Motion artifacts of the aorta simulating aortic dissection on spiral CT

Quality control of postoperative radiotherapy for non-small cell lung cancer: A study of mediastinal shift

PURPOSE

This study aimed to assess the shifting patterns of the mediastinum, including the target volume and the isocenter point during the postoperative radiotherapy (PORT) process of non-small cell lung cancer (NSCLC), and to observe the occurrence of radiation injury. Additionally, we investigated the significance of mid-term assessment during the implementation of the PORT process.

MATERIAL AND METHODS

We established coordinate axes based on bone anatomy and measured the mediastinum's three-dimensional direction and the shift of the isocenter point's shift in the PORT process. Statistical analysis was performed using Wilcoxon, Kruskal-Wallis, and the Chi-square test. P<0.05 was considered statistically significant.

RESULTS

In this study, the analysis of patients revealed that the shift of anterior and posterior mediastinum (X), left and right mediastinum (Y), upper and lower mediastinum (Z), anterior and posterior isocenter point (Xi), and the left and right isocenter points (Yi) in the PORT process were 0.04-0.53, 0.00-0.84, 0.00-1.27, 0.01-0.86, and 0.00-0.66cm, respectively. The shift distance of the mediastinum was Z>Y>X, and the shift distance of the isocenter point was Xi>Yi. According to the ROC curve, the cut-off values were 0.263, 0.352, 0.405, 0.238, and 0.258, respectively, which were more significant than the cut-off values in 25 cases (25%), 30 cases (30%), 30 cases (30%), 17 cases (17%), and 15 cases (15%). In addition, there was a significant difference in the shift of the mediastinum and the isocenter point (all P=0.00). Kruskal-Wallis test showed no statistically significant difference between mediastinal shift and resection site in X, Y, and Z directions (P=0.355, P=0.239, P=0.256), surgical method (P=0.241, P=0.110, P=0.064). There was no significant difference in the incidence of RE and RP in PORT patients (P>0.05). No III-IV RP occurred. However, the incidence of ≥ grade III RE in the modified plan cases after M-S was significantly lower than in the original PORT patients, 0% and 7%, respectively (P=0.000).

CONCLUSION

In conclusion, this study provides evidence that mediastinal shift is a potential complication during the PORT process for patients with N2 stage or R1-2 resection following radical resection of NSCLC. This shift affects about 20-30% of patients, manifesting as actual radiation damage to normal tissue and reducing the local control rate. Therefore, mid-term repositioning of the PORT and revision of the target volume and radiation therapy plan can aid in maintaining QA and QC during the treatment of NSCLC patients and may result in improved patient outcomes.

A low threshold to ECG-gated repeat CTA reduces the risk of false-positive diagnosis of type A dissection in interhospital referrals: a case series study

Background

False-positive diagnosis of acute Stanford type A aortic dissection (AAD) on computed tomography angiography (CTA) is still an issue and may lead to substantial consequences. Given that electrocardiography (ECG)-gated CTA provides greater diagnostic safety, it may be assumed that interhospital referrals with a diagnosis of AAD based on non-ECG-gated pre-referral CTA carry an elevated risk of false-positive diagnosis.

Patients and methods

We reviewed a series of patients in whom a diagnosis of AAD based on non-ECG-gated pre-referral CTA was subsequently proven false by ECG-gated CTA. The artifacts that gave rise to the misdiagnosis, as well as the diagnostic pathways followed and the consequences of false-positive diagnosis were investigated.

Results

In 5 patients, ECG-gated repeat CTA revealed artifacts in the pre-referral scans that had led to false-positive diagnosis and referral for emergent surgery. In the first case, the patient proceeded to surgery. In 4 subsequent cases, ECG-gated CTA was ordered because a false-positive diagnosis was suspected. We found that ECG-gated CTA rather than echocardiography provided sufficient information to rule out AAD in each of these cases. Comparison between pre-referral non-ECG-gated scans and ECG-gated repeat CTA demonstrated the wide range of artifacts that may give rise to a diagnosis of AAD.

Conclusion

Patient condition permitting, the threshold to ECG-gated repeat CTA should be low when doubt arises with regard to a diagnosis of AAD based on non-ECG-gated CTA in interhospital referrals.

