冠状动脉解剖变异的CTA影像特征分析

目的:分析冠状动脉解剖变异的CT血管造影(computed tomography angiography,CTA)影像特征。方法:回顾分析2010年6月到2014年4月间PACS存储的12326例心脏CTA图像资料,记录解剖变异冠状动脉的名称、开口起源位置、数目、行程状态及终止部位表现及其与毗邻结构的关系。结果:共有700例心脏有冠状动脉解剖变异,以冠状动脉开口起源异常最多见,共622例(622/12326,5.05%),其中左和右冠状动脉开口高位350例(350/12326,2.84%),左和右冠状动脉开口于对侧窦166例(166/12326,1.35%),冠状动脉双开口70例(70/12326,0.57%),左和右冠状动脉开口于窦间36例(36/12326,0.29%);其次为数目异常29例(29/12326,0.24%),包括左、右单支冠状动脉19例(19/12326,0.15%)和冠状动脉分支(LCx)缺如10例(10/12326,0.08%);冠状动脉终止异常(冠脉动脉-动脉圆锥和/或肺动脉瘘)29例(29/12326,0.24%)。VR是显示冠状动脉解剖变异最重要的后处理方法。结论:冠状动脉解剖变异CTA表现复杂多样,心脏CTA能够准确显示冠状动脉解剖变异种类及其毗邻关系。     

Optimizing Radiation Dose Levels in Prospectively Electrocardiogram-Triggered Coronary Computed Tomography Angiography Using Iterative Reconstruction Techniques: A Phantom and Patient Study

Aim

To investigate the potential of reducing the radiation dose in prospectively electrocardiogram-triggered coronary computed tomography angiography (CCTA) while maintaining diagnostic image quality using an iterative reconstruction technique (IRT).

Methods and Materials

Prospectively-gated CCTA were first performed on a phantom using 256-slice multi-detector CT scanner at 120 kVp, with the tube output gradually reduced from 210 mAs (Group A) to 125, 105, 84, and 63 mAs (Group B–E). All scans were reconstructed using filtered back projection (FBP) algorithm and five IRT levels (L2-6), image quality (IQ) assessment was performed. Based on the IQ assessment, Group D(120 kVp, 84 mAs) reconstructed with L5 was found to provide IQ comparable to that of Group A with FBP. In the patient study, 21 patients underwent CCTA using 120 kV, 210 mAs with FBP reconstruction (Group 1) followed by 36 patients scanned with 120 kV, 84 mAs with IRT L5 (Group 2). Subjective and objective IQ and effective radiation dose were compared between two groups.

Results

In the phantom scans, there were no significant differences in image noise, contrast-to-noise ratio (CNR) and modulation transfer function (MTF) curves between Group A and the 84 mAs, 63 mAs groups (Groups D and E). Group D (120 kV, 84 mAs and L5) provided an optimum balance, producing equivalent image quality to Group A, at the lowest possible radiation dose. In the patient study, there were no significant difference in image noise, signal-to-noise ratio (SNR) and CNR between Group 1 and Group 2 (p = 0.71, 0.31, 0.5, respectively). The effective radiation dose in Group 2 was 1.21±0.14 mSv compared to 3.20±0.58 mSv (Group 1), reflecting dose savings of 62.5% (p<0.05).

Conclusion

iterative reconstruction technique used in prospectively ECG-triggered 256-slice coronary CTA can provide radiation dose reductions of up to 62.5% with acceptable image quality.     

Run-Off Computed Tomography Angiography (CTA) for Discriminating the Underlying Causes of Intermittent Claudication

AimTo evaluate run-off computed tomography angiography (CTA) of abdominal aorta and lower extremities for detecting musculoskeletal pathologies and clinically relevant extravascular incidental findings in patients with intermittent claudication (IC) and suspected peripheral arterial disease (PAD). Does run-off CTA allow image-based therapeutic decision making by discriminating the causes of intermittent claudication in patients with suspected peripheral arterial disease PAD?ResultsWhile focused on vascular imaging, CTA image quality was sufficient for evaluation of the MSK system in all cases. The underlying cause of IC was diagnosed in run-off CTA as vascular, MSK and a combination in n = 138 (65%), n = 10 (4%), and n = 66 (31%) cases, respectively. Specific vascular or MSK therapy was recorded in n = 123 and n = 9 cases. In n = 82, no follow-up was possible. Clinically relevant extravascular incidental findings were detected in n = 65 patients (30%) with neoplasia, ascites and pleural effusion being the most common findings.DiscussionRun-off CTA allows identification of vascular, MSK, and combined causes of IC in patients with suspected PAD and can guide specific therapy. CTA also allowed confident detection of crEVIF although detection did not necessarily trigger workup or treatment.     

