Pulmonary embolism: comprehensive diagnosis by using electron-beam CT for detection of emboli and assessment of pulmonary blood flow

P:URPOSE: To comprehensively assess thoracic anatomy and pulmonary microcirculation in pulmonary embolism by using computed tomographic (CT) angiography of the pulmonary arteries combined with functional CT imaging of blood flow. MATERIALS AND METHODS: Twenty-two patients suspected of having acute pulmonary embolism underwent contrast material-enhanced thin-section electron-beam CT angiography of the pulmonary arteries. In addition, in each patient, a dynamic multisection blood flow CT study was performed on a 7.6-cm lung volume with electrocardiographic gating. Pulmonary blood flow was calculated, and perfusion parameters were visualized on color-coded maps. The color-coded maps and CT angiograms were independently evaluated, segment by segment, by two readers for perfusion deficits and the presence of clots, respectively. The results were compared. RESULTS: Mean pulmonary blood flow was 0.63 mL/min/mL in the occluded segments versus 2.27 mL/min/mL in the nonoccluded segments (P: =.001). The sensitivity and specificity of perfusion maps for the presence of segmental pulmonary embolism compared with those of CT angiography were 75.4% and 82.3%, respectively, with positive and negative predictive values of 79.6% and 84.7%, respectively. The false-negative findings were caused mainly by partial occlusion of vessels. In eight patients, a substantial alternative or additional pathologic entity was diagnosed. CONCLUSION: By combining CT angiography and dynamic CT imaging, a comprehensive and noninvasive diagnosis of thoracic structure and function is feasible with a single modality.     

Clinical usefulness of imaging performed after CT angiography that was negative for pulmonary embolus in a high-risk oncologic population

OBJECTIVE: The purpose of our study was to determine the prevalence and types of additional imaging examinations that were performed, and whether anticoagulation therapy was started or continued, after CT angiography showed no pulmonary embolus in a high-risk oncologic population. MATERIALS AND METHODS: We reviewed the radiology report for each CT angiogram that was obtained for clinically suspected pulmonary embolism at our institution (a tertiary cancer center) during a 25-month period. The radiology information system was then searched for any additional confirmatory radiologic examinations performed within 2 days after a negative finding on CT angiography. Medical records were reviewed to determine whether anticoagulation therapy was started or continued despite a negative finding on CT angiography. RESULTS: Two hundred seventy-six CT angiograms were obtained in 260 oncology patients who were clinically suspected of having pulmonary embolism. The findings from 203 CT angiograms (74%) were interpreted as negative; 56 (20%), as positive; and 17 (6%), as equivocal for pulmonary embolism. Fifty-eight patients (21%) with negative findings on CT angiography subsequently underwent additional imaging, the results of which were potentially clinically important in 6% of the patients. Six patients began to receive and two continued to undergo anticoagulation therapy despite negative findings on CT angiography; three of the six patients received anticoagulation for new-onset atrial fibrillation. CONCLUSION: Negative results of CT angiography for pulmonary embolism did not deter referring physicians from ordering other confirmatory imaging tests in 21% of patients in a high-risk oncologic population. Those additional tests rarely revealed results that might have been clinically important.     

Ultrafast computed tomography in experimental pulmonary embolism.

Computed tomography (CT) has proven useful in the diagnosis of central pulmonary embolism; however, its ability to detect peripheral emboli has not been established. The authors evaluate the usefulness of ultrafast CT (UFCT) in detecting experimental peripheral pulmonary emboli. Three Gelfoam emboli measuring 0.7 x 1.5 cm were introduced into the pulmonary arteries of each of seven dogs, and contiguous, 3-mm, axial UFCT images from the lung apex to the base were obtained after the administration of a contrast bolus. After scanning, the dogs were killed, and the locations of the emboli were determined by a pulmonary pathologist blinded to the imaging results. Concomitantly, the locations of the emboli on the UFCT images were determined by consensus of three chest radiologists blinded to the autopsy results. All 21 emboli were identified on UFCT images; the locations of the emboli corresponded exactly with the autopsy findings. The authors conclude that UFCT can reliably detect Gelfoam emboli in second- to fourth-division pulmonary vessels. Further studies are needed to determine if in vivo blood clots can be similarly visualized.     

