Multiplanar and three-dimensional reconstruction techniques in CT: impact on chest diseases

The purpose of this review is to capture the current state-of-the art of the technical aspects of multiplanar and three-dimensional (3D) images and their thoracic applications. Planimetric and volumetric analysis resulting from volumetric data acquisitions obviates the limitations of segmented transverse images. Among the 3D reconstruction techniques currently available, the most recently introduced technique, i. e., volume rendering, has to be evaluated in comparison with 3D shaded surface display and maximum or minimum intensity projection. Slabs are useful in detecting and localizing micronodular or microtubular patterns and in analyzing mild forms of uneven attenuation of the lungs. Three-dimensional angiography is helpful in the pretherapeutic evaluation and posttreatment follow-up of pulmonary arteriovenous malformations, in the comprehension of the postoperative reorientation of the pulmonary vessels, in the surgical planning of pulmonary tumors, and in the diagnosis of marginated thrombi. The systemic supply to the lung and superior vena cava syndromes are also relevant to these techniques. In acquired or congenital tracheobronchial diseases including stenosis, extraluminal air and complex airway anatomy, multiplanar and 3D reformations have a complementary role to both transaxial images and endoscopy. New developments are also expected in various topics such as 3D conformal radiation therapy, planning of intraluminal bronchoscopic therapy, virtual endoscopy, and functional imaging of the bronchial tree. Miscellaneous clinical applications are promising in the analysis of diaphragmatic morphology and pathophysiology, in the volumetric quantification of the lung parenchyma, and in the vascular components of the thoracic outlet syndromes. Received 5 September 1997; Accepted 8 September 1997     

Spiral CT angiography and surgical correlations in the evaluation of intracranial aneurysms

We investigated the accuracy of spiral computed tomography angiography (CTA) in the detection and study of intracranial aneurysms by comparing CTA with selective angiograms and surgical findings. Twenty-six patients (9 men and 17 women; mean age 53.1 ± 1.8 years) with suspected intracranial aneurysms were submitted to CTA (1- to 2-mm slices, pitch 1:1, 24 s, RI = 1) after a conventional CT examination showing subarachnoid hemorrhage (SAH) in 19 cases and during neuroradiological investigations performed for other reasons in 7 cases. One hundred twenty to 150 ml iodate contrast agent (0.3–0.4 gI/ml) were injected intravenously at 5 ml/s rate and with 12- to 25-s delay calculated with a preliminary test bolus. Three-dimensional shaded surface display (3D SSD) and maximum intensity projection (MIP) reconstructions were obtained from axial images. Then, within 48 h, all patients were submitted to digital subtraction angiography (DSA), with separate assessment of CTA and DSA findings. Twenty-two aneurysms shown by CTA were confirmed at DSA and surgery (true positives), whereas the vascular lesion was not confirmed at DSA in 2 cases (false positives). The presence of intracranial aneurysms was excluded at both CTA and subsequent DSA in 7 cases (true negatives) and there were no false negatives; sensitivity was 100 %, specificity 77.8 %, and diagnostic accuracy 93.5 %. Computed tomography angiography aneurysm location was confirmed at surgery in all cases, with very high accuracy in assessing the presence of an aneurysm neck (100 %). Computed tomography angiography accurately depicted the aneurysm shape in 20 of 22 cases, but failed to depict its multilobed nature in 2 cases. The mean aneurysm diameter calculated at CTA was 0.99 ± 0.12 cm vs 1.09 ± 0.11 cm at surgery (p < 0.01). The present results suggest that the high sensitivity of CTA, if confirmed by further studies, might help in avoiding having to resort to arteriography after negative CTA in SAH patients. Received 15 July 1997; Revision received 30 September 1997; Accepted 5 November 1997     

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     

Bolus timing in high-pitch CT angiography of the aorta

Objective

To investigate the bolus geometry in high-pitch CT angiography (CTA) of the aorta without ECG synchronisation in comparison to single-source CT.

Methods

Overall 160 consecutive patients underwent CTA either in conventional single-source mode with a pitch of 1.2 (group 1), or in dual-source mode with a pitch of 3.0 (groups 2, 3 and 4) using different contrast media timings with bolus triggering at 140 HU (5 s, group 1; 10 s, group 2; 12 s, group 3; 14 s, group 4). Contrast material, saline flush, flow rate and kV/mAs settings were kept equal for optimum comparability. Aortic attenuation was measured along the z-axis of the patient at different anatomic landmarks and subjective image quality was compared.

