Quantitative cardiac x-ray imaging

X-ray imaging plays a key role in the diagnosis and treatment of coronary heart disease. X-ray imaging is currently used to provide anatomical information regarding vessel lumen, identifying the stenotic lesions (narrowings of the artery) caused by coronary disease. However, appearance of a stenosis on X-ray imaging does not accurately predict the extent which it restricts the flow of blood in the vessel. Other physiological measurements are available in the catheterisation laboratory to supplement the X-ray imaging, but these do not fully describe the coronary haemodynamics. This thesis presents a method of using X-ray angiography to measure the absolute flow of blood in the coronary arteries. A method of calibrating the differential signal in an X-ray angiogram produced per unit volume of contrast agent is described. Using the calibration, a second injection of contrast agent, where all of the blood in one of the coronary arteries is replaced by contrast agent, allowed the flow of contrast agent, which was assumed to be the same as the flow of blood, to be calculated. Steps were taken to reduce the radiation dose delivered by the flow measurement imaging, and to overcome the motion of the heart within the computer analysis. Testing was performed in phantoms to validate the technique before a trial in humans. The phantom experiments indicated that the X-ray flow measurements were accurate and reproducible. The human trial indicated a moderate correlation between the X-ray flow and reference thermodilution flow measurements, although the lack of a dedicated infusion catheter may have affected the accuracy of the reference measurements. The X-ray flow measurements were on average 25% lower than the reference. The results demonstrate that the X-ray measurement of flow can be integrated into the clinical routine in the catheterisation laboratory, although further clinical testing is required.