DOI: 10.1148/radiol.2272001767
(Radiology 2003;227:434-439.)
© RSNA, 2003
Assessment of Inter- and Intraobserver Agreement between Intravascular US and Aortic Angiography of Thoracic Aortic Injury1
David E. Lee, MD,
Bulent Arslan, MD,
Rodolfo Queiroz, MD and
David L. Waldman, MD
1 From the Department of Radiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 648, Rochester, NY 14642. Received November 6, 2000; revision requested December 23; final revision received August 5, 2002; accepted September 26. Address correspondence to D.E.L. (e-mail: david_lee@urmc.rochester.edu).
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ABSTRACT
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PURPOSE: To compare inter- and intraobserver agreement at thoracic aortic angiography with that at intravascular ultrasonography (US) in the work-up of patients suspected of having thoracic aortic injury.
MATERIALS AND METHODS: Three blinded readers performed a retrospective review of 95 thoracic aortic angiograms and 23 intravascular US images obtained in patients suspected of having traumatic aortic injury. Inter- and intraobserver agreement in the interpretation of the thoracic aortic angiograms and intravascular US images were determined by using Cohen 
statistics. In addition, differences among demographic groups were evaluated by using bivariate analysis.
RESULTS: Interobserver agreement was lowest in the interpretation of indeterminate angiograms ( = 0.55) and highest in the interpretation of determinate angiograms ( = 0.71). In contrast, interobserver agreement in the interpretation of intravascular US images was excellent. For all groups, intraobserver agreement in the interpretation of aortic angiograms was substantial and overall agreement was good ( = 0.88). Intraobserver agreement in the interpretation of intravascular US images was excellent ( = 1.00). Differences among demographic groups were not found to be significant.
CONCLUSION: Intravascular US is an adjunct to aortic angiography and yields excellent overall inter- and intraobserver agreement. Subgroups of patients who are suspected of having aortic injury and have indeterminate angiograms may benefit from undergoing intravascular US.
© RSNA, 2003
Index terms: Aorta, injuries, 562.412, 562.413, 563.412, 563.413 • Aorta, US, 562.1289, 563.1289 • Aortography, 562.121, 563.121 • Ultrasound (US), intravascular, 562.1289, 563.1289
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INTRODUCTION
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Aortic injury in the setting of thoracic trauma is a devastating and life-threatening injury. Mortality is high: An estimated 10%–20% of patients survive the injury (1). For those patients with thoracic trauma who reach a trauma center, timely and accurate diagnosis is essential in choosing the appropriate surgical or endovascular intervention. The reference standard to diagnose or exclude an aortic transection is thoracic aortic angiography (2); however, with the emergence of other modalities such as computed tomography (CT), magnetic resonance angiography, and transesophageal echocardiography, alternative noninvasive imaging examinations are now available for the detection of aortic injury (3–7).
The use of intravascular ultrasonography (US) enables not only cross-sectional but also high-frequency-transducer intraluminal imaging of the thoracic aorta, which may be efficiently performed immediately following angiography. The purpose of this study was to compare the degree of inter- and intraobserver agreement at thoracic aortic angiography with the degree of inter- and intraobserver agreement at intravascular US in the context of visualizing traumatic thoracic aortic injury.
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MATERIALS AND METHODS
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We retrospectively reviewed all of the thoracic aortic angiograms and intravascular US images that were obtained at our institution from August 1997 through June 2000. Informed consent was obtained from all patients, and the institutional review board at our institution approved the study. Three independent readers (D.L.W., R.Q., D.E.L.) reviewed a total of 95 thoracic aortic angiograms and 23 intravascular US images, all of which were obtained in a total of 95 patients. There were 29 (31%) female and 66 (69%) male patients, and the mean patient age was 41.8 years (range, 11–93 years) (Table 1).
All of the readers are board-certified radiologists who practice vascular interventional radiology full time. Two of the three readers (D.L.W., D.E.L.) have a certificate of added qualification in vascular interventional radiology. The third reader (R.Q.) is eligible for a certificate of added qualification and has 1 year of fellowship experience in vascular interventional radiology.
