CT angiography

The advent of spiral (helical, volume ) CT has revolutionised the performance of body CT and allowed the development of CT angiography (CTA). CT angiography is a non-invasive method of visualising the vascular system and in some instances can replace conventional angiography. In spiral CT a volume of data is obtained rapidly with no respiratory misregistration at peak vascular opacification following the peripheral injection of contrast. Appropriate timing will ensure that either the venous or arterial tree is visualised and from the volume of data multiple overlapping slices can be obtained to generate 2D and 3D images with no increase in radiation to the patient. CT angiography may be performed as a dedicated study or be undertaken retrospectively using post-processing of data from a conventional diagnostic spiral scan to provide additional information about the vascular tree. When undertaken as a dedicated study CTA is quicker, less invasive and less costly than a conventional angiogram with a decrease in the radiation dose to the patient; however, the spatial resolution is limited with vessels less than 2 mm not visualised and there is no contrast saving. Received: 25 March 1998; Revision received: 16 July 1998; Accepted: 22 July 1998     

Detection of pulmonary nodules with overlapping vs non-overlapping image reconstruction at spiral CT

The aim of this study was to analyze whether overlapping image reconstruction increases numbers of pulmonary nodules detected at helical CT. Forty-eight helical CT scans (21with a slice thickness of 10 mm; 27 with a slice thickness of 5 mm) of patients with known pulmonary nodules were reconstructed both with overlapping and non-overlapping image reconstruction. Two readers recorded number and size of pulmonary nodules as well as diagnostic confidence. With overlapping image reconstruction each reader diagnosed more pulmonary nodules (slice thickness 10 mm: +24.0 and +26.7 %, both p < 0.01; slice thickness 5 mm: +9.5 and +11.9 %, both not significant) and more “definite” nodules (slice thickness 10 mm: +20.3 %, p < 0.05, and +30.8 %, p < 0.005; slice thickness 5 mm: +18.0 and +17.0 %, both p < 0.05). Nodules diagnosed with overlapping image reconstruction only were almost exclusively smaller than the slice thickness. The increase in number of nodules detected was not associated with a decrease in diagnostic confidence. Overlapping image reconstruction improves detection of pulmonary nodules smaller than the slice thickness at spiral CT. Received: 8 April 1998; Revision received: 16 July 1998; Accepted: 9 September 1998     

螺旋CT在叶内型肺隔离症诊断中的价值

目的 探讨螺旋CT在叶内型肺隔离症诊断中对异常供血动脉显示的作用和方法。方法 将14例肺隔离症患者的螺旋CT扫描方案分为2组，第1组8例，单层螺旋扫描；层厚3mm，床进4.5mm/s，重建间隔1.5mm者5例，多层螺旋扫描；实际层厚2.5mm，有效层厚3.2mm者3例。对比剂流率2.5ml/s；启动智能扫描探测到腹主动脉上段强化最佳时开始扫描，扫描资料交工作站行三维图像后处理。第2组6例为单层螺旋扫描，其中5例扫描层厚5mm，床进5mm/s；1例扫描层厚10mm，床进10mm/s。结果 病灶位于右下肺2例，左下肺12例，表现肿块者11例，边缘清楚的结节者3例。14例均见异常供血动脉，发自腹主动脉11例，胸主动脉2例，脾动脉1例；其中多层螺旋CT三维图像后处理显示异常供血动脉最佳。上述异常供血动脉均经外科手术证实。引流静脉均未显示。结论 在肺隔离症定性诊断中，多层螺旋CT横断面结合三维图像后处理利于显示异常供血动脉，有可能替代传统的血管造影。     