Computed Tomography Imaging Artifact Simulating Type A Aortic Dissection

Contrast-enhanced computed tomography (CT) is an effective tool for assessment of thoracic aortic disease in the modern era. Here, we describe a case of Type A aortic dissection incidentally detected by CT in a 63-year old man. Upon more precise imaging with electrocardiography (ECG)-gated CT, the dissection vanished, revealing it to be an aortic motion artifact. This report highlights the importance of motion artifacts mimicking a dissection flap. CT imaging gated with ECG can distinguish a dissection flap from an artifact.

Recommendations for accurate CT diagnosis of suspected acute aortic syndrome (AAS)--on behalf of the British Society of Cardiovascular Imaging (BSCI)/British Society of Cardiovascular CT (BSCCT)

Accurate and timely assessment of suspected acute aortic syndrome is crucial in this life-threatening condition. Imaging with CT plays a central role in the diagnosis to allow expedited management. Diagnosis can be made using locally available expertise with optimized scanning parameters, making full use of recent advances in CT technology. Each imaging centre must optimize their protocols to allow accurate diagnosis, to optimize radiation dose and in particular to reduce the risk of false-positive diagnosis that may simulate disease. This document outlines the principles for the acquisition of motion-free imaging of the aorta in this context.

ECG-gated Versus Non-ECG-gated High-pitch Dual-source CT for Whole Body CT Angiography (CTA)

RATIONALE AND OBJECTIVES

To investigate motion artifacts, image quality, and practical differences in electrocardiographic (ECG)-gated versus non-ECG-gated high-pitch dual-source computed tomography angiography (CTA) of the whole aorta.

MATERIALS AND METHODS

Two groups, each including 40 patients, underwent either ECG-gated or non-ECG-gated high-pitch dual-source CTA of the whole aorta. The aortic annulus, aortic valve, coronary ostia, and the presence of motion artifacts of the thoracic aorta as well as vascular contrast down to the femoral arteries were independently assessed by two readers. Additional objective parameters including image noise and signal-to-noise ratio were analyzed.

RESULTS

Subjective and objective scoring revealed no presence of motional artifacts regardless of whether the ECG-gated or the non-ECG-gated protocol was used (P > 0.1). Image acquisition parameters (examination length, examination duration, radiation dose) were comparable between the two groups without significant differences. The aortic annulus, aortic valve, and coronary ostia were reliably evaluable in all patients. Vascular contrast was rated excellent in both groups.

CONCLUSIONS

High-pitch dual-source CTA of the whole aorta is a robust and dose-efficient examination strategy for the evaluation of aortic pathologies whether or not ECG gating is used.

Multi-modality image-based computational analysis of haemodynamics in aortic dissection

Aortic dissection is a disease whereby an injury in the wall of the aorta leads to the creation of a true lumen and a false lumen separated by an intimal flap which may contain multiple communicating tears between the lumina. It has a high associated morbidity and mortality, but at present, the timing of surgical intervention for stable type B dissections remains an area of debate. Detailed knowledge of haemodynamics may yield greater insight into the long-term outcomes for dissection patients by providing a greater understanding of pressures, wall shear stress and velocities in and around the dissection. In this paper, we aim to gather further insight into the complex haemodynamics in aortic dissection using medical imaging and computational fluid dynamics modelling. Towards this end, several computer models of the aorta of a patient presenting with an acute Stanford type B dissection were created whereby morphometric parameters related to the dissection septum were altered, such as removal of the septum, and the variation of the number of connecting tears between the lumina. Patient-specific flow data acquired using 2D PC-MRI in the ascending aorta were used to set the inflow boundary condition. Coupled zero-dimensional (Windkessel) models representing the distal vasculature were used to define the outlet boundary conditions and tuned to match 2D PC-MRI flow data acquired in the descending aorta. Haemodynamics in the dissected aorta were compared to those in an equivalent ‘healthy aorta’, created by virtually removing the intimal flap (septum). Local regions of increased velocity, pressure, wall shear stress and alterations in flow distribution were noted, particularly in the narrow true lumen and around the primary entry tear. The computed flow patterns compared favourably with those obtained using 4D PC-MRI. A lumped-parameter heart model was subsequently used to show that in this case there was an estimated 14 % increase in left ventricular stroke work with the onset of dissection. Finally, the effect of secondary connecting tears (i.e. those excluding the primary entry and exit tears) was also studied, revealing significant haemodynamic changes when no secondary tears are included in the model, particularly in the true lumen where increases in flow over \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$+200\,\%$$\end{document}+200% and drops in peak pressure of 18 % were observed.

