Objectives: To assess the diagnostic performance and clinical efficacy of metal artefact reduction using monoenergetic imaging with dual-energy computed tomography (DECT). Materials: A total of 30 patients with 32 metal device regions were examined using the DECT protocol with 100 kVp and 140 kVp spectra. Specific post-processing software was used to generate optimised monoenergetic images and standard combined images by filtered back projection. Two independent observers subjectively graded the degree of artefact and diagnostic quality of the two sets of images on a five-point rating scale. The beamhardening artefact (mean density of the most pronounced streak 1 cm from the device) was compared between both groups. Qualitative assessment by type of device (internal or external device) was performed. Results: A total of 32 examinations with 19 internal, 10 external, and 3 internal + external implanted metal devices were performed. Monoenergetic imaging was rated superior for artefact reduction in 75% cases and for diagnostic quality in 78% cases, compared with standard combined imaging by filtered back projection (p < 0.001). The mean density of beam hardening artefacts improved from-725.22 HU in standard combined imaging to-519.02 HU using monoenergetic imaging (p = 0.025). The presence of an external metal device adversely affected the artefact reduction performance of monoenergetic imaging (p = 0.045), without significantly affecting diagnostic quality. Conclusion: Monoenergetic extrapolation using DECT can significantly reduce metal artefact and improve diagnostic quality compared with filtered back projection. Its performance was adversely affected by the presence of an external device.

Objective: To investigate the procedural complication rate, restenosis rate, and clinical outcomes after carotid angioplasty and stenting in patients with radiation-associated carotid stenosis. Methods: All patients with a history of head and / or neck radiation referred to Queen Elizabeth Hospital, Hong Kong, for carotid angioplasty and stenting for carotid artery stenosis between January 2008 and December 2013 were identified. Their clinical information, and procedural and imaging findings were reviewed. All procedures were performed by a dedicated team of neurointerventionists. The mean degree of stenosis was 75.1% (range, 50.0%-94.1%). Standardised, regular postoperative follow-up with clinical and Doppler ultrasound assessments was scheduled for all patients. Results: Forty-five carotid arteries in 40 patients with a history of head and neck irradiation were stented in this study. The mean age was 63.3 years; 36 (90.0%) patients had radiotherapy for nasopharyngeal carcinoma. The mean time interval between radiotherapy and carotid angioplasty and stenting was 228.8 months (range, 8-487 months). The mean degree of stenosis was 75.1%. Fourteen (31.1%) patients who underwent carotid angioplasty and stenting had contralateral carotid artery occlusion. Embolic protection devices were used in 37 (82.2%) procedures. There was one (2.2%) procedural complication, with dissection of the left common carotid artery during catheterization for left internal carotid artery stenting. The mean follow-up period was 29 months (range, 1-66 months). The ipsilateral stroke-free survival rates were 97.8% at 6 months, 95.1% at 1 year, and 84.0% at 5 years. The restenosis-free survival rates were 95.0% at 6 months, 92.5% at 1 year, and 74.0% at 5 years. No 30day mortality was identified. Two subarachnoid haemorrhages and one transient ischaemic attack occurred in the 30-day postoperative period. On subsequent follow-up, four (10.3%) patients died at a mean interval of 19 months after the procedure. Conclusion: We demonstrated that carotid angioplasty and stenting is safe in patients with radiation-associated carotid artery stenosis. The long-term clinical outcomes of ischaemic neurological event and restenosis were satisfactory.

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