64-slice CT: Most Dose Efficient For Evaluating Pregnant Patients With Possible Pulmonary Emboli

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, MD, lead author of the study. During the first, second and third trimester the 4-slice scanner measured .082, .077 and .067 cGy; the 16-slice scanner measured .054, .025 and .084; and the 64-slice scanner measured .032, .016 and .053.

“For all three trimesters the 64-slice scanner imparted a statistically lower fetal dose than the 4- or 16-slice scanners. This is attributable to shorter scan times and less scatter radiation,” he 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 4-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,” said Dr. Gilet.

This study will be exhibited at the 2009 ARRS Annual Meeting in Boston, MA, April 26-30.