Imaging modalities for the early diagnosis of acute aortic syndrome

The term acute aortic syndrome (AAS) incorporates aortic dissection, intramural haematoma, and penetrating atherosclerotic ulcer. The common feature of these entities is disruption of the medial layer of the aortic wall. Owing to the life-threatening nature of these conditions, prompt and accurate diagnosis is of paramount importance--misdiagnosis can be fatal. The noninvasive imaging techniques that have a fundamental role in the diagnosis and management of patients with AAS include CT, MRI, transoesophageal echocardiography (TEE), and transthoracic echocardiography (TTE). CT is the most-commonly used imaging modality owing to its wide availability, accuracy, and large field of view. CT plus TTE is the best combination for diagnosing AAS and its complications, and allows important morphological and dynamic aspects of AAS to be assessed and appropriately managed. Ideally, TEE should be performed immediately before surgery or endovascular treatment, in the operating theatre and under general anaesthesia. In stable patients with an uncertain diagnosis of intramural haematoma despite high clinical suspicion, MRI is the technique of choice to make a definitive diagnosis. Imaging techniques have an important role in the primary diagnosis, treatment strategy, and risk stratification of patients with AAS.

The right sided great vessels by cardiac multidetector computed tomography: normative reference values among healthy adults free of cardiopulmonary disease, hypertension, and obesity

RATIONALE AND OBJECTIVES

We sought to derive normative reference values for the thoracic great vessels using multidetector computed tomography (MDCT) in a healthy normotensive non-obese population free of cardiovascular disease.

MATERIALS AND METHODS

Non-gated axial computed tomography (CT) of the chest has traditionally been used to evaluate normal great vessel anatomy for prognosis and management. However, non-gated axial chest CT cannot account for the obliquity, systolic expansion, and non-axial motion of the great vessels during the cardiac cycle and may misclassify patients as normal or abnormal for prognostic and management purposes. To date, normative reference values for double-oblique, short-axis great vessel diameters have not been established using current generation electrocardiogram (ECG)-gated 64-detector row MDCT. A total of 103 (43% women, age 51 +/- 14 years) consecutive normotensive, non-obese adults free of cardiopulmonary or great vessel structural disease, arrhythmias, or significant coronary artery disease were studied by MDCT. Individuals underwent examination for determination of end-diastolic (ED) pulmonary artery (PA) and superior vena cava (SVC) dimensions in double-oblique short axes for comparison with the ascending aorta and the right-sided cardiac chambers.

RESULTS

For right sided great vessels, the 5th to 95th interval was 1.89-3.03 cm for ED PA diameter and 1.08-4.42 cm(2) for SVC cross-sectional area. The pulmonary artery to ascending aortic (PA-to-Ao) ratio was 0.66-1.13. In multivariate analysis, the PA was significantly associated with weight, whereas the PA-to-Ao ratio was inversely associated with age. Axial PA measurements were significantly higher and PA-to-Ao measurements significantly lower than corresponding short axis measurements (P = .04 and P < .001, respectively).

CONCLUSIONS

This study establishes ECG-gated MDCT reference values for right-sided great vessel dimensions derived from a healthy population of individuals free of cardiovascular disease, hypertension, and obesity. The traditional axial PA-to-Ao discriminant value of 1 for pulmonary hypertension is a poor diagnostic tool because it encompasses normal patients and is negatively affected by age. Thoracic great vessels should be measured by CT in ECG-gated double-oblique short-axis for accurate quantitation. These data may serve as a reference to identify right-sided great vessel pathology in individuals being referred for ECG-gated MDCT imaging.

Diagnosis with ECG-gated MDCT of floating thrombus in aortic arch in a patient with type-A dissection

Multidetector computed tomography has been shown to be accurate in noninvasive assessment of chest vascular disease. The motion artifacts of the thoracic aorta and the supra-aortic vessels were significantly reduced in the electrocardiogram (ECG)-gated data acquisition. This positive effect of ECG synchronization is more pronounced in the region of the ascending aorta, aortic arch, and proximal descending aorta.

MDCT Angiography of Acute Chest Pain: Evaluation of ECG-Gated and Nongated Techniques

OBJECTIVE

The objective of our study was to compare MDCT angiography protocols used in patients with acute chest pain caused by vascular, nonvascular, and cardiac abnormalities.

