A technique for assessing the progression of multilateral dysfunction, e.g. bilateral diseases is described. The process consists of two stages: firstly, a 'health measure' is computed for each of the features of the multi-lateral dysfunction. One example is in terms of the progression of Parkinson's disease by applying it to the uptake of imaging agent in the two striata of the brain, which can be viewed using SPECT imaging. In this example, a characteristic graph for each striatum is matched to a family of such graphs in order to quantify the state of each striatum as a health measure. Then the lower health measure is plotted against the higher health measure. This point is then projected onto a previously computed disease progression trajectory which is used to assign a percentage to the progression of the disease, from 0% normal to 100% extreme progression of the disease. In addition to the disease progression percentage, the technique also provides a confidence measure of the accuracy of this estimation. The invention is applicable to other forms of multilateral dysfunction, including other human or animal conditions and dysfunction in non-biological systems such as mechanical, electrical or electronic systems. <IMAGE> <IMAGE> <IMAGE>
Characterisation of disease progression