and weighting said comparative index by said number.
6 . A method as claimed in claim 1 , wherein calculating a measure reflecting b) comprises identifying a convex hull of the calcific deposits and deriving a value representative of the convex hull by calculating one of the perimeter of the convex hull and the area within the convex hull.
7 . A method as claimed in claim 6 , further comprising calculating a value indicative of the total area of the calcific deposits and dividing the value representative of the convex hull by the total area.
8 . A method as claimed in claim 6 , further comprising counting the number of calcific deposits and deriving a value indicative of the product obtained by multiplying the number of calcific deposits with the value representative of the convex hull.
9 . A method as claimed in claim 1 , wherein calculating a measure reflecting a) comprises:
identifying a convex hull of each individual calcific deposit;
deriving a value representative of each convex hull by calculating one of the perimeter of the convex hull or the area within the convex hull and summing the values;
calculating a value indicative of the total area of the calcific deposits; and
dividing the sum of values representative of the convex hulls by the value indicative of the total area of calcific deposits.
10 . A method as claimed in claim 1 , wherein calculating a measure reflecting a) comprises deriving a value indicative of the result of calculating the ratio of the square of the perimeter to the area for each calcific deposit and summing the ratios.
11 . A method as claimed in claim 1 , wherein calculating a measure reflecting a) comprises deriving a value indicative of the result of calculating the ratio of the square of the sum of the perimeters of the calcific deposits to the sum of the areas of the calcific deposits.
12 . A method as claimed in claim 1 , wherein calculating a measure reflecting a) or b) further comprises calculating a value indicative of a fractal dimension of the calcific deposits.
13 . A method as claimed in claim 12 , further comprising using a box counting method to calculate a value indicative of the fractal dimension of the calcific deposits.
14 . A method as claimed in claim 1 , wherein calculating a measure reflecting b) further comprises calculating a value indicative of the entropy of the calcific deposits.
15 . A method as claimed in claim 1 , wherein calculating a measure reflecting b) further comprises calculating a value indicative of the sum of the distances between calcific deposits.
16 . A method as claimed in claim 1 , wherein the blood vessel is an artery.
17 . A method as claimed in claim 1 , wherein the blood vessel is an aorta.