Right ventricular dysfunction secondary to acute massive pulmonary embolism detected by helical computed tomography pulmonary angiography

OBJECTIVE: Acute massive pulmonary embolism causes abrupt pulmonary arterial hypertension and right ventricular dysfunction (RVD). Patients with RVD have a worse prognosis than those with normal right ventricular function. Consequently, recognizing the RVD at the time of pulmonary embolism is useful for risk stratification and enables more aggressive therapy. The study compared the accuracy of helical computed tomographic (CT) scans with echocardiography in the detecting of RVD in patients with acute massive pulmonary embolism. MATERIALS AND METHODS: Specifically, this work reviewed the CT pulmonary angiograms of 14 patients who were positive for acute massive pulmonary embolism during a 52-month period. CT scans were reviewed for findings indicating RVD. Scans were considered positive for RVD if the right ventricle was dilated or there was leftward shift of the interventricular septum. Echocardiographic reports serving as the reference standard for the diagnosis of RVD were also reviewed. CT study results were then correlated with echocardiography results. RESULTS: Among 14 patients with massive pulmonary embolism, echocardiography identified 12 patients having RVD, whereas the remaining two patients were negative for RVD. Meanwhile, CT correctly identified 11 of 12 patients as having RVD, and was negative for RVD in the remaining 3 patients. Correlated with echocardiography, CT scan for RVD detection had a sensitivity of 91.6% and a specificity of 100%. CONCLUSIONS: CT can accurately detect RVD in patients with acute massive pulmonary embolism. However, this result requires confirmation using a larger prospective cohort study.     

Clinical usefulness of computed tomography study without contrast injection in the evaluation of acute pulmonary embolism

OBJECTIVE: To evaluate the percentage of cases in which emboli can be detected in unenhanced scans and to identify the cases in which they appear hyperattenuating or hypoattenuating in comparison to the circulating blood. METHOD: An angio-computed tomography (CT) scan was performed before and after contrast injection in 140 consecutive patients after clinical suspicion of pulmonary embolism. A radiologist analyzed the examination results thus obtained. The enhanced scan was analyzed first, and after detecting the thrombus, the unenhanced scan was evaluated. RESULTS: Fifty-one examinations were positive for a pulmonary embolism; in 21 cases, it was possible to identify the embolus even in the unenhanced scans. In 10 cases, the clots were hyperattenuating in comparison to the circulating blood; in 5 cases, they were hypoattenuating; and in 6 cases, they were mixed hyper-hypoattenuating. CONCLUSION: In a relatively high percentage of cases, particularly those of central thromboembolism, it is possible to identify and characterize the clots even in unenhanced scans.     

Central pulmonary thromboembolism: diagnosis with spiral volumetric CT with the single-breath-hold technique--comparison with pulmonary angiography.

Forty-two patients were prospectively evaluated with spiral volumetric computed tomography (CT) and selective pulmonary angiography of each lung to detect central pulmonary thromboembolism. Spiral volumetric CT images obtained with either 90 mL of 30% contrast material or 120 mL of 12% contrast material were graded as excellent or good in 98% of the examinations (41 patients). Diagnosis of pulmonary embolism with spiral volumetric CT was based on the direct visualization of intraluminal clots: partial filling defects (n = 41; 37%), complete filling defects (n = 51; 46%), "railway track" signs (n = 6; 5%), and mural defects (n = 14; 12%). All 23 patients with normal findings of spiral volumetric CT had normal findings of pulmonary angiography. With spiral volumetric CT, the finding of 112 central emboli (eight main, 28 lobar, and 76 segmental) corresponded exactly to the angiographic findings, but nine intersegmental lymph nodes were erroneously interpreted as filling defects. In one case of normal pulmonary angiographic findings, asymmetry in pulmonary arterial perfusion was misinterpreted as pulmonary embolism with spiral volumetric CT. Spiral volumetric CT can reliably depict thromboemboli in second- to fourth-division pulmonary vessels.     

64层螺旋CT肺动脉造影在肺动脉栓塞诊断中的应用

目的 探讨64层螺旋CT肺动脉造影(CT pulmonary angiography,CTPA)对肺动脉栓塞(pulmonary embolism,PE)的诊断价值.方法 回顾分析24例肺动脉栓塞患者的64层螺旋CT增强图像,将原始图像复制到EBW4.0工作站,对肺动脉主干及分支进行多平面重建(MPR),最大密度投影(MIP)及容积重建(VR)分析.结果 24例患者中,共检出了76处肺动脉及其分支的栓子.其中,左、右肺动脉主干14处(右主干10处、左主干4处),肺叶动脉24处,肺段动脉26处,亚肺段动脉12处.CT表现为肺动脉主干或分支内混合性、附壁性、中心性充盈缺损,可分为完全性或部分性.结论 64层CTPA具有准确、高效、无创等优点,可直观、立体地观察到肺动脉血栓的大小、分布、范围及类型,是临床诊断及观察疗效的首选方法,有望成为肺动脉栓塞检查的“金标准”.     

