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CT Venography and Compression Sonography Are Diagnostically Equivalent: Data from PIOPED II

¹ Department of Diagnostic Radiology, Medical College of Wisconsin, 9200 W Wisconsin Ave., Milwaukee, WI 53226-3596.
² Department of Research, St. Joseph Mercy Hospital–Oakland, Pontiac, MI.
³ Department of Medicine, Wayne State University, Detroit, MI.
⁴ Corporate Offices, The Methodist Hospital, Houston, TX.
⁵ Office of the Dean, Weill Cornell Medical College, New York, NY.
⁶ Department of Surgery, University of Michigan, Ann Arbor, MI.
⁷ Department of Radiology, Washington University, St. Louis, MO.
⁸ Department of Medicine, University of Calgary, Calgary, Alberta, Canada.
⁹ Department of Radiology, Weill Cornell Medical Center, New York, NY.

Received April 9, 2007; accepted after revision May 22, 2007.

 
Supported by grants HL63899, HL63928, HL63931, HL063932, HL63940, HL63941, HL63942, HL63981, HL63982, and HL67453 from the U.S. Department of Health and Human Services, Public Health Services, National Heart, Lung, and Blood Institute, Bethesda, MD.

Address correspondence to L. R. Goodman (lgoodman{at}mcw.edu).

Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
OBJECTIVE. The purpose of this study was to compare the clinical value of CT venography (CTV) after MDCT angiography (CTA) with venous compression sonography for the diagnosis of venous thromboembolism (VTE). The Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II) showed that lower extremity imaging detects about 7% more patients requiring anticoagulation than CTA alone.

SUBJECTS AND METHODS. PIOPED II was a prospective multicenter study investigating the accuracy of CTA alone and CTA and CTV together. A composite reference standard was used to confirm, or rule out, pulmonary embolus. Adequate quality CTV and sonographic images were obtained in 711 patients.

RESULTS. There was 95.5% concordance between CTV and sonography for the diagnosis or exclusion of deep venous thrombosis (DVT); the kappa statistic was 0.809. The sensitivity and specificity of combined CTA and CTV were equivalent to those of combined CTA and sonography. Diagnostic results in subgroups, including patients with signs or symptoms of DVT, asymptomatic patients, and patients with a history of DVT, were similar whether CTV or sonography was used. Patients with signs or symptoms of DVT were eight times more likely to have DVT, and patients with a history of DVT were twice as likely to have positive findings.

CONCLUSION. CTV and sonography showed similar results in diagnosing or excluding DVT. The incidence of positive studies in patients without signs, symptoms, or history of DVT is low. In terms of clinical significance, CT venography and lower extremity sonography yield equivalent diagnostic results; the incidence of positive studies in patients without signs, symptoms, or history of DVT is low; thus the choice of imaging technique can be made on the basis of safety, expense, and time constraints.

Keywords: CT venography • deep venous thrombosis • lower extremity Doppler sonography • pulmonary embolus

Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
In the Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II), MDCT angiography (CTA) of the pulmonary arteries—in combination with venous phase imaging of the deep veins of the pelvis and thigh, CT venography (CTV)—had a higher sensitivity, 90%, than CTA alone, 83% [1]. Specificities were similar, 95% and 96%, respectively [1]. On the basis of this observation, the PIOPED II investigators recommended that if CT is appropriate, CTA should be obtained in combination with CTV—in most patients [2]. Disadvantages of CTV, however, include a larger volume of IV contrast material, additional pelvic radiation, and possibly higher expense. Accordingly, in some patients such as young women, sonography might be a preferable option provided that its diagnostic accuracy is not worse than that of CTV. Although there are some data suggesting diagnostic equivalence, no large prospective database with uniform diagnostic criteria has been used to evaluate this issue.

This article evaluates whether CTV and venous sonography are equivalent in the diagnostic evaluation of patients with suspected acute pulmonary embolism (PE) in a large, multiinstitutional prospective study.

Subjects and Methods

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PIOPED II was a prospective multicenter investigation of the accuracy of CTA alone and combined with CTV for the diagnosis of acute PE and venous thromboembolism (VTE). All patients who were more than 18 years old who had clinically suspected acute PE were eligible for recruitment, and exclusion criteria were previously described [1]. All enrolled patients gave consent to undergo diagnostic testing, including CTA and CTV; ventilation–perfusion (V/Q) scanning; sonography; and, if necessary, pulmonary digital subtraction angiography [1]. The protocol and consent forms were approved by the institutional review board of each center and by the data safety monitoring board appointed by the National Heart, Lung, and Blood Institute, the research sponsor. All of the Standards for Reporting Diagnostic Accuracy (STARD) were met [3, 4]. A composite reference test was used: PE was diagnosed if there was a high probability ventilation–perfusion (V/Q) without a prior PE, a positive digital subtraction angiography, or a positive sonography without a previous deep venous thrombosis (DVT) at that site and a nondiagnostic V/Q (not normal and not high probability; this was used as a surrogate for the diagnosis of PE). PE was excluded by a negative digital subtraction angiography, normal V/Q, or low or very low probability V/Q with a low (< 2) clinical probability score by the Wells criteria [5] and negative sonography [1].

