A comparative study of different Cardiac CT protocols
Authors: TM Shafeeque 
Published: November 2013

Back ground The volume of cardiac diagnostic procedures involving the use of ionizing radiation has increased rapidly in recent years. Coronary computed tomography angiography (CCTA) has been increasingly used in the diagnosis of coronary artery disease (CAD). The CT is an excellent technique to make a diagnosis of disorders in many different parts of the body, however, because the heart is constantly beating, CT scan could never be used to image it in the past. The main advantages of coronary CT is non-invasiveness, rapid acquisition of high-resolution images and high diagnostic accuracy .With rapid improvements in spatial and temporal resolution, CCTA not only visualizes coronary anatomy and characterizes plaque components, but also allows for quantitative analysis of coronary stenosis. OBJECTIVE. The purpose of this study was to assess and compare the radiation doses of different coronary CTA (CTA) protocols: second-generation dual-source 128-MDCT, and single-source 64-MDCT. MATERIALS AND METHODS. CT Systems and Protocols Coronary CTA protocols used with two different systems were evaluated: a single-source 64-MDCT scanner with adaptive section collimation (Somatom Definition 64 AS), and a second-generation dual-source 128-MDCT scanner (Somatom Definition Flash). DISCUSSIONS This study highlights two important findings in the radiation dose associated with the prospective ECG-triggered CCTA. Firstly, a low radiation dose can be achieved in CCTA between different generations of CT scanners with the application of the prospective ECG-triggering protocol. Secondly, BMI affects the radiation dose significantly. RESULTS. Regardless of coronary CTA protocol and CT system, imaging at 100 kV lowered the ED 40-50%. In retrospectively gated 120-kV coronary CTA, the ED ranged from 4.4-21 mSv and in prospectively triggered 120-kV step and shoot coronary CTA, the ED ranged from 3.08- to 7.8 mSv. The lowest ED of all protocols (1.2 mSv) was observed in prospectively triggered high-pitch 100-kV coronary CTA performed with dual-source 128-MDCT. Patient measurements showed similar dose reductions for prospective triggering and low voltage settings without an influence on signal-to-noise ratio or image quality. CONCLUSION. In conclusion, a low radiation dose can be achieved in a low and regular heart rate with a prospective ECG-triggering protocol, regardless of the CT scanner generation. Although there is no significant difference in the effective dose between genders, BMI is identified as the main factor that significantly affects the radiation dose in prospective ECG-triggered CCTA in this study. A combination of prospective triggering with low voltage settings and high pitch is an effective measure for reducing the ED of coronary CTA to values of 1.2-4.8 mSv. it offers a dose reduction potential of more than 80%, which to our knowledge has not been achieved with any other coronary CTA technique. the High-pitch helical coronary CTA is associated with a very low radiation dose is one of the good option for any general coronary screening with the limitation of single phase images and the prospective sequencial mode is almost (95%) suit for all patients with bit more radiation dose than high pitch with the advantage of multiphase and diagnostic accuracy.