The Wall Eclipsing Sign on Pulmonary Artery Computed Tomography Angiography Is Pathognomonic for Pulmonary Artery Sarcoma

Background

The objective of this study was to evaluate the imaging characteristics of pulmonary artery sarcoma (PAS) on pulmonary artery computed tomography angiography (PACTA) that can be used to differentiate between PAS and pulmonary thromboembolic diseases, including chronic thromboembolic pulmonary hypertension (CTEPH) and acute pulmonary embolism (APE).

Methods

The clinical data and imaging characteristics of 12 patients with PAS, 156 patients with CTEPH, and 426 patients with APE who were treated at Beijing Anzhen Hospital from January 2007 to August 2013 were retrospectively analyzed. All patients underwent PACTA before treatment, and the diagnoses of PAS and CTEPH were all confirmed by surgical biopsy.

Results

All 12 PAS patients were initially misdiagnosed and received inappropriate thrombolytic and/or anticoagulant therapy before they were referred for surgical intervention. The mean time from PACTA to surgical intervention was 5.5±3.7 months (range 2–11 months). On PACTA, the PAS lesion always eclipsed the wall of the pulmonary artery before infiltrating outside the pulmonary artery, which was termed the wall eclipsing sign. This sign was observed in all PAS patients but was not observed in any CTEPH or APE patients.

Conclusions

PAS is a rare neoplasm with a poor prognosis, and is easily misdiagnosed as thromboembolic disease. The wall eclipsing sign on PACTA is pathognomonic for PAS, and patients with this sign should be investigated to confirm the diagnosis and should undergo surgical intervention as soon as possible, rather than receiving thrombolytic or anticoagulant therapy.     

Automated Axial Right Ventricle to Left Ventricle Diameter Ratio Computation in Computed Tomography Pulmonary Angiography

ResultsThe CAD system analyzed correctly 92.4% (183/198) of CTPA studies. The mean difference between automated and manually computed axial RV/LV ratios was 0.03±0.22. The correlation between the RV/LV diameter ratio obtained by the CAD system and that obtained by the radiologist was high (r=0.81). Compared to the radiologist, the CAD system equally achieved high accuracy for the composite outcome, with areas under the receiver operating characteristic curves of 0.75 vs. 0.78. Similar results were found for 30-days PE-specific mortality, with areas under the curve of 0.72 vs. 0.75.ConclusionsAn automated CAD system for determining the CT derived RV/LV diameter ratio in patients with acute PE has high accuracy when compared to manual measurements and similar prognostic significance for two clinical outcomes.     

Positive Association of Coronary Calcium Detected by Computed Tomography Coronary Angiography with Periprocedural Myocardial Infarction

Background

Periprocedural myocardial infarction (PMI) may occur in approximately 5% to 30% of patients undergoing percutaneous coronary intervention. Whether the morphology of coronary plaque calcium affects the occurrence of PMI is unknown.

Materials and Methods

A total of 616 subjects with stable angina and normal baseline cardiac troponin I levels who had undergone computed tomography angiography (CTA) were referred to elective percutaneous coronary intervention. The morphology of coronary calcium was determined by CTA analysis. PMI was defined as an elevation in 24-h post-procedural cardiac troponin I levels of > 5 times the upper limit of normal with either symptoms of myocardial ischemia, new ischemic electrocardiographic changes, or documented complications during the procedure. Logistic regression was performed to identify the effect of the morphology of coronary calcium on the occurrence of PMI.

Results

According to the presence or morphology of coronary calcium as shown by CTA, 210 subjects were grouped in the heavy calcification group, 258 in the mild calcification group, 40 in the spotty calcification group and 108 in the control group. The dissection rate was significantly higher in the heavy calcification group than in the control group (7.1 % vs. 1.9%, p = 0.03). The occurrence of PMI in the heavy calcification group was significantly higher than that in the control group (OR 4.38, 95% CI 1.80–10.65, p = 0.001). After multivariate adjustment, the risk of PMI still remained significantly higher in the heavy calcification group than in the control group (OR 4.04, 95% CI 1.50–10.89, p = 0.003).

