Automatic computation of liver and lung perfusion parameters through the analysis of CT image sequences

Abstract

Computed Tomography perfusion (CTp) is a promising technique for early assessment of the effectiveness of the new anti-angiogenic therapies for cancer treatment. Nonetheless, some difficulties to achieve standardized results in the examinations have slowed down its application in the daily clinical practice. This Thesis addresses three important open issues: a lack of methods to measure results reliability, the clinical relevance of the global perfusion parameter values commonly utilised, a critical revision of protocols of the multi-centre studies. In this work, lung and liver CTp examinations were considered, being among the most studied sites in oncology. First, I set up and validated an error index capable to measure the quality of perfusion results. After that, structured regions affected by noise (e.g., artefacts), vessels or bronchi have been looked for on whole slices. Also exploiting a new error index, an adaptive algorithm has allowed detecting and excluding all those regions automatically. The common practice in CTp perfusion studies is providing one averaged value only for each perfusion parameter, computed on the whole tumour, to reduce data variability, but at the expense of tumour heterogeneity. Accordingly, whole lung lesions were considered to inquire into the clinical representativeness of global perfusion values. After proposing a statistical index to quantify tumour functional heterogeneity, it has been proved that using one global value even misleads clinical considerations. The last part of the Thesis regards the activities carried out in the widest European multi-centre study on liver CT. Some algorithms to improve the accuracy of perfusion results were developed to favour comparisons of multi-centre CTp examinations. Some meaningful results regarding baseline and blood flow values of liver are discussed, highlighting whether different CT scanners affect CTp outcomes. Finally, tentative guidelines are provided to help considering all the concealable sources of heterogeneity in advance, before planning the protocols.