Functional CT Imaging of the Lung: Subtraction CT as a novel technique
Two important functions of the lungs that are needed for the exchange of oxygen and carbon dioxide are ventilation and perfusion. One or both of these functionalities could be hampered as a result of cardiopulmonary disease. Pulmonary embolism is one of those diseases where perfusion in the lung is reduced, because a blood clot is lodged in a pulmonary artery, disturbing blood flow. In the Netherlands, pulmonary embolism occurs in approximately 10,000 to 12,500 patients per year, and resulting in significant morbidity and mortality.
Computed tomography (CT) imaging is currently the method of choice to diagnose pulmonary embolism. However, the disadvantage of this conventional CT technique is that usually only the pulmonary embolism can be seen, with no information obtained on the effect of the embolism on the perfusion distal from the clot, and therefore on the functionality of the lung. Lately, new imaging techniques have been developed with the added goal of depicting anatomical and functional information with one technique. One of these techniques, dual-energy CT, depicts the iodine enhancement in the pulmonary parenchyma, reflecting the perfusion status at a single time point. Since dual-energy CT has the disadvantage of requiring dedicated hardware, subtraction CT was developed, which requires only specific software and has the advantage of higher signal- and contrast-tonoise ratio than dual-energy CT.
In this thesis, we investigate the physical and clinical performance of subtraction CT to determine its limitations and clinical added value.