Conclusions

The morphology of coronary calcium determined by CTA may help to predict the subsequent occurrence of PMI. A large amount of coronary calcium may be predictive of PMI.     

头颅电子计算机断层扫描血管造影和头颅磁共振血管成像在颅内动脉瘤中诊断价值比较的回顾性研究

摘要 目的：研究对比头颅电子计算机断层扫描血管造影（CTA）和头颅磁共振血管成像（MRA）在颅内动脉瘤中诊断价值。方法：回顾性分析医院2019年1月2日～2020年12月15日收治的60例疑似颅内动脉瘤患者资料,所有受试者均开展头颅CTA检查、MRA检查以及数字减影血管造影（DSA）检查。以DSA检查结果为金标准,比较头颅CTA和头颅MRA诊断颅内动脉瘤的效能。此外,对比头颅CTA和头颅MRA诊断不同分级、不同部位颅内动脉瘤的符合率。结果：DAS检查结果显示确诊动脉瘤患者48例,共检出动脉瘤74个,CTA检出动脉瘤65个,MRA检出动脉瘤51个,CTA动脉瘤检出率高于MRA检出率（均P＜0.05）。以DSA结果为金标准,CTA诊断颅内动脉瘤的灵敏度、特异度以及准确度分别为94.20%（65/69）、60.00%（3/5）、91.89%（68/74）,均高于MRA的82.26%（51/62）、41.67%（5/12）、75.68%（56/74）（均P＜0.05）。CTA诊断1级颅内动脉瘤的符合率为13.85%（9/65）,高于MRA的7.84%（4/51）（P＜0.05）。各种检查方式诊断不同部位颅内动脉瘤的符合率对比均无明显差异（均P＞0.05）。结论：CTA诊断颅内动脉瘤的灵敏度、特异度以及准确度均高于MRA,可提高对小直径肿瘤的检出率。然而,MRA具有无辐射、检测费用少、安全性高等优势,临床实际工作中可综合选择合理的检查方式。     

System Matrix Analysis for Computed Tomography Imaging

In practical applications of computed tomography imaging (CT), it is often the case that the set of projection data is incomplete owing to the physical conditions of the data acquisition process. On the other hand, the high radiation dose imposed on patients is also undesired. These issues demand that high quality CT images can be reconstructed from limited projection data. For this reason, iterative methods of image reconstruction have become a topic of increased research interest. Several algorithms have been proposed for few-view CT. We consider that the accurate solution of the reconstruction problem also depends on the system matrix that simulates the scanning process. In this work, we analyze the application of the Siddon method to generate elements of the matrix and we present results based on real projection data.     

The Association of Brachial-Ankle Pulse Wave Velocity with Coronary Artery Disease Evaluated by Coronary Computed Tomography Angiography

The aim of this study was to investigate whether brachial-ankle pulse wave velocity (baPWV) is associated with the severity of coronary artery disease (CAD) assessed by coronary computed tomography angiography (CCTA), and to evaluate baPWV as a predictor of obstructive CAD on CCTA. A total of 470 patients who underwent both baPWV and CCTA were included. We evaluated stenosis degree and plaque characteristics on CCTA. To estimate the severity of CAD, we calculated the number of segment with plaque (segment involvement score; SIS), stenosis degree-weighted plaque score (segment stenosis score; SSS), and coronary artery calcium score (CACS). The mean baPWV was 1,485 ± 315 cm/s (range, 935-3,175 cm/s). Non-obstructive (stenosis < 50%) and obstructive (stenosis ≥ 50%) CAD was found in 129 patients (27.4%) and 144 (30.6%), respectively. baPWV in patients with obstructive CAD was higher than that of patients with non-obstructive (1,680 ± 396 cm/s versus 1,477 ± 244 cm/s, P < 0.001) or no CAD (1,680 ± 396 cm/s versus ± 196 1,389 cm/s, P < 0.001). baPWV showed significant correlation with SSS (r = 0.429, P < 0.001), SIS (r = 0.395, P < 0.001), CACS (r 0.346, P < 0.001), and the number of segment with non-calcified plaque (r 0.092, P = 0.047), mixed plaque (r = 0.267, P < 0.001), and calcified plaque (r = 0.348, P < 0.001), respectively. The optimal baPWV cut-off value for the detection of obstructive CAD was 1,547 cm/s. baPWV ≥ 1,547 cm/s was independent predictor for the obstructive CAD. In conclusion, baPWV is well correlated with the severity of CAD evaluated by CCTA. baPWV has the potential to predict severity of coronary artery atherosclerosis.     