SUBJECTS AND METHODS

In four groups of 20 patients with chest pain each, four MDCT protocols were used based on monitoring vascular attenuation: pulmonary embolism (150 H at pulmonary artery), aortic dissection (200 H at aortic arch), chest pain (200 H at pulmonary artery), and chest pain with ECG gating (150 H at pulmonary artery). Vascular enhancement was assessed by attenuation measurements taken from locations in the pulmonary artery (n = 3) and thoracic aorta (n = 4). The appearance of the coronary artery in regard to opacification and motion was assessed on a scale of 1 to 5 (best).

RESULTS

The mean pulmonary artery and aorta attenuation (372 H and 352 H, respectively) was significantly higher (p < 0.005, Student's t test) and the number of vessel attenuation points measuring less than 200 H (1/140) was significantly smaller (p < 0.001, chi-square test) in the chest pain compared with the dissection (318 H, 310 H; 16/140), gated chest pain (304 H, 286 H; 17/14), and pulmonary embolism (302 H, 220 H; 28/140) groups. The median coronary artery visualization score was 4; the proximal regions received a significantly (p < 0.005, Mann-Whitney test) higher grade compared with the middle and distal regions (medians, 5, 4, and 2, respectively). Artifacts were noted on the gated scans.

CONCLUSION

The chest pain protocol can be used to assess both the pulmonary arteries and the thoracic aorta, whereas the ECG-gating protocol appears to be a promising adjunct for a comprehensive single chest pain protocol.

Multi-detector row computed tomography: imaging in acute aortic syndrome

Acute aortic syndromes (AAS) encompass a spectrum of emergencies. These include those non-traumatic disease entities of the aorta namely, penetrating atherosclerotic ulcer, intramural haematoma, dissection and aneurysm rupture. The various types of AAS cannot be reliably differentiated on clinical grounds alone. Acute thoracic aortic injury is usually included in this group even though clinical presentation is different, i.e., in the context of trauma, the imaging features are very similar. Differentiation of AAS from acute coronary syndrome (ACS) is important, however, it must be remembered that ACS may occur as a result of AAS. Now electrocardiogram (ECG)-gating technology is widely available, ECG-gated multi-detector row computed tomography (MDCT) is a powerful clinical tool in the acute emergency setting, which enables rapid and specific diagnosis of aortic pathology. ECG-gated MDCT significantly reduces motion artefact, avoids potential pitfalls in diagnosis and often provides diagnostic information about the coronary arteries. It should be used as a first-line imaging technique. This article examines the role of MDCT imaging and cardiac gating in the assessment of AAS and discusses the differentiation of this spectrum of aortic diseases with reference to the key imaging findings as obtained by experience in our institution.

Incidental findings computed tomography of the thorax

Numerous findings incidental to the stated indication for obtaining a computed tomogram (CT) of the chest are encountered. While some findings are life threatening (eg, pulmonary embolism), others are clearly benign (pulmonary hamartoma, vertebral hemangioma). This article discusses management issues related to the detection of unexpected findings in different compartments of the thorax. In the future, more detailed outcome data will be available to better guide medical decision-making.

Transferring Diagnosis Versus Actual Diagnosis at a Center for Thoracic Aortic Disease

BACKGROUND

Lack of physician awareness of thoracic aortic disease has received increased media attention. As a referral center for thoracic aortic disease our institutional experience confirms discrepancies between the transferring diagnosis and the actual pathologic diagnosis. A retrospective review was undertaken to identify the incidence and sources for disparate diagnoses.

METHODS

Medical records from 100 consecutive patients transferred to The University of Florida--Shands Hospital between April 2002 and October 2003 were reviewed. To identify sources for error, the charts of 24 patients with diagnostic discrepancies were examined in detail with attention to outside radiologic reports, level of physician experience, and additional diagnostic testing required.

RESULTS

The transferring diagnosis of 24 patients was different from the final aortic pathologic disease. The most common discrepancies were misclassifications of dissections and aneurysms. Seven patients had either no leak or no dissection. Two patients had misleading "pulsation artifacts" on their computed tomographic scans. In half of the patients diagnostic differences were secondary to initial misinterpretation by the referring radiologist. Seventeen of 24 patients underwent additional diagnostic testing. Misdiagnoses were more common when the referring physician was not a surgeon (15 of 24). The diagnosis of 5 patients was confirmed only in the operating room.

