Dose of reduced z-axis length of computed tomography angiography (CTA) of the chest for pulmonary embolism using 64-detector rows and adaptive iterative reconstruction techniques

The objective of this study is to compare the dose of CT angiography (CTA) for the diagnosis of pulmonary embolism (PE) performed using a reduced z-axis to conventional CTA for PE, both using adaptive iterative reconstruction technique on a 64-detector row device. The institutional review board approved a waiver of informed consent. A study was performed to consecutive patients having CTA for PE in the emergency department (ED). The patients underwent a reduced z-axis CTA from the top of the aortic arch to the bottom of the heart using the appropriate CT parameters and standard IV contrast injections. All patients had scans performed with 40 % ASIR and had a breast shield placed to limit breast dose. Per ED ordering criteria, the reduced z-axis protocol was appropriate for patients under 50 years old with no significant comorbidity. The control group consisted of patients from the same time period under 50 years of age who received a full z-axis scan. Technical parameters were the same for both groups other than scan length. Dose–length product (DLP) and volume CT dose index (CTDIvol) were the parameters used to evaluate differences in radiation dose to patients. The average effective dose of the full z-axis group was significantly higher (10.9 mSv (SD 4.7, range = 2.8–22)) compared to the reduced z-axis group (5.5 mSv (SD 3.0, range = 1.6–13, p < 0.001). The average effective dose for the reduced z-axis group was 49 % less than that of the full z-axis group. Reducing the z-axis of a CTA for PE significantly reduces effective radiation dose.