Oh Lawrence Chia-Wei, Lau Kenneth Kwok-Pan, Devapalasundaram Ashwini, Buchan Kevin, Kuganesan Ahilan, Huynh Minh
1 Monash Health, Clayton, Victoria, Australia.
2 Department of Diagnostic Imaging, Monash Health, Clayton, Victoria, Australia.
Br J Radiol. 2019 Aug;92(1100):20190083. doi: 10.1259/bjr.20190083. Epub 2019 Jun 20.
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, < .001,r: 0.556) and calcification artefact reduction (U: 2040.50, < .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.
焦点尺寸部分决定了CT系统的空间分辨率。许多CT管有两种焦点尺寸，较精细的焦点尺寸虽能实现更详细的成像，但会以光子强度降低和热量产生增加为代价。改进的X射线技术以及各代迭代重建技术的发展，使得在CT血管造影中能够使用精细焦点技术。CT颈部血管造影（CTNA）通常作为中风成像的一部分或在创伤情况下进行。本前瞻性研究旨在评估精细焦点扫描在改善CTNA血管清晰度、减少血管钙化和动脉搏动伪影方面的效果。
纳入所有年龄和性别的连续成年CTNA患者。在最初4个月内，所有CTNA均采用1×1毫米的标准焦点尺寸（SFSS）进行扫描，而在接下来的4个月中，CTNA采用0.5×1毫米的精细焦点尺寸（FFSS）进行扫描。由两名盲法放射科医生使用5分制对主动脉弓、头臂干、锁骨下动脉、颈总动脉、颈动脉分叉、颈内动脉、颈外动脉和椎动脉的血管清晰度、钙化情况和动脉搏动伪影进行随机评估。对结果进行比较。
在采用SFSS扫描的43例患者（平均年龄60岁）中有97个钙化动脉节段，在采用FFSS扫描的48例患者（平均年龄62岁）中有113个钙化动脉节段。30%的患者颈动脉狭窄>50%。其余动脉未发现闭塞或夹层。曼-惠特尼检验显示，FFSS在血管清晰度方面表现明显更好（U：48238.50，P<.001，r：0.556），在减少钙化伪影方面也表现更好（U：2040.50，P<.001，r：0.564）。动脉搏动伪影没有显著减少。
精细焦点技术可改善CTNA的血管清晰度并减少钙化光晕伪影。这些益处可能会改善对动脉管腔狭窄和血管壁病变（包括斑块形态）的评估。
钙化尤其是血管壁钙化产生的束硬化伪影常常会降低血管腔的清晰度，从而影响对管腔狭窄的准确评估。精细焦点技术具有减少血管壁钙化束硬化伪影和提高血管壁清晰度的优势，因此可能会改善对动脉管腔狭窄和血管壁病变（包括斑块形态）的评估。在不久的将来，它可能会成为一项重要的CT成像技术。
