Optimisation of contrast medium volume and injection-related factors in CT pulmonary angiography: 64-slice CT study.

OBJECTIVE: To compare the image quality of computed tomography pulmonary angiography (CTPA) obtained with the injection of various low doses of contrast medium (CM) with different injection-related factors.

METHODS: A total of 90 patients (42 females, 48 males; 54.3 +/- 18.6 years) undergoing CTPA were included. Three CM protocols, each containing 30 patients, were created. Protocols 1, 2 and 3 consisted of a CM of 60 ml, 55 ml and 50 ml, and a bolus trigger level of 120 HU, 90 HU and 75 HU, respectively. Injection was uniphasic for protocols 1 and 2 (flow rate 5 ml/s), and biphasic for protocol 3 (flow rates 5 and 4 ml/s); with saline flushing afterwards. Enhancement was measured in three central and six peripheral pulmonary arteries.

RESULTS: The mean attenuation value for pulmonary arteries was over 250 HU for all protocols. There was no difference between the attenuation levels with the protocols (p > 0.05). The percentage of pulmonary arteries exceeding optimal attenuation (> or =250 HU) showed that protocols 2 and 3 were 90-100% successful (p < 0.05).

CONCLUSION: The use of proper injection-related factors during CTPA, such as a low trigger level and a high flow rate with saline injection following a decreased CM volume (55 ml or 50 ml), will enable adequate pulmonary artery contrast enhancement.