Multislice CT angiography

Multislice CT has overcome past limitations of CT angiography (CTA): Scan length and spatial resolution can be simultaneously optimized with multislice CTA, contrast medium can be saved, and the evaluation of large anatomic areas and vessels smaller than 1 mm become possible. This article describes how to optimize scanning protocols and contrast injection, and discusses the main clinical applications of this new technique. Only three main scanning protocolssuffice for all indications. A high speed / high-volume protocol (using 4*2mm or 4*2.5mm collimation) can be employed to scan the chest or abdomen in 8-10s, or to cover the whole abdominal aorta and the peripheral runoff including the feet within 40-65s. A high resolution protocol (using 4*1mm or 4*1.25mm) can be employed for the aorta and most regional vascular beds. It allows for near isotrophic imaging and depicts fine vascular structures with excellent detail. Ultra-high resolution protocols (using 2*0.5mm or 4*0.5mm collimation) yield totally isotropic data sets, and are mainly reserved for cerebrovascular imaging. Image processing techniques, and, in particular, volume rendering have made image presentation faster and easier. Multislice CTA exceeds MRA in spatial resolution and is now able to display even small vascular side branches. Its main indications will be aortic diseases, suspected pulmonary embolism but also renal artery stenoses, preoperative workup of abdominal or cerebral vessels, and acute vascular diseases. Multisplice CTA will become a strong competitor of other minimally invasive vascular imaging techniques.     

Multislice CT: technical principles and future trends

Multislice scanning has substantially improved the performance of CT scanners, and thus the relation between scan duration, available scan length, and spatial resolution along the patient axis (z-axis). Near-isotropic imaging of whole organ systems is already possible with 4-slice scanners, but only with 8- to 16-slice scanners can the scan duration be shortened as well. Reconstructing overlapping thin-section data (“secondary raw data set”) provides the basis for image reconstruction in any desired plane. By using thick multiplanar reformation (MPR) techniques, image quality can be improved while keeping patient dose low. Using unfavorable scanning parameters, exposure dose can be substantially increased compared with single-slice scanning, but thick MPR and individual-dose modulation techniques can provide the basis for dose reduction. Low-kVp scanning, in particular, is useful in children and slim adults and is an excellent technique to improve image contrast in CT angiographic studies. Short spiral scans should be avoided with multislice CT since overranging (extra rotations at the beginning and end of the scan, used for data interpolation) can substantially increase patient dose. Future trends include the introduction of thinner detector rows, wider detector arrays, faster tube rotation, and area detectors than can also be used for fluoroscopy. Noise-reduction techniques and individual dose modulation will gain importance with higher isotropic resolution. Functional and perfusion imaging, as well as advanced image processing and computer-aided diagnosis programs, will add to the possibilities of the next generation of multislice CT scanners.     

Complications of tracheal and thoracic surgery: the role of multisection helical CT and computerized reformations

Helical computed tomography (CT) has an important role in the evaluation of a wide range of congenital and acquired thoracic abnormalities. The development of advanced computerized reformations enables the generation of bronchographic and bronchoscopic images of the tracheobronchial tree, as well as angiographic images of pulmonary arteries and veins. Additionally, it provides coronal and sagittal reconstruction imaging of parenchymal abnormalities. This information is obtained by a 20-30s procedure on a typical single channel system, which makes helical CT an optimal technique for the evaluation of patients undergoing major upper airways and thoracic interventions. The recent introduction of multisection CT scanners allows faster imaging of patients with thinner collimation, thus improving spatial resolution along the longitudinal (z) axis of the patient along with reduction of motion artefacts. This article demonstrates the use of dual and quad-section helical CT in the postoperative evaluation of patients undergoing laryngo-tracheal and thoracic interventions, including laryngoplasty, tracheal endoscopic laser ablation, lobectomy, pneumonectomy, lung transplantation, sleeve resection, pulmonary angioplasty, and pulmonary artery thromboendarterectomy. Emphasis is given to the additive value of using computerized reformations over axial images, especially for delineation of complex postoperative anatomical details in the tracheobronchial tree and pulmonary vasculature.     

