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Objectives: The objective of this study was to determine the optimal scan delay quantitatively and qualitatively in cerebral CT angiography (CTA) with a test injection method at the circle of Willis (cW). Methods: 66 consecutive patients suspected of having unruptured intracranial aneurysms underwent CTA using 40 ml of 370 mg iodine ml−1 contrast material (CM). After the time until CM arrival at the cW (TcW) was calculated, scan delay was divided into three groups according to TcW and scan duration (SD) between the second cervical vertebra and cW as follows: [(TcW+6)–SD] in 21 patients (Group A); [(TcW+8)–SD] in 23 patients (Group B); and [(TcW+10)–SD] in 22 patients (Group C). Arterial and venous attenuation in the intracranial vessels was measured. Mean attenuation values were compared quantitatively. The arterial enhancement and venous overlap at the cW and above the cW were qualitatively compared among the three groups. Results: Mean arterial attenuation in Groups B and C was significantly higher than that in Group A. Mean venous attenuation in Group C was significantly higher than those in Groups A and B. Arterial enhancement above the cW showed a significant difference between Groups A and C, and at the cW between Groups A and B, and Groups A and C. There was a significant difference in venous overlap among the three groups, except for that at the cW between Groups B and C. Conclusions: Setting scan delay as [(TcW+8)–SD] s can produce the best performance both quantitatively and qualitatively. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to examine attenuation values in the central vein and perivenous artefacts at the subclavian vein in cervical CT angiography (CTA) when using 40ml contrast material (CM) followed by different volumes (25ml vs 40 ml) of saline flush (SF). Methods: 61 patients underwent CTA between the aortic arch (AA) and distal to the circle of Willis (cW). After calculating test-bolus time to peak enhancement at the cW (Tc), scanning delay was represented as [(Tc + 4) - scan duration between AA and cW] s. 28 patients (Group A) received 40 ml of 370mg iodine (I) ml-1 CM followed by 25 ml of SF, and 33 patients (Group B) received the same CM followed by 40 ml of SF, both administered through the right antecubital vein. Arterial attenuation was measured at seven points in the aorto-carotid artery and at three points in the vertebrobasilar artery. Venous attenuation in the central vein was measured at four points. Mean attenuation values were analysed quantitatively. Axial and post-processing threedimensional images were assessed qualitatively. Results: When Groups A and B were compared, there were no differences in the mean attenuation values in either the aorto-carotid artery (p=0.78) or the vertebrobasilar artery (p=0.82). Mean venous attenuation values were lower (p=0.002) in Group B than in Group A. Although the qualitative assessment of arterial images showed no differences between the two groups overall, perivenous artefacts at the subclavian vein were assessed as less prominent (p<0.01) in Group B. Conclusions: When compared with CTA followed by 25 ml of SF, CTA followed by 40 ml of SF can reduce venous attenuation values and perivenous artefacts at the subclavian vein. [ABSTRACT FROM AUTHOR]