Radiation Dose Optimization During Cardiac Computed Tomography Examination Using Phantom Model

Abstract

Rapid progress in the field of Cardiac Computed Tomography (CT) is raised by the advances in CT scanner technology as well as multiple clinical trials demonstrating its role in coronary artery disease and other indications. The cardiovascular imager today is responsible for delivering diagnostic image quality while striking a balance with optimized radiation dose. Radiation dose is the result of multiple scanner and patient related factors. The aim of this study was to optimize radiation dose to the patients undergoing the cardiac CT examination. The investigation was performed using GE light speed VCT health care machine – 64 slice General Electric's Multi detector at Department of cardiology king Fahd hospital. The phantom (Catphan 600) was used to assess the image quality. 10 cm Unfors pencil ionization chamber and Unfors CTDI phantom were used to measure radiation dose. Current routine cardiac protocol was selected and used to scan the phantoms. The image quality in terms of noise, spatial resolution and low contrast resolution (CNR) were assessed and the results recorded. These measurements were carried out for two different modes of scan namely helical and prospective modes. The result of the study revealed the correlation between kVp with spatial resolution and contrast resolution, as well as measured dose length product and computed tomography dose index volume (CTDIvol). DLP and CTDIvol were increased almost linearly with increased kVp, but the spatial resolution was 6 lp/cm with 80 kVp while the 100, 120 and 140 kVp give same value (7lp/cm). Correlation was also vi noticed between mAs and spatial resolution contrast resolution, and measured dose length product and computed tomography dose index volume. The spatial resolution was 6 lp/cm for the mAs from 600 to 800 and 7 lp/cm for 900 and 1000 mAs. And the relation between the mAs with the contrast resolution was reversely increased with decreased contrast. While the DLP and CTDIvol was increased with increased mAs. Regarding the relation between the pitch and spatial resolution, contrast resolution, DLP and CTDIvol, the spatial resolution was 6 lp/cm for pitch of 0.2 and 0.24, while it was 7 lp/cm for pitch of 0.3, and the contrast resolution was decreased with increased pitch, the DLP and CTDIvol were increased with increased helical pitch. For scanning mode, the study discusses two types; helical and prospective gating, the helical mode gives 7lp/cm for spatial resolution and 2.31 for contrast while prospective gating mode give a 6 lp/cm and 1.96 for contrast. To identify which one was better, it was clear that the helical was better for spatial and contrast resolutions while the prospective mode was better for the patient dose. The study concluded that the decrease in scan parameters (kVp and mAs) lead to high radiation dose reduction but will degrade the image quality, the use of prospective mode reduced radiation dose further in comparison to helical mode accompanied with more improvement in the image quality.