Possible pulmonary embolus: evaluation with digital subtraction versus cut-film angiography--prospective study in 80 patients

Detection of simulated pulmonary embolism in a porcine model using hyperpolarized 3He MRI

Several radiological imaging modalities are available to assist with the clinical diagnosis of pulmonary embolism (PE). The most frequently used techniques-nuclear medicine ventilation-perfusion (VP) scan, computed tomography (CT), magnetic resonance angiography (MRA), and pulmonary angiography (PA)-all have literature-supported, substantial limitations with respect to timeliness and patient safety. Hyperpolarized 3He magnetic resonance gas distribution imaging (HP 3He MRI) recently has shown potential as a safer and faster alternative. In this study, we performed HP 3He MRI on a porcine model (N = 6) of simulated PE using selective occlusion balloon catheterization (N = 4) and nonselective aged autologous clot injection (N = 1). The technique was also performed on a normal pig and again after the animal was killed. Temporal depletion of regional HP 3He MRI signal intensity provided for a qualitative assessment of simulated PE (N = 4), and regional PAO2 (alveolar partial pressure of oxygen) was calculated in affected airspaces for a quantitative assessment of simulated PE (N = 1). The preliminary results suggest that HP (3)He MRI shows promise as a means of assessing regional pulmonary perfusion abnormalities in the porcine models of simulated PE that were used in this study.

Diagnosis of pulmonary embolism with various imaging modalities

Pulmonary embolism (PE) is a major health concern that affects approximately 600,000 new patients annually. The diagnosis of PE can be difficult to make, and several imaging studies have been developed to aid in this process. Initial evaluation involves the acquisition of a chest radiograph. Findings on radiography, however, are often non-specific. The gold-standard study historically has been pulmonary angiography, with increasing diagnostic yield since the implementation of digital subtraction technology. This is an invasive procedure, however, but the incidence of major complications is low. Less invasive modalities have been developed and include ventilation-perfusion lung scans. These are used as one of the initial screening tests in evaluation of patients with suspected PE. The presence of a high-probability scan usually indicates the presence of a PE, although few patients have high probability scans. The test is significantly affected by underlying pulmonary disease or previous PE. Given this, ventilation-perfusion lung scans are limited as a primary diagnostic tool in the evaluation of suspected PE. Helical computed tomography (CT) is currently under much scrutiny as a diagnostic tool for PE. Currently a prospective, multicenter trial evaluating its efficacy (PIOPED II) has been initiated, but the results are pending. Preliminary reports suggest the helical CT and venous phase CT may become a first line study in patient evaluation. The diagnosis of PE is challenging and several imaging modalities are currently used to assist the clinician. Currently, multiple modalities are often required to make the diagnosis. With the advent of new technology and improved imaging techniques, the diagnosis of PE will become easier.

CT for thromboembolic disease

Pulmonary embolism (PE) and deep venous thrombosis (DVT) constitute the two clinical manifestations of venous thromboembolic disease (VTE). The recent innovation of computed tomography venography (CTV) in conjunction with CT pulmonary arteriography (CTPA) provides a single noninvasive diagnostic test that can evaluate both components of VTE. PE is often an underestimated, underdiagnosed, and, consequently, undertreated disease entity. Herein, we review the epidemiology of thromboembolic disease, the diagnostic algorithm used in evaluation of patients with suspected VTE, and protocols for performing CTPA and CTV. Interpretation of these examinations is discussed in detail, because CTPA may pose new challenges to the practicing radiologist.

Acute pulmonary thromboembolism: comparison of the diagnostic capabilities of conventional film-screen and digital angiography

STUDY OBJECTIVE

To compare digital to conventional film-screen pulmonary angiography for the diagnosis of acute pulmonary embolism (PE) in a clinical population.

DESIGN

Retrospective review of patient data, ventilation/perfusion (V/Q) lung scintigraphy reports, and pulmonary angiographic reports.

SETTING

University hospital, division of interventional radiology.

PATIENTS AND METHODS

Patient data from 307 film-screen and 266 digital angiograms were analyzed for demographics, V/Q lung scintigraphy findings, and pulmonary artery pressures to define patient populations. The interpretations of film-screen pulmonary angiography were then compared with digital angiography interpretations for the entire group of interventional radiologists as well as the two interventionists who practiced throughout the study interval to determine any difference in rates of diagnosis of acute PE between the two techniques.