We performed a subset analysis to assess inter- and intraobserver agreement of angiographic interpretations with the angiograms divided into two subgroups: the images obtained in the patients who had determinate angiographic findings and those obtained in the patients who had indeterminate findings. In addition, differences among demographic groups were evaluated by using bivariate analysis and not found to be significant (Table 1).
The patients who had indeterminate angiograms underwent intravascular US examinations. The baseline characteristics that accounted for the indeterminate angiograms were an aortic tortuosity (10 [44%] of 23 angiograms), a sharp or irregular ductal bump (11 [48%] of 23 angiograms), a subtle filling defect (one [4%] of 23 angiograms), or a technically inadequate examination (two [9%] of 23 angiograms).
In all cases, thoracic aortic angiography was performed with a 6-F pigtail catheter (Angiodynamics, Queensbury, NY), which was advanced to the level of the aortic root after access was obtained within the common femoral artery by using the Seldinger technique. Initially, angiograms were obtained in a left anterior oblique projection for visualization of the entire aorta to the level of the esophageal hiatus. A second orthogonal view in an anteroposterior (17 of 95 angiograms), right anterior oblique (31 of 95 angiograms), or lateral (47 of 95 angiograms) projection also was obtained. The second projection was chosen at the discretion of the operator at the time of imaging and therefore was not the same in all patients.
Film hard-copy images were used for all examinations in the early, middle, and late arterial phases of the contrast material (iohexol, Omnipaque 300; Amersham Health, Princeton, NJ) injection. All hard-copy images were made available to the interpreters. Real-time runs were not used for the blinded review. All of the complications encountered in performing aortic angiography were minor. Three (3%) of the 95 patients had a local access site hematoma, which was managed by means of manual compression on the groin and did not require either blood transfusion or surgical intervention.
All of the patients with thoracic aortic angiograms that were considered to be indeterminate by the operator at the time of the study underwent intravascular US. The cases in which intravascular US was performed required placement of an 8-F vascular sheath (Boston Scientific, Watertown, Mass). An indeterminate angiogram was defined as that which was difficult to interpret owing to (a) a tortuous aorta, (b) a sharp or irregular ductal bump, (c) a technically inadequate examination, and/or (d) subtle filling defects. Subsequently, after a 0.035-inch polytetrafluoroethylene-coated guide wire was advanced into the thoracic aorta, a 6-F 12.5-MHz monorail intravascular US probe (Boston Scientific) was advanced to the level of the aortic root. The probe was retracted along the length of the thoracic aorta while imaging was performed. All intravascular US examinations were recorded on a videotape, and printed images of the ascending aorta, aortic arch, and descending thoracic aorta were produced for the medical record. These videotapes were made available to the interpreters after the names of the patients were deleted by our video laboratory personnel.
Each patient underwent approximately 10 minutes (range, 6–20 minutes) of intravascular US, and the interpreters were free to rewind and forward the US tapes as needed. In those patients who underwent intravascular US, no complications related to either the angiographic or the intravascular US procedure were noted.
Thoracic aortic angiography and intravascular US were performed during the same examination. Thus, to eliminate any potential bias that could have ensued because both types of images were interpreted in a tandem fashion in the angiographic suite, the readers were blinded to each other’s findings, the patient’s demographic information, the diagnostic report, the subset analysis, and the findings of the other imaging study. To determine intraobserver variability, all angiographic and intravascular US images were double read by reader 3 (D.E.L.), who has a certificate of added qualification in interventional radiology.
The readers were required to interpret the images as positive or negative. A positive interpretation at aortic angiography was defined as the identification of an outpouching of contrast, a sharp edge or angle associated with a ductal bump, and/or extravasation of contrast material. A positive interpretation at intravascular US was defined as the identification of discontinuity in the intima, intimal disruption, or an intraluminal or intramural echo. Periaortic fluid was considered to be a nonspecific finding and not specific for an aortic injury.
