Radiation Dose and Vessel Attenuation at High-Speed CTA of the Torso: Intra-Individual and Inter-Individual Comparison with Conventional CTA

Purpose
Latest generation CT systems enable scanning of the entire torso at high pitch. We evaluated the radiation dose and vessel attenuation at high-speed CT angiography (CTA) of the thorax and abdomen/pelvis, with comparison to conventional CTA.

Method and materials
We searched PACS for all patients who underwent CTA of the thorax and abdomen/pelvis to evaluate the aorta between September 2009 and March 2011. This retrospective study included 110 patients (67 male, mean age 64±15 years), of which 47 had undergone high-speed CTA on a 2nd generation dual-source CT system. Selection of the high-pitch scan protocol was based on patient size (≤30kg/m2 body mass index). Main indications were suspected aortic syndrome (n=11), follow-up of aneurysm (n=36) or dissection (n=20), or post aortic repair (n=37). Contrast medium enhancement in the ascending aorta (AscA), thoracic descending aorta (DescA), abdominal aorta (AbdA) and common iliac arteries (IlA) was measured. Radiation dose and vessel attenuation in patients undergoing high-speed CTA was compared with those in patients undergoing conventional CTA. For patients with high-speed CTA, comparison was also made with prior conventional CTA, if available.

Results
All scans were considered of diagnostic quality for their indication. At high-speed CTA, mean kV and mAs were 118±7 and 197±78, respectively, compared to 120±1 and 259±78 for conventional CTA (p<0.05). Mean volume CT dose index (CTDIvol), Dose Length Product (DLP), and effective dose (ED) were 8.28±2.37mGy, 575±176mGy*cm, and 8.0±2.5mSv at high-speed CTA versus 18.22±7.59mGy, 1151±472mGy*cm, and 16.1±6.6mSv at conventional CTA (p<0.001). Mean vessel attenuation at high-speed CTA was not different from conventional CTA (346±91 vs 336±67 HU for AscA, 344±100 vs 331±63 HU for DescA, 348±90 vs 327±63 HU for AbdA and 347±102 vs 326±68 HU for IlA, p=ns), while significantly less iodine contrast medium was injected for high-speed CTA (102±18mL vs 110±17mL, p<0.05). In 19 patients who had undergone both high-speed and conventional CTA, radiation dose was reduced by 45% (p<0.001), while differences in contrast medium volume and enhancement were non-significant.

Conclusion
High-speed CTA of the aorta results in up to 50% reduction of radiation dose, with maintained image quality and vessel attenuation.

Clinical relevance/application
High-speed CTA is a promising technique for significantly reducing CTA-related radiation dose in non-obese patients.

Submission Type: Scientific Presentations RSNA 2011

Authors: R Vliegenthart, MD,PHD, Groningen, Groningen NETHERLANDS; G W Rowe, BS; P Apfaltrer, MD; R Brothers, RT; M Oudkerk, MD, PhD; U Schoepf, MD