Radiologists may use lower voltage in CT exam for pulmonary embolism

November 30, 2010

Using 80-kVp CT pulmonary angiography for patients suspected of CT pulmonary embolism reduces radiation exposure, significantly increases contrast medium attenuation in the pulmonary arteries, and doesn’t look much different from standard dose, according to a study presented Tuesday at the RSNA meeting.

Using 80-kVp CT pulmonary angiography for patients suspected of CT pulmonary embolism reduces radiation exposure, significantly increases contrast medium attenuation in the pulmonary arteries, and doesn’t look much different from standard dose, according to a study presented Tuesday at the RSNA meeting. 

Radiologists are always looking for a way to reduce dose for their patients while also maintaining image quality. For patients suspected of pulmonary emboli, Dr. Guilia Zamboni, from the radiology department at the University of Verona in Italy, and colleagues, compared 50 patients undergoing CT pulmonary angiography (CTPA) at 80 kVp with 50 patients undergoing CTPA at 120 kVp.

“If we look at a head-to-head comparison between the two protocols, we don’t see significant differences between them just eyeballing the images,” Zamboni said.

The researchers also found mean attenuation was significantly higher in the test group than in the control group in the main pulmonary trunk, right pulmonary artery, and left pulmonary artery. However, no significant difference was observed in attenuation of the aorta.

In addition, the radiation dose was significantly lower in the test group than in the control group, as measured by CT dose index (5.483 ± 0.7778 mGy versus 13.1 ± 3.855 mGy; p <0.0001) and dose length product (173.87 ± 24.323 mGy x cm versus 418.52 ± 109.28 mGy x cm; p <0.0001).

Zamboni also said at first the researchers were wary of scanning patients weighing more than 120 kg with the reduced voltage because they were afraid they would get with nondiagnostic scans. But after scanning more and more patients with increasing confidence, they scanned a 200-kg patient at the lower voltage and the image quality was fine for him as well.

“The image quality was deemed diagnostic, though not the best I’ve ever done,” Zamboni said.

The biggest limitation is not weight, but whether a patient can raise his or her arms, she said.

“If the patient cannot raise their arms above their shoulders, we don’t use the lower voltage protocol because it would significantly lower the image quality,” Zamboni said.