Eight (8%) patients had surgical confirmation and six (6%) patients autopsy confirmation of the angiographic and/or intravascular US findings, and 77 (81%) patients were followed up by using medical chart reviews or telephone calls from 6 to 40 months after hospital discharge. We could not follow up four patients after discharge. These four patients were considered to be in stable condition at the time of their discharge.
A valuable quality of a viable diagnostic imaging technique is the uniformity of image interpretation by different trained readers. Cohen statistics (
= .05) were used to compare the degree of inter- and intraobserver agreement at aortic angiography with the degree of inter- and intraobserver agreement at intravascular US.
A computer program (Statview; SAS Institute, Cary, NC) was used to maintain the patient database. In addition, analyses and power calculations were performed by using statistical analysis software (SAS Institute). The power of the Cohen statistic was determined by using the method described by Fleiss (8).
To assess interobserver reliability, we used MACRO language in the SAS System (SAS Institute). The program is called MAGREE (SAS Institute), and it computes estimates and tests of agreement among multiple readers when the responses are on a nominal or ordinal scale. A composite statistic, as well as the standard error of the statistic and a Z score, is computed. We then calculated the 95% CIs associated with the statistic (Table 2). If the lower limit of the 95% CI is negative, then we must reject the null hypothesis, which is that there is no agreement between the readers. Another way to look at this is to examine the Z score. If the Z score is 1.96 with one differential fragment, then we can also reject the null hypothesis.
Pair-wise comparisons were calculated by using the agree option of the PROC FREQ procedure in the SAS software program; the results are shown in Table 3.
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TABLE 3. Interobserver Reliability of Intravascular US in 23 Subjects Who Underwent Intravascular US and Angiography
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Finally, intraobserver pair-wise comparisons were calculated for one observer (D.E.L.); the results are shown in Tables 4 and 5.
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TABLE 5. Intraobserver Reliability of Reader 3 at Intravascular US in 23 Subjects Who Underwent Intravascular US and Angiography
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RESULTS
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Angiographic Evaluation
The indications for aortic angiography included abnormal chest radiography and/or CT findings of an appropriate mechanism of injury. Ninety-one chest radiographs and 86 CT images were interpreted as showing abnormal findings. The results are summarized in Table 1.
A total of 95 thoracic aortic angiograms were obtained for possible detection of aortic injury. In eight (8%) of the 95 patients in whom these angiograms were obtained, the aortic injuries were confirmed at surgery. Four of these eight patients also underwent intravascular US because their aortic angiograms were indeterminate at the time of examination. The remaining 87 (92%) patients had no evidence of injury at angiographic evaluation. Nineteen of these 87 patients also underwent intravascular US. Six patients died after undergoing angiography, and the autopsies confirmed causes of death other than aortic injury. All angiograms were correctly interpreted at the time of angiography. Seventy-seven patients were alive for 6–40 months after discharge. Four patients were stable at discharge; however, further follow-up was not possible.
Interobserver Variability
For evaluation of reader agreement, all angiograms (n = 95) and intravascular US images (n = 23) were read independently by the three readers. Reader agreement findings for two readers in the interpretation of all angiograms ( = 0.495 for readers 1 and 2, = 0.825 for readers 1 and 3, = 0.593 for readers 2 and 3), the interpretation of the determinate angiograms ( = 0.554 for readers 1 and 2, = 0.882 for readers 1 and 3, = 0.654 for readers 2 and 3), and the interpretation of the indeterminate angiograms ( = 0.395 for readers 1 and 2, = 0.747 for readers 1 and 3, = 0.495 for readers 2 and 3) are summarized in Table 2. There was complete agreement in each group of readers in the interpretation of the intravascular US images ( = 1.00, Table 3).
Intraobserver Variability
Intraobserver agreement was determined by having all of the angiograms and intravascular US images double read by reader 3, who was blinded to the previous reading findings. The data presented in Table 4 demonstrate the overall agreement in the interpretation of aortic angiograms ( = 0.888), determinate angiograms ( = 1.00), and indeterminate angiograms ( = 0.775). The data in Table 5 show that agreement in the interpretation of intravascular US images ( = 1.00) was substantial. The lowest level of agreement was that in the interpretation of indeterminate angiograms.
