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Vascular and Interventional Radiology |
1 Henry Ford Heart and Vascular Institute, 6525 Second Ave, Detroit, MI 48202-3006 (P.D.S., J.W.H.)
2 Department of Radiology, Michigan State University, East Lansing, Mich (A.G.).
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: Data are from examinations of 375 patients with angiographically diagnosed PE who participated in the Prospective Investigation of Pulmonary Embolism Diagnosis. The average co-positivity of readings of the pulmonary angiograms was evaluated in relation to the order of the largest pulmonary artery that showed PE.
RESULTS: Among 217 patients whose angiograms showed PE in main or lobar pulmonary arteries, as well as in smaller orders of arteries, there was an average co-positivity of 98% (95% CI = 96%, 98%). Among 136 patients whose pulmonary angiograms showed PE in segmental or subsegmental pulmonary arteries but not in larger orders of arteries, the average co-positivity was 90% (95% CI = 85%, 95%). Among 22 patients with PE limited to the subsegmental arteries, the average co-positivity was 66% (95% CI = 46%, 86%).
CONCLUSION: Conventional pulmonary angiography is not precise for the diagnosis of PE limited to subsegmental arteries. To evaluate subsegmental arteries, techniques that improve the visualization of PE in small arteries should be used.
Index terms: Embolism, pulmonary, 60.72 • Pulmonary angiography, 944.122, 60.1241 • Pulmonary arteries, stenosis or obstruction, 944.77 • Pulmonary arteries, thrombosis, 944.77
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The overall agreement between readers (ie, both readers agreed that PE was present, PE was absent, or PE was uncertain) of 1,099 pulmonary angiograms in the collaborative Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) was 81% (3). The average co-positivity was 88%. Reader agreement was described in detail with regard to the quality of the angiograms, but reader agreement (ie, co-positivity) with regard to the order of the branch of the pulmonary artery (ie, main, lobar, segmental, or subsegmental) with PE was given without a description of all of the data (3). The purpose of this investigation was to describe in detail interobserver variability in relation to the order of the largest branch of the pulmonary artery that showed PE. This information may be useful in assessing the extent to which conventional pulmonary angiography can be used as a benchmark for the evaluation of newer techniques.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Six clinical centers participated in PIOPED: Duke University, Henry Ford Hospital, Massachusetts General Hospital, University of Michigan, University of Pennsylvania, and Yale University. The patients were approached for recruitment into PIOPED if they had symptoms that were suggestive of acute PE within 24 hours of entering the study, were aged 18 years or older, and had no contraindication to undergoing pulmonary angiography (ie, pregnancy, serum creatinine level > 260 µmol/L, or hypersensitivity to contrast material). The recruited patients consented to undergoing pulmonary angiography provided that their ventilation-perfusion lung scan result was abnormal. Written informed consent was obtained from all of the patients after the nature of the procedure had been fully explained. Then the patients were selected for the angiographic arm of PIOPED by using random sampling. The investigation was approved by the review board of each of the participating institutions.
Pulmonary angiograms were obtained by using the femoral venous Seldinger technique with multiple side-hole 6–8-F pigtail catheters (4). The catheter was directed to the proximal portion of the pulmonary artery of the lung with the greatest ventilation-perfusion scan abnormality. Initial imaging was performed in the anteroposterior projection after the injection of 40–50 mL of 76% iodinated (ie, ionic) contrast material at a rate of 20–35 mL/sec over 2 seconds. Imaging rates were three images obtained per second for 3 seconds followed by one image per second for 4–6 seconds. Either the images were not magnified, or a low magnification of 1.4 was used. A 12:1 grid was used.
The radiographic factors were a peak of 70–80 kV and 0.025–0.04 seconds at 1,000 mA, with a focal spot of 1.2–1.5 mm. If emboli were not identified, injections of contrast material were repeated, and magnification (x1.8–2.0) oblique views of the areas suspicious for PE were obtained. Oblique views were obtained without a grid. The radiographic parameters used to obtain oblique views were a peak of 78–88 kV and 0.04–0.08 seconds at 160 mA, with a 0.3–0.6-mm-diameter focal spot. If no emboli were found in the first lung, or if bilateral angiography in the clinical center was performed routinely, identical techniques were used for imaging the second lung.
Criteria for the diagnosis of PE were the identification of an embolus (ie, filling defect) obstructing a vessel or the outline of an embolus within a vessel (4). If two readers disagreed on the angiographic findings, the interpretations were adjudicated by readers who were randomly selected from the remaining clinical centers. If the adjudicating readers did not agree with either of the first two readers, the angiograms were presented to a panel of angiographers for final adjudicated interpretations.
There were 217 patients with PE in the main or lobar pulmonary arteries. These patients may also have had PE in smaller orders of arteries. There were 136 patients with PE in segmental pulmonary arteries but no evidence of PE in the main pulmonary artery or the lobar arteries. They may have had PE additionally in subsegmental pulmonary arteries. The PIOPED database does not allow us to know whether PE in segmental or subsegmental branches influenced the interpretation of PE in the larger orders of arteries. Twenty-two patients had PE limited to subsegmental pulmonary arteries.
