Comparison of 40 and 60 milliliters of contrast in assessment of the carotid artery by computed tomography angiography

Applications of Dual-Energy Computed Tomography for Artifact Reduction in the Head, Neck, and Spine

Conventional computed tomography (CT) uses a polychromatic energy beam to offer superb anatomic detail of the head and spine. However, technical challenges remain that can degrade the diagnostic image quality of these examinations. Dual-energy CT analyzes the changes in attenuation of soft tissues at different energy levels, from which different reconstructions can be made to yield the optimal contrast-to-noise ratio, reduce beam-hardening artifact, or evaluate tissue composition. In this article, selective applications of the dual energy CT technique are discussed, highlighting a powerful tool in the diagnostic CT evaluation of the head, neck, and spine.

Optimal scan timing for artery-vein separation at whole-brain CT angiography using a 320-row MDCT volume scanner

OBJECTIVE

A 320-row multidetector CT (MDCT) is expected for a good artery-vein separation in terms of temporal resolution. However, a shortened scan duration may lead to insufficient vascular enhancement. We assessed the optimal scan timing for the artery-vein separation at whole-brain CT angiography (CTA) when bolus tracking was used at 320-row MDCT.

METHODS

We analyzed 60 patients, who underwent whole-brain four-dimensional CTA. Difference in CT attenuation between the internal carotid artery (ICA) and the superior sagittal sinus (D_att) was calculated in each phase. Using a visual evaluation score for the depiction of arteries and veins, we calculated the difference between the mean score for the intracranial arteries and the mean score for the veins (D_score). We assessed the time at which the maximum D_att and D_score were simultaneously observed.

RESULTS

The maximum D_att was observed at 6.0 s and 8.0 s in the arterial-dominant phase and at 16.0 s and 18.0 s in the venous-dominant phase after the contrast media arrival time at the ICA (T_aa). The maximum D_score was observed at 6.0 s and 8.0 s in the arterial-dominant phase and at 16.0 s in the venous-dominant phase after the T_aa. There were no statistically significant differences in D_att (p = 0.375) or D_score (p = 0.139) between these scan timings.

CONCLUSION

The optimal scan timing for artery-vein separation at whole-brain CTA was 6.0 s or 8.0 s for the arteries and 16.0 s for the veins after the T_aa. Advances in knowledge: Optimal scan timing allowed us to visualize intracranial arteries or veins with minimal superimposition.

A reduced contrast volume acquisition regimen based on cardiovascular dynamics improves visualisation of head and neck vasculature with carotid MDCT angiography

PURPOSE

To investigate enhancement of head and neck arteries during carotid computed tomography angiography using a reduced volume contrast regimen and craniocaudal scan acquisition.

MATERIALS AND METHODS

Two hundred and two patients underwent carotid angiography using a 64 channel computed tomography scanner. Patients were allocated to one of two acquisition/contrast regimens: regimen A, the department's standard protocol, consisting of a caudocranial scan direction with 100mL of contrast intravenously; regimen B, involving a craniocaudal scan direction and approximately 50 mL of contrast using a timing dictated by patient hemodynamics. Attenuation profiles of cranial arteries and veins in 6 anatomical segments were assessed and arteriovenous contrast ratios (AVCR) calculated. Receiver operating characteristic (ROC) analysis was performed using DBM methodology.

RESULTS

Arterial attenuation was up to 54% (p<0.01) higher following regimen B compared with A. Attenuation in the veins were significantly lower in regimen B than in regimen A with a maximum reduction of up to 93% (p<0.0001). With regimen B, there were significant (p<0.0001) improvements in AVCR at a variety of anatomical sites. The ROC analysis demonstrated a significantly higher Az score for the novel regimen compared with regimen A (p<0.002) with inter-neuroradiologist agreement increasing from poor to moderate.

CONCLUSION

Significant improvements in visualisation of head and neck arterial vasculature can be achieved with a CT acquisition regimen using low contrast volume and injection timing based on patient specific contrast formula and craniocaudal scan direction.

Cerebral CT angiography using a small volume of concentrated contrast material with a test injection method: optimal scan delay for quantitative and qualitative performance

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 (T(cW)) was calculated, scan delay was divided into three groups according to T(cW) and scan duration (SD) between the second cervical vertebra and cW as follows: [(T(cW)+6)-SD] in 21 patients (Group A); [(T(cW)+8)-SD] in 23 patients (Group B); and [(T(cW)+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 [(T(cW)+8)-SD] s can produce the best performance both quantitatively and qualitatively.

Comparison of different volumes of saline flush in the assessment of perivenous artefacts in the subclavian vein during cervical CT angiography

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 40 ml contrast material (CM) followed by different volumes (25 ml 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 370 mg 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 three-dimensional 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.