Type 2 DM is a disease with both metabolic and vascular components . Patients with DM should always control their risk factors and recognize the signs and symptoms of potentially fatal complications as early as possible. Plaque morphology directly correlates with the risk of embolism and occlusion , thus detecting plaques at an early stage is of great clinical importance. As a noninvasive modality, multidetector CT angiography (MDCTA) offers some potential for plaque analysis [12, 13]. DSCTA offers many advantages over conventional MDCTA. First, DSCTA can differentiate materials by analyzing their attenuation differences . As a result, bone and calcified plaque can be removed from vessels with iodine contrast. Second, reduction in radiation dose is an important characteristic of DSCTA. Zhang et al.  reported that compared with conventional bone-subtraction CTA, DE-BR-CTA showed a 60% reduction in radiation dose for dual-source CTA, avoiding the additional preliminary unenhanced CT acquisition. Third, DSCTA has faster scan acquisition and higher spatial resolution, allowing DSCT acquisition with minimal patient motion registration artifact and better visualization of mixed and noncalcified plaques in small vessels [14, 16]. Furthermore, DSCTA has advanced postprocessing methods, especially easy-to-use bone-removal algorithms for direct visualization of complex vasculature, and high quality DSA-like imaging .
In our study, the metabolic disorders in patients with symptomatic DM predominantly included hypertension, glucose metabolism abnormalities, and dyslipidemia. A high incidence and wide distribution of plaques were identified in the present study. The heavy plaque burden in patients with DM was probably because there were more cerebrovascular risk factors resulting from metabolic disorders that have been described as the cause of atherosclerosis of the carotid and cerebrovascular arteries [17, 18]. Guidelines for treatment of specific conditions with respect to metabolic disorders are being developed  and should be promoted by healthcare educators and providers.
Regarding the composition of atherosclerotic plaques in patients with type 2 DM, we found that there were relatively more noncalcified and calcified plaques and less mixed plaques, which was consistent with previous studies [1, 20]. These observations may suggest a more rapid development of atherosclerosis in the presence of DM, with faster progression from noncalcified lesions to completely calcified lesions . A faster progression of atherosclerosis has also been suggested previously on the basis of event rates in patients with DM undergoing nuclear perfusion imaging . Interestingly, a recent study using MDCT demonstrated that a higher proportion of mixed plaque was found in diabetics than in nondiabetics . However, the number of study subjects was small and they were all asymptomatic for cardiac symptoms. There is no clear explanation for this difference. Despite many controversies, noncalcified plaques have been suggested as potentially vulnerable to trigger plaque rupture or embolism . It is important to evaluate the CeVD potential and treat the remediable plaques in a timely manner.
The present study demonstrated that patients with symptomatic type 2 DM showed a significantly higher prevalence of nonobstructive lesions (91%), confirming the findings of previous studies [1, 24, 25]. Using 64-slice MDCT, Scholte et al.  showed that coronary plaques of patients with type 2 DM were primarily nonobstructive (82%). Saely et al. reported a similar relationship between DM and nonobstructive plaques by invasive coronary angiography . It has been suggested that plaque rupture may occur frequently in nonobstructive plaques . This finding is of clinical importance since these plaques may be vulnerable to rupture and may be related to the high morbidity and mortality in patients with DM.
As was shown in this study, the noncalcified plaques were primarily located in the intracranial arteries, mixed plaques in the intracranial arteries and intracranial ICA and calcified plaques in the intracranial ICA and extracranial arteries. A similar distribution of calcified plaques has been shown in another study using 16-slice MDCT . In our study, a higher incidence of noncalcified plaque detected in intracranial vessels could be attributed to better visualization of noncalcified plaques in small vessels by DSCTA. In addition, we found a relatively high incidence of mixed plaque in the vessels located next to the cranium, due to the high spatial resolution of DSCTA with easy-to-use bone-removal algorithms that provides a direct visualization of complex vasculature .
In our study, the most common site of plaques was the cavernous portion of ICA. Wojak et al.  confirmed this, reporting that intracranial atherosclerotic stenosis typically occurred in the petrous cavernous siphon segments of ICA. Furthermore, Masuoka et al.  investigated the cause of development of atheromatous plaque around the cavernous portion of ICA using serial 3-mm sections of 32 intracranial ICA segments obtained from 50 cadavers, and found that the external elastic lamina disappeared in the cavernous portion of ICA; intimal thickening of ICA frequently appeared in the horizontal segment of the cavernous portion of ICA, which was the most common site of stenosis. Change in the elasticity of the arterial wall in the cavernous portion was suggested to be an important factor in the process of atherosclerosis in the intracranial ICA.
Outlining the significance of our study, the prevalence and morphology of carotid and cerebrovascular atherosclerotic plaques in patients with symptomatic type 2 DM by DSCTA has been systematically reported for the first time. The DSCT findings, which depended on a large study sample with cutting-edge technology, accurately reflects characteristics of plaque and stenosis in patients with symptomatic type 2 DM, and can be used to conduct a further treatment plan.
There were several limitations to this study. First, this study is a single centre, retrospective study. A study with a larger patient population from various centers is warranted to confirm these data. Second, the visualization of noncalcified plaques by DSCT is limited by plaque size; smaller plaques located predominantly in the smaller arteries may therefore be difficult to identify accurately with the current generation of CT scanners.