Combined CT pulmonary angiography and venography for diagnosis of pulmonary embolism and deep vein thrombosis: radiation dose

CT venography for the diagnosis of postpartum venous thromboembolism: a prospective multi-center cohort study

OBJECTIVES

To assess the role of CT venography (CTV) in the diagnosis of venous thromboembolism (VTE) during the postpartum period.

MATERIALS AND METHODS

This multicenter prospective cohort study was conducted between April 2016 and April 2020 in 14 university hospitals. All women referred for CT pulmonary angiography (CTPA) for suspected pulmonary embolism (PE) within the first 6 weeks postpartum were eligible. All CTPAs were performed on multidetector CT machines with the usual parameters and followed by CTV of the abdomen, pelvis, and proximal lower limbs. On-site reports were compared to expert consensus reading, and the added value of CTV was assessed for both.

RESULTS

The final study population consisted of 123 women. On-site CTPA reports mentioned PE in seven women (7/123, 5.7%), all confirmed following expert consensus reading, three involving proximal pulmonary arteries and four limited to distal arteries. Positive CTV was reported on-site in nine women, five of whom had negative and two indeterminate CTPAs, bringing the VTE detection rate to 11.4% (14/123) (95%CI: 6.4-18.4, p = 0.03). Expert consensus reading confirmed all positive on-site CTV results, but detected a periuterine vein thrombosis in an additional woman who had a negative CTPA, increasing the VTE detection rate to 12.2% (15/123) (95%CI: 7.0-19.3, p = 0.008). Follow-up at 3 months revealed no adverse events in this woman, who was left untreated. Median Dose-Length-Product was 117 mGy.cm for CTPA and 675 mGy.cm for CTPA + CTV.

CONCLUSION

Performing CTV in women suspected of postpartum PE doubles the detection of venous thromboembolism, at the cost of increased radiation exposure.

CLINICAL RELEVANCE STATEMENT

CTV can help in the decision-making process concerning curative anticoagulation in women with suspected postpartum PE, particularly those whose CTPA results are indeterminate or whose PE is limited to the subsegmental level.

KEY POINTS

Postpartum women are at risk of pulmonary embolism, and CT pulmonary angiography can give equivocal results. CT venography (CTV) positivity increased the venous thromboembolism detection rate from 5.7 to 11.4%. CTV may help clinical decision-making, especially in women with indeterminate CTPA results or subsegmental emboli.

Advances in the Diagnosis of Venous Thromboembolism: A Literature Review

The incidence of venous thromboembolism (VTE), including lower extremity deep vein thrombosis (DVT) and pulmonary embolism (PE) is increasing. The increase in suspicion for VTE has lowered the threshold for performing imaging studies to confirm diagnosis of VTE. However, only 20% of suspected cases have a confirmed diagnosis of VTE. Development of pulmonary embolism rule-out criteria (PERC) and update in pre-test probability have changed the paradigm of ruling-out patient with low index of suspicion. The D-dimer test in conjunction to the pre-test probability has been utilized in VTE diagnosis. The age appropriate D-dimer cutoff and inclusion of YEARS algorithm (signs of the DVT, hemoptysis and whether PE is the likely diagnosis) for the D-dimer cutoff have been recent updates in the evaluation of suspected PE. Multi-detector computed tomography pulmonary angiography (CTPA) and compression ultrasound (CUS) are the preferred imaging modality to diagnose PE and DVT respectively. The VTE diagnostic algorithm do differ in pregnant individuals. The prerequisite of avoiding excessive radiation has recruited planar ventilation-perfusion (V/Q) scan as preferred in pregnant patients to evaluate for PE. The modification of CUS protocol with addition of the Valsalva maneuver should be performed while evaluating DVT in pregnant individual.

Combined MR Imaging for Pulmonary Embolism and Deep Venous Thrombosis by Contrast-enhanced MR Volume Interpolated Body Examination

MR pulmonary angiography (MRPA) combined with indirect MR venography (MRV) was attempted by using 3D contrast-enhanced MR volume interpolated body examination (VIBE) sequence. Agreement rate for deep venous thrombosis (DVT) detection between MRV and duplex sonography (DUS) was evaluated; the potential of this method for venous thromoembolism (VTE) was also investigated. Thirty-four patients with DUS-identified DVT were enrolled in this study. MRI was performed after a single administration of Gadopentetate dimeglumine. Fat-suppressed 3D VIBE was applied for visualizing pulmonary arteries, abdominal veins, pelvic and leg veins, ranging from lung apex to ankle level. Two radiologists observed the MR images in consensus, recorded the location and number of emboli. MRV images were assessed based on per-vein segment. The agreement rate between MRV and DUS for venous segment-to-segment comparison was analyzed by Wilcoxon rank sum test. All the patients were diagnosed as having DVT by MRV. MRV detected 55 more venous segments with thrombi than DUS based on per-vein segment analysis. Twenty-three patients with pulmonary embolism (PE) were detected by MRPA. Twenty-one patients underwent both pulmonary CT angiography and MRPA, and consistency for PE detection was 100%. Total examination time of the combined MR protocol was 7 min for each patient. The contrast-enhanced VIBE sequence proves to be a feasible and reliable method for VTE diagnosis in one-stop MR scanning procedure, and contrast-enhanced VIBE performs better to depict DVT than DUS on per-vein segment basis.