Non-traumatic thoracic emergencies: CT diagnosis of acute pulmonary embolism: the first 10 years

Over the past 10 years, spiral CT angiography of the pulmonary arteries has reached a high accuracy in the evaluation of pulmonary embolism. Major advantages of CT compared with ventilation/perfusion lung scintigraphy and pulmonary angiography is direct visualization of clots in the pulmonary arteries, and to provide alternative findings or diagnosis. The recent introduction of multislice CT has improved the evaluation of peripheral pulmonary arteries, enabling high-resolution CT examinations over the entire thorax in a short breathhold. The examination techniques, imaging findings, pitfalls, and results of CT in the diagnosis of pulmonary embolism are reviewed in comparison with other diagnostic tests.     

Thromboembolic disease detection at indirect CT venography versus CT pulmonary angiography

PURPOSE: To assess the incremental increase in thromboembolic disease detection at indirect computed tomographic (CT) venography versus CT pulmonary angiography and to determine the importance of scan interval for indirect CT venography on the basis of thrombus length. MATERIALS AND METHODS: Institutional review board approval was obtained, and informed consent was not required. The study included 1590 consecutive patients undergoing CT pulmonary angiography for the suspicion of pulmonary embolism. Two minutes after completion of pulmonary angiography, a contiguous indirect CT venography was performed from the iliac crest to the popliteal fossa. The presence of pulmonary embolism or deep venous thrombosis (DVT) was recorded for all patients. The lengths of all deep venous thrombi found in the first 378 consecutive patients were recorded. RESULTS: Pulmonary embolism was detected in 243 (15%) of 1590 patients at CT pulmonary angiography, and DVT was detected in 148 (9%) patients at indirect CT venography. Among 148 patients with DVT, pulmonary embolism was detected in 100 patients at CT pulmonary angiography. Thus, the addition of indirect CT venography to CT pulmonary angiography resulted in a 20% incremental increase in thromboembolic disease detection compared with that at CT pulmonary angiography alone (99% confidence interval: 17%, 23%). Among the 378 patients, DVT was present in 33 patients at indirect CT venography. Two (6%) of 33 patients had clots measuring 2 cm or less, six (18%) had clots measuring 3-4 cm, and 25 (76%) had clots measuring more than 4 cm in length. CONCLUSION: The addition of indirect CT venography to CT pulmonary angiography incrementally increases the detection rate of thromboembolic disease by 20%. Performance of indirect CT venography by using contiguous section intervals, with a section width of 1 cm, is recommended to accurately detect DVT.     

Comparison of interpretations of CT angiograms in the evaluation of suspected pulmonary embolism by on-call radiology fellows and subsequently by radiology faculty

OBJECTIVE: Our objective was to evaluate interobserver variability in interpretations performed by on-call radiology fellows and subsequently by attending radiologists of CT angiograms obtained for clinically suspected pulmonary embolism and to evaluate factors contributing to discrepancies. MATERIALS AND METHODS: Written interpretations made by on-call fellows were compared with reports approved by attending radiologists for all CT angiograms obtained for suspected pulmonary embolism after work hours and on weekends in a recent 19-month period. Interpretations were stratified as positive, negative, or equivocal for pulmonary embolism. In cases of discordant interpretations, those CT angiograms were rereviewed by two thoracic radiologists; then patient medical records were reviewed for evidence of clinical effect. Technical and patient-related reasons for discordant interpretations of CT angiograms were recorded. RESULTS: Six hundred fifty-eight oncology patients were examined on CT angiography; five were examined twice. The fellows reported 137 CT angiograms (21%) as positive, 498 (75%) as negative, and 28 (4%) as equivocal for pulmonary embolism. Interpretations of the fellows and attending radiologists agreed in 93% (615/663) of CT angiograms (kappa = 0.80). The concordance rates for CT angiograms interpreted by fellows as positive (89%, 122/137), negative (96%, 479/498), and equivocal (50%, 14/28) were significantly different from each other (p < 0.001 for each). A significantly greater proportion of CT angiograms with discordant interpretations was reported to be technically limited (p < 0.01). No clear adverse clinical events were attributed to discordant interpretations of CT angiograms, although the death of one patient in that subgroup was of indeterminate cause. CONCLUSION: In the evaluation of CT angiograms obtained for suspected pulmonary embolism, on-call fellows showed good agreement with attending radiologists. CT angiograms with discordant interpretations often were limited by technical or patient-related factors.     

