Impact of Iodine Delivery Rate with Varying Flow Rates on Image Quality in Dual-Energy CT of Patients with Suspected Pulmonary Embolism

Rationale and Objectives: To prospectively compare four contrast material injection protocols for dual-energy computed tomography (CI) pulmonary angiography (DE-CTPA) in patients with suspected pulmonary embolism (PE). Materials and Methods: One hundred twenty consecutive patients were randomized to contrast material injection protocols defined by different iodine concentrations and iodine delivery rates (IDRs): (A) 80 mL iopromide 370/4 mUsec = IDR 1.4 gl/sec; (B) 80 mL iopromide 370 at 3 mUsec = IDR 1.1 gl/sec; (C) 98 mL iopromide 300 at 4.9 mUsec = IDR 1.4 gl/sec; and (D) 98 mL iopromide 300 at 3.7 mUsec = IDR 1.1 gl/sec. Attenuation values were measured in the inflow tract (subclavian vein-superior vena cava-right atrium), target tract (right ventricle-pulmonary trunk-pulmonary arteries), and outflow tract (left atrium-left ventricle-ascending aorta). Two readers assessed subjective image quality of CTPA images and iodine perfusion maps. The number of artifacts due to hyperdense contrast material on iodine perfusion maps was recorded. Results: Target tract attenuation was highest for protocol A with 374 +/- 98 Hounsfield units (HU) (highly concentrated contrast material/high IDR). This was significant compared to protocols B and D (P = .0118, P = .0427) but not compared to protocol C (P =.3395). No significant difference in target tract attenuation was found between protocols B (309 80 HU), protocol C (352 +/- 119 HU), and D (325 +/- 74 HU). CTPA and iodine perfusion map image quality for protocol A was rated significantly higher compared to all other protocols (median score = 5/4; P < .0001 for both) with moderate interreader agreement (kappa = 0.58/0.47). Protocols A and B displayed increased artifacts on iodine perfusion maps compared to protocols C and D (3 versus 2). Conclusion: Despite increased artifacts on iodine perfusion maps, highly concentrated iodinated contrast material combined with high flow rates provides improved diagnostic image quality and has the highest target-tract attenuation for DE-CTPA protocols.