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Optimization of contrast medium protocol in CT coronary arteriography: constant injection dose rate adapted to body weight

Background Fixed dose contrast medium (CM) injection protocols are often used in CT coronary arteriography (CTCA). However, vascular enhancement is related to body weight and injection dose rate. Purpose To compare aortic enhancement and coronary imaging quality between a fixed dose CM injection protocol and one adapted to body weight with a constant injection dose rate in mg I/kg/s. Material and Methods One hundred consecutive patients undergoing CTCA were randomized to two groups; group I received 65 mL CM (370 mg I/mL) at 5 mL/s and group II received 0.9 mL CM (370 mg I/mL) per kg during 12 s resulting in a constant injection dose rate of 28 mg I/kg/s.The groups were re-divided according to body weight: IA ≤ 70 kg, IB >70 kg, IIA ≤ 70 kg, IIB >70 kg. Aortic attenuation was measured and coronary imaging quality was graded using a four-grade scale. Results The resulting mean CM dose, aortic attenuation and score of coronary imaging quality in groups IA/IB/IIA/IIB were 24/24/19/27 g I, 437/403/448/440 HU and 2.8/2.3/2.7/2.6, respectively. CM dose and aortic attenuation were significantly different between groups IA and IIA (p < 0.001, p = 0.01), as well as between groups IB and IIB (p < 0.001, p < 0.001).There was no statistically significant difference regarding coronary imaging quality between groups IA and IIA (p = 0.30), while there was a significant difference between groups IB and IIB (p < 0.001). Conclusion In CTCA, body weight-adapted CM injection protocols using a constant dose rate can help save CM doses in slimmer patients and improve aortic enhancement and coronary imaging quality in heavier patients compared to fixed dose protocols.