Angiography

 

Angiography is a medical procedure that uses X-rays to examine blood vessels, especially to find out if the patient has a blockage in a coronary artery.  This technique is able to show blood vessels more clearly on X-rays by using a dye which is injected into the patients’ bloodstream. The X-ray images created during this process are called angiograms.  A further technique that is called computed tomography coronary angiography (CTCA) is able to see images inside the artery. Prior to the images being taken a contrast dye is injected into a vein: this dye highlights any blockages in the coronary arteries.  The computed tomography coronary angiography method provides excellent sensitivity of at least 99% and gives a negative predictive value (the probability that the patient with a negative screening test genuinely doesn’t have the disease) of 97% in the detection of coronary artery disease.  Over the past decade, advancements in angiography have increased gantry spin times and faster single heartbeat scanning, including improvement to a temporal resolution to bring about a reduction in radiation exposure. The increased gantry spin times combined with multidetector technology have enabled specific algorithms that allow whole heart scanning in a single heartbeat. This is demonstrated by the time required for a single rotation of an X-ray tube being reduced by increasing the gantry spin times. This procedure effectively reduces by 50% by introducing a second X-ray tube. The patient is then transported through the z-axis to cover the whole heart in a single acquisition to produce the angiogram.  In addition, other angiography machines have the ability to increase the number of detector rows from 256 to 320 slices which allows coverage of the entire heart in a single acquisition. The advantage of this approach is that the X-ray tube is only on for a small amount of time and therefore reduces the artefacts during the whole image acquisition in one sequence. Most of the CTCA machines have the above features and some include a heart rate control function to reduce the effective radiation dose. Currently, CTCA is now recommended as the first-line investigation for patients with typical or atypical chest pain.