Fat-suppressed magnetic resonance volume interpolated examination for deep venous thrombosis compared with duplex sonography

The aim of the present study was to evaluate magnetic resonance venography (MRV) scanned by breath-hold volume interpolated body examination with spectral fat saturation (VIBE-fs), combined with Dixon fat-suppressed VIBE (VIBE-Dixon) by using a 1.5T MR scanner for detecting deep venous thrombosis (DVT) compared with duplex sonography. A total of 31 patients with DVT were identified using duplex sonography and were enrolled in the present study for MRV examination, from the inferior vena cava to the ankle level after injection of gadopentetate dimeglumine. Venous segment-to-segment comparison was assessed for DVT detection between MRV and duplex sonography. A total of two radiologists separately performed subjective image quality assessment using a 5-point scale. Cohen's κ coefficient, Wilcoxon rank sum test and intraclass correlation coefficient values were used for statistical analysis. Of the 303 evaluated vein segments, duplex sonography identified 119 (39.3%; 119/303) venous segments with thrombus, while MRV detected 170 (56.1%; 170/303) venous segments with thrombus. The diagnostic agreement rate of DVT between duplex sonography and MRV was poor in the deep femoral vein and anterior tibial veins, while it was excellent in the inferior vena cava (IVC), common iliac vein, external iliac vein, femoral vein, popliteal vein, posterior tibial veins and peroneal veins. In addition, poor reliability was detected in the deep femoral vein, anterior tibial veins and peroneal veins, but good to excellent reliability was observed in IVC, common iliac vein, external iliac vein, femoral vein, popliteal vein and posterior tibial veins. Furthermore, image quality scores of each venous segment between the two radiologists indicated no statistical difference. Therefore, MRV scanned using VIBE-fs for the suprainguinal and VIBE-Dixon for the infrainguinal region may be a useful method for detecting DVT compared with duplex sonography. The results of present study proved this MR protocol to be a beneficial alternative imaging modality for the detection of DVT when duplex sonography is inadequate or not able to be performed.

Magnetic resonance angiography imaging of pulmonary embolism using agents with blood pool properties as an alternative to computed tomography to avoid radiation exposure

PURPOSE

To evaluate the feasibility and accuracy of a combined magnetic resonance angiography (MRA) - magnetic resonance venography (MRV) protocol using contrast agents with blood pool properties, gadofosveset trisodium and gadobenate dimeglumine, in the evaluation of pulmonary embolus (PE) and deep venous thrombosis (DVT) as compared to the standard clinical reference imaging modalities; computed tomography pulmonary angiography (CTPA) and color-coded Duplex ultrasound (DUS).

MATERIALS AND METHODS

This prospective clinical study recruited patients presenting to the emergency department with clinical suspicion for PE and scheduled for a clinically indicated CTPA. We performed both MRA of the chest for the evaluation of PE as well as MRV of the pelvis and thighs to evaluate for DVT using a single contrast injection. MRA-MRV data was compared to the clinical reference standard CTPA and DUS, respectively.

RESULTS

A total of 40 patients were recruited. The results on a per-patient basis comparing MRA to CTPA for pulmonary embolus yielded 100% sensitivity and 97% specificity. There was a small subset of patients that underwent clinical DUS to evaluate for DVT, which demonstrated a sensitivity and specificity of 100% for MRV.

CONCLUSIONS

This single-center, preliminary study using contrast agents with blood pool properties to perform a relatively rapid combined MRA-MRV exam to image for PE and above knee DVT shows potential as an alternative imaging choice to CTPA. Further large-scale, multicentre studies are warranted.

Use of Computed Tomography and Magnetic Resonance Imaging in Central Venous Disease

Successful management of acute deep vein thrombosis and post-thrombotic syndrome depends on careful patient selection and detailed investigation of thrombus extent, composition, and anatomy. This article reviews the use of computerized tomography and magnetic resonance imaging in the assessment of central deep veins of the pelvis and addresses new developments within the field. Despite drawbacks of each imaging modality, when contemplating deep venous reconstruction, cross-sectional imaging should be considered for preoperative planning and to compliment intraoperative imaging tools, including intravascular ultrasound and contrast venography.

High energy injury is a risk factor for preoperative venous thromboembolism in the patients with hip fractures: A prospective observational study

BACKGROUND

The purpose of this study was to identify the incidence of preoperative venous thromboembolism (VTE), and determine if high energy hip fracture affects preoperative VTE occurrence.

METHODS

Three-hundred nine patients (244 low and 61 high energy injuries) treated between March 2015 and March 2017 were included in this study. Indirect multidetector computed tomographic venography for the detection of preoperative VTE was performed at admission. The incidence of preoperative VTE was compared between high and low energy injury hip fractures. Logistic regression analysis was used to identify independent risk factors for preoperative VTE.

RESULTS

The overall incidence of preoperative VTE was 18.4% (56 of 305 patients). Preoperative VTE was identified in 17 (27.9%) and 39 (16.0%) patients in the high and low energy injury groups, respectively (p = 0.034). Multivariate logistic regression analysis showed that high energy injury, history of VTE, and myeloproliferative disease were significant predictive factors of preoperative VTE (OR = 2.451; 95% CI = 1.227-4.896, OR = 11.174; 95% CI = 3.500-35.673, OR = 6.936; 95% CI = 1.641-29.321, respectively) CONCLUSION: Because high energy hip fracture is significantly associated with preoperative VTE occurrence, preoperative evaluation and proper thromboprophylaxis should be performed for patients with a high-energy hip fracture.

Diagnosis of acute pulmonary embolism

Advances in the management of patients with suspected pulmonary embolism (PE) have improved diagnostic accuracy and made management algorithms safer, easier to use, and well standardized. These diagnostic algorithms are mainly based on the assessment of clinical pretest probability, D-dimer measurement, and imaging tests-predominantly computed tomography pulmonary angiography. These diagnostic algorithms allow safe and cost-effective diagnosis for most patients with suspected PE. In this review, we summarize signs and symptoms of PE, current existing evidence for PE diagnosis, and focus on the challenge of diagnosing PE in special patient populations, such as pregnant women, or patients with a prior VTE. We also discuss novel imaging tests for PE diagnosis and highlight some of the additional challenges that might require adjustments to current diagnostic strategies, such as the reduced clinical suspicion threshold, resulting in a lower proportion of PE among suspected patients as well as the overdiagnosis of subsegmental PE.

Preoperative Prevalence of and Risk Factors for Venous Thromboembolism in Patients with a Hip Fracture: An Indirect Multidetector CT Venography Study

BACKGROUND

This retrospective cohort study investigated the prevalence of and risk factors for preoperative venous thromboembolism (VTE) in patients with a hip fracture and a delay of >24 hours from injury to surgery.

METHODS

This observational study included 208 patients with a hip fracture surgically treated at 1 university hospital between December 2010 and August 2014. Patients underwent indirect multidetector computed tomographic (MDCT) venography for preoperative VTE detection after admission. Overall VTE risk and median time from injury to CT scan were calculated. Age, sex, fracture type, time from injury to CT scan, body mass index, preinjury mobility score, previous anticoagulation treatment, previous hospitalization for VTE, varicose veins, and medical comorbidities were considered potential risk factors.

RESULTS

The prevalence of preoperative VTE was 11.1% (23 of 208 patients), including 12 patients with deep vein thrombosis alone, 7 patients with pulmonary embolism alone, and 4 patients with both. The mean time from injury to CT scan was 4.9 days. The delay from the time of injury to CT scan averaged 7.6 days for patients who developed preoperative VTE, compared with 4.2 days for patients who had not developed VTE. In the adjusted models, female sex, subtrochanteric fracture, pulmonary disease, cancer, previous hospitalization for VTE, and varicose veins were risk factors for VTE. The final multivariate logistic regression analysis demonstrated that female sex (odds ratio [OR] = 5.86; 95% confidence interval [CI] = 1.21 to 28.21), subtrochanteric fracture (OR = 22.17; 95% CI = 4.02 to 122.06), pulmonary disease (OR = 21.10; 95% CI = 5.35 to 83.21), and previous hospitalization for VTE (OR = 16.36; 95% CI = 3.41 to 78.43) increased the risk of VTE.

CONCLUSIONS

Our findings show a high prevalence of preoperative VTE in patients with a hip fracture. Therefore, preoperative investigation for VTE should be routinely considered for patients in whom surgery is delayed for >24 hours. At this time, indirect MDCT venography seems to be effective and useful.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Management of Venous Thromboembolisms: Part I. The Consensus for Deep Vein Thrombosis

Deep vein thrombosis (DVT) is a potentially catastrophic condition because thrombosis, left untreated, can result in detrimental pulmonary embolism. Yet in the absence of thrombosis, anticoagulation increases the risk of bleeding. In the existing literature, knowledge about the epidemiology of DVT is primarily based on investigations among Caucasian populations. There has been little information available about the epidemiology of DVT in Taiwan, and it is generally believed that DVT is less common in Asian patients than in Caucasian patients. However, DVT is a multifactorial disease that represents the interaction between genetic and environmental factors, and the majority of patients with incident DVT have either inherited thrombophilia or acquired risk factors. Furthermore, DVT is often overlooked. Although symptomatic DVT commonly presents with lower extremity pain, swelling and tenderness, diagnosing DVT is a clinical challenge for physicians. Such a diagnosis of DVT requires a timely systematic assessment, including the use of the Wells score and a D-dimer test to exclude low-risk patients, and imaging modalities to confirm DVT. Compression ultrasound with high sensitivity and specificity is the front-line imaging modality in the diagnostic process for patients with suspected DVT in addition to conventional invasive contrast venography. Most patients require anticoagulation therapy, which typically consists of parenteral heparin bridged to a vitamin K antagonist, with variable duration. The development of non-vitamin K oral anticoagulants has revolutionized the landscape of venous thromboembolism treatment, with 4 agents available,including rivaroxaban, dabigatran, apixaban, and edoxaban. Presently, all 4 drugs have finished their large phase III clinical trial programs and come to the clinical uses in North America and Europe. It is encouraging to note that the published data to date regarding Asian patients indicates that such new therapies are safe and efficacious. Ultimately, our efforts to improve outcomes in patients with DVT rely on the awareness in the scientific and medical community regarding the importance of DVT.

KEY WORDS

Combination therapy; Hypertension; α1-blocker.

Comparison of the image qualities of filtered back-projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction for CT venography at 80 kVp

PURPOSE

To evaluate the subjective and objective qualities of computed tomography (CT) venography images at 80 kVp using model-based iterative reconstruction (MBIR) and to compare these with those of filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR) using the same CT data sets.

MATERIALS AND METHODS

Forty-four patients (mean age: 56.1 ± 18.1) who underwent 80 kVp CT venography (CTV) for the evaluation of deep vein thrombosis (DVT) during 4 months were enrolled in this retrospective study. The same raw data were reconstructed using FBP, ASIR, and MBIR. Objective and subjective image analysis were performed at the inferior vena cava (IVC), femoral vein, and popliteal vein.

RESULTS

The mean CNR of MBIR was significantly greater than those of FBP and ASIR and images reconstructed using MBIR had significantly lower objective image noise (p < .001). Subjective image quality and confidence of detecting DVT by MBIR group were significantly greater than those of FBP and ASIR (p < .005), and MBIR had the lowest score for subjective image noise (p < .001).

CONCLUSION

CTV at 80 kVp with MBIR was superior to FBP and ASIR regarding subjective and objective image qualities.

KEY POINTS

• MBIR provides superior image quality compared with FBP and ASIR • CTV at 80kVp with MBIR improves diagnostic confidence in diagnosing DVT • CTV at 80kVp with MBIR presents better image quality with low radiation.

Feasibility of detecting pulmonary embolism using noncontrast MRI

Purpose. The purpose of this study was to evaluate the feasibility of detecting pulmonary emboli utilizing noncontrast magnetic resonance imaging techniques in patients with known pulmonary embolism. Materials and Methods. Eleven patients were enrolled in a study to evaluate right ventricular function by cardiac MRI in patients diagnosed with acute pulmonary embolism on CT pulmonary angiogram. Cardiac MRI was performed as soon as possible following pulmonary embolism detection. Two independent observers reviewed the precontrast portion of each MRI, scoring right, left, and lobar arteries as positive or negative for PE. The CTs were reviewed and interpreted in the same manner. Results. MRI was obtained on average of 40 hours after the CT. Forty-eight vessels were affected by PE on CT, 69% of which were identified on MRI. All eight pulmonary emboli located in the right or left pulmonary arteries were detected on MRI. Of the 15 pulmonary emboli that were not detected on MRI, 7 were subsegmental, 6 were segmental, and 2 were located in a branch not included in the MRI field of view. Conclusions. Most pulmonary emboli detected on CT were identified on noncontrast MRI, even though our MRI protocol was not optimized for pulmonary artery visualization.

Diagnosis of DVT: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Objective testing for DVT is crucial because clinical assessment alone is unreliable and the consequences of misdiagnosis are serious. This guideline focuses on the identification of optimal strategies for the diagnosis of DVT in ambulatory adults.

METHODS

The methods of this guideline follow those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that clinical assessment of pretest probability of DVT, rather than performing the same tests in all patients, should guide the diagnostic process for a first lower extremity DVT (Grade 2B). In patients with a low pretest probability of first lower extremity DVT, we recommend initial testing with D-dimer or ultrasound (US) of the proximal veins over no diagnostic testing (Grade 1B), venography (Grade 1B), or whole-leg US (Grade 2B). In patients with moderate pretest probability, we recommend initial testing with a highly sensitive D-dimer, proximal compression US, or whole-leg US rather than no testing (Grade 1B) or venography (Grade 1B). In patients with a high pretest probability, we recommend proximal compression or whole-leg US over no testing (Grade 1B) or venography (Grade 1B).

CONCLUSIONS

Favored strategies for diagnosis of first DVT combine use of pretest probability assessment, D-dimer, and US. There is lower-quality evidence available to guide diagnosis of recurrent DVT, upper extremity DVT, and DVT during pregnancy.

Current approach to the diagnosis of acute nonmassive pulmonary embolism

Pulmonary embolism is a common and potentially lethal disease. Given the variable presentation and associated morbidity of this condition, an accurate and efficient diagnostic algorithm is required. Clinical pretest probability serves as the root of any diagnostic approach. We, thus, review several clinical decision rules that may help standardize this determination. Using a review of the literature, the accuracy, predictive values, and likelihood ratios for several diagnostic tests are described. The combination of these tests, based on the pretest probability of disease, can be used in a Bayesian fashion to make accurate treatment decisions. A completely noninvasive diagnostic algorithm for patients presenting with suspected acute pulmonary embolism is proposed.

Peripartum pulmonary embolism

Pregnancy is an example of Virchow's triad predisposing to the development of venous thromboembolism (VTE). Specific risk factors for antepartum and postpartum VTE have been identified. The diagnosis of pulmonary embolism in pregnancy is complicated by the physiologic changes of pregnancy as well as physicians' apprehension about ordering radiologic studies during pregnancy because of concerns with fetal well-being. Therapy for VTE is complicated by pregnancy physiology affecting medication pharmacokinetics and bioavailability, and the unpredictable occurrence of labor during therapeutic anticoagulation.

Venous thromboembolism: additional diagnostic value and radiation dose of pelvic CT venography in patients with suspected pulmonary embolism

PURPOSE

To assess the additional diagnostic value of indirect CT venography (CTV) of the pelvis and upper thighs performed after pulmonary CT angiography (CTA) for the diagnosis of venous thromboembolism (VTE).

MATERIALS AND METHODS

In a retrospective analysis, the radiology information system entries between January 2003 and December 2007 were searched for patients who received pulmonary CTA and additional CTV of the pelvis and upper thighs. Of those patients, the radiology reports were reviewed for the diagnosis of pulmonary embolism (PE) and deep venous thrombosis (DVT) in the pelvic veins and veins of the upper thighs. In cases with an isolated pelvic thrombosis at CTV (i.e. which only had a thrombosis in the pelvic veins but not in the veins of the upper thigh) ultrasound reports were reviewed for the presence of DVT of the legs. The estimated radiation dose was calculated for pulmonary CTA and for CTV of the pelvis.

RESULTS

In the defined period 3670 patients were referred to our institution for exclusion of PE. Of those, 642 patients (353 men, 289 women; mean age, 65±15 years, age range 18-98 years) underwent combined pulmonary CTA and CTV. Among them, PE was found in 227 patients (35.4%). In patients without PE CTV was negative in all cases. In patients with PE, CTV demonstrated pelvic thrombosis in 24 patients (3.7%) and thrombosis of the upper thighs in 43 patients (6.6%). Of those patients 14 (2.1%) had DVT in the pelvis and upper thighs. In 10 patients (1.5%) CTV showed an isolated pelvic thrombosis. Of those patients ultrasound reports were available in 7 patients, which revealed DVT of the leg veins in 5 cases (1%). Thus, the estimated prevalence of isolated pelvic thrombosis detected only by pelvic CTV ranges between 1-5/642 patients (0.1-0.7%). Radiation dose ranges between 4.8 and 9.7 mSv for additional CTV of the pelvis.

CONCLUSION

CTV of the pelvis performed after pulmonary CTA is of neglectable additional diagnostic value for the detection of VTE, because the additional radiation dose is high and isolated pelvic DVT is very rare. Venous imaging of the legs (preferably by radiation-free ultrasound) is sufficient for the diagnosis of underlying DVT in patients with suspected PE.

Magnetic resonance imaging and computed tomography developments in imaging of venous thromboembolism

Venous thromboembolism (VTE) is a disease that causes high morbidity and mortality in the population. At present the first-line imaging test for a suspected pulmonary embolism (PE) is computed tomography (CT) pulmonary angiography, and ultrasonography is widely used for the diagnosis of deep-vein thrombosis (DVT). Although these modalities are proven to be safe and accurate, unresolved issues remain, such as whether CT scanning in patients with a suspected PE should be extended to the legs. Another issue is the diagnosis of recurrent DVT. Magnetic resonance imaging (MRI) offers a number of advantages in the imaging of VTE. Recent developments of scanning protocols with shorter acquisition times, sometimes complemented by navigator gating or making use of endogenous contrast, offer new perspectives for the use of MRI. This review provides an overview of state of the art MRI techniques for the diagnosis of PE and DVT. Furthermore, the use of new contrast agents such as fibrin labeling to detect thrombi are addressed.

Testing low-risk patients for suspected pulmonary embolism: a decision analysis

STUDY OBJECTIVE

The Pulmonary Embolism Rule-out Criteria (PERC) identifies low-risk patients who are treated in the emergency department for suspected pulmonary embolism and for whom testing may be deferred. The purpose of this study is to develop a decision model to determine whether certain elements not included in the PERC methodology could better estimate the testing threshold for pulmonary embolism (ie, the pretest probability below which a patient should not be tested for pulmonary embolism). In addition, we determine which risks and benefits of pulmonary embolism evaluation and treatment have the greatest effect on the testing threshold.

METHODS

We built decision models of low-risk patients with suspected pulmonary embolism, as determined by the PERC. We obtained model inputs from the literature or by using clinical judgment when data were unavailable. One-way sensitivity analysis derived the testing threshold, and 2-way sensitivity analysis was used to determine the main drivers of the testing threshold.

RESULTS

We found an average testing threshold of 1.4% across all age and sex cohorts. Two-way sensitivity analysis demonstrated that risk of major bleeding from anticoagulation, mortality from contrast-induced renal failure, risk of cancer from computed tomography scan, and mortality from both treated and untreated pulmonary embolism had the greatest effects on the testing threshold.

CONCLUSION

We found a testing threshold for the PERC similar to that calculated by the Pauker and Kassirer method, using somewhat different assumptions. The 5 major drivers for the testing threshold are variables for which there is a paucity of literature to assess accurately for low-risk patients.

Negative predictive value of computed tomography pulmonary angiography with indirect computed tomography venography in intensive care unit patients

PURPOSE

The aim of the study was to evaluate the negative predictive value (NPV) of combined computed tomography (CT) pulmonary angiography (CTPA) and indirect CT venography (CTV) in the intensive care unit (ICU) setting.

MATERIALS AND METHODS

We retrospectively reviewed the records of 181 consecutive ICU patients who underwent CTPA/CTV. Radiology reports were examined to determine whether the study was positive for pulmonary embolism (PE), PE and deep venous thrombosis (DVT), or DVT alone; indeterminate; or negative. Results that were reported as negative were further evaluated for evidence of PE or DVT within 30 days by imaging, clinical evaluation, or autopsy data. The outcomes were evaluated for significance by calculating the rate ratio and 95% confidence interval.

RESULTS

A total of 41 patients (22.7%) were diagnosed with venous thromboembolism, 29 (70.7%) with PE, 8 (19.5%) with PE and DVT, and 4 (9.8%) with DVT. Seven studies were considered nondiagnostic. Seventeen deaths occurred within 30 days of CTA/CTV, of which none was felt to be related to PE/DVT. Of the 140 studies read as negative or nondiagnostic, 4 were determined to have venous thromboembolism (3 PEs and 1 DVT) within 30 days of the initial study (NPV = 97.1%). If patients who received prophylactic anticoagulation or inferior vena cava interruption (n = 25) were excluded, NPV decreases to 96.5%

CONCLUSION

A negative CTPA/CTV is reliable for the exclusion of significant venous thromboembolism in ICU patients.

The role of multidetector computed tomography angiography for the diagnosis of pulmonary embolism

From a radiological point of view, computed tomography pulmonary angiography (CTPA) has effectively become the de-facto first-line imaging test for the evaluation of pulmonary embolism (PE), as patients with a high-quality negative CTPA do not require further examination or treatment for suspected PE. We are likely to see further technical developments in CT technology in the near future. These advances will most likely further improve image quality. Several questions or issues remain, including strategies for further imaging when CT is inconclusive or contraindicated, issues regarding radiation exposure, the prevalence of PE in specific populations, best tests and pathways in specific patient groups, including patients with specific comorbidities such as oncology patients or patients with chronic obstructive pulmonary disease. Also, the question whether all PE patients need anticoagulation, the clinical effect of follow-up imaging, and the accuracy of different clinical prediction rules, remains.

Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC)

Non-thrombotic PE does not represent a distinct clinical syndrome. It may be due to a variety of embolic materials and result in a wide spectrum of clinical presentations, making the diagnosis difficult. With the exception of severe air and fat embolism, the haemodynamic consequences of non-thrombotic emboli are usually mild. Treatment is mostly supportive but may differ according to the type of embolic material and clinical severity.

Routine pelvic and lower extremity CT venography in patients undergoing pulmonary CT angiography

OBJECTIVE

The purpose of our study was to assess the utility of performing routine pelvic and lower extremity CT venography (CTV) along with pulmonary CT angiography (CTA) in all patients evaluated for pulmonary embolism.

MATERIALS AND METHODS

Eight hundred twenty-nine consecutive patients (281 men and 548 women) underwent CTA-CTV for pulmonary embolism. Reports were evaluated as follows: positive or negative for pulmonary embolism with or without deep venous thrombosis (DVT) or with nondiagnostic CTV. Coexisting factors of malignancy, previous venous thromboembolism (VTE), recent surgery, and cardiovascular disease comprised the high-risk group of 446 patients. The remaining 383 patients formed the low-risk group. Statistical analysis included four binary predictors (previous VTE, malignancy, cardiovascular disease, and surgery) and three binary outcome variables (pulmonary embolism, DVT, and VTE). Chi-square test and univariate and multivariate regression analyses were performed.

RESULTS

VTE, pulmonary embolism, and DVT occurred in 152 (18.3%), 124 (15.0%), and 61 (7.3%) of 829 patients, respectively. Between the high-risk and low-risk groups, prevalence of VTE was 114 (25.6%) of 446 and 38 (9.9%) of 383 patients, respectively (p < 0.001); prevalence of pulmonary embolism was 92 (20.6%) of 446 and 32 (8.3%) of 383 patients, respectively (p < 0.001). Isolated DVT was found in 28 (3.4%) of 829 patients. The incremental value of CTV for the entire cohort was 3.4%, 0.72% in the low-risk group (six of 829) and 2.6% (22 of 829) in the high-risk group. For outcome variable VTE, malignancy and previous VTE were statistically significant (p = 0.04 and p < 0.001, respectively); for pulmonary embolism, malignancy and previous VTE were statistically significant (p = 0.03 and p = 0.005, respectively); for DVT, only previous VTE was statistically significant (p < 0.001).

CONCLUSION

CTV should not be performed routinely in all patients evaluated for pulmonary embolism and may only be useful in patients with a high probability of pulmonary embolism, including those with a history of VTE and possible malignancy.

Imaging of deep vein thrombosis

Background

Deep vein thrombosis of the leg affects 1–2 per cent of the population with an annual incidence of 0·5–1 per 1000. It presents with non-specific symptoms and signs making clinical diagnosis difficult. Techniques to image and diagnose this condition are advancing rapidly.

Methods and results

A literature review from 1980 to 2007 was undertaken using PubMed, The Cochrane Library, Medline and Embase. The most frequently used diagnostic test is duplex ultrasonography which is accurate above the knee and has a low cost, but is limited by inaccuracy when assessing the pelvic and distal veins and in diagnosing a new thrombosis in the post-thrombotic limb. Magnetic resonance imaging (MRI) and sonographic elasticity imaging are more recent techniques that have shown promise in overcoming these limitations. However, their availability is currently restricted because they are expensive. Computed tomography (CT) is sensitive, specific and provides good imaging of the pelvis. It has the advantage that it can be performed at the same time as CT pulmonary angiography.

Conclusion

MRI has some specific advantages over duplex ultrasonography, but requires refinement before it can be used clinically. Venography or CT venography should be considered when duplex scanning is inadequate.

CT Venography for Deep Venous Thrombosis: Continuous Images Versus Reformatted Discontinuous Images Using PIOPED II Data

OBJECTIVE

This study was designed to determine whether discontinuous CT of the lower extremities for the detection of deep venous thrombosis (DVT) yields results similar to those of complete helical imaging using cases from the Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II).

MATERIALS AND METHODS

In PIOPED II, CT venography followed CT angiography (CTA) to detect pulmonary embolus, using 7.5-mm continuous helical imaging from the iliac crest to the tibial plateau. DVT was detected in 105 of 737 patients (14.2%). We randomly chose 54 positive cases and 96 negative cases for our study. The continuous helical images were reformatted as 7.5-mm images and two of every three images were deleted. These images (7.5 mm; skip = 15 mm) were then sent--without identifying information--to the original reviewers. From 1 to 3.5 years had elapsed since the original interpretations. The results of the new interpretations were compared with the original CT venography consensus interpretations of PIOPED II.

RESULTS

There was agreement for the presence of DVT in at least one leg (same leg) or for the absence of DVT in both legs in 133 of the 150 study patients (89%). The kappa statistic showed substantial agreement between the consensus interpretations and the test interpretations (kappa = 0.75; 95% CI = 0.64-0.86) per patient.

CONCLUSION

There was good--but not perfect--agreement between continuous helical and discontinuous axial imaging for the detection of DVT. Given the vagaries of interobserver and intraobserver variation, there appears to be little difference between the two approaches. Adopting discontinuous imaging and other dose-reduction strategies can reduce pelvic radiation by more than 75%.

CT venography vs ultrasound in the diagnosis of thromboembolic disease in patients with clinical suspicion of pulmonary embolism

To assess the reliability of indirect computed tomography venography (CTV) in the detection of deep venous thrombosis (DVT) in patients with clinical suspicion of pulmonary embolism (PE). 235 consecutive patients with suspicion of PE underwent an imaging protocol composed of a CT pulmonary angiography (CTPA), a CTV and an ultrasound study of the deep venous system, which was considered the "gold standard." Sensitivity, specificity, and predictive values were calculated for CTV. ith CTV, 30 (12.8%) cases of DVT were detected, 9 (3.8%) of them without pulmonary embolism in CTPA, increasing the diagnosis of thromboembolic disease in 3.8%. However, six of these nine diagnoses were false positives, and CTV missed six cases of DVT. CTV rendered a sensitivity of 58.8%, specificity of 95.0%, a positive predictive value of 66.7%, and a negative predictive value of 93.2%. In patients with clinical suspicion of pulmonary embolism, ultrasound is preferred to CTV for the detection of DVT.

Benefit of CT venography for the diagnosis of thromboembolic disease

OBJECTIVE

The aim of this study was to determine the benefit of lower extremity CT venography (CTV) with pulmonary CT angiography (CTA) for diagnosing thromboembolic (TE) disease.

SUBJECTS AND METHODS

Reports of all CTAs and CTVs over a 3-year interval (Group I) and CTAs, CTVs, and lower extremity Doppler ultrasounds (US) over a 1 1/2-year subset (Group II) were reviewed. Patient population was inpatients and emergency department patients who were assessed for pulmonary embolism (PE) and deep venous thrombosis (DVT) at a tertiary care hospital. Reported results for CTA or CTV were categorized as positive (CTA(P), CTV(P)), negative (CTA(N), CTV(N)), or indeterminate for PE or DVT. When CTV and US results were discrepant, medical records were reviewed for clinical management. Additional benefit of CTV was assessed by chi-square analysis.

RESULTS

In Group I, 737 (81.1%) of 909 CTAs from combined CTA/CTV studies were negative. The diagnosis rate of TE disease increased from 13.0% to 17.3% with the addition of CTV(P)s (P=.01). Of the 119 cases in Group II undergoing combined CTA, CTV, and US, CTV and US were both positive in eight and both negative in 88. Of the seven discordant CTVs and USs with clinical follow-up, five CTVs were positive while USs were negative, three of which were treated clinically for TE disease, while two were considered falsely positive. As CTA also proved positive in one of the three, CTV therefore affected management in two of these five cases and increased the rate of thromboembolism diagnosis from 21.0% to 22.6%; however, this was not significant (P>.05). Two CTV(N)s were managed as false negatives.

CONCLUSIONS

The combined use of CTA and CTV significantly increases the rate of TE disease over CTA alone. In cases in which ultrasound is performed, however, there is no significant advantage to performing combined CTA/CTV studies.

Evidence-based Practice in Radiology: Steps 3 and 4—Appraise and Apply Diagnostic Radiology Literature

Several paradigms for evidence-based practice (EBP) exist. One model proposes that specialist academic centers should primarily construct valid guidelines for various topics in medicine (top-down model). An alternative model integrates "the best research evidence with clinical expertise and patient values" (bottom-up model). Whereas the former model inherently implies a central specialized process, the latter implies that practitioners working in nonspecialist centers can learn and implement a standardized set of tools with which to ask a question, search and appraise the literature, and then apply best current evidence in a local setting. This article focuses on appraising the literature and applying retrieved results and is part of a series on EBP in radiology. This article describes a clinical scenario in which a new respirologist at a hospital requests indirect computed tomographic (CT) venography as part of a work-up of a patient with a high pretest probability for pulmonary embolism and a positive d-dimer test result. Many controversies surround the technique of indirect CT venography, and difficult topics such as this are ideally suited to the tools of EBP. This article will describe how to approach such a scenario.

Computed tomography pulmonary angiogram diagnosis of pulmonary embolism

Over the last decade, contrast-enhanced spiral CT has been established as a non-invasive alternative to catheter angiography and is now regarded as the first-line imaging investigation for the diagnosis of pulmonary embolism (PE). The reported sensitivities for the diagnosis of PE of spiral CT vary from 45 to 100% and the specificities vary from 78 to 100%. Prospective outcome studies have shown a high negative predictive value for a single-detector spiral CT for PE. Patients' outcomes were not adversely affected in these studies when anticoagulation was withheld after a negative CT pulmonary angiogram. The main limitation of single-detector spiral CT has been its limited ability to detect isolated subsegmental PE. However, multidetector spiral CT allows evaluation of pulmonary vessels down to sixth-order branches and significantly increases the rate of detection of PE in segmental and subsegmental levels. The interobserver correlations for diagnosis of subsegmental PE with multidetector spiral CT exceed the reproducibility of selective pulmonary angiography. If appropriate equipment is available (multidetector CT), then CT pulmonary angiogram is safe to be used as the first-line imaging investigation for the diagnosis of PE.

Does Multi–Detector Row CT Pulmonary Angiography Reduce the Incremental Value of Indirect CT Venography Compared with Single–Detector Row CT Pulmonary Angiography?

PURPOSE

To compare retrospectively the incremental value of indirect computed tomographic (CT) venography performed after multi-detector row CT pulmonary angiography and single-detector row CT pulmonary angiography for the diagnosis of venous thromboembolism (VTE).

MATERIALS AND METHODS

The institutional ethics committee approved this study; informed consent was not required. The authors retrospectively reviewed results of 1100 combined single-detector row CT pulmonary angiographic and indirect CT venographic examinations (542 men, 558 women; mean age, 61 years +/- 17 [standard deviation]) (group 1) and 308 combined multi-detector row CT pulmonary angiographic and indirect CT venographic examinations (150 men, 158 women; mean age, 62 years +/- 18) (group 2), performed in 1408 patients suspected of having pulmonary embolism (PE). Frequency of deep venous thrombosis (DVT), PE, and VTE, and the incremental value of indirect CT venography were recorded in both groups. Data were compared by means of the Student t test for continuous data and z statistics for independent proportions.

RESULTS

VTE, PE, and DVT were found in 23.3% (n = 256), 19.9% (n = 219), and 18.3% (n = 201) of the 1100 patients in group 1, respectively, and in 23.7% (n = 73), 17.2% (n = 53), and 18.8% (n = 58) of the 308 patients in group 2, respectively (P values ranging from .273 to .876). The incremental value of indirect CT venography was 14.4% (37 of 256 patients) in group 1 and 27.4% (20 of 73 patients) in group 2.

CONCLUSION

Despite potential improved accuracy of multi-detector row CT pulmonary angiography for the diagnosis of PE, the addition of indirect CT venography increased the diagnosis of VTE in 27.4% of patients.

Experience in 207 Combined MRI Examinations for Acute Pulmonary Embolism and Deep Vein Thrombosis

OBJECTIVE

The purpose of this study was to prospectively assess the feasibility and quality of combined MRI examinations consisting of thoracic MRI for suspected pulmonary embolism (PE) and MR venography for deep vein thrombosis (DVT), to assess the diagnostic yield of a combined examination for detecting thromboembolism compared with each component alone, and to retrospectively assess the concordance of duplex sonography and MR venography.

SUBJECTS AND METHODS

Two hundred twenty-one consecutive patients (119 men, 102 women; mean age, 51 years; range, 31-86 years) with suspected PE were examined using a multitechnique thoracic MRI protocol (real-time MRI using true fast imaging with steady-state precession [FISP], perfusion MRI, and MR angiography) followed by stepping-table MR venography.

RESULTS

Two hundred twenty-one thoracic MRI examinations were performed. Two hundred eighteen MR venography examinations were scheduled, of which five (2.3%) were not performed for clinical or technical reasons and six were not performed after negative thoracic MRI. Among 207 combined examinations, PE was diagnosed in 76 and DVT in 78 examinations. Thirteen patients without PE showed DVT; thus, MR venography detected 17% additional cases of thromboembolism. Agreement with duplex sonography was good at the upper leg (kappa = 0.87-0.89) but moderate at the pelvis (kappa = 0.59-0.65).

CONCLUSION

A combined "one-stop-shopping" MRI approach for PE and DVT was routinely feasible and detected 17% more cases of thromboembolism compared with separate examinations. MRI may be considered a second-line technique to avoid contraindications to CT but also a primary comprehensive technique for diagnosing thromboembolism.

Diagnosis of suspected venous thromboembolic disease in pregnancy

Venous thromboembolic disease is a leading cause of maternal mortality during pregnancy. Early and accurate radiological diagnosis is essential as anticoagulation is not without risk and clinical diagnosis is unreliable. Although the disorder is potentially treatable, unnecessary treatment should be avoided. Most of the diagnostic imaging techniques involve ionizing radiation which exposes both the mother and fetus to finite radiation risks. There is a relative lack of evidence in the literature to guide clinicians and radiologists on the most appropriate method of assessing this group of patients. This article will review the role of imaging of suspected venous thromboembolic disease in pregnant patients, highlight contentious issues such as radiation risk, intravenous contrast use in pregnancy and discuss the published guidelines, as well as suggesting an appropriate imaging algorithm based on the available evidence.

O desafio de diagnosticar tromboembolia pulmonar aguda em pacientes com doença pulmonar obstrutiva crônica

Tromboembolia pulmonar aguda e exacerbação aguda de doença pulmonar obstrutiva crônica são doenças comuns. A doença pulmonar obstrutiva crônica é um fator clínico de risco para tromboembolia pulmonar aguda. As apresentações clínicas da tromboembolia pulmonar aguda e da exacerbação aguda da doença pulmonar obstrutiva crônica freqüentemente mimetizam-se tanto que pode ser difícil distingui-las. Anormalidades estruturais nos pulmões com doença pulmonar obstrutiva crônica tornam também difícil a interpretação de testes não invasivos de diagnóstico, como o mapeamento de ventilação e perfusão pulmonares. Assim, diagnosticar tromboembolia pulmonar aguda em pacientes com doença pulmonar obstrutiva crônica é uma tarefa desafiadora. Com o objetivo de atualizar o assunto e oferecer sugestões de conduta, nós avaliamos artigos abordando este tema, incluindo relatos e séries de casos, abordagens diagnósticas de tromboembolia pulmonar aguda e fizemos algumas reflexões. A probabilidade clínica de tromboembolia pulmonar aguda em cenários de doença pulmonar obstrutiva crônica é usualmente intermediária, o mapeamento de ventilação e perfusão pulmonares é predominantemente de probabilidade intermediária e os algoritmos de conduta os deveriam assim considerar.

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.