基于CTA的在体女性盆腔静脉血管网数字化三维模型构建的方法及意义

目的:探讨利用CTA原始数据集构建在体女性盆腔静脉血管网数字化三维模型的方法及意义。方法:基于双源CTA技术,获取1例宫颈癌患者的Dicom 3.0原始二维断层图像数据集。利用Mimics 10.01软件分别对骨盆、盆腔动脉血管网以及盆腔静脉血管网进行三维重建并配准融合。结果:构建的盆腔静脉血管网数字化三维模型可以清楚地显示下腔静脉、髂总静脉、髂外静脉、髂内静脉及其初级属支,以及双侧卵巢静脉等。与重建的骨盆、盆腔动脉血管网配准融合后,各支静脉血管的解剖走形及引流区域变得更加清晰明确。结论:基于CTA的计算机三维重建技术是一种研究女性盆腔静脉血管网的好方法,具有较大的运用价值。     

The Impact of Iterative Reconstruction on Computed Tomography Radiation Dosimetry: Evaluation in a Routine Clinical Setting

Purpose

To evaluate the effect of introduction of iterative reconstruction as a mandated software upgrade on radiation dosimetry in routine clinical practice over a range of computed tomography examinations.

Methods

Random samples of scanning data were extracted from a centralised Picture Archiving Communication System pertaining to 10 commonly performed computed tomography examination types undertaken at two hospitals in Western Australia, before and after the introduction of iterative reconstruction. Changes in the mean dose length product and effective dose were evaluated along with estimations of associated changes to annual cancer incidence.

Results

We observed statistically significant reductions in the effective radiation dose for head computed tomography (22–27%) consistent with those reported in the literature. In contrast the reductions observed for non-contrast chest (37–47%); chest pulmonary embolism study (28%), chest/abdominal/pelvic study (16%) and thoracic spine (39%) computed tomography. Statistically significant reductions in radiation dose were not identified in angiographic computed tomography. Dose reductions translated to substantial lowering of the lifetime attributable risk, especially for younger females, and estimated numbers of incident cancers.

Conclusion

Reduction of CT dose is a priority Iterative reconstruction algorithms have the potential to significantly assist with dose reduction across a range of protocols. However, this reduction in dose is achieved via reductions in image noise. Fully realising the potential dose reduction of iterative reconstruction requires the adjustment of image factors and forgoing the noise reduction potential of the iterative algorithm. Our study has demonstrated a reduction in radiation dose for some scanning protocols, but not to the extent experimental studies had previously shown or in all protocols expected, raising questions about the extent to which iterative reconstruction achieves dose reduction in real world clinical practice.     

Coronary Computed Tomography Angiography Based Assessment of Endothelial Shear Stress and Its Association with Atherosclerotic Plaque Distribution In-Vivo

Purpose

The relationship between low endothelial shear stress (ESS) and coronary atherosclerosis is well established. ESS assessment so far depended on invasive procedures. The aim of this study was to demonstrate the relationship between ESS and coronary atherosclerosis by using non-invasive coronary computed tomography angiography (CTA) for computational fluid dynamics (CFD) simulations.

Methods

A total number of 7 consecutive patients with suspected coronary artery disease who received CTA and invasive angiography with IVUS analysis were included in this study. CTA examinations were performed using a dual-source scanner. These datasets were used to build a 3D mesh model. CFD calculations were performed using a validated CFD solver. The presence of plaque was assumed if the thickness of the intima-media complex exceeded 0.3 mm in IVUS. Plaque composition was derived by IVUS radiofrequency data analysis.

