ABOUT PULMONARY EMBOLISM: Pulmonary embolism arises from thromboembolic disease, which causes blood clots to form in the blood vessels of the legs. Most pulmonary embolisms occur when a blood clot breaks free from an artery in the leg and travels to the lungs. More than 600,000 people in the U.S. suffer from pulmonary embolism every year, and 10 percent of those cases are fatal.
HOW CT SCANS WORK: CT scans use X-rays to image the body. X-rays can pass through most materials. It all depends on the size of the atoms that make up the material; larger atoms absorb X-ray photons, while smaller atoms do not, and the X-rays pass right through. For instance, the soft tissue in the body is composed of smaller atoms, so it doesn't absorb X-rays very well. But calcium atoms in the bones are much larger and do absorb X-rays. A camera on the other side of the patient records the patterns of X-ray light passing through the patient's body. In a CT scan, a series of X-ray beams is directed through the body from different angles. This creates cross-sections so scientists can get a better view of the body. The images are put together by computer into a stack of pictures that can be viewed rapidly, like flipping through a deck of cards.
THE STUDY: Researchers at New York Presbyterian Hospital in New York City studied more than 1,500 patients undergoing two different types of CT scanning techniques for suspected pulmonary embolism. CT pulmonary angiography (CTPA) scans the lungs to detect the presence of blood clots. But many of the clots in smaller arteries are not visible on this type of scan, so thromboembolic disease can do undiagnosed in some patients. Indirect CT venography (CTV) scans the leg and pelvic veins, giving doctors a more complete picture of what is happening in the body.
RESULTS: Combining CTPA and CTV scans increased the detection rate of thromboembolic disease by 20 percent. Adding indirect CTV following a CTPA exam requires no additional contrast material and takes only three minutes to perform. It also eliminates the need for a separate examination of the patient's lower extremities, which can delay diagnosis.