A CT angiogram of the chest (often called a CTA) produces detailed images of the blood vessels in your chest, including the pulmonary arteries, the aorta, and the veins that carry blood back to your heart. It’s most commonly ordered to check for blood clots in the lungs, but it can also reveal aortic aneurysms, tears in the aortic wall, coronary artery blockages, and a range of non-vascular findings like enlarged lymph nodes or fluid around the lungs.
Blood Clots in the Lungs
The single most common reason doctors order a chest CTA is to look for pulmonary embolism, a blood clot that has traveled to the lungs. On the images, a clot shows up as a “filling defect,” meaning a dark spot where contrast dye should be flowing but can’t get through. At the site of the clot, the artery may actually appear wider than normal because the clot gets pushed outward by blood flow, expanding the vessel wall.
The scan can also distinguish between a fresh clot and one that’s been there for weeks or months. Chronic clots look different: they create irregular surfaces along the inner vessel wall, web-like bands across the artery, and areas where the vessel abruptly narrows. This distinction matters because acute and chronic clots are treated differently.
For detecting pulmonary embolism, CTA has a specificity between 89% and 97%, meaning false positives are uncommon. Sensitivity ranges from 66% to 93% depending on the study and scanner generation, so while a positive result is highly reliable, a negative result occasionally misses smaller clots in the tiniest branches of the pulmonary arteries.
Aortic Dissection and Aneurysms
A chest CTA is one of the fastest ways to diagnose an aortic dissection, a life-threatening tear in the inner wall of the aorta. The key finding is an intimal flap: a thin line of tissue separating the normal blood channel (the true lumen) from a new, abnormal channel (the false lumen) where blood has forced its way between the layers of the aortic wall. The flap typically curves toward the false lumen, which wraps around the true lumen. Beyond simply detecting the tear, CTA provides precise measurements of how far the dissection extends, how wide each channel is, and whether the tear involves the branches that supply blood to the brain, kidneys, or gut.
For thoracic aortic aneurysms, the scan measures the widest diameter of the aorta at each level. As a general benchmark, an ascending aorta 4 cm or wider (in people under 60) or a descending aorta wider than 3 cm suggests dilation. A diameter 1.5 times the expected normal size qualifies as an aneurysm. The scan also shows whether there’s a layer of clotted blood lining the inside of the aneurysm wall (mural thrombus), how the aneurysm relates to nearby structures, and whether branch arteries are involved. These measurements guide decisions about whether monitoring or surgical repair is appropriate.
Coronary Arteries and the Heart
While a dedicated coronary CT angiogram is a separate, more focused exam, a standard chest CTA can reveal calcified plaque in the coronary arteries. A coronary-specific CTA goes further, looking for both calcified and soft plaque buildup in the artery walls and estimating how much narrowing exists. This is different from a coronary calcium scan, which only measures calcium deposits without assessing the soft, fatty plaques that can also restrict blood flow.
The heart chambers and valves are also visible on chest CTA images. Radiologists can spot an enlarged heart, fluid in the sac surrounding the heart (pericardial effusion), or structural abnormalities, even when those weren’t the reason the scan was ordered.
Non-Vascular Findings
Because CTA captures the entire chest in high-resolution cross-sections, it shows far more than just blood vessels. The lung tissue itself is visible, so radiologists routinely note lung nodules, areas of infection or inflammation, and signs of emphysema or scarring. Pleural effusions (fluid between the lung and the chest wall) are easy to spot.
The scan also reveals structures in the mediastinum, the central compartment of the chest between the lungs. Enlarged lymph nodes show up in 1% to 6% of screening CT scans, and while most are benign, they can occasionally point to lymphoma, sarcoidosis, or metastatic cancer. Masses in the front of the mediastinum may represent thymic tumors or other growths. These “incidental findings” aren’t what the scan was ordered for, but catching them early can be clinically significant.
What the Scan Involves
The actual scanning portion takes only a few minutes, and the newest machines can image the entire chest in under 30 seconds. Before the scan, an IV line delivers iodine-based contrast dye into a vein in your arm. When the contrast enters your bloodstream, you may feel a warm flush through your body, notice a metallic taste in your mouth, or feel a slight burning at the injection site. All of these sensations are normal and fade within seconds.
You’ll typically be asked not to eat for about two and a half hours beforehand, though clear liquids like water, black coffee, or apple juice are usually fine up to two hours before the scan. You can take your regular medications with water. The radiation dose for a chest CT is approximately 6 mSv, which is roughly equivalent to about two years of natural background radiation exposure.
Kidney Function and Contrast Safety
Because the contrast dye is filtered through your kidneys, your care team will check your kidney function before the scan. The key number is your eGFR (estimated glomerular filtration rate), a measure of how well your kidneys clear waste. If your eGFR is above 45, contrast is generally safe. Between 30 and 45, a radiologist will weigh the risks and benefits before proceeding. Below 30, contrast is typically not given. If your kidney function has been borderline in the past, expect to have blood work done the same day as the scan rather than relying on older lab results.