Interleaving cerebral CT perfusion with neck CT angiography. Part II: clinical implementation and image quality

Abstract

Objectives: Feasibility evaluation of the One-Step Stroke Protocol, which is an interleaved cerebral computed tomography perfusion (CTP) and neck volumetric computed tomography angiography (vCTA) scanning technique using wide-detector computed tomography, and to assess the image quality of vCTA.

Methods: Twenty patients with suspicion of acute ischaemic stroke were prospectively scanned and evaluated with a head and neck CTA and with the One-Step Stroke Protocol. Arterial enhancement and contrast-to-noise ratio (CNR) in the carotid arteries was assessed. Three observers scored artefacts and image quality of the cervical arteries. The total z-coverage was evaluated.

Results: Mean enhancement in the carotid bifurcation was rated higher in the vCTA (595 ± 164 HU) than CTA (441 ± 117 HU). CNR was rated higher in vCTA. Image quality scores showed no significant difference in the region of the carotid bifurcation between vCTA and CTA. Lower neck image quality scores were slightly lower for vCTA due to artefacts, although not rated as diagnostically relevant. In ten patients, the origin of the left common carotid artery was missed by 1.6 ± 0.8 cm. Mean patient height was 1.8 ± 0.09 m. Carotid bifurcation and origin of vertebral arteries were covered in all patients.

Conclusions: The One-Step Stroke Protocol is feasible with good diagnostic image quality of vCTA, although full z-coverage is limited in tall patients.

Key points: • Interleaving cerebral CTP with neck CTA (One-Step Stroke Protocol) is feasible • Diagnostic quality of One-Step Stroke Protocol neck CTA is similar to conventional CTA • One-Step Stroke Protocol neck CTA suffers from streak artefacts in the lower neck • A limitation of One-Step Stroke Protocol CTA is lack of coverage in tall patients • Precise planning of One-Step Stroke Protocol neck CTA is necessary in tall patients.

Keywords: Angiography; Brain; Multidetector computed tomography; Perfusion; Stroke.

Fig. 1

Schematic overview of the One-Step Stroke Protocol with 3D volume rendering of the head CTP and volume neck CTA. The One-Step Stroke Protocol consists of a 16-cm volumetric whole-brain CTP acquisition that is interrupted as soon as contrast material is detected in the arteries of the central slab of the 3D volume. Within 1.8 s, the table is then rapidly moved to the neck, where a 16-cm volumetric scan is performed with 0.5 s acquisition time. The table is then automatically moved back to the brain to resume the CTP acquisition. Note that the arterial enhancement in the neck is excellent because the contrast reaches the neck earlier than the brain and the enhancement curve in the neck is shifted to the left

Fig. 2

Comparison of the neck CTA of the One-Step Stroke Protocol (a, b and c) and the conventional CTA (d, e and f) in a patient with sudden weakness of the right hand and leg. a and d Axial images at the level above the carotid bifurcation (window centre, 200 HU; window width 700 HU). The left internal carotid artery shows a pinpoint stenoses, plaque and calcifications. In this subject, the origin of the left common carotid artery was missed by 2 cm. Image quality was rated equally good at the level of the carotid bifurcation between the One-Step Stroke Protocol and the conventional CTA protocol. b and e Coronal maximum intensity projections with 10 mm reconstructions; c and f are sagittal maximum intensity projections with 10 mm reconstructions (window centre, 200 HU; window width 700 HU)

Fig. 3

Example of streak artefacts in the lower neck. Using a wide window setting (a) of W/L = 900/100, the image quality remains diagnostic for the vascular structures but at a narrower window setting (b) of 500/150, these band-like artefacts render some soft tissue structures invisible