A method for volumetric characterisation of perivascular tissue using data gathered from a computed tomography scan along a length of a blood vessel, the method comprising: quantifying radiodensity in each of one or more concentric layers of perivascular tissue; and determining whether one or more of the quantified radiodensity values are above or below a baseline radiodensity value; and the method further comprising: determining a plot of the fold change in the quantified radiodensity relative to baseline radiodensity in each of the one or more concentric layers of perivascular tissue with respect to distance from the outer wall of the blood vessel up to an end distance; determining the area of the region bound by the plot of the fold change in the quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the end distance; and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. quantifying radiodensity in each of one or more concentric layers of perivascular tissue; and determining whether one or more of the quantified radiodensity values are above or below a baseline radiodensity value; and the method further comprising: determining a plot of the fold change in the quantified radiodensity relative to baseline radiodensity in each of the one or more concentric layers of perivascular tissue with respect to distance from the outer wall of the blood vessel up to an end distance; determining the area of the region bound by the plot of the fold change in the quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the end distance; and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. determining a plot of the fold change in the quantified radiodensity relative to baseline radiodensity in each of the one or more concentric layers of perivascular tissue with respect to distance from the outer wall of the blood vessel up to an end distance; determining the area of the region bound by the plot of the fold change in the quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the end distance; and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease.