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Morphologic Assessment of Patent Ductus Arteriosus in Adults Using Retrospectively ECG-Gated Multidetector CT

¹ Department of Cardiology, South West Cardiothoracic Centre, Plymouth National Health Service Trust, Derriford, Plymouth PL6 8DH, United Kingdom.
² Department of Radiology, Plymouth National Health Service Trust, Plymouth PL6 8DH, United Kingdom.

Received October 4, 2002; accepted after revision March 12, 2003.

 
Address correspondence to G. J. Morgan-Hughes.

Supported in part by a grant from the Royal College of Radiologists.

Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
OBJECTIVE. Noninvasive imaging of a persistently patent ductus arteriosus in adults remains a challenge. Bearing in mind the excellent spatial resolution provided by multidetector CT (MDCT), we postulated that MDCT might be used to evaluate this anatomic defect. We sought to show that MDCT can depict in detail patent ductus arteriosus in adults and allow determination of the size of the duct, degree of calcification, and morphologic classification.

CONCLUSION. MDCT represents a novel method of noninvasively assessing patent ductus arteriosus in adults that provides detailed anatomic information. Comparison with invasive angiographic findings is needed to validate the technique of sizing of ducts using MDCT.

Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Clear diagnostic imaging of a suspected persistently patent ductus arteriosus in adult patients is difficult to achieve, and information provided by imaging, such as the size and morphology of the duct, is crucial to the planning of optimal treatment. Not all patients with patent ductus arteriosus are suitable candidates for transcatheter closure. Traditionally, the initial noninvasive diagnostic investigation is performed with Doppler echocardiography and MRI [1]. In children, the size and morphology of the patent ductus arteriosus can be predicted using Doppler echocardiography, but such assessment is not often possible in adults [2]. Although echocardiography and MRI are complementary techniques, the latter has additional value in revealing thoracic aortic anomalies and the anatomy of the proximal pulmonary arteries [3].

The initial descriptions of the reliable assessment of left-to-right shunting possible with MRI [4, 5] led to the use of contrast-enhanced MR angiography to noninvasively evaluate patent ductus arteriosus in adults. However, MRI has limitations as a method of assessing vascular calcification, and occasional contraindications to the use of the technique remain. Full assessment of patients with suspected patent ductus arteriosus is still performed with invasive angiography, often immediately before planned transcatheter closure.

MRI has become established as a tool in the assessment of congenital heart disease in adults despite the once-limited availability of MR scanners in certain countries, such as the United Kingdom [6]. In contrast, multidetector CT (MDCT) scanners are widely available. Clinical trials of noninvasive coronary angiography using retrospectively ECG-gated MDCT have shown that this modality can accurately depict the surface anatomy of the heart with three-dimensional (3D) reconstructions [7]. Acquired aortic abnormalities such as aneurysms and dissections have been diagnosed with 3D helical CT [8, 9]. More recently, the technique has been shown to clearly reveal the shape and spatial resolution of the heart and great arteries in neonates and infants with complex congenital heart disease [10]. In addition, ECG-gated MDCT provides accurate quantification of vascular calcium, and postprocessing techniques such as virtual angioscopy allow visualization of the interior of the lumen vessels [11]. We therefore postulated that MDCT could play a role in the noninvasive assessment of patent ductus arteriosus in adults.

The objective of our study was to show that MDCT can accurately reveal patent ductus arteriosus in adults, allowing determination of the size of the duct, extent of calcification, and morphologic type according to the angiographic classifications originally described by Krichenko et al. [12]. We aimed to assess the relative merits of two commonly used CT reconstruction techniques and evaluate the feasibility of virtual angioscopy (i.e., a fly-through) of the patent ductus arteriosus.

Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Patient Population
Between January 1, 2002, and July 1, 2002, six patients with the diagnosis of patent ductus arteriosus were identified and constituted our study population. All patients had previously undergone assessment for standard clinical indications. Our study protocol was approved by the local institutional review board, and all patients gave written informed consent before undergoing ECG-gated MDCT.

MDCT
According to the findings of a previous investigation [12], the mean (± SD) angiographic diameter of the narrowest portion of a patent ductus arteriosus can be as small as 3.2 (± 1.0) mm. Because this size is similar to that of a coronary artery, we relied on acquisition parameters adapted from standard protocols for noninvasive coronary angiography to provide optimal spatial resolution (0.6 x 0.6 x 1.2 mm) and a temporal resolution of less than 250 msec. Gating MDCT thoracic aorta studies to the cardiac cycle has been shown to produce significantly fewer motion artifacts than does the standard nongated acquisition protocol [13]. Therefore, we used retrospective ECG gating to acquire MDCT scans on an MX8000 scanner (Philips Medical Systems, Cleveland, OH) during a single breath-hold of 35 sec or less (effective slice thickness, 4 x 1.3 mm; table feed per rotation, 1.5 mm; rotation, 500 msec; 120 kV; and 300 mAs per slice). The field of view was adapted to the volume of the aortic arch and pulmonary trunk (range, 180-220 mm). Contrast enhancement was achieved with 150 mL of contrast medium (Ultravist 300 [iopromide], Schering, Berlin, Germany) injected at 4 mL/sec through an 18-gauge catheter into an antecubital vein. Scanning initiation was triggered by identification of a density of 150 H in the ascending aorta. Images were reconstructed from four diastolic data sets centered at 37.5%, 50%, 62.5%, and 75% of the R-R interval and were then transferred to a workstation (MX View, Philips Medical Systems) for processing.

Multiplanar reformations were used as the initial evaluation of MDCT reconstructions from each of the four data sets for each patient. The data set with the least aortic motion artifacts (judged by the method described by Roos et al. [13]) was then selected as representing the optimal reconstruction window setting. The selected images were displayed using three visualization techniques and were assessed by the consensus of two observers unaware of the details of the clinical investigations. Two of the techniques, multiplanar reformation and volume-rendered 3D reconstruction, are in standard clinical use (Figs. 1A, and 1B). These two techniques were evaluated for their value in determining the size of the patent ductus arteriosus, extent of calcification, and morphologic classification of the duct. Calcification was classified by subjective assessment as being absent to minimal, mild, moderate, or severe. The imaging data obtained from these two methods were compared with the imaging data from the earlier assessment performed for clinical indications. The third technique, virtual angioscopic reformation using Voyager software (Philips Medical Systems), is not in standard clinical use and is not equivalent to invasive angioscopy. However, Voyager is the standard software on the MX View workstation, and we used the software to generate 3D volumes of data so that we could assess the potential clinical use of a fly-through of the patent ductus arteriosus in all patients.

View larger version (99K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —72-year-old man with severely calcified patent ductus arteriosus who presented with New York Heart Association grade III dyspnea [14] and atrial fibrillation. Patient required aortic valve replacement for coexisting aortic stenosis. Because of severe calcification, patient underwent transcatheter duct closure as separate procedure before aortic valve surgery. Axial multiplanar reformation of retrospectively ECG-gated multidetector CT (MDCT) shows severely calcified duct (arrow) extending anteriorly from distal anterior aortic arch.

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —72-year-old man with severely calcified patent ductus arteriosus who presented with New York Heart Association grade III dyspnea [14] and atrial fibrillation. Patient required aortic valve replacement for coexisting aortic stenosis. Because of severe calcification, patient underwent transcatheter duct closure as separate procedure before aortic valve surgery. Volume-rendered three-dimensional MDCT reconstruction shows calcified duct.

Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
All patients had previously undergone Doppler echocardiography, and two patients had undergone MRI. Three patients subsequently underwent transcatheter closure of the duct, but only one of these patients had detailed invasive angiographic data available for later comparison with the MDCT scans. All MDCT scans were of diagnostic quality, despite the broad spectrum of demographic and clinical characteristics of the patients.

One patient had New York Heart Association grade III dyspnea [14], and two patients had rapid or irregular heartbeats. Five of the six patients were found to have a patent ductus arteriosus. The sixth patient was found on MDCT to have no evidence of communication between the aorta and pulmonary artery. The prior diagnosis of patent ductus arteriosus based on clinical and echocardiographic findings was categorically refuted, and this patient was excluded from further analysis. Sizing and morphologic classification of patent ductus arteriosus were completed for the five remaining patients using MDCT. Calcification was observed in three patients. No complications were encountered.

Image Data Reconstruction
Selection of the optimal reconstruction window settings and the subsequent evaluation of the MDCT scans using the three visualization techniques took approximately 1 hr. However, a considerable portion of the time was taken up by assessment of the images produced with virtual angioscopy, the one technique that we evaluated that is not in standard clinical use.

Multiplanar Reformation
Contrast material-to-soft tissue resolution was excellent in all patients. All five patients had ducts that extended anteriorly from the anterior border of the descending aorta to the superior aspect of the main pulmonary artery, adjacent to the left pulmonary artery bifurcation. Using multiplanar reformations of the true and oblique axial, sagittal, and coronal section data, we measured the absolute diameter of the narrowest, the widest, and the longest portions of the duct (Figs. 2A, 2B, and 2C). We obtained the mean of the values from the three planes for measuring the size of the duct (Table 1). Calcification of the patent ductus arteriosus and adjacent aorta was readily assessed using axial multiplanar reformations (Table 1). The effect of age on duct calcification was evident, with the younger patients having minimal or no calcification (Fig. 3) and the older patients having severe calcification (Fig. 1A).

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —72-year-old man with severely calcified patent ductus arteriosus. Narrowest portion of duct (arrow), at pulmonary insertion, is shown on multiplanar reformations of retrospectively ECG-gated multidetector CT scans obtained in coronal (A), sagittal (B), and axial (C) planes.

View larger version (95K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —72-year-old man with severely calcified patent ductus arteriosus. Narrowest portion of duct (arrow), at pulmonary insertion, is shown on multiplanar reformations of retrospectively ECG-gated multidetector CT scans obtained in coronal (A), sagittal (B), and axial (C) planes.

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —72-year-old man with severely calcified patent ductus arteriosus. Narrowest portion of duct (arrow), at pulmonary insertion, is shown on multiplanar reformations of retrospectively ECG-gated multidetector CT scans obtained in coronal (A), sagittal (B), and axial (C) planes.

View larger version (83K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3. —22-year-old man with patent ductus arteriosus (arrow) who was evaluated for heart murmur found by army medical personnel. Patient subsequently developed New York Heart Association grade I dyspnea [14]. On axial multiplanar reformation from retrospectively ECG-gated multidetector CT, no ductal calcification is seen. This finding is in marked contrast to severely calcified ducts seen in older patients (Fig. 1A).

Volume-Rendered 3D Reconstruction
For all five patients analyzed, volume-rendered 3D reconstructions provided clear visualization of the duct without significant motion artifact (Fig. 1B). The angiographic classification devised by Krichenko et al. [12] divides patent ductus arteriosus into groups A-E and subdivides the ducts in groups A and B according to the relationship of the pulmonary insertion of the duct with the trachea. Two volume-rendering methods may be used to visualize this relationship. In one of these methods, different 3D presets and slabs orientated in a sagittal plane are used to simulate the lateral angiographic view. Three-dimensional visualization of both the patent ductus arteriosus and the trachea may also be achieved by volume rendering two data volumes simultaneously. This latter technique is slightly more time-consuming than the former and requires a considerable amount of volume rendering but provides excellent results (Figs. 4A, and 4B). The morphologic classifications of the ducts are given in Table 1. Although severe calcification was obvious on 3D reconstructions (Fig. 1B), no judgment about ducts with lesser degrees of calcification could be made.

View larger version (112K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —72-year-old man with severely calcified patent ductus arteriosus that was morphologic classification type A1 [12]. Volume-rendered three-dimensional (3D) multidetector CT (MDCT) model of trachea was needed for morphologic classification.

View larger version (81K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —72-year-old man with severely calcified patent ductus arteriosus that was morphologic classification type A1 [12]. True sagittal volume-rendered 3D MDCT model in which both duct and trachea are displayed shows exact relationship of patent ductus arteriosus to trachea, which allowed morphologic classification.

Virtual Angioscopy
For virtual angioscopy, we loaded a previously saved 3D volume of tissue data into the virtual angioscopy software to combine with axial MDCT data for navigation (Fig. 5A). Initiating virtual angioscopy in the main pulmonary artery allowed us to identify the left and right pulmonary arteries and the patent ductus arteriosus (Figs. 5B and 5C). In all patients, we were able to fly-through the patent ductus arteriosus and continue navigating down into the descending aorta. Three of the five patients had clearly visible calcifications (Fig. 6) that corresponded to the calcification seen on the axial MDCT scans and 3D reconstructions. We were not able to take quantitative measurements using virtual angioscopy because the current computer analysis software does not give accurate vessel diameters.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —Technique of virtual angioscopy is applied to images of noncalcified patent ductus arteriosus in 50-year-old woman with New York Heart Association grade II dyspnea [14] and body mass index of 36. Three-dimensional model of aortic arch and pulmonary trunk generated from multidetector CT (MDCT) data is used for navigation. Duct is indicated by arrow.

