Clinical Feasibility of Arterial Phase Dual Energy Computed Tomography Imaging For Endovascular Aortic Aneurysm Repair

Abstract

Objective: Triple phase (non-contrast, arterial, venous) single energy CT (SECT) scans are often used to monitor patients after endovascular thoracoabdominal aortic aneurysm repair. We investigated the feasibility of replacing non-contrast and arterial phase SECT scans with a single arterial phase dual energy CT (DECT) scan and generating virtual non-contrast images.

Methods: 22 patients were imaged using a novel DECT protocol.  Each patient received 120-150 ml of contrast agent prior to scanning the chest, abdomen and pelvis with the following parameters: tube voltage, 140 kVp (Tube A), 80 kVp (Tube B); tube current-time product, 110 mAs (Tube A), 467mAs (Tube B) with anatomic-based modulation employed for each tube; gantry rotation time, 500 ms; slice collimation, 14 x 1.2 mm; pitch, 0.6. Both an 80 kVp and a 140 kVp image set were reconstructed (3.0 mm slice thickness, medium smooth kernel [D30f]. Virtual non-contrast images were created from the 80 and 140 kVp images based on a three material decomposition technique for separating iodine from surrounding tissue. Arterial images were created by combining 80 and 140 kVp images in 30:70 ratio. A second scan was performed covering the same range after a 5 minute delay to capture the venous phase using our standard SECT protocol: tube voltage, 120 kVp; tube current-time product, 270 mAs with anatomic-based modulation, gantry rotation time, 500 ms; slice collimation, 24 x 1.2 mm; pitch, 0.8, slice thickness, 3 mm; medium smooth kernel (B31f). For both SECT and DECT scans, the dose-length product was recorded and noise in the thoracic and abdominal aorta was measured.

Results: Standard non-contrast and arterial phase SECT scans were replaced with a single, novel arterial phase DECT scan in post-endovascular aortic stent patients. Virtual non-contrast, arterial, and venous phase images sufficient for diagnostic evaluation were obtained for all patients. Replacement of two of three standard SECT scans with one DECT scan resulted in an overall dose savings of 30%. Noise from DECT compared to SECT images was equivalent in the thoracic aorta (p=0.068) but lower in the abdominal aorta (p<0.001).

Conclusion: Reconstruction of virtual non-contrast and arterial phase images for evaluation after endovascular thoracoabdominal aortic aneurysm repair is feasible from a single arterial DECT acquisition. In comparison to standard practice using only SECT, the use of DECT is associated with reduced x-ray exposure and lower image noise.

Authors: Numburi U, Schoenhagen P, Greenberg RK, Saba OI, Flamm SD, Halliburton SS