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Detecting Pulmonary Emboli with Helical Computed Tomography
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What is the problem and what is known about it so far?
Pulmonary emboli are pieces of blood clots that break off from clots in the legs (and sometimes other parts of the body) and travel through the circulatory system to the lungs. Pulmonary emboli can block blood flow to the lungs, which in turn can prevent sufficient oxygen from getting to the tissues. They can cause shortness of breath, chest pain, coughing up blood, and death. Pulmonary emboli can be diagnosed in many ways, including ultrasound tests to look for the source of clots in the legs, as well as special blood tests, lung scans, and dye tests of the arteries in the lung (angiography). Helical computed tomography (CT) is a relatively new way to examine the lungs for pulmonary emboli. This test uses a computer to display two- or three-dimensional images made from x-rays that pass through the body as a CT machine is rotated around the patient. Helical CT scans are widely available. However, their accuracy in detecting pulmonary emboli is not established.
Why did the researchers do this particular study?
The researchers wanted to measure the accuracy of helical CT in detecting pulmonary emboli.
Who was studied?
The study included 299 patients with suspected pulmonary emboli who were seen in an emergency center and in whom the disease could not be ruled out by a special blood test (d-dimer).
How was the study done?
The researchers used standard techniques to make a definite diagnosis of pulmonary emboli (the “gold standard”). These techniques included clinical assessments, ultrasound tests of the legs, radionuclide lung scans, and pulmonary angiography. All patients also had helical CT scans. Radiologists who were not aware of the results of the standard tests read the CT scans. The researchers compared the results of the CT scans with the results of the standard tests.
What did the researchers find?
Standard tests (the gold standard) showed that 118 patients (39%) actually had pulmonary emboli. Helical CT scans were positive in only 70% of the patients with pulmonary emboli and in 9% of those without pulmonary embolism.
What were the limitations of the study?
The standard techniques used by the researchers to diagnose pulmonary emboli may not have detected all such emboli. The technology of CT scans is changing; whether the more recent types of CT scans are more accurate in diagnosing pulmonary emboli than the type used in this study is an open question.
What are the implications of the study?
Helical CT alone is not a sensitive enough technique for detecting pulmonary emboli. It should not be used as a single test to rule out this condition.
Article and Author Information
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The summary below is from the full report titled “Performance of Helical Computed Tomography in Unselected Outpatients with Suspected Pulmonary Embolism.” It is in the 17 July 2001 issue of Annals of Internal Medicine (volume 135, pages 88-97). The authors are A Perrier, N Howarth, D Didier, P Loubeyre, P-F Unger, P de Moerloose, D Slosman, A Junod, and H Bounameaux.
- Copyright ©2004 by the American College of Physicians
