Evaluation of automated attenuation-based tube current adaptation for coronary calcium scoring in MDCT in a cohort of 262 patients

Abstract

The aim of our study was to evaluate attenuation-based tube current adaptation in coronary calcium scoring using ECG-gated multi-detector-row CT (MDCT). A total of 262 patients underwent non-enhanced cardiac MDCT. Group 1 was scanned using a standard protocol with 120 kV and 150 mAs(eff). Groups 2-4 were scanned using an attenuation-based dose-adaptation template (CARE Dose) with different effective reference mAs settings (150, 180, 210 mAs(eff)). Body-mass index (BMI) and CT-dose index values were calculated for each patient. Image noise and subjective image quality were assessed. Regression analysis was performed, and the variation coefficient of image noise was determined. Compared to the standard scan protocol a dose reduction of 31.1% for group 2 and 20.1% for group 3 was observed. Measurement variation of image noise was smaller for the attenuation-based dose adaptation protocols (group 2-4) (16.2-17.1%) compared to the standard scan protocol (32.3%). Regression analysis of groups 2-4 showed better correlation with improved dose usage based on BMI (all P <or= 0.001). Median image quality was "excellent" in groups 2-4 and "good" in group 1. Automated attenuation-based tube current adaptation in coronary calcium scoring is technically feasible, can decrease patient dose, and reduces variation in image noise as a sign of improved dose usage.

Radiation dose values for various coronary calcium scoring protocols in dual-source CT

“…A recent phantom study on CS has shown that size-specific tube current values yielded comparable data among different patient sizes and thus recommended the implementation of adjusted tube current time product settings for small, medium and large patients [9]. This is in line with the results from the study of Muhlenbruch et al [10] who adjustedsimilar to our protocol E-the tube current to the patients body constitution by means of attenuationbased tube current modulation.…”

“…The main reason for this is that the tube voltage in the study by Mahnken et al [38] was set to 140 kV whereas in our study all scans were performed at either 100 or 120 kV in this overweight patient cohort leading to an increased image noise. However, the measured mean image noise levels were close to the image noise recommendation for coronary calcium scoring of 25 HU [10].…”

“…Recently, Muhlenbruch et al [10] showed that use of attenuation-based tube current for CS leads to a more balanced image noise and reduces the radiation dose as compared to a fixed tube current. By doing so, the dose usage can be optimized without overexposure in low weighted or underexposure in overweight patients.…”

“…Protocol A Retrospective ECG-gating (i.e., helical mode) with ECG-pulsing at 70% of the RRinterval and a reduction of tube current to 4% outside a reconstruction window (minimum width starting at 70% of the RR-interval) using a tube voltage of 120 kV and a tube current time product of 80 mAs per rotation (n = 20), in accordance to the literature [10,23]. Protocol B Retrospective ECG-gating (i.e., helical mode) with ECG-pulsing at 70% of the RRinterval and a reduction of tube current to 4% outside a reconstruction window (minimum width starting at 70% of the RR-interval) using a tube voltage of 100 kV and a tube current time product of 80 mAs per rotation (n = 20), in accordance to the literature [12].…”

“…In order to keep radiation exposure as low as reasonably achievable (ALARA), recent modifications of multi-slice CT scanning protocols have been implemented, such as the use of a low tube current [8,9], attenuation-based tube current modulation [10], and use of low tube voltage protocols [11,12]. In general, two modes of phase synchronization have been traditionally used, i.e., the retrospective electrocardiography (ECG)-gating technique [13,14] that acquires continuous data in a helical (spiral) mode and the prospective ECGtriggering technique [15,16] that obtains data at predefined time points of the cardiac cycle in an axial step-and-shoot mode, the latter usually being associated with a lower radiation dose.…”