Chest pain and other symptoms can occur as a result of blockages in the arteries that supply the heart; these arteries are called the "coronary arteries". Blockages in the coronary arteries may decrease blood flow and oxygen delivery to the heart muscle, causing chest pain or other "anginal" symptoms. Coronary angiography is a commonly used test to visualize coronary artery disease or blockages but may not provide all the answers physicians need to assess patients with symptoms like chest pain. Two options for coronary angiography exist, invasive angiography and cardiac computed tomography angiography (CCTA). CCTA is completed by injecting contrast into a peripheral vein (not an artery) and then imaging when the coronary arteries fill with contrast. The imaged coronary arteries may be blocked partially, completely or not at all. While a blockage that occludes greater than 70% of an artery is highly correlated with chest pain or other anginal symptoms, occlusions of 40% or more may or may not decrease heart blood flow. Often multiple imaging studies are needed to evaluate whether blood flow is decreased in the setting of partial coronary artery blockages including non-invasive heart imaging to assess heart blood flow.
One type of nuclear imaging is termed positron emission tomography (PET). In order to differentiate blockages that have poor heart perfusion with activity, nuclear PET images are taken at rest, when flow should be normal, and then repeated after the investigators "stress" the heart with medications. If blood flow is decreased during stress, a "defect" on the PET images is seen.
An alternative, non-invasive technique to test for heart blood flow/perfusion to to measure heart blood flow as computed tomography (CT) contrast goes in and comes out. Preliminary studies in animals and humans to assess heart blood flow/perfusion using contrast-enhanced cardiac CT have been promising, but further work is needed. Combining CCTA with CT blood flow/perfusion measurements in the same setting could lead to a single, accurate diagnostic test that measures coronary artery blockage as well as blood flow.
One limitation of CT imaging is the amount of radiation that can be given. The CCTA radiation dose is currently less than both nuclear PET imaging and invasive coronary angiography. However, if CT blood flow imaging is added to routine CCTA to assess heart perfusion and coronary blockages in one test, the radiation dose may be higher.
The primary purpose of this research project is to test the diagnostic accuracy of various cardiac CT perfusion techniques as compared to the best non-invasive test of blood flow, cardiac PET perfusion imaging. The investigators goal is to use the least amount of radiation to achieve a high diagnostic accuracy for CCTA as well as CT blood flow/perfusion. The investigators goal is to have CT heart blood flow/perfusion radiation doses that are the same or less than nuclear blood flow imaging. The investigators have estimated that they need as few as 4 low radiation dose images of the heart to allow accurate heart blood flow measurement.
