The difference between a CTA test and an angiogram is that a CTA test is relatively non-invasive and an angiogram, also known as a digital subtraction angiogram, is an invasive test. CTA is a special type of CT exam that is performed by injecting a contrast agent into a blood vessel followed by a CT scan, which is primarily used for vascular imaging and is a relatively noninvasive test. Digital subtraction angiography is an invasive test that uses a puncture needle, catheter, or other device to puncture the patient’s artery, deliver the catheter to the examination site, and perform a pressurized injection of contrast under X-ray. Either test is used to check for lesions in the blood vessels, and different imaging methods are chosen depending on clinical needs.