Survey on the use of pulmonary scintigraphy, spiral CT and conventional pulmonary angiography for suspected pulmonary embolism in the British Isles

AIM: To determine current clinical practice in the radiological diagnosis of acute pulmonary embolism and assess the use of spiral volumetric computed tomography. METHOD: A survey of 327 acute hospitals including cardiothoracic and orthopaedic tertiary referral centres was undertaken to assess current utilization of lung scintigraphy, spiral computed tomography and pulmonary angiography in the investigation of suspected pulmonary embolism. Responses were received from 215/327 (66%) centres. RESULTS: Lung scintigraphy was provided by 208 hospitals (144 on-site and 64 off-site). Spiral CT services were provided by 111 (52%) hospitals (on- or off-site), 142 (66%) units had access to angiographic facilities. Sixty-three centres out of 215 (29%) offered both on-site lung scintigraphy and spiral CT while only 41/215 (19%) hospitals were able to undertake all three tests on-site. On average, 501 perfusion (Q) or ventilation-perfusion (V/Q) scintigrams were performed per hospital per year with 26 spiral CT studies and just 4.6 pulmonary angiograms. CONCLUSION: These data suggest that lung scintigraphy is frequently the only imaging test in patients other than chest radiography, despite the large number of indeterminate results reported in most series.     

Air trapping on CT of patients with pulmonary embolism

OBJECTIVE: We evaluated the relationship of air trapping to mosaic perfusion in patients with pulmonary embolism. SUBJECTS AND METHODS: Forty-one consecutive patients with suspected pulmonary embolism underwent expiratory CT followed by helical CT angiography. After excluding 12 patients who had airway disease or were smokers, we divided the patients into two groups: those with (n = 15) and without (n = 14) pulmonary embolism. For each patient, six expiratory images were evaluated for the presence of air trapping, and the corresponding six images from CT angiography were evaluated for the presence of mosaic perfusion. Clot locations were assessed on CT angiography and were correlated with the presence of air trapping and mosaic perfusion. RESULTS: In patients with pulmonary embolism, mosaic perfusion was identified in 32 areas (seven patients, 46.7%), and air trapping was identified 68 areas (nine patients, 60%). Of the 32 areas of mosaic perfusion, 23 areas (71.9%) showed air trapping on expiratory CT scans. Of the 68 areas with air trapping on expiratory scans, 23 areas (33.8%) showed mosaic perfusion on inspiratory scans, and 44 areas (64.7%) had clots in the arteries leading to them. Clots were more frequently identified in areas of lower attenuation on inspiratory CT scans and air trapping (21/23) than in those of normal attenuation on inspiratory CT scans and air trapping (23/45) (p < 0.005). Only one patient without pulmonary embolism had air trapping (p < 0.005). CONCLUSION: Air trapping is common in pulmonary embolism and may be the cause of mosaic perfusion. Air trapping can be seen distal to vessels not showing pulmonary embolism.     

Utilization patterns and diagnostic yield of 3421 consecutive multidetector row computed tomography pulmonary angiograms in a busy emergency department

OBJECTIVE: To compare examination volume and diagnostic yield of computed tomography (CT) pulmonary angiography (CTPA) and ventilation-perfusion (V/Q) scintigraphy for detection of suspected pulmonary embolism (PE) in emergency department patients. METHODS: Every CTPA and V/Q scan result for emergency department patients between October 2001 and September 2005 were reviewed. Patients with prior PE and follow-up examinations were excluded. RESULTS: A total of 3421 CTPA examinations and 198 V/Q scans met inclusion criteria. Average CTPA examinations completed per month increased 227%, from 33.4 to 109.2 for the first and last 24-month periods, respectively. Ventilation-perfusion scintigraphy volume decreased 80% (from 6.9 to 1.4 per month). Total diagnoses of PE per month increased 89% from 4.0 to 7.5, whereas the percentage of positive CTPA examinations dropped from 9.8% to 6.8%. CONCLUSIONS: Availability of CT in the emergency department and lower physician thresholds for test utilization have increased the use of CT pulmonary angiography and increased detection of PE.     