CONCLUSIONS

A significant incidence of disparate diagnosis was identified between transferring facilities and our referral center. Discrepancies were secondary to initial radiographic misinterpretation and the complexity of thoracic aortic pathologic disease. Medical schools and continuing medical education programs should place increased emphasis on thoracic aortic disease in their curricula.

Effects of Heart Rate on Motion Artifacts of the Aorta on Non-ECG-Assisted 0.5-Sec Thoracic MDCT

OBJECTIVE

Our aim was to evaluate the effects of heart rate on aortic motion artifacts on 0.5-sec non-ECG-assisted thoracic MDCT.

MATERIALS AND METHODS

A total of 124 non-ECG-assisted thoracic MDCT scans with satisfactory simultaneous ECG data were reviewed. Scans were grouped according to patient heart rates (beats per minute [bpm]: group A, 46-55; B, 56-65; C, 66-75; D, 76-85; E, 86-95; and F > 95). The groups were compared regarding the presence, locations, and spatial distributions of pulsation artifact, number of slices affected, maximum amplitude of pulsation, continuity of artifact, and the presence of superior vena cava (SVC) pseudoflaps.

RESULTS

Of the 124 scans, 114 (91.9%) had aortic motion artifacts, with prevalence ranging from 85.3% (66-75 bpm) to 100% (65 bpm or less). Of the 114 motion artifacts, all affected the ascending aorta, 105 (92.1%) involved the left anterior and right posterior aspects of the aortic circumference, and 106 (93%) were associated with SVC pseudoflaps. Group B had significantly greater numbers of images with artifacts (p < 0.001-0.006), greater artifact amplitudes (p < 0.001-0.002), and a higher continuity trend for the artifacts (p = 0.003-0.194) than did the other five groups.

CONCLUSION

Aortic motion artifacts are frequently seen on thoracic MDCT, especially in patients with heart rates of 65 bpm or less. The presence of a SVC pseudoflap is helpful for distinguishing artifacts from dissection. If aortic disease is suspected, then measures to reduce motion artifact, such as ECG-gating, should be considered.

Electrocardiographic assistance in multidetector CT of thoracic disorders

ECG-synchronized multislice spiral CT (MSCT) allows a significant reduction of cardiac motion artefacts and as a result a virtually artefact-free display of intrathoracic structures. With their advantages in imaging geometry and continuous spiral image acquisition multislice CT scanners provide superior image quality and spatial resolution in these patients. Possible clinical applications for ECG assistance in MSCT include CT angiography of the coronary arteries, functional cardiac CT imaging and imaging of the cardiac valves, CT angiography of the aorta or pulmonary vascular tree as well as ECG-gated imaging of the lung parenchyma. Prospective ECG triggering and retrospectively ECG-gated image reconstruction comprise the technical corsage for reduction of pulsation artefacts in cardiac and other thoracic CT applications. In addition the development of time-optimised reconstruction algorithms for retrospective cardiac gating in 8- and 16 slice spiral CT scanners have enabled further improvements in temporal resolution. This overview describes the technique, its clinical indications and the merits of electrocardiographic assistance in MSCT of chest disorders.

Imaging of aortic dissection by helical computed tomography (CT)

Aortic dissection is the most frequent cause of aortic emergency, and its outcome is still frequently fatal. The management of this pathology has changed with the development of endovascular means. Nowadays, imaging modalities are helpful in management decision-making by providing information such as identification of entry tears along the aorta and involvement of the visceral branches of the abdominal aorta. Multi-slice CT scanning now appears to be the modality of choice for complete examination of the entire aorta. We review the parameters of image acquisition and contrast injection; appearances on CT of acute and chronic dissection are illustrated. Diagnostic pitfalls in CT imaging of acute dissection are discussed. Imaging of the post-surgical aorta and of chronic dissection is outlined. Intra-mural hematoma and penetrating aortic ulcer are subtypes of aortic dissection, and their appearances on CT scanning are also presented.

Thoracic involvement of type A aortic dissection and intramural hematoma: diagnostic accuracy--comparison of emergency helical CT and surgical findings

PURPOSE

To assess the accuracy of various findings at emergency helical computed tomography (CT) for the evaluation of thoracic involvement of type A aortic dissection (AD) and type A intramural hematoma (IMH) and to compare these findings with those at surgical confirmation.

