[Application of iodine contrast agent optimization protocol with fixed injection time in triple-rule-out CT...

To investigate the feasibility of using optimized protocol of iodine contrast agent with fixed injection time in triple-rule-out CT examination of acute chest pain patients.

A prospective study was conducted. The patients who underwent triple-rule-out CT examination of acute chest pain at the Second Hospital of Shanxi Medical University from September 2017 to June 2018 were enrolled. According to the patient's body mass index (BMI), they were divided into BMI ≤ 23 kg/m² group and BMI > 23 kg/m² group. The patients in each group were subdivided into two subgroups according to the random number table, and they were given two iodine contrast injection protocols with fixed injection time (14 s). Protocol 1 was performed with 55 mL of total iodinated contrast media: iodinated contrast media was first injected at 5.0 mL/s for 8 s, followed by the same contrast media injection at 2.5 mL/s for 6 s, finally followed by injection of 40 mL of saline at a rate of 2.5 mL/s. Protocol 2 with 60 mL of total iodinated contrast media: iodinated contrast media was first injected at 5.0 mL/s for 10 s, followed by the same contrast media injection at 2.5 mL/s for 4 s, finally followed by injection of 40 mL of saline at a rate of 2.5 mL/s. The primary and objective evaluation was conducted on the image quality of the patients' blood vessels in different segments. The primary score, CT value and contrast-to-noise ratio (CNR) of the pulmonary artery, coronary artery, aorta and total effective radiation dose for the examination were recorded.

A total of 92 patients were enrolled in the analysis. There were 44 patients in BMI≤ 23 kg/m² group, in which 22 patients received in protocol 1 and protocol 2, 48 patients in BMI > 23 kg/m² group, in which 24 patients in protocol 1 and protocol 2, respectively. There was no significant difference in the effective radiation dose between the two subgroups receiving different injection protocols in different BMI groups (mSv: 6.7±1.1 vs. 6.5±0.8 between protocol 1 and protocol 2 in BMI ≤ 23 kg/m² group; 7.8±1.0 vs. 8.0±1.1 between protocol 1 and protocol 2 in BMI > 23 kg/m² group, both P > 0.05). In BMI ≤ 23 kg/m² group, the CT value, CNR and primary scores of pulmonary artery images in patients receiving protocol 2 were significantly higher than those receiving protocol 1 [CT value (HU): 584±110 vs. 472±86 for main pulmonary artery, 561±93 vs. 467±78 for left pulmonary artery, 555±91 vs. 472±83 for right pulmonary artery; CNR: 24.2±7.5 vs. 18.7±4.6 for main pulmonary artery, 23.2±6.8 vs. 18.6±4.8 for left pulmonary artery, 22.9±6.7 vs. 18.8±4.7 for right pulmonary artery; primary score: 4.0 (4.0, 4.0) vs. 3.5 (3.0, 4.0), all P < 0.05]; and there was no statistically significant difference in the primary or objective evaluation of coronary artery or aortic image quality between the two protocols. In BMI > 23 kg/m² group, the CT value, CNR and primary scores of coronary artery and aortic images in patients receiving protocol 2 were significantly higher than those receiving protocol 1 [CT value (HU): 369±63 vs. 315±61 for proximal right coronary artery (RCA), 388±63 vs. 323±63 for proximal left coronary artery (LCA), 328±83 vs. 272±51 for ascending aorta, 348±82 vs. 272±49 for aortic arch; CNR: 15.0±4.6 vs. 12.3±4.7 for proximal RCA, 15.7±3.8 vs. 12.8±5.2 for proximal LCA, 13.2±5.3 vs. 10.4±4.1 for ascending aorta, 14.1±5.3 vs. 10.4±3.9 for aortic arch; primary score: 4.0 (3.0, 4.0) vs. 3.0 (3.0, 4.0) for coronary, 4.0 (3.0, 4.0) vs. 3.0 (2.0, 4.0) for aorta; all P < 0.05]; and there was no statistically significant difference in the primary or objective evaluation of pulmonary artery image quality between the two protocols.

The effective radiation dose of triple-rule-out CT examination of acute chest pain is relatively low. The low-dose iodine contrast agent application program with fixed injection time can meet the needs of clinical diagnosis of triple-rule-out CT examination of acute chest pain patients. For patients with BMI ≤ 23 kg/m², both protocols 1 and 2 can obtain excellent image quality; in order to avoid the influence of superior vena cava artifacts, protocol 1 is recommended. For patients with BMI > 23 kg/m², application protocol 2 can obtain stable, excellent image quality that is more suitable for clinical applications.