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DISCUSSION
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The work-up of patients suspected of having aortic injury has been a subject of debate. Thoracic aortic angiography is the current reference standard for the diagnosis of aortic injury, although there have been technological advances in other modalities, which have made the preferred method of imaging for establishing a diagnosis a topic of debate (5,9). Smith et al (5) have advocated the use of transesophageal echocardiography in the evaluation of the thoracic aorta, citing a faster response time and similar sensitivity and specificity compared with these factors in aortic angiography. They concluded that transesophageal echocardiography was comparable to and more time efficient than aortic angiography (5). Conversely, recent technological advances in cross-sectional imaging have resulted in several claims that CT is sufficient to determine the presence or absence of aortic injury (10,11).
The purpose of this study was to compare intravascular US with aortic angiography in an attempt to ascertain the role of intravascular US in the evaluation of patients suspected of having aortic injury. Uflacker et al (12) discussed various imaging characteristics of intravascular US in the setting of aortic injury and concluded that it is an effective means of identifying aortic injuries. In their series, intravascular US depicted intramural hematomas that not only were not seen at aortic angiography but also had a ductus diverticulum, which was erroneously interpreted as a pseudoaneurysm. Williams et al (13,14) described the use of intravascular US for the detection of traumatic aortic injury in select cases in which aortic angiography was inconclusive. However, they did not advocate the routine use of intravascular US because of the high cost of US probes and the necessity of larger sheath sizes. The small numbers of patients in their reported experience precluded the determination of inter- and intraobserver agreement to assess the validity of intravascular US.
In our study, we compared inter- and intraobserver agreement at intravascular US and aortic angiography. The data emphasize that intravascular US is an excellent modality for examining the thoracic aorta: There were perfect inter- and intraobserver variability scores. As noted in Tables 2 and 3, interobserver agreement at aortic angiography was observed to be moderate in the interpretation of the indeterminate angiograms and substantial in the interpretation of the determinate angiograms. In such cases, performing intravascular US in conjunction with aortic angiography may help reduce the number of instances in which patients are subjected to surgical procedures when they do not need them and ensure that the patients who do have aortic injuries are identified so that timely interventions can be performed. The addition of intravascular US, particularly when angiograms are indeterminate, may be important for patient care.
All of the angiograms that were associated with subsequent intravascular US were labeled as indeterminate, meaning that these images were difficult to interpret owing to aortic tortuosity, irregular or sharp angles at the level of the ligamentum arteriosum, subtle filling defects, or, in some cases, a technically difficult or inadequate angiographic examination. This selection bias likely accounted for the lower values for the interpretation of this subgroup of angiograms. The angiograms in this subset were more difficult to interpret. All three readers correctly interpreted the intravascular US images obtained in the patients with these indeterminate angiograms. The data suggest that intravascular US may have an adjunctive role in the imaging of patients who have angiograms that are difficult to interpret (ie, indeterminate).
The time required to perform intravascular US in this setting is minimal. Although there is a learning curve associated with learning to prepare the probe and interpret the images, in the hands of an experienced operator, intravascular US may add approximately 10 minutes to the total examination time. In all instances in the present study, the intravascular US probe was advanced over a guide wire when it traversed a site of possible aortic injury. It is our opinion that this device combination poses no greater risk than does advancing a diagnostic catheter and guide wire for aortic angiography. A complication would be more likely if we were trying to pass the intravascular US probe and guide wire over an obviously injured area, but such injuries would be apparent at aortic angiography, and, thus, intravascular US would not be required.
In our institution, intravascular US is reserved for indeterminate cases, and if the patient has an aortic injury, the need to determine that injury outweighs the minimal risk, if any, posed by passing a second guide wire. Also, in the present study no patient who underwent aortic angiography or intravascular US had complications related to traversing the site of injury. Although we experienced no difficulty in using a monorail system, theoretically, a true over-the-wire system may afford greater ease of tractability across a suspected site of injury.