Pulmonary vein varix: diagnosis with multi-slice helical CT

The diagnosis of a pulmonary vein varix with a recently introduced new CT technology, multi-slice helical CT, is discussed. The advantage of multi-slice helical CT lies in increased thin-slice coverage during a single breath hold, which is the predominant factor limiting scan time. This CT technique facilitates the diagnosis of vascular pulmonary pathology. Received: 6 September 1999; Revised: 16 December 1999; Accepted: 15 February 2000     

Multislice computed tomography perfusion imaging for visualization of acute pulmonary embolism: animal experience

The purpose of our animal study was to evaluate a new computed tomography (CT) subtraction technique for visualization of perfusion defects within the lung parenchyma in subsegmental pulmonary embolism (PE). Seven healthy pigs were entered into a prospective trial. Acute PE was artificially induced by fresh clot material prior to the CT scans. Within a single breath-hold, whole thorax CT scans were performed with a 16-slice multidetector-row CT scanner (SOMATOM Sensation 16; Siemens, Forchheim, Germany) before and after intravenous application of 80 ml of contrast medium with a flow rate of 4 ml/s, followed by a saline chaser. The scan parameters were 120 kV and 100 mAs_eff, using a thin collimation of 16×0.75 mm and a table speed/rotation of 15–18 mm (pitch, 1.25–1.5; rotation time, 0.5 s). Axial source images were reconstructed with an effective slice thickness of 1 mm (overlap, 30%). A new automatic subtraction technique was used. After 3D segmentation of the lungs in the plain and contrast-enhanced series, threshold-based extraction of major airways and vascular structures in the contrast images was performed. This segmentation was repeated in the plain CT images segmenting the same number of vessels and airways as in the contrast images. Both scans were registered onto each other using nonrigid registration. After registration both image sets were filtered in a nonlinear fashion excluding segmented airways and vessels. After subtracting the plain CT data from the contrast data the resulting enhancement images were color-encoded and overlaid onto the contrast-enhanced CT angiography (CTA) images. This color-encoded combined display of parenchymal enhancement of the lungs was evaluated interactively on a workstation (Leonardo, Siemens) in axial, coronal and sagittal plane orientations. Axial contrast-enhanced CTA images were rated first, followed by an analysis of the combination images. Finally, CTA images were reread focusing on areas with perfusion deficits indicating PE on the color-coded enhancement display. Subtraction was feasible for all seven studies. In one animal, opacification of the pulmonary arteries was suboptimal owing to heart insufficiency. In the remaining six pigs, a total of 37 perfusion defects were clearly assessable downstream of occluded subsegmental arteries, showing lower or missing enhancement compared with normally perfused lung parenchyma. Indeterminate findings from CTA showed typical PE perfusion defects in four out of six cases on CT subtraction. Additionally, 22 peripheral triangular-shaped enhancement defects were delineated. Nine of these findings were reclassified as definitely being caused by PE on second reading of the CTA data sets. Our initial results have shown that this new subtraction technique for perfusion imaging of PE is feasible, using routine contrast delivery. Dedicated examination protocols are mandatory for adequate opacification of the pulmonary arteries and for optimization of data sets for subsequent subtraction. Perfusion imaging allows a comprehensive assessment of morphology and function, providing more accurate information on acute PE.This paper contains data on behalf of the Amersham Health Research Fellowship Grant, ECR 2003.     

Helical CT evaluation of aortic aneurysms and dissection: a pictorial essay

The relative noninvasive nature, easy accessibility, convenience and accuracy of helical CT in the rapid evaluation of not only the aorta and its branches, but the entire thorax/abdomen, makes it the best suited imaging modality for use in evaluation of aortic aneurysms and dissection. Excellent vascular opacification, the advantage of reconstructing overlapping scans without respiratory misregistration, multiplanar reconstruction and 3D rendering of the vessels highlight the benefits of helical CT. Helical CT evaluation combines the advantages of conventional CT, giving true information about the exact transverse and longitudinal extent of the aneurysm, the vessel wall, luminal thrombus and structures around the aorta, and those of aortography in the form 3D volumetric information display. The purpose of this essay is to present a spectrum of aortic aneurysms and dissection to highlight the role of helical CT in their evaluation.     