Results

Plaque was present in 32.1% of all analyzed cross-sections. Plaque prevalence was highest in areas of low ESS (49.6%) and high ESS (34.8%). In parts exposed to intermediate-low and intermediate-high ESS few plaques were found (20.0% and 24.0%) (p<0.001). Wall thickness was closely associated with local ESS. Intima-media thickness was 0.43±0.34mm in low and 0.38±0.32mm in high ESS segments. It was significantly lower when the arterial wall was exposed to intermediate ESS (0.25±0.18mm and 0.28 ± 0.20mm) (p<0.001). Fibrofatty tissue was predominately found in areas exposed to low ESS (p≤0.023).

Conclusions

In this study a close association of atherosclerotic plaque distribution and ESS pattern could be demonstrated in-vivo. Adding CFD analysis to coronary CTA offers the possibility to gather morphologic and physiologic data within one non-invasive examination.     

Optimal Iodine Staining of Cardiac Tissue for X-Ray Computed Tomography

X-ray computed tomography (XCT) has been shown to be an effective imaging technique for a variety of materials. Due to the relatively low differential attenuation of X-rays in biological tissue, a high density contrast agent is often required to obtain optimal contrast. The contrast agent, iodine potassium iodide (), has been used in several biological studies to augment the use of XCT scanning. Recently was used in XCT scans of animal hearts to study cardiac structure and to generate 3D anatomical computer models. However, to date there has been no thorough study into the optimal use of as a contrast agent in cardiac muscle with respect to the staining times required, which has been shown to impact significantly upon the quality of results. In this study we address this issue by systematically scanning samples at various stages of the staining process. To achieve this, mouse hearts were stained for up to 58 hours and scanned at regular intervals of 6–7 hours throughout this process. Optimal staining was found to depend upon the thickness of the tissue; a simple empirical exponential relationship was derived to allow calculation of the required staining time for cardiac samples of an arbitrary size.     

Ectopic Blood Supply of Hepatocellular Carcinoma as Depicted by Angiography with Computed Tomography: Associations with Morphological Features and Therapeutic History

Objective

To investigate the associations of ectopic blood supply of hepatocellular carcinoma (HCC) with its morphological features and therapeutic history.

Methods

Three hundred and six patients with 373 HCC lesions were enrolled in this study, and underwent biphasic contrast-enhanced scans on a 64-section MDCT. The anatomy of ectopic blood supply, morphological characteristics of HCC including the size, location and pseudocapsule, and history of transcatheter arterial chemoembolization (TACE) therapy were quantitively assessed and statistically analyzed.

Results

Ectopic blood supply was found in 30.8% (115/373) lesions. The ectopic arteries were predominantly composed of inferior phrenic artery (86/115) followed by left and right gastric artery (25/115). Tumor size, location, status of pseudocapsule, and history of TACE therapy could impact the origination of ectopic arteries (all p<0.05).

Conclusion

The ectopic feeding arteries of HCC predominantly composed of the perihepatic arteries are associated with the morphological features of the tumor and therapeutic history.     

320排CT冠脉造影检查对冠状动脉斑块成分分析可行性初探

目的:研究320排CT冠脉造影对分析冠状动脉轻度及重度狭窄患者斑块成分的价值。方法:2011年4月-2012年5月间我院1132例(62±12岁,42%女性)冠心病患者行320排CT冠状动脉造影检查,依据美国心脏协会16分段标准,分析每一例患者每一节段血管狭窄程度及斑块性质,CT斑块分型如下:Ⅰ型为钙化斑块,Ⅱ型为钙化为主的混合斑块,Ⅲ型为非钙化为主的混合斑块,Ⅳ型为非钙化斑块。比较不同狭窄程度组斑块类型差别。结果:共363例为冠脉血管正常人群,冠状动脉狭窄患者共769例,其中管腔狭窄程度<50%的轻度人群为367例,重度狭窄组(≥50%)为402例。重度狭窄患者组冠脉血管混合斑块数量较多,而非钙化斑块相对较少(Ⅰ～Ⅳ型斑块所占比例分别为22%,,39%,21%,18%),轻度狭窄患者组各斑块所占比例分别为29%,29%,26%,16%(p=0.006)。结论:随着冠状动脉狭窄程度的不同,冠状动脉粥样硬化斑块的类型也不尽相同,重度狭窄人群组中混合斑块较多而非钙化斑块较少。320排CT冠脉造影可对冠状动脉斑块成分进行分析。     

Validation of a Low Dose Simulation Technique for Computed Tomography Images

Purpose

Evaluation of a new software tool for generation of simulated low-dose computed tomography (CT) images from an original higher dose scan.