Intravascular US is limited in the evaluation of branch vessels. Although interrogation of the great vessels could be performed with intravascular US, the examination would prove to be arduous and time-consuming. Aortic angiography is superior to intravascular US in this respect. Other limitations of this study included difficulty in establishing a good reference standard. All patients who did not have surgical or autopsy confirmation of aortic injury were followed up clinically; however, theoretically, a small proportion of patients in this group could have developed a posttraumatic pseudoaneurysm, which may not have become clinically apparent. The patients did not undergo follow-up imaging.
The small number of patients who underwent intravascular US and the small number of positive examinations also precluded a statistically valid comparison between the two imaging modalities. A multicenter trial is needed to adequately achieve this goal. The performance of intravascular US only in cases of indeterminate angiograms also introduced bias, which may have affected the intra- and interobserver values.
One advantage of intravascular US over angiography is in the identification of tiny intimal tears. If the outer wall of the aorta is not distorted, these cases are very difficult to diagnose with angiography. Consequently, one might speculate that pseudoaneurysms that develop years after the injury may be due to these tiny intimal injuries, which may have been missed at aortic angiography. In Figure 1, an angiogram depicts a slight irregularity at the ductal bump that could be interpreted as normal; however, the intravascular US image clearly shows the injury, which was confirmed at surgery and pathologic analysis. Intravascular US also clearly depicts intramural and intraluminal abnormalities, which may not be apparent on thoracic angiograms (Fig 2). We believe that if the criterion of (a) an intimal flap, (b) an intimal flap with an accompanying pseudoaneurysm, or (c) intramural or intraluminal hematomas is strictly followed, intravascular US can be a powerful imaging adjunct to aortic angiography. These criteria may serve to limit the number of false-positive results for patients who may have a ductus diverticulum, which can be mistaken for a pseudoaneurysm, or for those who have the nonspecific finding of periaortic fluid.
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Figure 1a. Thoracic aortic injury of the intimal flap in a 36-year-old man who was involved in a high-speed motor vehicle accident and demonstrated mediastinal widening at chest radiography. (a) Anteroposterior and (b) left anterior oblique angiograms show no discernible injury, except a slight irregularity (arrow in b) at the medial aspect of the proximal descending aorta in the left anterior oblique projection; this is a commonly seen normal variant. (c) The intravascular US image clearly shows an intimal injury (straight arrows) along the anteromedial aspect of the thoracic aorta, just distal to the left subclavian artery. The curved arrow points to the intravascular US probe.
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Figure 1b. Thoracic aortic injury of the intimal flap in a 36-year-old man who was involved in a high-speed motor vehicle accident and demonstrated mediastinal widening at chest radiography. (a) Anteroposterior and (b) left anterior oblique angiograms show no discernible injury, except a slight irregularity (arrow in b) at the medial aspect of the proximal descending aorta in the left anterior oblique projection; this is a commonly seen normal variant. (c) The intravascular US image clearly shows an intimal injury (straight arrows) along the anteromedial aspect of the thoracic aorta, just distal to the left subclavian artery. The curved arrow points to the intravascular US probe.
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Figure 1c. Thoracic aortic injury of the intimal flap in a 36-year-old man who was involved in a high-speed motor vehicle accident and demonstrated mediastinal widening at chest radiography. (a) Anteroposterior and (b) left anterior oblique angiograms show no discernible injury, except a slight irregularity (arrow in b) at the medial aspect of the proximal descending aorta in the left anterior oblique projection; this is a commonly seen normal variant. (c) The intravascular US image clearly shows an intimal injury (straight arrows) along the anteromedial aspect of the thoracic aorta, just distal to the left subclavian artery. The curved arrow points to the intravascular US probe.