MATERIALS AND METHODS

Fifty-seven patients with acute chest pain underwent emergency helical CT and subsequent surgery for type A AD or IMH. Patients in whom AD or IMH was detected in three segments of the thoracic aorta or those in whom there was a site of any entry tear, arch branch vessel involvement, pericardial effusion, or aortic arch anomaly were examined at helical CT. Sensitivity, specificity, and accuracy of helical CT, along with 95% CIs, were calculated by using surgical confirmation as the reference standard.

RESULTS

For the detection of AD or IMH of the thoracic aorta, the accuracy of helical CT was 100%. The sensitivity, specificity, and accuracy, respectively, were 82%, 100%, and 84% for an entry tear; 95%, 100%, and 98% for arch branch vessel involvement; and 83%, 100%, and 91% for pericardial effusion. These values were all 100% for aortic arch anomalies.

CONCLUSION

Emergency helical CT of the thorax depicts findings that are highly accurate in the evaluation of acute type A AD and IMH.

Thoracic aorta at multi-detector row CT: motion artifact with various reconstruction windows

The authors assessed motion artifact of the thoracic aorta in 25 patients who underwent multi-detector row computed tomography (CT) with retrospective electrocardiographic (ECG) gating. CT reconstructions centered at four phases of diastole were compared for five different levels of the thoracic aorta. A significant positive correlation was observed between heart rate and motion artifact (r = 0.72, P <.001). The optimal reconstruction phase varied between patients, and this was directly related to heart rate. For patients with a heart rate of 70 beats per minute, the reconstruction phase centered at 75% of the R-R interval had the significantly least motion artifact (P =.004). Conversely, the optimal reconstruction phase for patients with heart rates above 70 beats per minute was centered at 50% of the R-R interval (P =.09).

Refined computed tomography of the thoracic aorta: the impact of electrocardiographic assistance

There have been a number of advances in helical computed tomography (CT) in recent years, which have had a beneficial impact on the quality of imaging of the thoracic aorta. These advances include sub-second gantry rotation, multislice acquisition, and the use of electrocardiographic (ECG) assistance. We examine these techniques with emphasis on the principles behind ECG assistance and its use to reduce aortic motion artefact. We highlight examples of ECG-assisted multislice CT in a spectrum of pathologies of the thoracic aorta.

Role of computed tomography and magnetic resonance imaging in assessment of acute aortic syndromes

Acute aortic syndromes refer to the spectrum of aortic emergencies that include nontraumatic diseases of the aorta, such as aortic dissection, intramural hematoma, penetrating atherosclerotic ulcer, aortic aneurysm leak, as well as traumatic aortic transection. Patients presenting with nontraumatic acute aortic syndromes usually have a similar clinical profile; hence, clinical diagnosis is difficult. Computed tomography (CT) and magnetic resonance imaging (MRI) allow for specific diagnosis of the underlying condition. Traumatic rupture of the aorta is one of the most dreaded complications of blunt chest trauma; therefore, in patients with high-risk deceleration injuries, radiographic assessment of the aorta is crucial. Imaging methods should detect even subtle aortic wall disruption and should provide a mechanism for communicating the findings to the surgical team. Noninvasive, cross-sectional imaging techniques have proven efficacy in the diagnosis of aortic pathology and have largely replaced aortography. Both CT and MR imaging provide aortogram-like reconstruction of the original data sets, and in addition to assessing the aortic lumen, permit detailed evaluation of the aortic wall, as well as comprehensive assessment of thoracic and abdominal viscera. This article addresses the role of different imaging modalities in assessment of acute aortic syndromes, with focus on CT and MRI, and with discussion of the key imaging findings that allow distinction among the various aortic pathologies.

What margins are necessary for incorporating mediastinal nodal mobility into involved-field radiotherapy for lung cancer?

PURPOSE

The mobility of mediastinal nodes was studied on multiple CT scans of the thorax from patients with non-small-cell lung cancer.

PATIENTS AND METHODS

A total of 10 enlarged mediastinal nodes/masses were identified in 8 patients with non-small-cell lung cancer. Nodal locations were classified using the Naruke/ATS-LCSG system, and between 3 and 6 scans were available for each site. The CT data sets were coregistered, and the contoured nodes were automatically projected onto the initial planning CT scan. An encompassing nodal volume (ENV) of all contours of a particular node was manually contoured on all scans. Individual nodal volumes were expanded in three dimensions to establish additional margins required to encompass the ENV.