Materials and Methods

Original CT scan data (100 mAs, 80 mAs, 60 mAs, 40 mAs, 20 mAs, 10 mAs; 100 kV) of a swine were acquired (approved by the regional governmental commission for animal protection). Simulations of CT acquisition with a lower dose (simulated 10–80 mAs) were calculated using a low-dose simulation algorithm. The simulations were compared to the originals of the same dose level with regard to density values and image noise. Four radiologists assessed the realistic visual appearance of the simulated images.

Results

Image characteristics of simulated low dose scans were similar to the originals. Mean overall discrepancy of image noise and CT values was −1.2% (range −9% to 3.2%) and −0.2% (range −8.2% to 3.2%), respectively, p>0.05. Confidence intervals of discrepancies ranged between 0.9–10.2 HU (noise) and 1.9–13.4 HU (CT values), without significant differences (p>0.05). Subjective observer evaluation of image appearance showed no visually detectable difference.

Conclusion

Simulated low dose images showed excellent agreement with the originals concerning image noise, CT density values, and subjective assessment of the visual appearance of the simulated images. An authentic low-dose simulation opens up opportunity with regard to staff education, protocol optimization and introduction of new techniques.     

多层螺旋CT对胃癌术前分期的准确性评价

目的:评价多层螺旋CT对胃癌术前分期的准确性.方法:对78例经胃镜活捡证实为胃癌的患者进行MSCT增强扫描,其中67例经历了手术治疗,并获得术后病理结果.由两位资深放射科医师对影像学资料进行分析,轴位和MPR影像用于术前TNM分期,N分期分别采用UICCTNM分期和日本分期,两种分期的准确性比较采用McNemar检验进行统计学分析.结果:轴位和轴位结合MPR影像的总体T分期准确率分别为67%(45/67)和78%(52/67)(P＜0.05),总体N分期的准确率分别是61%(41/67)和67%(45/67)(P＞0.05,日本分期),54%(36/67)和60%(40/67)(P＞0.05,UICC TNM分期),总体M分期准确率为93%(73/78).结论:服水低张动态增强MSCT对胃癌术前TNM分期具有很高的准确性,MPR能提高胃癌T分期的准确率,但不能提高N分期的准确率.     

Screening of Miners and Millers at Decreasing Levels of Asbestos Exposure: Comparison of Chest Radiography and Thin-Section Computed Tomography

Background

Chest radiography (CXR) is inferior to Thin-section computed tomography in the detection of asbestos related interstitial and pleural abnormalities. It remains unclear, however, whether these limitations are large enough to impair CXR´s ability in detecting the expected reduction in the frequency of these asbestos-related abnormalities (ARA) as exposure decreases.

Methods

Clinical evaluation, CXR, Thin-section CT and spirometry were obtained in 1418 miners and millers who were exposed to progressively lower airborne concentrations of asbestos. They were separated into four groups according to the type, period and measurements of exposure and/or procedures for controlling exposure: Group I (1940–1966/tremolite and chrysotile, without measurements of exposure and procedures for controlling exposure); Group II (1967–1976/chrysotile only, without measurements of exposure and procedures for controlling exposure); Group III (1977–1980/chrysotile only, initiated measurements of exposure and procedures for controlling exposure) and Group IV (after 1981/chrysotile only, implemented measurements of exposure and a comprehensive procedures for controlling exposure).

Results

In all groups, CXR suggested more frequently interstitial abnormalities and less frequently pleural plaques than observed on Thin-section CT (p<0.050). The odds for asbestosis in groups of decreasing exposure diminished to greater extent at Thin-section CT than on CXR. Lung function was reduced in subjects who had pleural plaques evident only on Thin-section CT (p<0.050). In a longitudinal evaluation of 301 subjects without interstitial and pleural abnormalities on CXR and Thin-section CT in a previous evaluation, only Thin-section CT indicated that these ARA reduced as exposure decreased.

Conclusions

CXR compared to Thin-section CT was associated with false-positives for interstitial abnormalities and false-negatives for pleural plaques, regardless of the intensity of asbestos exposure. Also, CXR led to a substantial misinformation of the effects of the progressively lower asbestos concentrations in the occurrence of asbestos-related diseases in miners and millers.