Functional lung imaging in humans using Positron Emission Tomography

Abstract

This thesis deals with a method of functional lung imaging using Positron Emission Tomography (PET). In this technique, a radioactive tracer, nitrogen-13, is dissolved in saline solution, and injected into a peripheral vein. By analysis of the tracer kinetics through the lung, measured using PET, a three-dimensional image of perfusion and ventilation can be generated. In the first part of this thesis, a new tracer-preparation system, suitable for use in human subjects, is described. The system is remotely operated, highly automated, and incorporates numerous redundant safeguards to protect the patient. The second part of the thesis details a formal approach to the analysis of the experimental data. A model of the tracer in the right heart and lungs is developed, and used to estimate physiological parameters for large to medium-sized regions of diseased lung. As regions of interest are made smaller, the amount of imaging noise in PET data increases. Consequently parameter estimates become less reliable as finer resolution is used. In order to retain as much spatial information as possible, a new approach is explored, in which voxels with similar kinetics are grouped together, and parameters are estimated for the whole group; in this way, spatial resolution is conserved at the expense of parametric discretization. The viability of the approach is demonstrated by high-resolution analysis of ventilation dysfunction in asthmatic subjects.