RESULTS

The mean volume of nodes studied ranged from 0.8 to 23.2 cc. The addition to individual nodes of a margin of 5 mm was found to result in a mean ENV coverage of >or=95% at all sites. For individual nodes at locations N4R, N5, and N6, however, the coverage ranged from 87.8% to 92.6%.

CONCLUSION

The addition of a margin of 5 mm to individual mediastinal nodes seems to be adequate to account for variations in both contouring and mobility.

Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multi-detector row CT

The authors compared prospective (n = 20) and retrospective (n = 20) electrocardiography (ECG)-assisted multi-detector row computed tomography (CT) with non-ECG-assisted multi-detector row CT (n = 20) of the thoracic aorta with regard to reduction of motion-related artifacts. Image quality was rated for transverse source and sagittal oblique images of the thoracic aorta, including the aortic valve. ECG-assisted multi-detector row CT compared with non-ECG-assisted multi-detector row CT showed a significant reduction in motion artifacts for the entire thoracic aorta.

Characterization of artifact simulating aortic dissection in computed tomography imaging

An artifact simulating aortic dissection has been seen in computed tomography (CT) and reported in numerous journals. The purpose of this study is to determine the origin. A phantom was constructed to simulate the motion of the ascending aorta during the cardiac cycle. Technique factors such as scan time, slice thickness, pitch, and reconstruction algorithms were examined for their effect on the simulated dissection appearance. Change in the angle of the simulated aorta with respect to the scanner axis was also studied. CT images displaying the simulated aortic dissection are obtained reproducibly. The amplitude of the artifact is more pronounced for increased scan time. The artifact amplitude is proportional to the displacement of the phantom. The simulated aortic dissection seems to be more pronounced when the scan time is comparable to the cycling time of aortic motion.

Volumetric quantification of coronary artery calcifications using dual-slice spiral CT scanner: improved reproducibility of measurements with 180 degrees linear interpolation algorithm

PURPOSE

The purpose of this work was to determine the reproducibility of coronary total calcium score (TCS) with dual-slice helical CT and compare three acquisition protocols.

METHOD

Fifty patients (59 +/- 10 years old) underwent dual-slice helical CT (collimation = 2 x 2.5 mm) and coronary angiography. Two successive scans were performed, resulting in three sets of images: pitch = 1, 360 degrees linear interpolation (LI) (A360); pitch = 1, 180 degrees LI (A180); and pitch = 1.5, 180 degrees LI (B180). TCS values, calculated using a volumetric method with a threshold of 90 HU, were compared, and the interscan variation was determined. Diagnostic performances were compared with receiver operating characteristic curves.

RESULTS

Protocol A360 provided significantly lower TCS than protocols A180 and B180 (p < 0.0001). No statistical difference was seen between A180 and B180, which provided the lowest interscan variation (40 +/- 58%). However, no significant clinical impact of the observed interscan variations was found.

CONCLUSION

Reproducibility of TCS with dual-slice helical CT is improved by the 180 LI algorithm. However, dual-slice helical CT is not sufficiently reproducible to allow serial quantification of TCS over time.

Imaging of aortic aneurysms and dissection: CT and MRI

There are numerous approaches to the diagnosis of aortic aneurysms and aortic dissection. Echocardiography, computed tomography (CT), and magnetic resonance imaging (MRI) have enthusiastic proponents promoting each technique, which to some extent obscures the real value of each technique. This review examines the role of these techniques in the diagnosis of aortic disease, with special reference to the most recent published literature and an emphasis on the use of CT and MRI. For most patients with chronic aortic disease, MRI is the most appropriate investigation. In acute situations, CT scanning is usually the most useful technique, with echocardiography added for those with ascending aortic disease or cardiac complications.

Dual-slice helical CT of the thoracic aorta

With the advent of helical CT, the capability of noninvasive imaging of the thoracic aorta has been enhanced considerably. In this article, we describe the potential of helical CT using dual-slice technology to evaluate thoracic aortic diseases such dissection, aneurysm, trauma, infection, inflammation, thromboembolic disease, and postoperative complications. Technical considerations for optimal CT imaging as well as limitations of helical CT are highlighted.