Effect of different scanning threshold triggers on the image quality of brain computed tomography angiography: a randomized controlled trial.

Background: The scanning trigger threshold affects image quality. The aim of this study was to investigate the effect of different scanning trigger thresholds on brain computed tomography angiography (CTA) image quality.

Methods: In this prospective study, 80 patients undergoing brain CTA examinations with dual-layer CT (DLCT) were randomly divided into group A and group B, with 40 patients in each group. In group A, the CT value of the internal carotid artery at the level of the fourth cervical vertebra was monitored, and the scan was initiated once the CT value reached 100 Hounsfield units (HU). In group B, the trigger threshold was set at 60 HU, with all other parameters kept consistent with those of group A. Finally, the image quality of the 50-keV virtual monoenergetic images (VMIs) was evaluated, including the CT values of the internal carotid artery (CT), middle cerebral artery (CT), sinus confluence (CT), cerebral white matter (CT), background noise (BN), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and subjective scoring.

Results: All images met the diagnostic imaging requirements. Group B showed significantly lower values than did group A for CT (371.97±51.81 442.64±83.39 HU), CT (345.80±50.72 405.87±82.81 HU), CT (90.44±21.30 138.87±37.37 HU), CT (31.98±5.66 38.86±5.68 HU), SNR (108.64±21.05 126.79±30.87), and CNR (98.58±19.72 114.65±29.56) (all P values <0.05) but the value for BN was not significantly different (P>0.05). However, the subjective scores in group B were significantly higher than those in group A (χ=19.013; P<0.05).

Conclusions: For brain CTA imaging in DLCT (50 keV VMIs), lowering the scan trigger threshold to 60 HU helped to reduce venous artifacts and improve image quality (as evidenced by improved subjective scores) and also suggests the potential for a further reduction of the contrast dose.