Results

The most homogeneous enhancement of the aorta was reached with a delay of 10 s after reaching the trigger threshold. The imaging length was not significantly different, but the examination time was significantly (p < 0.001) shorter in the high-pitch group (7.7 s vs. 1.7 s for group 1 vs. 2, 3 and 4).

Conclusion

In high-pitch CT angiography using a start delay of 10 s after a trigger threshold of 140 HU in the descending aorta is reached, a homogenous contrast along the z-axis is accomplished.     

小儿头颅螺旋CT血管造影三维重建技术的探讨

目的 对小儿头颅螺旋ＣＴ血管造影（ＳＣＴＡ）三维重建技术及其临床应用进行探讨。材料与方法 ３４例均因神经系统症状就诊,其中男２１例,女１３例。年龄１～１３岁。采用ＧＥ Ｓｙｎｅｒｇｙ进行ＳＣＴＡ。层厚１～３ｍｍ,螺距１～１．５。三维重建图像处理均采用最大强度投照法（ＭＩＰ）和表面遮盖显示法（ＳＳＤ）,并采取多个角度观察、分析。结果 ３４例ＣＴ血管造影（ＣＴＡ）均能显示颅底动脉环的解剖关系,大脑前、     

多层螺旋CT血管成像对椎基底动脉供血不足病因诊断的应用

目的探讨多层螺旋CT血管成像（MSCTA）对椎基底动脉供血不足（VBI）病因诊断的价值。资料与方法对12例无症状者及42例临床拟诊VBI患者行椎动脉MSCTA检查,原始数据于图形工作站行三维图像处理。结果12例无症状患者中椎动脉发育异常1例,迂曲1例,其他椎动脉及基底动脉无异常。42例拟诊VBI患者,先天发育变异13例,迂曲5例,盘绕3例,钩椎关节增生压迫（Ⅱ＋Ⅲ度）20例,椎体横行移位致血管变形1例,粥样硬化斑块20例,局限性狭窄2例。结论MSCTA可清晰显示椎基底动脉全程及其与颈椎的解剖关系,直观显示发育变异,对椎动脉流人孔的显示具有明显优势,可作为VBI的常规影像检查方法。     

CT appearance of complications related to thoracic endovascular aortic repair (TEVAR): a pictorial essay

Thoracic endovascular aortic repair (TEVAR) is a recognized treatment for various diseases involving the thoracic aorta. Patients treated with TEVAR require lifelong surveillance for potential complications, with CT being highly utilized in most centres. Endoleak is the most common complication and can be detected using CT. However, other complications such as stent strut perforations and end organ ischemia can also be detected on CT. The purpose of this pictorial essay is to illustrate the CT appearance of post-TEVAR complications encountered in our institution and to highlight their significance.     

Automatic 3D vascular tree construction in CT angiography

This study presents an automatic method for 3D reconstruction of vascular trees using computed-tomography angiographic (CTA) images. The program starts with the CTA slices, performs a sequential procedure of 3D image formation, preprocessing, segmentation, thinning, skeleton pruning and tree construction. It ends with vascular trees along with quantitative data about the trees such as values of diameter, length and bifurcation angles. All the involved algorithms are presented with the emphasis given to the skeleton pruning and tree construction algorithms. The skeletons obtained using a 3D thinning algorithm may contain cycles, spurs, isolated sticks, and non-unit-width parts, which hinder tree construction. As a solution to this problem, a skeleton pruning and tree construction algorithm is proposed. At each stage of the automatic procedure, 3D rendering is provided for visual inspection of the computed results. In the final output, the constructed vascular trees are visualized by rendering the 3D trees and the 3D binary image together in a transparent display mode. The program is carried out in a fully automatic fashion, with a few default settings. Occasionally, user intervention is needed at the 3D segmentation stage to impose an appropriate threshold when the automatic 3D segmentation is obviously sub-optimal for vessel delineation. Experimental demonstrations on both coronary artery phantom and a cast of coronary artery tree of a swine animal model are provided.     

