Contrast medium protocols in chest CT

Evaluation of personalized strategies

Abstract

The use of intravenous contrast medium (CM) is important in computed tomography (CT) imaging. Iodinated CM, with their high atomic number, are particularly effective in attenuating x-ray beams. This results in improved visualization and differentiation of structures within the body, including in chest CT. The required CM dose vary depending on anatomical region and clinical indication. With the increased variation in patient size globally, personalized CM dosing has become increasingly important. Therefore, research focusing on CM dose optimization is of great importance to ensure high image quality and sustainable use of resources. The first aim of the thesis was to investigate the variation and degree of consensus in chest CT protocols. The study population included members of the European Society of Thoracic Imaging (ESTI), all hospitals in Norway, and university hospitals in Sweden and Denmark. Survey data was collected using an online survey (for ESTI members) or personal email. The study provided data about the most common CM strategies in chest CT. Overall, the results showed large variations in all included CM parameters. Most of the respondents used a fixed strategy for CM dosing, injection rate, and scan delay. The study emphasized the need for further research on personalization of CM dosing as well as the development of standardized protocols and consensus guidelines. The secondary aim was to investigate variations in four different CM dosing protocols used in chest CT imaging regarding to objective image quality. Data was collected using two randomized controlled trials including a total of 364 participants prospectively categorized as normal, muscular, or overweight, based on their respective body compositions. In paper II, a fixed-dose protocol was compared with a combined total body weight and body compositiontailored protocol, while in paper III, CM dose based on the patients’ individual lean body mass (LBM) or body surface area (BSA) was compared with the fixed-dose protocol. Image quality was evaluated based on objective image quality parameters, with a focus on vascular CM attenuation. In the fixed-dose group, 94% of the patients achieved the predefined optimal vascular attenuation, 99% in the body composition-tailored group and LBM group, and 98% in the BSA group. As expected, we observed only minor variations in mean vascular attenuation in normal body composition category patients. Still, our results consistently demonstrated a clear correlation between patient size, CM dose, and vascular attenuation. In paper II, our results showed lower mean vascular attenuation using the fixed-dose protocol compared to a body composition-tailored protocol in muscular and overweight patients. Despite lower CM doses per kg total body weight, the body composition tailored protocol achieved comparable image quality in overweight patients to that of normal category patients, while the higher CM doses in muscular patients, resulted in increased attenuation. In paper III, the highest mean vascular attenuation was observed in the overweight body composition category using both LBM and BSA, while in muscular body composition patients, the highest mean vascular attenuation was achieved using LBM. Importantly, the fixed-dose protocol resulted in the highest degree of outliers, indicating less homogenous image quality. In conclusion, by tailoring CM protocols based on body parameters, more optimized examinations can be achieved, reducing the risk of suboptimal CM use and enhancing overall image quality. This thesis provides new insight into the variations in CM protocols currently used in routine chest CT. Also, the findings from the current studies contribute to a more sustainable use of CM by emphasizing the importance of personalized dosing to improve image quality, ensure consistency, and explore the potential for overall CM reduction in chest CT scans.