RESULTS

There was no significant difference between the patient populations studied by film-screen or digital techniques for the data reviewed. Digital angiography utilized significantly more contrast material (digital, 173 mL; film-screen, 145 mL; p < 0.01) and a greater number of angiographic views (digital, 3.6 views per patient; film-screen, 3.4 views per patient; p = 0.04) when compared with film-screen angiography. There was no difference between the two techniques in the rates of diagnosis of acute PE, for individual radiologists or overall.

CONCLUSIONS

Digital and film-screen pulmonary angiography possess equivalent diagnostic capabilities for acute PE as used in a clinical setting.

Current strategies for the diagnosis of pulmonary embolus

Venous thromboembolic disease (VTD), comprising venous thrombosis and pulmonary embolus, is responsible for innumerable deaths every day. Wide variance in its presentation and clinical manifestations and the resultant difficulties in achieving its diagnosis have confounded attempts to define optimal diagnostic and treatment strategies. Those strategies should be predicated on the understanding of the manifestations of VTD and of the attributes and interrelationship of the various modalities available for its diagnosis. This review will present an overview of the literature describing those modalities, their strengths and deficiencies, and their current value in algorithms for the diagnosis of VTD.

Clinical validity of a normal pulmonary angiogram in patients with suspected pulmonary embolism--a critical review

AIM

To determine the validity of a normal pulmonary angiogram in the exclusion of pulmonary embolism (PE), based on the safety of withholding anticoagulant therapy in patients with a normal pulmonary angiogram.

MATERIALS AND METHODS

A review of English reports published between 1965 and April 1999 was carried out. Eligible articles described prospective studies in patients with suspected PE and a normal pulmonary angiogram, who remained untreated and were followed-up for a minimum of 3 months. Articles were evaluated by two authors, using pre-defined criteria for strength of design. End points consisted of fatal and non-fatal recurrent thromboembolic events. A sensitivity analysis was performed, by removing one study at a time from the overall results and by comparing pre- and post-1990 publications.

RESULTS

Among 1050 patients in eight articles included in the analysis, recurrent thromboembolic events were described in 18 patients (1.7% 95% CI: 1.0-2.7%). These were fatal in three patients (0.3% 95% CI: 0.02-0.7%). The recurrence rate of PE decreased from 2.9% (95% CI: 1.4-6.8%) before 1990 to 1.1% (95% CI: 0.5-2.2%) after 1990.

CONCLUSION

It would appear that the ability to exclude PE by angiography has improved over the years, as indicated by recurrence rate of PE. The low recurrence rate of PE supports the validity of a normal pulmonary angiogram for the exclusion of PE.

Diagnostic strategies for suspected pulmonary embolism

Pulmonary embolism often remains a difficult diagnosis for the clinician, particularly in patients with comorbidity factors. This is in contrast with the availability of effective treatment, which should be prescribed as soon as possible. To date, there is still no ideal diagnostic test that is accurate, safe, readily available and cost-effective. Recent technical advances in computed tomography, magnetic resonance imaging and laboratory findings have raised new possibilities in the diagnosis of pulmonary embolism. This review covers the performance of different diagnostic tests, and focuses on the advantages and limitations of single diagnostic tests and the clinical usefulness of these tests in diagnostic strategies.

Development of rotational digital angiography system--clinical value in acute pulmonary thromboembolism

A rotational digital angiography system was newly developed by authors. During the rotation, a pulse exposure is done at every 1.25 degrees by computer control, so that 288 different projectional images can be acquired following a single injection of contrast medium. Because rotational image data can be easily reconstructed to 3-D images, more useful diagnostic informations are obtained. Rotational digital angiography was performed for 15 patients with acute pulmonary thromboembolism, and massive thromboemboli were revealed in all patients. The diagnostic usefulness of this new system has also proven to be improved in the interventional procedures. At the appropriate angle, the thrombosed vessels were clearly distinguished. Thus, as the tip of the catheter was advanced to the target site, the thrombosed lesion could be exclusively treated by interventional techniques. The device has, therefore, been found to be of great value in the diagnosis and intervention of acute pulmonary thromboembolism.