Three-dimensional contrast-enhanced magnetic resonance angiography of the thoracic vasculature

Magnetic resonance angiography (MRA) has become a useful non-invasive imaging technique for the assessment of vascular disease. Due to limitations such as respiratory motion artefacts, saturations problems, and long acquisition times, applications of MRA in the thorax have largely been restricted to imaging of the aorta. The recent introduction of breath-hold three-dimensional (3D) contrast-enhanced MRA promises not only to enhance conventional MR protocols for aortic imaging, but to extend the clinical indications of MRI to diseases affecting other vascular structures of the thorax, most notably the pulmonary arteries. This article describes the technical aspects of contrast-enhanced 3D MRA and reviews existing and potential future clinical applications. Received 17 September 1996; Revision received 6 November 1996; Accepted 8 November 1996     

Right middle lobe torsion: evaluation with CT angiography

A case of right middle lobe torsion occurring after a right upper lobectomy is described. HR-CT angiography was successful in identifying the obstructed right middle lobe bronchus and the avascular nature of the infected and displaced right middle lobe. This detailed information, obtainable from present day multislice HR-CT scanners with the right CT protocols, seems to diminish the need for further confirmation by other methods.     

Helical CT of the urinary organs

Despite of the diagnostic potential of conventional CT (CCT), limitations being inherent in this technology reduce its diagnostic confidence and limit clinical CT applications as 3D imaging. Helical CT (HCT) has far overcome the limitations of CCT and has become the standard CT technology. After a short overview on the technique of HCT and its advantages over CCT, the impact of HCT on the detection of disorders of the urinary organs is discussed. Due to the high quality of 3D reconstructions, vessels are visualized free of artefacts resulting in a dramatic improvement and acceptance of CT angiography, which has become a clinically important examination in the evaluation of obstructive renal artery disease. Fast HCT provides a precise assessment of the three phases of the nephrogram and it is a prerequisite for an improved depiction of abnormal vascular perfusion and impaired tubule transit of contrast material. Helical CT enables an improved characterization of cystic mass lesions reducing the diagnosis of indeterminate masses and thus facilitating a better therapeutic management. The diagnosis of renal cell carcinomas (RCC) has improved due to an increased sensitivity in detecting small RCCs, and an increased specificity in the diagnosis of neoplastic lesions. Improved staging of RCCs is the result of accurate assessment of venous tumour extension. When planning nephron-sparing surgery 3D display of the renal tumour helps to determine the resectability of the mass depicting its relation to major renal vessels and the renal collecting system. In the evaluation of renal trauma HCT provides shorter scanning time and thus fewer artefacts in the examination of traumatized patients who cannot cooperate adequately. Three-dimensional postprocessing modalities allow the assessment of the renal vascular pedicel by CT angiography and improve the demonstration of complex lacerations of the renal parenchyma. In the evaluation of the upper urinary tract unenhanced HCT has become the imaging method of choice in the diagnosis and differential diagnosis of acute flank pain since it is highly sensitive and specific in detecting calculus disease. Unenhanced HCT may furthermore demonstrate causes of flank pain unrelated to urolithiasis. Gapless volume scanning and improved resolution in the z-axis during the excretory phase enables improved visualization of the renal collecting systems and ureters, resulting in a better demonstration of intraluminal and extraluminal pathology.     

Three-dimensional cholangio-spiral CT demonstration of a post-traumatic bile leak in a child

Bilioma is a rare complication of traumatic liver injury, and the precise site of bile leak is often difficult to demonstrate with a non-invasive technique. We report a case of post-traumatic bile leak in a 15-year-old girl in whom spiral CT after intravenous cholangiography allowed excellent preoperative demonstration of the extent of the liver rupture and an exact location of the bile leak. We think that spiral-CT cholangiography could be an accurate, non-invasive technique to investigate the biliary system in cases of paediatric liver trauma. Received: 2 December 1997; Revision received: 3 April 1998; Accepted: 6 May 1998     

Assessment of vascular invasion in pancreatic head cancer with multislice spiral CT: value of multiplanar reconstructions