We assume that the PE identified by using pulmonary angiography was acute PE on the basis of the clinical presentations. All of the patients had symptoms of acute PE within 24 hours of entering the study.
Statistical Methods
The average co-positivity, expressed as a percentage, was the average percentage of agreement on positivity between reader 1 and reader 2 and between reader 2 and reader 1. Examples of calculations of co-positivity are shown in Tables 1–3. The 95% CI of co-positivity was plus or minus 1.96 times the standard error of the co-positivity. Comparison of the co-positivity readings of PE in various orders of pulmonary arteries was made with a 
2 test. Probability values of less than .05 were considered to be significant.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Pulmonary angiograms in which the largest orders of arteries with PE were segmental branches were obtained in 136 (36%) of the 375 patients with PE. These patients may have had PE in subsegmental branches as well. In interpreting the angiograms obtained in these patients, the average co-positivity was 90% (95% CI = 85%, 95%) (Table 2).
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Intrareader comparisons were made in PIOPED (5). Angiographers read a group of pulmonary angiograms and at a later date, reread the same angiograms. The angiographers agreed with themselves on the interpretation of 64 (89%) of 72 angiograms (Cohen 
statistic, 0.74).
In the Urokinase Pulmonary Embolism Trial (6), correlation coefficients were computed for the analysis of each panel member's reading relative to that of each of the other two members. A subjective PE severity rating for every satisfactory angiogram was made by each panelist by using a four-point scale in which 0 was normal, 1 was mild, 2 was moderate, and 3 was severe. The correlation coefficients for preeffusion subjective estimates of severity given by three pairs of panelists were 0.79, 0.86, and 0.78. Correlation coefficients were also calculated for subjective estimates of the difference between preinfusion and postinfusion angiograms on the basis of a seven-point scale that ranged from marked worsening (-3) to complete improvement (+4). The correlation coefficients for paired subjective evaluations of change of severity were 0.70, 0.64, and 0.71. The correlation coefficients for pairs of panelists who assessed the severity of PE on the pulmonary angiograms by using an objective severity index were 0.81, 0.83, and 0.82. The correlation coefficients for change of severity based on an objective severity index were 0.55, 0.66, and 0.63.
In the present evaluation of interobserver agreement, there was a clear relation between the order of the largest branch of the pulmonary artery involved and reader agreement on the presence of PE. Six percent of patients in PIOPED had PE limited to subsegmental pulmonary arteries (7). For PE limited to subsegmental branches, there was 66% co-positivity. Because the number of patients with PE limited to subsegmental branches was small, the 95% CI of the co-positivity was large. Even so, there was a significantly decreased co-positivity for readings of PE in subsegmental branches compared with the co-positivity for readings of PE in main or lobar pulmonary arteries (P < .001) and compared with that for readings of PE in segmental arteries (P < .05). Others have reported a lower percentage of agreement on positivity when PE was limited to subsegmental pulmonary arteries. Quinn and associates (8) reported agreement on two of 15 (13%) PEs limited to subsegmental pulmonary arteries. Diffin and colleagues (9) observed PE limited to subsegmental pulmonary arteries in five (17%) of 29 patients. The initial average interobserver agreement was 45%, and there was unanimous consensus agreement on the findings in 79% of patients who had isolated subsegmental arterial PE (9).
Techniques that augment conventional angiography might be used to improve the visualization of PE in small arteries. Such techniques include cineangiography (10), balloon-occlusion angiography (11,12), superselective angiography (13), and wedge arteriography (14).
Concern about the reliability of contrast-enhanced spiral and electron-beam CT in subsegmental pulmonary arteries has been expressed (15). Gadolinium-enhanced MR angiography also lacks definition in subsegmental pulmonary arteries (2), although techniques for high-definition MR imaging may offer better resolution (16). The data that we present in this study indicate that precise evaluation of subsegmental pulmonary arteries by using conventional pulmonary angiograms may be difficult. If pulmonary angiography is to be used as a benchmark for the evaluation of new technologies in which subsegmental pulmonary arteries are imaged, then ancillary pulmonary angiographic techniques that improve the imaging of small vessels should be used.
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Footnotes |
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Address reprint requests to P.D.S.
Abbreviations: PE = pulmonary embolism PIOPED = Prospective Investigation of Pulmonary Embolism Diagnosis
Author contributions: Guarantor of integrity of entire study, P.D.S.; study concepts and design, P.D.S., A.G.; definition of intellectual content, P.D.S., A.G.; literature research, P.D.S., A.G.; clinical studies, P.D.S., A.G.; data acquisition, P.D.S., A.G.; data analysis, J.W.H.; statistical analysis, P.D.S.; manuscript preparation, P.D.S.; manuscript editing, P.D.S., A.G.; manuscript review, P.D.S., A.G., J.W.H.
Received July 15, 1997;
revision requested August 19, 1997; revision received July 28, 1998;
accepted October 19, 1998.
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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