PIOPED II nurse coordinators prospectively recorded, using a preenrollment questionnaire, both a history of DVT requiring anticoagulation and current symptoms (swelling or pain) and physical examination evidence (edema, erythema, tenderness, palpable cord) of DVT [1]. Patient height and weight were also recorded, and a body mass index (BMI) was calculated.

Of the 773 patients with complete data, 4-MDCT was used in 691 (89%), 8-MDCT was used in 37 (5%), and 16-MDCT was used in 45 (6%) (Table 1). Low-osmolar nonionic contrast material (135 mL) was injected through an arm vein at 4 mL/s. Patients with a BMI of > 35 received 150 mL. After a 3-minute delay, the deep leg veins were scanned from the inferior vena cava confluence (iliac crest) through the popliteal veins (tibial plateau). Helical CT venography used 7.5-mm collimation, 7.5-mm reconstruction, table speed of 30 mm per rotation, and pitch of 1.5. Tube current was 180 mA and 120 kVp (increased to 140 kVp in patients > 250 lb [113 kg]), and rotation time was 1 second.

Venous Sonography
Each patient also underwent venous duplex sonography of the common femoral, femoral, popliteal, and proximal greater saphenous veins using B-mode real-time compression sonography performed in transverse orientation in combination with color duplex sonography, with and without distal augmentation assessing flow.

Image Interpretation
All CT images were interpreted on a diagnostic monitor or workstation by a local reviewer for patient care purposes and later by two independent central reviewers from other institutions. At the time of scanning, a density reading (in Hounsfield units) was recorded for the right common femoral vein. In addition, each central reviewer was asked to score subjectively the presence or absence of motion, the adequacy of venous contrast enhancement, and a final 3-point grading of CTV quality. The criterion for acute DVT was a complete or partial central filing defect [6]. The criteria for chronic DVT included small vessels, thick eccentric walls, recanalization, and calcification. If two reviewers did not agree on the presence of thrombi in at least one leg or the absence of thrombi in both legs, scans were sent to a third reviewer.

The criteria for acute DVT on sonography included noncompressibility of the vein in combination with at least one of the following: vein enlarged in size, a hypoechoic vein lumen, or the absence of significant collateral veins [7, 8]. No independent reference standard was established for DVT. Therefore, CTV and sonography could only be compared for concordance or discordance. Local sonographic interpretations were accepted as correct because sonography does not lend itself to central reading. Before the PIOPED II trial, a quality control committee visited each sonography department to assure image quality and uniform reporting.

Data Analysis
Confidence intervals were calculated using binomial distribution. The single unweighted kappa statistic was used to test for agreement between individual CTV reviewers and between consensus interpretations for CTV and sonography [9]. We performed subgroup analyses to evaluate concordance between CTV and sonography in patients with and without a history of DVT and patients with and without current signs and symptoms of DVT.

Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
For all 1,062 patients who underwent CTV, the femoral vein density was > 90 H in 817 (77%), was 70–90 H in 213 (20%), and was < 70 H in 42 (4%). Subjectively, 48 studies (4.5%) showed poor contrast enhancement, three (0.28%) had unacceptable motion, and 21 (2%) were considered inadequate for interpretation by two reviewers. Overall, 43 (4%) of CTV examinations were eliminated due to quality issues or lack of reviewer consensus. In patients in whom the BMI was available, 170 (20%) of 857 were considered very obese (BMI > 35). In this group, 58 (34%) of 170 CTV examinations were graded as less than optimal quality. This is significantly worse than the remaining patients, for whom there were suboptimal results in only 126 (18%) of 687 (p < 0.001).

There were 711 patients with adequate quality results on both CTV and sonography. The two techniques agreed in more than 95.5% (679/711) of the patients. Both techniques were negative in 598 (84%) of 711 patients; both were positive in 81 (11%) of 711. CTV was positive and sonography was negative in 17 (2%), and CTV was negative and sonography was positive in 15 (2%) (Table 1). The kappa statistic of agreement between the consensus CTV interpretation and the single sonographic interpretation was 0.809 or almost perfect [9].

