Improved depiction of atherosclerotic carotid artery stenosis in virtual monoenergetic reconstructions of venous phase dual-layer computed tomography in comparison to polyenergetic reconstructions.

OBJECTIVES: To compare virtual monoenergetic images (VMI) reconstructed from venous phase Dual-Layer CT (DLCT) with polyenergetic images (PI) of DLCT-Angiography (DLCT-A) regarding vessel contrast and image quality especially in sight to atherosclerotic carotid artery stenosis. METHODS & MATERIALS: 25 DLCT-A and 55 venous phase DLCT were analyzed in this retrospective study. For objective analysis PI and VMI (40-120 keV) were assessed comparing attenuation, standard deviation, signal-/contrast- to noise ratios (SNR, CNR) in the common carotid artery (CCA), vertebral artery, sternocleidomastoid muscle and air. For subjective analysis, vessel contrast, delineation of the superficial temporal artery, depiction of calcified plaque as well as vessel patency within the atherosclerotic stenosis of the internal carotid artery were rated and the extent of the calcified plaque and remaining vessel lumen were measured in venous phase DLCT. RESULTS: In venous phase DLCT, attenuation, SNR and CNR in the CCA increased with lower keV. Attenuation, SNR and CNR at 40 keV in the CCA were comparable to PI of DLCT-A (all: p > 0.05). Subjective image contrast, assessment of vessel patency within a stenosis as well as delineation of the superficial temporal artery were rated superior at 40-60 keV in comparison to PI of venous phase DLCT (all: p ≤ 0.05). Slightly more blooming of the atherosclerotic plaque was found in VMI at 40-60 keV. There was no difference of NASCET-criteria of carotid stenosis between VMI at different keV-levels and PI (p = 1.0). CONCLUSION: VMI at 40 keV reconstructed from venous phase DLCT yield an image quality equal to CT-Angiography, especially regarding vessel contrast. Perception and assessment of the carotid artery within an atherosclerotic stenosis are not impaired at low keV.