Regional pulmonary function analysis using image registration and 4DCT

Current radiation therapy (RT) planning for limiting lung toxicity is based on a uniform lung function with little consideration to the spatial and temporal pattern of lung function. Establishment of relationships between radiation dose and changes in pulmonary function can help predict and reduce the RT-induced pulmonary toxicity. Baseline measurement uncertainty of pulmonary function across scans needs to be assessed, and there is a great interest to compensate the pulmonary function for respiratory effort variations.

Respiratory-gated 4DCT imaging and image registration can be used to estimate the regional lung volume change by a transformation-based ventilation metric which is computed directly from the deformation field, or a intensity-based metric which is based on CT density change in the registered image pair. In this thesis, we have evaluated the reproducibility of regional pulmonary function measures using two repeated 4D image acquisitions taken within a short time interval for both transformation-based and intensity-based metrics. Furthermore, we have proposed and compared normalization schemes that correct ventilation images for variations in respiratory effort and assess the reproducibility improvement after effort correction.

The major contributions of this thesis include: 1) develop and validate a process for establishing measurement reproducibility in 4DCT-based ventilation, 2) evaluate reproducibility of the transformation-based ventilation measurement, 3) evaluate reproducibility of the intensity-based ventilation measurement, 4) develop and compare different ventilation normalization methods to correct for respiratory effort variation across scans.