High-Speed, Low Radiation-Dose CT Angiography of the Chest: Performance of an Individualized, Patient-Based Contrast Media Injection Algorithm

Purpose
Latest generation CT systems enable scanning the entire chest within less than one second, which poses new challenges for contrast media delivery. We evaluated the performance of a computerized algorithm for determining individualized, patient-based contrast media injection parameters for high-speed CT angiography (CTA) of the chest.

Method and material
91 patients underwent high-speed CTA of the chest using 128-slice dual-source CT (Flash, Siemens). Indications were CT pulmonary angiography (CTPA; n=34), coronary CTA (cCTA; n=19), and “triple-rule-out” (TRO) CT (n=38). cCTAs and TROs were ECG-triggered. Contrast medium was applied using a dual-syringe injector (Stellant D, Medrad). Based on patient-specific parameters (e.g., BMI, heart rate), scan duration, iodine concentration, and time-attenuation response of a test-bolus, a computerized algorithm (P3T) calculated an individualized triphasic (contrast, contrast/saline mix, saline) injection protocol for each patient. The algorithm determined delay time, contrast volume, injection rate, and contrast/saline mixing ratios. Target attenuation was set at >300HU in the pulmonary arteries for CTPA and TRO, >350HU in the coronaries and >200HU in the right ventricle for cCTA, and >350HU in the coronaries and aorta for TRO.

Results
All studies were considered of diagnostic quality for the respective indication. Mean scan duration was 0.88±0.11sec for CTPA, 0.30±0.03sec for cCTA, and 0.52±0.06sec for TROs. Mean Dose Length Products were 177±54mGy*cm for CTPA, 77±23mGy*cm for cCTA, and 165±34mGy*cm for TROs. The average contrast volume was 87±15ml for CTPA, 98±17ml for cCTA, and 99±18ml for TROs. In CTPA studies, the mean attenuation in the central pulmonary arteries was 443±129HU. At cCTA, mean attenuation was 492±156HU in the coronary arteries, 445±157HU in the left ventricle, and 321±168HU in the right ventricle. In TRO studies the mean attenuation was 403±83HU in the coronary arteries, 351±77HU in the pulmonary arteries, and 407±81HU in the descending aorta.

Conclusion
The computerized contrast media delivery algorithm evaluated here consistently reaches or exceeds the desired vascular target attenuation at high-speed, low radiation-dose CTA of the chest.

Clinical relevance/application
At sub-second, low radiation dose CTA of the chest, use of individualized, patient-based contrast media delivery protocols results in reliable, diagnostic contrast enhancement of all target vessels.

Submission Type: Scientific Presentations RSNA 2010

Authors: J M Barraza, BS, Charleston, SC; R Brothers, RT; C Kemper, PhD; J F Kalafut, MS; U J Schoepf, MD