Spiral CT of pulmonary embolism: diagnostic approach, interpretive pitfalls and current indications

The introduction of spiral CT has recently modified the diagnostic work-up of pulmonary embolism, because it is possible to depict noninvasively endoluminal clots in second- to-fourth-division pulmonary arteries. If this technique is currently considered a powerful imaging alternative for the detection of acute central emboli, it is mainly related to the possibility to obtain a uniform and high degree of arterial enhancement of pulmonary arteries down to 2–3 mm in diameter. Minimal experience in spiral CT angiography is necessary to achieve this goal and requires familiarity with both data acquisition and contrast medium injection. Numerous interpretive pitfalls exist in assessing spiral CT images, and certain caveats have to be heeded. However, their recognition becomes increasingly less problematic as the radiologist gains experience with spiral CT of the pulmonary vasculature. Therefore, the purpose of this article is to review the diagnostic approach to pulmonary embolism with spiral CT, with special emphasis on protocol parameters and scan interpretation. Received 21 January 1998; Accepted 4 February 1998     

Reassessment of pulmonary angiography for the diagnosis of pulmonary embolism: relation of interpreter agreement to the order of the involved pulmonary arterial branch

PURPOSE: To reassess the validity of conventional pulmonary angiography in the diagnosis of pulmonary embolism (PE) in main, lobar, segmental, and subsegmental pulmonary arteries. 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% Cl = 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% Cl = 85%, 95%). Among 22 patients with PE limited to the subsegmental arteries, the average co-positivity was 66% (95% Cl = 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.     

螺旋CT肺动脉造影对肺栓塞的诊断

目的：评价螺旋CT及其肺动脉造影诊断肺动脉栓塞（PE）的价值。方法：回顾性分析12例PE患,均行螺旋CT容积扫描,并在工作站进行图像后处理,获得肺动脉多平面重建图像及三维立体图像。结果：对12例196支肺动脉分支进行分析,受累率为46.4%;栓子发生在主肺动脉、左右肺动脉干及叶段肺动脉。多平面重建图像上表现为充盈对比剂血管内有充盈缺损区,或其远侧方无对比剂充填区。肺动脉成像示,主干血管内可见充盈缺损影,或呈截断状影;叶栓塞或段栓塞亦呈突然“截断状”,其远侧方肺动脉分支不显影或呈纤维状。结论：螺旋CT肺动脉造影不仅可以获得轴位图像,而且可以获得立体图像,可多轴向旋转观察PE部位,是诊断叶或段以上PE可靠而直观的检查方法。     

Accuracy of CT angiography versus pulmonary angiography in the diagnosis of acute pulmonary embolism: evaluation of the literature with summary ROC curve analysis

RATIONALE AND OBJECTIVES: The authors performed this study to estimate, by using published data, the sensitivity and specificity of computed tomographic (CT) angiography in the evaluation of suspected acute pulmonary embolism (PE). MATERIALS AND METHODS: Summary receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity and specificity of CT angiography in the diagnosis of acute PE. Pulmonary angiography was used as the diagnostic standard of reference. The authors reviewed the results of 11 independent studies published in the English-language literature between January 1992 and June 1999. RESULTS: The sensitivity of CT angiography in the diagnosis or exclusion of PE in the central pulmonary arteries (to the level of the segmental pulmonary arteries) ranged from 0.74 to 0.81 on the basis of specificities of 0.89-0.91. The sensitivity of CT angiography in the diagnosis or exclusion of PE in all pulmonary arteries (to the level of the subsegmental pulmonary arteries) was 0.68 on the basis of a specificity of 0.91. CONCLUSION: On the basis of the studies in the current literature, most of which used 5.0-mm collimation and single-detector CT, CT angiography may be less accurate in the diagnosis of PE than previously reported. With improvements in data acquisition, particularly the use of thinner section collimation and multidetector CT, and in the increased use of workstations for data analysis, the accuracy and utility of CT angiography will require continued investigation.     

Severity of acute pulmonary embolism: evaluation of a new spiral CT angiographic score in correlation with echocardiographic data

