Efficacy of fine focal spot technique in CT angiography of neck.

Abstract

Focal spot size partially defines spatial resolution of a CT system. Many CT tubes have two focal spot sizes, with the finer one allowing more detailed imaging at the cost of photon intensity and increased heat production. Improved X-ray technology and advancement of various generations of iterative reconstruction allow the use of fine focal spot technique in CT angiography. CT neck angiography (CTNA) has been commonly performed as part of stroke imaging or in the trauma setting. This prospective study aimed to assess the efficacy of fine focal spot scanning in vessel clarity improvement, vessel calcification and arterial pulsation artefact reduction on CTNA. Consecutive adult patients of all ages and genders who presented for CTNA were included. All CTNA were scanned with standard focal spot size (SFSS) of 1 × 1 mm in first 4 months while the CTNA in the following 4 months with fine focal spot size (FFSS) of 0.5 × 1 mm. Vessel clarity, calcification and arterial pulsation artefact of arch of aorta, brachiocephalic, subclavian, common carotid, carotid bifurcation, internal carotid, external carotid and vertebral arteries were assessed randomly using a 5-point scale by two blinded radiologists. Results were compared. There were 43 patients (mean age 60) with 97 calcified arterial segments in SFSS and 48 patients (mean age 62) with 113 calcified arterial segments in FFSS. 30 % of patients had > 50% carotid artery stenosis. No occlusion or dissection was found in the remaining arteries. Mann-Whitney test showed FFSS performed significantly better for vessel clarity (U: 48238.50, p < .001,r: 0.556) and calcification artefact reduction (U: 2040.50, p < .001,r: 0.564). There was no significant reduction for arterial pulsation artefact. Fine focal spot technique improves vessel clarity and reduces calcification blooming artefact in CTNA. These benefits may potentially improve the assessment of arterial luminal stenosis and vessel wall pathology, including plaque morphology. Beam hardening artefact from calcification particularly in the vessel wall can often reduce the clarity of vessel lumen thus affect accurate assessment of luminal stenosis. Fine focal spot technique has the advantages of reducing beam-hardening artefact of vessel wall calcifications and improving vessel wall clarity, thus it may potentially improve the assessment of arterial luminal stenosis and vessel wall pathology, including plaque morphology. It may become an important CT imaging technique in near future.