The use of multiplanar reconstructions (MPRs) generated from multislice spiral CT (MSCT) data sets in the preoperative assessment of vascular invasion in pancreatic cancer was evaluated. Forty patients underwent biphasic high-resolution MSCT prior to surgery for pancreatic head cancer. Image reconstruction included thin-slice axial, sagittal and coronal MPRs as well as an MPR perpendicular to the course of a major peripancreatic vessel in proximity to the tumor. CT criteria for vascular invasion were: (1) circumferential involvement >180° and (2) vessel narrowing. Imaging findings of 52 vessels were correlated with surgical and histopathological reports. Regarding the CT criterion circumferential involvement, vascular invasion was demonstrated on axial MPRs with a sensitivity and specificity of 58 and 97%. For the assessment with coronal and sagittal MPRs sensitivity was only 47%. Vascular invasion was recognized best on perpendicular MPRs with a sensitivity, specificity and accuracy of 74, 97 and 88%, respectively. Vessel narrowing was a less reliable CT criterion for vascular invasion, mainly due to the lower specificity of 91% obtained with each available MPR. Thin-slice MPRs oriented perpendicularly to a possibly invaded vessel exactly depict the grade of circumferential involvement and thus have the capability to improve the assessment of vascular invasion in pancreatic cancer.     

CT angiography of lower extremity vascular bypass grafts

Over the past several years computed tomography (CT) technology has advanced to such a degree that CT angiography (CTA) has become the study of choice at our institution for imaging lower extremity vascular bypass grafts. CTA quickly provides anatomic information about the state of the graft and identifies virtually all forms of bypass graft failure and related complications. Furthermore, detailed vascular anatomy is seen beyond the graft and affords sufficient anatomic detail for surgical revision without the need for other angiographic studies. Although catheter angiography, duplex-ultrasound, magnetic resonance angiography, and nuclear medicine studies all continue to play some role in the evaluation of vascular grafts, they are more often used as problem solving modalities when CTA findings are equivocal. Whereas it was once essential to catheterize directly through a failing bypass graft or pass catheters into the graft from a distant arterial puncture to obtain an angiogram of a failing bypass graft, CTA produces arteriograms with only intravenous contrast administration, a brief visit to the CT scanner, and return to daily activities without catheterization, discomfort, or risk to the bypass conduit.     

Multiphase contrast-enhanced CT of the liver with a multislice CT scanner

Our objective was to assess the effects of the injection rate of contrast material and of a 5% dextrose flush on enhancement in multiphase hepatic CT using a multislice CT scanner. Most patients had chronic hepatitis and/or liver cirrhosis. One hundred eighty examinations, in which two sequential acquisitions were performed during a single breath-hold followed by third- and fourth-pass acquisitions, were randomized into four protocols: contrast injection at 0.1 ml/kg body weight s^–1 over 21 s without and with a 30-ml flush in groups 1 and 2, respectively, and contrast injection at 0.07 ml/kg body weight s^–1 over 30 s without and with a flush in groups 3 and 4, respectively. Contrast enhancement in each acquisition was measured in the aorta, portal vein, and liver. The visualization of hepatic arterial branches was scored by visual assessment. The highest aortic enhancement was observed in the first-pass acquisition in all groups. At the higher injection rate (groups 1 and 2), aortic enhancement in the first-pass acquisition was significantly more intense, whereas portal venous and hepatic enhancement was significantly less intense. The use of a flush considerably improved aortic enhancement at the beginning of the second-pass acquisition. In the visual assessment of hepatic arterial branches, the protocols with the higher injection rate received significantly higher grades. Multislice CT permits the entire liver to be imaged during an almost exclusively arterial phase by shortening the injection duration for a given volume of contrast material. Electronic Publication     

分离团注技术在CTU检查中的优势

目的探讨在CTU检查中利用分离团注技术提高全尿路的显示情况,即同时显示双侧肾盂肾盏,双侧输尿管及膀胱。方法泌尿系统螺旋CT扫描的病例60例,30例行分离团注技术,30例单次团注技术,扫描包括常规平扫、皮质期、髓质期、延迟期,延迟期进行三维重建显示全尿路,分析比较两组成像质量。结果①单次团注组肾盂输尿管全段及膀胱显示优19例,显示良好10例,显示一般1例。分离团注组肾盂输尿管全段及膀胱显示优良22例,显示良好8例;②单次团注输尿管扩张:左侧起始段46.1,中下段45.3,右侧起始段55.1,中下段37.4。右侧起始段55.1,中下段37.4。分离团注输尿管扩张:左侧起始段55.3,中下段59.4。右侧起始段63,中下段46.7;③输尿管内中心密度:单次团注P:0.8072,分离团注P:0.8854。结论应用分离团注技术进行CTU扫描,使第一次对比剂注射剂量相对减少,在降低患者对比剂反应的同时,又可获得优质的可用于诊断的清晰尿路全程影像。     

Precision and accuracy in CT attenuation measurement of vascular wall using region-of-interest supported by differentiation curve

Objectives

To evaluate the precision and accuracy in CT attenuation measurement of vascular wall using region-of-interest (ROI) supported by differentiation curves.