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Figure 2a. Thoracic aortic injury, an intimal flap with an intraluminal hematoma, in a 59-year-old woman who was involved in a high-speed motor vehicle accident. (a) Transverse contrast material-enhanced chest CT image shows a slight haziness in the mediastinal fat, with no other definite evidence of aortic injury. (b) Angiogram shows an area of subtle filling defect (arrow) at the level of the ductus arteriosum. (c) Subsequently obtained intravascular US image clearly shows an intraluminal hematoma (arrows) at the anterior aspect of the proximal descending aorta. (d) Findings on the fluoroscopic image of the radiopaque probe (arrow) confirmed the level of injury. This patient underwent surgical repair of her aortic injury after evaluation of the intravascular US findings. Aortic injury with an intraluminal hematoma was confirmed at surgical pathologic analysis. The patient was in stable condition when she was discharged from the hospital.
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Figure 2b. Thoracic aortic injury, an intimal flap with an intraluminal hematoma, in a 59-year-old woman who was involved in a high-speed motor vehicle accident. (a) Transverse contrast material-enhanced chest CT image shows a slight haziness in the mediastinal fat, with no other definite evidence of aortic injury. (b) Angiogram shows an area of subtle filling defect (arrow) at the level of the ductus arteriosum. (c) Subsequently obtained intravascular US image clearly shows an intraluminal hematoma (arrows) at the anterior aspect of the proximal descending aorta. (d) Findings on the fluoroscopic image of the radiopaque probe (arrow) confirmed the level of injury. This patient underwent surgical repair of her aortic injury after evaluation of the intravascular US findings. Aortic injury with an intraluminal hematoma was confirmed at surgical pathologic analysis. The patient was in stable condition when she was discharged from the hospital.
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Figure 2c. Thoracic aortic injury, an intimal flap with an intraluminal hematoma, in a 59-year-old woman who was involved in a high-speed motor vehicle accident. (a) Transverse contrast material-enhanced chest CT image shows a slight haziness in the mediastinal fat, with no other definite evidence of aortic injury. (b) Angiogram shows an area of subtle filling defect (arrow) at the level of the ductus arteriosum. (c) Subsequently obtained intravascular US image clearly shows an intraluminal hematoma (arrows) at the anterior aspect of the proximal descending aorta. (d) Findings on the fluoroscopic image of the radiopaque probe (arrow) confirmed the level of injury. This patient underwent surgical repair of her aortic injury after evaluation of the intravascular US findings. Aortic injury with an intraluminal hematoma was confirmed at surgical pathologic analysis. The patient was in stable condition when she was discharged from the hospital.
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Figure 2d. Thoracic aortic injury, an intimal flap with an intraluminal hematoma, in a 59-year-old woman who was involved in a high-speed motor vehicle accident. (a) Transverse contrast material-enhanced chest CT image shows a slight haziness in the mediastinal fat, with no other definite evidence of aortic injury. (b) Angiogram shows an area of subtle filling defect (arrow) at the level of the ductus arteriosum. (c) Subsequently obtained intravascular US image clearly shows an intraluminal hematoma (arrows) at the anterior aspect of the proximal descending aorta. (d) Findings on the fluoroscopic image of the radiopaque probe (arrow) confirmed the level of injury. This patient underwent surgical repair of her aortic injury after evaluation of the intravascular US findings. Aortic injury with an intraluminal hematoma was confirmed at surgical pathologic analysis. The patient was in stable condition when she was discharged from the hospital.
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In summary, intravascular US is an adjunct to aortic angiography and yields excellent overall inter- and intraobserver agreement. Subgroups of patients who are suspected of having aortic injury and have indeterminate angiograms may benefit from undergoing intravascular US. Such subgroups include those of patients with tortuous thoracic aortas, subtle filling defects, or sharp or indistinct angles at the level of the ductus arteriosum and those of patients in whom the angiographic examination was technically inadequate.
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ACKNOWLEDGMENTS
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The authors thank Janet Poles for assistance with manuscript preparation and Theresa Kubera and Margaret Kowaluk for photography.
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FOOTNOTES
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Author contributions: Guarantors of integrity of entire study, D.E.L., B.A.; study concepts and design, all authors; literature research, D.E.L., B.A.; clinical studies, D.E.L., B.A.; data acquisition, D.E.L., B.A.; data analysis/interpretation, all authors; statistical analysis, D.E.L., B.A.; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, all authors.
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REFERENCES
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ABSTRACT
INTRODUCTION
