64-Slice CT Proves Dose-Effective for Evaluating Pregnant Patients with Possible Pulmonary Emboli

The 64-slice computed tomography (CT) scanner delivers the most efficient radiation dose to pregnant patients with possible pulmonary emboli (PE), providing less risk to the fetus, according to recent findings.

Simulated pulmonary and pelvic studies were performed on anthropomorphic (human-like) phantoms to determine the estimated dose range for fetal exposure using CT scanners. "The 64-slice is the most dose-efficient when the fetus is outside the direct scan field for pulmonary angiograms,” said Anthony Gilet, M.D., from the State University of New York (SUNY) Stony Brook University Medical Center (Stony Brook, NY, USA), and lead author of the study.

During the first, second, and third trimester the four-slice scanner measured 0.082, 0.077, and 0.067 cGy, respectively; the 16-slice scanner measured 0.054, 0.025, and 0.084 cGy, respectively; and the 64-slice scanner measured 0.032, 0.016, and 0.053 cGy, respectively. "For all three trimesters the 64-slice scanner imparted a statistically lower fetal dose than the four- or 16-slice scanners. This is attributable to shorter scan times and less scatter radiation,” Dr. Gilet said. However the results were dramatically different for abdominal exams. The 64-slice scanner for abdomen exams was 20% higher in dose during the third trimester than the four-slice and 16-slice scanners.

"This is likely attributable to the increased energy utilized to penetrate the larger amount of soft tissue in late pregnancy,” said Dr. Gilet. "Pregnant patients are always going to be at a greater risk both for PE and symptoms closely mimicking PE, so we will probably continue to do a significant number of pulmonary angiograms on these patients. These patients really need definitive diagnosis, and CT has shown to be the most accurate test at the most reasonable radiation exposure. Pregnant patients are also more likely to present with an atypical or clinically confusing case of possible appendicitis so CT does play a role in diagnosing these patients. However, it is important to emphasize alternative modalities with less or no radiation dose. As MR technology continues to improve it will likely take on a larger role in imaging during pregnancy.”

This study was presented at the 2009 American Roentgen Ray Society (ARRS) annual meeting in Boston, MA, USA, on April 26-30, 2009.

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