Feasibility of electron beam tomography in diagnosis of congenital heart disease: comparison with echocardiography

OBJECTIVE: To evaluate the feasibility of electron beam tomography (EBT) for morphological assessment of congenital heart disease. MATERIALS AND METHODS: Sixteen subjects were examined by EBT, transthoracic echocardiography, cardiac cine angiography and surgery. EBT scan was performed using single slice continuous volume mode to acquire high-resolution static image. Double dose contrast medium was injected by bolus technique after measuring scan delay time and calculation of proper injection rate. The results of EBT and echocardiography were compared based on the results of cardiac cine angiography and surgical findings. All anomalous components were evaluated in all subjects and grouped according to major cardiac structures. Statistical analysis was performed to compare two modalities' ability to evaluate the anomalies of major structures. RESULTS: EBT was more sensitive to evaluate the anomalies of systemic vessels, pulmonary vessels and small systemic arteries such as coronary artery. EBT was less sensitive to identify the abnormality of cardiac valves such as valvular regurgitation. There was no difference of sensitivity in evaluation of cardiac chambers and septa between the two modalities. CONCLUSION: EBT assisted by transthoracic echocardiography is excellent noninvasive modality to diagnose congenital heart disease.     

多层螺旋CT二维(2D)及三维(MPR)在周围型肺癌的临床应用

目的　探讨多层螺旋CT二维 (2D)和多平面重建技术 (MPR)在周围型肺癌的临床应用价值。方法　 17例周围型肺癌行多层螺旋CT扫描 (层厚 1～ 2mm)和多平面重建。结果　 2D图可显示周围型肺癌内部结构、分叶征、毛刺征、病灶周围血管、胸膜、纵隔结构的关系 ,但显示的范围、征象较局限。MPR可以多个方面显示肿块与胸膜、纵隔结构关系 ,MPR可多方面清楚显示肺癌本身征象和肺癌与周围组织的关系。结论　以 2D螺旋CT图为基础 ,结合MPR对诊断周围型肺癌有重要的临床应用价值     

CT in vascular pathologies

Since the introduction of helical scanners, CT angiography (CTA) has achieved an essential role in many vascular applications that were previously managed with conventional angiography. The performance of CTA is based on the accurate selection of collimation width, pitch, reconstruction spacing and scan delay, which must be modulated on the basis of the clinical issue. However, the major improvement of CT has been provided by the recent implementation of many post-processing techniques, such as multiplanar reformatting, shaded surface display, maximum intensity projections, 3D perspectives of surface and volume rendering, which simulate virtual intravascular endoscopy. The integration of the potentialities of the scanner and of the image processing techniques permitted improvement of: (a) the evaluation of aneurysms, dissection and vascular anomalies involving the thoracic aorta; (b) carotid artery stenosis; (c) aneurysms of abdominal aorta; (d) renal artery stenosis; (e) follow-up of renal artery stenting; and (f) acute or chronic pulmonary embolism. Our experience has shown that the assessment of arterial pathologies with CTA requires the integration of 3D post-processing techniques in most applications. Received 23 December 1997; Accepted 2 January 1998     

螺旋CT及三维重组技术在肺结核中的诊断价值

目的探讨螺旋CT及各种三维重组技术在肺结核诊断中的价值。方法回顾性分析经病理和临床证实的肺结核病例145例,全部病例行螺旋CT扫描,针对不同病例行CTVE、MPR及CPR等不同类型三维重组。结果螺旋CT(尤其是HRCT)能够显示小叶中心结节、树芽征、结核空洞、干酪肺炎、粟粒结节、支气管播散、支气管结核、淋巴结肿大和钙化等肺结核的不同表现。螺旋CT诊断正确率为96.6%,结合各种三维重组方式后,诊断正确率99.31%。结论螺旋CT结合各种三维重组法能够对肺结核做出准确诊断。     