View larger version (211K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —Technique of virtual angioscopy is applied to images of noncalcified patent ductus arteriosus in 50-year-old woman with New York Heart Association grade II dyspnea [14] and body mass index of 36. On MDCT virtual angioscopic image, view from distal main pulmonary artery is shown with left pulmonary artery (on right of image) and right pulmonary artery (on left of image) marked with bidirectional arrow. Patent ductus arteriosus (arrow) is visible in main pulmonary artery, adjacent to left pulmonary artery.

View larger version (192K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C. —Technique of virtual angioscopy is applied to images of noncalcified patent ductus arteriosus in 50-year-old woman with New York Heart Association grade II dyspnea [14] and body mass index of 36. MDCT virtual angioscopic image shows view through noncalcified duct, with pulmonary artery (PA) in foreground, duct (arrows) in center of image, and aorta (AO) visible.

View larger version (165K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6. —72-year-old woman who had severely calcified ductus arteriosus and underwent transcatheter duct closure. Note difference between this multidetector CT virtual angioscopic image of view through calcified duct and view through noncalcified duct seen in same type of image in Figure. 5C. Pulmonary artery (PA) is in foreground; duct, in center of image (arrows); and aorta, (AO) visible through duct.

Comparison with Traditional Imaging Data
Depiction of diastolic flow (or continuous flow) toward the main pulmonary artery from the region of the bifurcation of the pulmonary artery was regarded as echocardiographic evidence of patent ductus arteriosus. Echocardiography allowed accurate diagnosis in five of the six patients with patent ductus arteriosus, but it did not provide direct visualization of the patent ductus arteriosus in any of the patients (Figs. 7A, and 7B). No detailed information pertaining to size, calcification, or morphology of the duct was obtained with echocardiography, although approximate estimation of size was possible using shunt calculations. Contrast-enhanced MR angiography did provide direct visualization and allowed sizing of the duct in the two patients in whom it was performed. However, the 3D data did not allow morphologic classification, and no calcification assessment could be made.

View larger version (173K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A. —72-year-old man with patent ductus arteriosus. Transthoracic echocardiograms generated from parasternal short-axis projection obtained at level of aorta (AO) and main pulmonary artery (MPA) were helpful in determining correct diagnosis, but duct was not directly visualized on these or on any other echocardiograms. However, multidetector CT (Figs. 1A, and 1B) showed severe calcification of patent ductus arteriosus and allowed morphology to be classified as type A1 (Figs. 4A, and 4B). Pulmonary valve (PV) (arrow) is seen at top of image, and bifurcation of main pulmonary artery is seen at bottom.

View larger version (156K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B. —72-year-old man with patent ductus arteriosus. Transthoracic echocardiograms generated from parasternal short-axis projection obtained at level of aorta (AO) and main pulmonary artery (MPA) were helpful in determining correct diagnosis, but duct was not directly visualized on these or on any other echocardiograms. However, multidetector CT (Figs. 1A, and 1B) showed severe calcification of patent ductus arteriosus and allowed morphology to be classified as type A1 (Figs. 4A, and 4B). Diagnosis of patent ductus arteriosus was suggested by presence of diastolic flow originating from left of bifurcation of main pulmonary artery (arrow, left pulmonary artery is on right of image) and flowing up toward transducer.

In two patients, no intervention or invasive angiography has been performed as of this writing (one patient has refused further investigation, and the case of the other patient is under review). Two of the three patients who underwent transcatheter closure had only balloon sizing, and although invasive angiography was performed, detailed analysis of the duct was unfortunately not conducted for either patient. One patient underwent an angiographic assessment that provided full data on the size, calcification, and morphology of the duct. The corresponding absolute diameters at the narrowest and widest points and the length of the duct as measured on CT were 4.2, 8.2, and 11.2 mm, respectively, whereas on angiography these measurements were 4.0, 8.4, and 10.9 mm, respectively. Findings of angiography and MDCT were in agreement with respect to severe calcification and morphologic classification of A1, although the calcification was more obvious on MDCT. In the three patients who underwent intervention, the information provided by MDCT was available and found to be useful. One patient with coexisting aortic valve disease had been under consideration for surgical closure; the decision to close the duct percutaneously was made on the basis of the severe calcification seen on the MDCT scans.

Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Our study has shown that patent ductus arteriosus in adults can be clearly visualized using retrospectively ECG-gated MDCT. We used multiplanar reformation to measure the size of the patent ductus arteriosus and to assess the extent of calcification. Morphologic classification of the duct into the angiographically based groups and subgroups was readily performed using 3D reconstruction and volume-rendering techniques. Combining 3D reconstruction and volume rendering provided full data for evaluation of the ducts. Virtual angioscopy of the ducts, the third reconstruction technique, was achieved using postprocessing software and a 3D navigational model; virtual angioscopy allowed visualization of calcification within the duct.

Sizing a patent ductus arteriosus has traditionally required invasive techniques. Size remains an important factor in the evaluation of adults with patent ductus arteriosus. Accurate noninvasive sizing of the duct is important to selection of not only the correct device but also the mode of closure because not every duct is suitable for transcatheter closure. For example, in a patient with coexistent disease, surgery may be an option. Both the morphology and degree of calcification of the patent ductus arteriosus are important factors when surgery is considered. Patients with a heavily calcified duct or a duct exhibiting distortion or aneurysmal changes (morphologic types D and E) are not suitable candidates for surgery. Surgical closure in patients older than 60 years also carries a significant risk [15]. Reliable noninvasive depiction of these characteristics is invaluable. Certainly, knowledge of the anatomy of the patent ductus arteriosus and its relationship to the trachea is potentially useful information to have before undertaking transcatheter closure, bearing in mind the assistance that the tracheal air shadow provides as a fixed landmark during the procedure. The clinical usefulness of virtual angioscopy for the assessment of patent ductus arteriosus is not clear. We could confirm the persistent patency of the ductus arteriosus, and calcifications could be visualized with virtual angioscopy, but development of software that offers reliable quantification of internal vessel diameter is still required.

We found that in all five cases of patent ductus arteriosus, MDCT provided the clearest visualization of and morphologic information on the duct (Figs. 7A, and 7B). In one patient, MDCT allowed confirmation of the absence of a persistently patent ductus arteriosus. Confirmation of the diagnosis of suspected patent ductus arteriosus represents an obvious clinical use for MDCT. Three-dimensional MDCT angiography may also be considered as an alternative to invasive angiographic assessment and could aid in the decision-making regarding the preferred mode of patent ductus arteriosus closure in some patients. A more contentious issue is the usefulness of 3D MDCT angiography in patients with a clear diagnosis based on clinical and echocardiographic assessments who are undergoing routine patent ductus arteriosus closure. Three-dimensional images showing the anatomy of the patent ductus arteriosus and the spatial relations of adjacent structures provide invaluable information for surgeons. Whether such information is useful to interventional radiologists or cardiologists performing transcatheter closure and whether advantages related to complication rates and procedure times are sufficient to offset the disadvantage of radiation exposure during MDCT remain to be seen.

Persistently patent ductus arteriosus in adulthood is rare, and the size of our study population reflects this fact. One of the drawbacks of our study is that only limited invasive angiographic data were available for direct comparison in the sizing of the duct. A general disadvantage of retrospectively ECG-gated MDCT is the exposure to the required high radiation, estimated to be 3.9-5.8 mSv for cardiac studies [16].

In conclusion, we found that the MDCT acquisition protocol we described, combined with the images generated by the two reconstruction techniques commonly used in clinical practice, provides detailed assessment of persistently patent ductus arteriosus in adults. MDCT is an important imaging tool that should have a complementary role in imaging congenital heart disease. The widespread availability of MDCT makes it an attractive alternative to MRI for the evaluation of patients with patent ductus arteriosus. Further comparison of MDCT with invasive angiography and ideally with intravascular sonography would help to validate the technique of duct sizing with MDCT and to establish the usefulness of performing noninvasive sizing before undertaking transcatheter closure procedures.

References

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This Article Abstract Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Morgan-Hughes, G. J. Articles by Roobottom, C. Search for Related Content PubMed PubMed Citation Articles by Morgan-Hughes, G. J. Articles by Roobottom, C. Social Bookmarking                      What's this?