The purpose of this study was to investigate whether the severity of acute pulmonary embolism (PE) could be quantitatively assessed with spiral CT angiography (SCTA). Thirty-six consecutive patients without underlying cardiopulmonary disease and high clinical suspicion of PE underwent prospectively thin-collimation SCTA and echocardiography at the time of the initial diagnosis (T0) and after initial therapy (T1; mean interval of time T1–T2: 32 days). The CT severity score was based on the percentage of obstructed surface of each central and peripheral pulmonary arterial section using a 5-point scale (1: <25%; 2: 25–49%; 3: 50–74%; 4: 75–99%; 5: 100%). The sum of the detailed scores attributed to 5 mediastinal, 6 lobar and 20 segmental arteries per patient led to the determination of central, peripheral and global CT severity scores and subsequent determination of percentages of obstruction of the pulmonary circulation. Echocardiographic severity criteria included the presence of signs of acute cor pulmonale and/or systolic pulmonary hypertension (>40 mm Hg). The SCTA depicted acute PE in all patients at T0 with complete resolution of endovascular clots in 10 patients at T1. At T0, the mean percentage of obstruction of the pulmonary arterial bed was significantly higher in the 22 patients with echocardiographic signs of severity (56±13 vs 28±32%; p<0.001). A significant reduction in the mean percentage of pulmonary artery obstruction was observed in the 19 patients with resolution of echocardiographic criteria of severity between T0 and T1 T0: 57±14%; T1: 7±11%; p<0.001).The threshold value for severe PE on CT angiograms was 49% (sensitivity: 0.773; specificity: 0.214). The mean (±SD) pulmonary artery pressure was significantly higher in the 26 patients with more than 50% obstruction of the pulmonary artery bed (45±15 mm Hg) than in the 10 patients with less than 50% obstruction of pulmonary artery bed at T0 (31±11 mm Hg; p<0.01). The CT severity score evaluated in the present study enables quantitative assessment of acute PE severity on spiral CT angiograms, readily applicable in routine clinical practice. Electronic Publication     

Follow-up CT pulmonary angiograms in patients with acute pulmonary embolism

Computed tomographic (CT) angiography is associated with a non-negligible lifetime attributable risk of cancer. The risk is considerably greater for women and younger patients. Recognizing that there are risks from radiation, the purpose of this investigation was to assess the frequency of follow-up CT angiograms in patients with acute pulmonary embolism. This was a retrospective cohort study of patients aged ≥18 years with acute pulmonary embolism seen in three emergency departments from January 2013 to December 2014. Records of all patients were reviewed for at least 14 months. Pulmonary embolism was diagnosed by CT angiography in 600 patients. At least one follow-up CT angiogram in 1 year was obtained in 141 of 600 (23.5 %). Two follow-ups in 1 year were obtained in 40 patients (6.7 %), 3 follow-ups were obtained in 15 patients (2.5 %), and 4 follow-ups were obtained in 3 patients (0.5 %). Among young women (aged ≤29 years) with pulmonary embolism, 10 of 21 (47.6 %) had at least 1 follow-up and 4 of 21 (19.0 %) had 2 or more follow-ups in 1 year. Among all patients, recurrent pulmonary embolism was diagnosed in 15 of 141 (10.6 %) on the first follow-up CT angiogram and in 6 of 40 (15.0 %) on the second follow-up. Follow-up CT angiograms were obtained in a significant proportion of patients with pulmonary embolism, including young women, the group with the highest risk. Alternative options might be considered to reduce the hazard of radiation-induced cancer, particularly in young women.     

Risk of pulmonary embolism after a negative spiral CT angiogram in patients with pulmonary disease: 1-year clinical follow-up study

PURPOSE: To evaluate the effect of pulmonary disease on diagnostic utility of spiral computed tomographic (CT) angiography in clinical practice. MATERIALS AND METHODS: Three hundred thirty-four patients, including 215 patients with pulmonary disease (group 1) and 119 patients with no history of respiratory disorder (group 2), were referred for thin-collimation CT angiography of the pulmonary circulation as the first-line diagnostic test. Patients with negative angiograms who had not received anticoagulation therapy and who could be clinically followed up at 3 months, 6 months, and 1 year were considered in the final study groups (n = 185); 135 patients had lung disease (group 3), and 50 patients had no history of a respiratory disorder (group 4). RESULTS: Between groups 3 and 4, no significant differences were found in the referral location, age, and risk factors. Confident evaluation of pulmonary arteries down to the subsegmental level was performed in 31 (23%) patients in group 3 and in 15 (30%) in group 4 (P =.5). Three episodes of acute pulmonary embolism (PE), all fatal, were diagnosed in group 3 patients; two cases occurred 14 days and one case occurred 6 months after the negative spiral CT scan. The negative predictive value of spiral CT angiography was 98% (175 of 178) in the study group in which follow-up was performed, with no significant difference between the values in groups 3 (98% [132 of 135]) and 4 (100% [50 of 50]). CONCLUSION: Underlying respiratory disease does not affect the negative predictive value of thin-collimation CT angiography, which appears to be a reliable tool in the work-up in this subgroup of patients with acute PE.