Of the 711 patients with adequate results on both CTV and sonography, 689 (97%) had information on the presence or absence of signs and symptoms of DVT and 703 (99%) a history of DVT. The proportion of patients with positive CTV or positive sonography and clinical findings suggestive of DVT is shown in Table 2. The proportions were similar. Patients with signs and symptoms of DVT were eight times more likely to have a DVT than those without signs and symptoms (60–61% vs 8%) (p < 0.001). Patients with a history of DVT were more than twice as likely to have a new DVT (26–32% vs 13%) (p < 0.001). Table 3 shows that patients with signs or symptoms of DVT were more likely to have a PE (p < 0.01). In patients with PE, 19 (10%) of 189 had a DVT history, whereas in patients without PE, only 27 (4%) of 625 had a DVT history (p < 0.01).

The kappa statistic for agreement between CTV and sonography ranged between 0.718 and 0.850 in different patient subgroups regardless of signs and symptoms or history (Table 4). This level of agreement is considered substantial or almost perfect [9].

Among patients with PE by the reference test, irrespective of whether all patients were considered, whether only those diagnosed by a positive digital subtraction angiography or high-probability V/Q scan were considered, or whether only those with an interpretable CTA were considered, the proportion with a positive CTV and positive venous sonography was nearly the same (42–51%) and showed no statistically significant difference (Table 5). Similarly, the incidence of DVT was very low (0.9–1.5%) in patients without PE, regardless of the composite standard used to exclude PE. In Figures 1, 2, 3, flow charts trace various patient groups.

View larger version (14K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 —Flowchart shows incidence of deep venous thrombosis (DVT) in patients with positive results for pulmonary embolism (PE) on digital subtraction angiography or ventilation–perfusion scanning. Table summarizes results. Data in table are numbers of patients with percentages in parentheses. All differences are not significant. Numbers indicate number of patients, + indicates positive, – indicates negative. CTV = CT venography, CTA = CT angiography.

View larger version (21K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2 —Flowchart shows incidence of deep venous thrombosis (DVT) in patients with positive results for pulmonary embolism (PE) on CT angiography. Table summarizes results. Data in table are numbers of patients with percentages in parentheses. All differences are not significant. Numbers indicate number of patients, + indicates positive, – indicates negative. CTA = CT angiography, CTV = CT venography, DSA = digital subtraction angiography, V/Q = ventilation–perfusion scanning.

View larger version (21K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3 —Flowchart shows incidence of deep venous thrombosis (DVT) in patients without positive results for pulmonary embolism (PE) on digital subtraction angiography (DSA) or ventilation–perfusion (V/Q) imaging. Table summarizes results. Data in table are numbers of patients with percentages in parentheses. All differences are not significant. Numbers indicate number of patients, + indicates positive, – indicates negative. CTA = CT angiography, CTV = CT venography.

Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
There are clearly benefits to CTV as part of the evaluation for VTE. Among the 183 patients with PE by the reference test and adequate CT and CTV in PIOPED II, CTA showed PE in 150 and CTV showed DVT in an additional 14 [1]. Several studies in the literature have addressed the additional sensitivity for VTE of routine imaging of the legs after CTA. The results are widely divergent, with additional diagnoses of VTE ranging from 1% to 27% [6, 10–18]. Perrier et al. [17], using 4- and 16-MDCT scanners, found that sonography at the time of CTA increased the number of VTE diagnoses by only 1%. Conversely, Ghaye et al. [18], using 16-MDCT, came to a different conclusion: CTV increased the number of VTE diagnoses by 27%.

The overall quality of CTV was good, with 4% of scores judged unreadable. Similarly, 4% of CTV examinations had femoral vein density readings of < 70 H, a level deemed too low for confident diagnosis. Despite a slightly higher IV contrast dose and a higher kVp, obese patients (BMI > 35) were twice as likely to have suboptimal studies. Scattered radiation causing a decreased signal-to-noise ratio is most likely responsible. Obese patients also received less contrast agent per kilogram of body weight than nonobese patients.

CTV was positive more often (60%) in patients with signs and symptoms of DVT than in those without (8%). CTV also was positive more often (26%) in patients with a DVT history than in those without (13%). The conclusions based on history of DVT are limited because of 711 patients we identified only 34 who had a history of DVT. The data show, therefore, that asymptomatic patients and patients with no DVT history have a relatively low incidence of detectable DVT and derive less benefit from CTV or sonography than symptomatic patients.

Balanced against the benefits of CTV are the potential somatic and gonadal effects of pelvic radiation. Rademaker et al. [19], using single-detector CT, calculated an ovarian dose for CTV of 4.7 mSv and a testicular dose of 6.7 mSv. In PIOPED II, the patient radiation exposure varied with scanner generation and different manufacturers. The calculated pelvic dose for 10 consecutive PIOPED II patients imaged at one center using a 4-MDCT scanner (Hi-Speed Advantage, GE Healthcare) was 5.7 mSv [19, 20]. Using a 16-MDCT scanner (Sensation, Siemens Medical Solutions), the calculated pelvic dose was 6.15 mSv. Gonadal dose was not calculated in PIOPED II.

