Low-dose ultra-high-pitch computed tomography coronary angiography: identifying the optimum combination of iteration strength and radiation dose reduction strategies to achieve true submillisievert scans

PURPOSE To identify the optimum strength of advanced modeled iterative reconstruction (ADMIRE) to achieve the best subjective and objective image quality when combining three-dose reduction strategies, ultra-high-pitch computed tomography coronary angiography (FLASH CTCA; with sin-gle-dose ivabradine to lower heart rate), low tube voltage, and ADMIRE. METHODS Sixty consecutive patients underwent FLASH CTCA at 100 kVp in this single-center prospective study. Single-dose ivabradine was administered to patients whose heart rate was above 75 bpm. Images were reconstructed using the three highest strengths of ADMIRE (A3, A4, and A5). Objective and subjective image quality (using a Likert scale) were evaluated in the three datasets. RESULTS The signal strength remained unchanged but mean noise significantly reduced across the increas-ing strengths of ADMIRE [signal: 513.78 & PLUSMN; 101.7 Hounsfield units (HU) at A3, 515.6 & PLUSMN; 100.5 HU at A4, and 519.7 & PLUSMN; 107.9 HU at A5; noise: 23.4 & PLUSMN; 4.5 HU at A3, 20.2 & PLUSMN; 3.6 HU at A4, and 17.2 & PLUSMN; 3.3 HU at A5]. Signal-to-noise and contrast-to-noise ratios were the highest at A5, and A5 offered significantly higher Likert scores in image noise, vessel sharpness, and overall image quality than A3 or A4. Ad-ditionally, A5 did not interfere with image interpretation in any patient. CONCLUSION Using all three dose reduction strategies during FLASH CTCA along with single-dose ivabradine ad-ministration ensures minimal radiation exposure in daily practice. In this study, A5 datasets had the best overall subjective and objective image quality despite their "plastic appearance". In the future, enhanced dose reduction can be obtained by further lowering tube voltages.