Optimization of the Contrast Concentration for Low-Tube-Voltage Chest CT: A Randomized Controlled Trial with Low-Concentration Contrast Media

<b>Objective</b>: To evaluate the effect of low-concentration contrast media (LCCMs) on 100 kVp conventional chest CT by comparing the proportions of acceptable-quality scans obtained using various CM concentrations with those obtained using the standard protocol. <b>Materials and Methods</b>: This prospective, multicenter, randomized controlled trial enrolled adult patients with BMI < 30 who underwent enhanced chest CT between December 2023 and September 2024. Participants were randomly assigned to four groups: one control group (120 kVp, 320 mgI/mL) and three test groups using 100 kVp and standard CM (320 mgI/mL) or LCCMs (270 or 240 mgI/mL). Non-inferiority was tested based on the proportion of acceptable-quality scans independently assessed by two readers. Adverse reactions, including injection site pain and localized and systemic heat sensations, were recorded. <b>Results</b>: A total of 371 participants (mean age: 66.0, IQR: 58-73 years) were randomized. 100 kVp chest CT with LCCM groups showed non-inferior image quality to the standard protocol (270 mgI/mL: reader 1-98.33% confidence interval [CI]: -4.95, 9.37 and reader 2-98.33% CI: -7.11, 7.21; 240 mgI/mL: reader 1-98.33% CI: -6.44, 8.71 and reader 2-98.33% CI: -11.47, 5.11; all <i>p</i> < 0.001). Reader 2 reported a lower proportion of acceptable scans in the 320 mgI/mL low-voltage group (<i>p</i> = 0.11), whereas Reader 1 did not find significant inferiority (<i>p</i> = 0.003). Injection site pain, localized heat, and systemic heat were less frequent in LCCM groups, while systemic heat was only statistically significant (<i>p</i> = 0.003). <b>Conclusions</b>: Low-tube-voltage (100 kVp) chest CECT using LCCMs yields non-inferior image quality compared with the standard protocol while using conventional concentration contrast media under 100 kVp resulted in decreased proportion of diagnostically acceptable scans.