颈动脉和椎基底动脉16层螺旋CT减影成像的应用价值

目的:探讨颈动脉和椎基底动脉CTA减影技术的临床应用价值。方法:对43例患者行颈动脉和椎基底动脉CTA检查,原始数据在工作站进行减影和三维图像后处理。图像由2名观察者对颈动脉和椎基底动脉的显影情况进行评分,数据应用SPSS11.0进行统计学分析。结果:减影和非减影的颈动脉和椎基底动脉图像的观察评分有显著性差异。CTA减影血管重建后的图像质量优良,在显示颈动脉和椎基底动脉的完整性方面明显优于常规CTA血管重建。减影图像对于显示管壁钙化效果欠佳,需结合平扫和非减影图像进行钙化斑块评估。结论:CTA减影成像技术改善了对颈动脉和椎基底动脉复杂解剖及异常管壁结构的显示,结合非减影图像,可为临床提供更加丰富的诊断信息。     

多层螺旋CT三维重建在骨关节损伤方面的临床应用

目的：评价多层螺旋CT三维重建在骨关节损伤中的应用价值。资料与方法：对60例骨关节损伤患者进行多层螺旋CT扫描，重建骨关节三维图像。结果：全部病例经多平面重建和SVR－CT Bone技术满意地显示出三维重建图像。结论：多层螺旋CT骨关节三维重建能够直观、立体、清晰、多角度地显示骨关节损伤，具有较高的临床应用价值。     

256层CT血管成像对冠状动脉瘘的诊断价值

目的 探讨256层CT血管成像(CTA)对冠状动脉瘘(CAF)的诊断价值.方法 回顾性分析CAF 18例,对原始图像进行多平面重组(MPR)、曲面重组(CPR)、最大密度投影(MIP)及容积重建(VR)等后处理.结果 18例CAF中冠状动脉分支血管瘘入肺动脉5例;瘘入冠状静脉窦5例;瘘入右心房3例;瘘入左心房3例;瘘入右心室2例.5例冠状动脉 -肺动脉瘘可观察到畸形血管向肺动脉内供血,肺动脉主干内均可见对比剂呈"喷射"或"浓染"征.主肺动脉旁形成丛状或蔓藤状血管网2例.供血动脉区动脉瘤形成3例.结论 256层冠状动脉CTA能准确显示CAF变异血管的解剖细节及血流动力学改变情况,运用多种重建技术能够直观地显示CAF的畸形血管形态.     

螺旋CT在喉部病变的临床应用

目的探讨螺旋CT在喉部病变中临床应用价值.方法29例喉部病变进行螺旋CT扫描、多平面三维重建及CT仿真内窥镜成像,并与纤维喉镜及病理对照研究.结果螺旋CT轴位图像薄层重建、多平面三维重建、CT仿真内窥镜所见病变的形态学改变、与周围组织的关系及气道狭窄情况与纤维喉镜及术后病理相符合.结论螺旋CT薄层重建分辨率明显提高,图像更加清晰.对观察病变的部位、与周围组织关系及气道狭窄,多平面三维重建是对轴位图像的很好补充.CT仿真内窥镜可分别从头端或足端入内观察喉腔结构,是纤维喉镜的辅助手段.     

扫描方式对64层螺旋CT头颅CTA图像质量和辐射剂量影响的研究

目的：探讨64层螺旋CT扫描方式对头颅CTA图像质量和辐射剂量的影响。方法：采用GE Lightspeed VCT对100例需要行头颅CTA检查的患者进行对比研究,50例行螺旋扫描,另50例行轴层扫描。两组数据经过VR、MIP、去骨VR和多平面重组等方法后处理,然后由3组医师通过5分评价法对CTA图像质量进行主观评价,取其均值纳入统计学分析;记录每组扫描的容积剂量指数（CTDIvol）和剂量长度乘积（DLP）。对两组数据进行两独立样本t检验。结果：轴向扫描图像质量评分是（4．66±0．42）分、螺旋扫描CTA的成像质量评分（4．67±0．38）分;两组数据差异无统计学意义（P〉0．05）。轴向扫描、螺旋扫描的CTDIvol分别是45．71和54．18mGy;DLP分别是731．43和954．68mGy·cm。两组间差异有统计学意义（P〈0．05）,轴层扫描方式辐射剂量更低。结论：64层CT头颅CTA轴扫可以显著降低辐射剂量而不降低图像质量,在临床运用中值得关注。     