Study design

We used vascular models (actual attenuation value of the wall: 87 HU) with wall thicknesses of 1.5, 1.0, or 0.5 mm, filled with contrast material of 250, 348, or 436 HU. The nine vascular models were scanned with a 64-detector CT. The wall attenuation values were measured using three sizes (diameter: 0.5, 1.0, and 1.5 mm) of ROIs without differentiation curves. Sixteen measurements were repeated for each vascular model by each of two operators. Measurements supported by differentiation curves were also performed. We used analyses of variance with repeated measures for the measured attenuations for each size of the ROI.

Results

Without differentiation curves, there were significant differences in the attenuation values of the wall among the three densities of contrast material, and the attenuation values tended to be overestimated more as the contrast material density increased. Operator dependencies were also found in measurements for 0.5- and 1.5-mm thickness models. With differentiation curves, measurements were not possible for 0.5- and 1.0-mm thickness models. Using differentiation curves for 1.5-mm thickness models with a ROI of 1.0- or 1.5-mm diameter, the wall attenuations were not affected by the contrast material densities and were operator independent, measuring between 75 and 103 HU.

Conclusions

The use of differentiation curves can improve the precision and accuracy in wall attenuation measurement using a ROI technique, while measurements for walls of ≤1.0 mm thickness are difficult.     

Ultrasound in vascular pathologies

The choice of the optimal ultrasonic frequency for vascular studies is determined by the required resolution and penetration. Anatomical real-time two-dimensional imaging and blood flow studies provide complementary information. Intravascular scanning allows high-frequency ultrasound to be used, with correspondingly good spatial resolution. Contrast resolution is degraded by beam side lobes and the limited dynamic range of the ultrasonic pulse. The physics of ultrasonic scattering by blood, pulsed Doppler and duplex scanning and colour flow imaging performances determines the limits of clinical applications. Contrast agents enhance the echogenicity of blood, improving sensitivity and, through second harmonic detection, suppressing solid tissue echoes. Three-dimensional display, with segmentation by the presence of the flow signal, facilitates spatial perception. Clinical applications in vascular pathologies are summarised. Received 29 January 1998: Accepted 11 February 1998     

Follow-up study on in-stent thrombosis after carotid stenting using multidetector CT angiography

Introduction  The purpose of the present study was to evaluate the role of multidetector three-dimensional computed tomography angiography (3D CTA) for evaluating both the residual arterial lumen and the sequential change in the intraluminal diameter and thrombus formation following carotid artery stenting (CAS). Materials and methods  Twenty consecutive patients consisting of 23 successfully stented carotid arteries were examined by 3D CTA with volume-rendering at 2, 4, 8, 12 weeks and 6, 12 months of follow-up. Results  The eccentric in-stent hypodense area could be detected in ten of 23 (43.5%) carotid arteries at 2 weeks of follow-up, and they then gradually declined until they almost disappeared at 12 weeks. Eccentric in-stent hypodense areas in the acute and subacute phase (up to 12 weeks after CAS) were found in nine out of 16 carotid arteries with longer stents (3 or 4 cm in size) deployed across the carotid bifurcation, whereas no eccentric in-stent hypodense area could be observed in the patients with a short stent (2 cm) deployed only to the internal carotid artery. Seven of the ten observed eccentric hypodense areas presented on the dorsal surface at the carotid bifurcation level. Conclusion  Carotid 3D CTA for evaluating residual lumen and in-stent thrombus formation after CAS is considered to be a useful diagnostic method. To avoid stent occlusion, both the acute and subacute phases following CAS (up to 12 weeks) call for the administration of appropriate anti-platelet therapy and careful observations of the patients.     

Non-invasive imaging of abdominal vascular pathologies

With the advent of ultrasound (US), Doppler and color-flow Doppler imaging, computed tomography (CT), and magnetic resonance angiography (MRA) the ability for non-invasive studies of the abdominal vasculature has been enhanced considerably. In this paper an overview on various abdominal vascular pathologies is presented. Because of the dramatic improvements in image quality, special emphasis is given on the potential role of breathhold contrast-enhanced three-dimensional (3D) MRA which appears to be a versatile non-invasive alternative to conventional angiography. Received 25 November 1997; Accepted 22 December 1997