The close agreement between CTV and sonography shown in PIOPED II suggests that CTV and sonography are equally valid for the diagnosis of DVT. Our study is a large multiinstitutional prospective study comparing CTV and sonography in 711 patients. Other smaller, single institution studies have compared CTV and sonography and have shown good to excellent agreement. The methods of patient accrual, use of a reference standard, and reporting of results have varied from study to study, making exact comparison impossible. Three prospective studies totaling 257 patients have found CTV sensitivity to be 100% and specificity to range between 97% and 100% using sonography as the reference standard [6, 13–15]. Conversely, a retrospective study of 136 patients showed a sensitivity of 71% and a specificity of 93% [21]. In a prospective study of 61 ICU patients using a clinical standard as a reference, CTV and sonography were both judged to have identical sensitivity and specificity (70% and 96%, respectively) [16].

DVT was detected or excluded equally by CTV or sonography regardless of the presence or absence of PE. Similarly, DVT detection or exclusion did not seem to vary with the various composite scores used in PIOPED II.

The majority of patients studied in PIOPED II had neither signs nor symptoms of DVT nor history of DVT (90% and 93.5%, respectively). In these patients, CTV was positive in only 8% and 13%, respectively, versus 60% and 26% in those with signs and symptoms or a history of DVT. Perhaps asymptomatic patients of childbearing age should not undergo CTV but should undergo sonography as an alternative when lower extremity imaging is required along with CTA. Not surprisingly, patients with complaints of calf or thigh pain or swelling or signs of DVT had a much higher incidence of PE.

In PIOPED II, among the 105 patients in whom CTV showed DVT, in 89 (85%), thrombi were seen in the femoral or popliteal veins only; and in 13 (12%), thrombi were seen both in the thigh veins and the pelvic veins (distal inferior vena cava [IVC] and iliac veins) [1]. Isolated pelvic thrombi were seen in only three patients (3%). All three had positive CTA examination results for PE. Katz et al. [11] reviewed 100 consecutive positive CTV studies. Only nine of the 215 clots detected were in the pelvis (two, IVC; seven, iliac veins). The authors did not state how many were confined to the pelvis only or how often PE was present. Thus, CTV starting at the acetabula, rather than the iliac crest, covers 40% less of the pelvic anatomy with a proportional reduction in radiation and little loss of diagnostic information. We recently showed that reducing anatomic coverage using discontinuous imaging (5-mm slices every 2 cm) and using automatic tube current adjustment can reduce pelvic radiation by approximately 75% [22]. Perhaps only patients suspected of having pelvic thrombi, such as those who are postpartum or who have had pelvic surgery, should undergo scanning of the IVC and iliac veins as well.

In conclusion, PIOPED II showed that CTV and sonography gave similar results. When imaging of both the pulmonary arteries and the veins of the lower extremity is considered advantageous, the choice between CTA combined with CTV or sonography can be made based on factors other than test accuracy, such as cost, efficiency, or radiation dose.

Acknowledgments
 
We thank Sylvia Bartz for her help with manuscript preparation.

PIOPED II CT reviewers: Lawrence Goodman, chairperson, Medical College of Wisconsin; Claudia Henschke and David Yankelevitz, Cornell University; Page McAdams and Laura Heyneman, Duke University; Brannon Hatfield and Richard Woodcock, Emory University; David Spizarny, Henry Ford Hospital; Theresa McLoud, JoAnn Shepard, and Conrad Wittram, Massachusetts General Hospital; Paul Burrowes and John McGregor, University of Calgary; Ella Kazerooni and Smita Patel, University of Michigan; Jay Heiken and Pamela Woodard, Washington University.

PIOPED II sonography reviewers: Thomas W. Wakefield, chairperson, University of Michigan Medical Center; Grant Brunet, University of Calgary; Beverly Fex, University of Michigan Medical Center; Andrea M. Fisher, New York Hospital; Kevin Fiest, Duke University; Micky McPharlin, Henry Ford Hospital; Brian G. Rubin, Washington University Medical Center; Alex D. Shepard, Henry Ford Hospital; George Skardasis, Emory University; Arthur C. Waltman, Massachusetts General Hospital; Pamela K. Woodard, Mallinckrodt Institute of Radiology, Washington University Medical Center.

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 Goodman, L. R. Articles by Beemath, A. Search for Related Content PubMed PubMed Citation Articles by Goodman, L. R. Articles by Beemath, A. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?