Diagnostik der akuten Lungenembolie mittels Spiral-CT und 3D-Rekonstruktion Entwicklung eines Tiermodells und technischer Probekörper im Ex-vivo-Experiment

PURPOSE: To develop a model for simulation the CT morphologic situation of acute pulmonary embolism, to evaluate the accuracy of spiral CT and 3D reconstruction in the detection of artificial emboli and to investigate the influence of the orientation of emboli depending on z-axis orientation. MATERIALS AND METHODS: Standardized artificial emboli made of wax and of defined size and shape were positioned into the pulmonary arteries of porcine lungs. Castings of the embolized pulmonary arterial trees were made by injection of a special opaque resin. After performance of spiral CT the data sets of the emboli and the pulmonary arteries were post-processed. The 3D segmentations were compared with the anatomic preparation to evaluate the accuracy of spiral CT/3D reconstruction-technique. Technical specimens simulating CT-morphology of acute embolized vessels underwent spiral CT in six different positions with respect to the z-axis. The CT data were reconstructed using a standardized and a contrastadapted method with interactive correction. The 3D emboli were analysed under qualitative aspects, and measurements of their extent were done. RESULTS: In nearly 91%, there was complete agreement between CT and the corresponding findings at the anatomical preparation. Measurements of the 3D reconstructed technical specimens showed discrepancies of shape and size in dependence of the size of the original preparation, orientation and reconstruction technique. Overestimation up to 4 mm and underestimation to 2.2 mm were observed. Measurements of preparations with heights from 14 to 26 mm showed variances of +/- 1.5 mm (approximately 6-11%). CONCLUSION: The presented models are suitable to simulate CT morphology of acute pulmonary embolism under ex-vivo conditions. Accuracy in the detection of artificial emboli using spiral CT/3D reconstruction is affected by localization, size and orientation of the emboli and the reconstruction technique.     

64层螺旋CT肺部高分辨率图像质量影响因素的体模研究

目的 分析影响肺部高分辨率CT(HRCT)图像质量的主要因素,探讨常规肺部容积扫描条件下获得HRCT图像质量的可行性.方法 应用64层CT对Catphan500模具进行连续、重复扫描.对比内容:扫描方式(轴面扫描、螺旋扫描)、kV值(140、120 kV)、层厚(1.25、5.00 mm,其中5.00 mm图像折分为1.25 mm)、重建算法(骨+算法、肺算法).评价内容:空间分辨率、密度分辨率、图像噪声.统计分析采用析因设计方差分析.结果 扫描方式在密度分辨率(轴面扫描:11.44±0.04;螺旋扫描:12.61±0.04)、图像噪声(轴面扫描:5.89±0.05;螺旋扫描:6.92±0.05)上差异均有统计学意义(F值分别为539.61、179.02,P值均＜0.01),轴面扫描密度分辨率高于螺旋扫描,图像噪声低于螺旋扫描;重建算法间在空间分辨率(骨+:9.90±0.09;肺:7.40±0.09)、密度分辨率(骨+:11.39±0.04;肺:12.65±0.04)、图像噪声(骨+:6.55±0.05;肺:6.28±0.05)上差异均具有统计学意义(F值分别为375.00、627.95、13.97,P值均＜0.05),骨+算法优于肺算法但噪声值略高.结论 容积扫描在密度分辨率、图像噪声控制上较传统HRCT稍差,但在空间分辨率上容积扫描骨+算法重建与HRCT图像质量相当,用于显示肺内细节时容积高分辨率CT可代替常规HRCT.