Pulmonary embolism: comparison of gadolinium-enhanced MR angiography with contrast-enhanced spiral CT in a porcine model

RATIONALE AND OBJECTIVES

The purpose of this study was to compare gadolinium-enhanced magnetic resonance (MR) angiography with contrast material-enhanced computed tomography (CT) for the detection of small (4-5-mm) pulmonary emboli (PE), with a methacrylate cast of the porcine pulmonary vasculature used as the diagnostic standard.

MATERIALS AND METHODS

In 15 anesthetized juvenile pigs, colored methacrylate beads (5.2 and 3.8 mm diameter-the size of segmental and subsegmental emboli in humans) were injected via the left external jugular vein. After embolization, MR angiographic and CT images were obtained. The pigs were killed, and the pulmonary arterial tree was cast in clear methacrylate, allowing direct visualization of emboli. Three readers reviewed CT and MR angiographic images independently and in random order.

RESULTS

Forty-nine separate embolic sites were included in the statistical analysis. The mean sensitivity (and 95% confidence intervals) for CT and MR angiography, respectively, were 76% (68%-82%) and 82% (75%-88%) (P > .05); the mean positive predictive values, 92% (85%-96%) and 94% (88%-97%) (P > .05). In this porcine model, PE were usually seen as parenchymal perfusion defects (98%) with MR angiography and as occlusive emboli (100%) with CT.

CONCLUSION

MR angiography is as sensitive as CT for the detection of small PE in a porcine model.

Preclinical in vivo testing of the Arrow-Trerotola percutaneous thrombolytic device for venous thrombosis

PURPOSE

To test the safety and efficacy of using the Arrow-Trerotola percutaneous thrombolytic device (PTD) for treating deep vein thrombosis (DVT) in an animal model.

MATERIALS AND METHODS

An established canine model of iliocaval subacute thrombosis was used. Thrombosis was caused by balloon occlusion of the infrarenal inferior vena cava (IVC) for 7 (n = 12), 10 (n = 1), or 17 (n = 1) days. Treatment was performed with use of an 8-F, over-the-wire (0.035-inch) PTD with a 15-mm-diameter basket. The procedure was performed without IVC filtration. Two acute procedures were performed and 12 procedures were intended as survival procedures with 30-day follow-up. Pulmonary arteriography, blood gases, and pulmonary artery pressure measurement were performed before and after the procedure, and at follow-up. The animals were killed after the follow-up procedure and their IVC, iliac veins, and lungs were removed and examined histologically. Heparin was used intraprocedurally but thrombolytic agents were not used. Low-molecular-weight heparin was given daily after the procedure.

RESULTS

Thrombolysis was completely (12 of 13) or partially (one of 13) successful in all animals in the 7- and 10-day groups, but was unsuccessful in the animal in the 17-day group (n = 1). Variable amounts of segmental and subsegmental pulmonary emboli were found in all animals with small increases in pulmonary artery pressure. Two animals died within 6 days of the procedure, possibly due to pulmonary emboli. At 30-day follow-up, IVC patency was preserved in 80% (eight of 10) of animals, but significant caval narrowing due to intimal hyperplasia was noted at follow-up. All pulmonary emboli had resolved angiographically at follow-up, but evidence of recanalized or resolving pulmonary thromboemboli was found in seven of the 12 surviving animals. No acute vascular injury (eg, perforation) occurred.

CONCLUSION

The modified PTD used in this study is effective in treating subacute (<7 days old) venous thrombosis, but temporary filtration will probably be necessary to keep pulmonary emboli to a minimum during the procedure. The 30-day patency is encouraging. The results in this animal model indicate that the Arrow-Trerotola PTD may be useful in the percutaneous treatment of DVT in humans.

Imaging evaluation of suspected pulmonary embolism

Venous thromboembolism (VTE) is a common disorder that is difficult to diagnose clinically but carries significant morbidity and mortality if untreated. Additionally, although demonstrated to be of benefit in cases of proven deep vein thrombosis (DVT) and pulmonary embolism (PE), anticoagulation therapy is not without risk. Because the clinical exam is known to be unreliable for the detection of both DVT and PE, many imaging modalities have been used in the diagnostic imaging algorithm for the detection of VTE, including chest radiography, ventilation/perfusion (V/Q) scintigraphy, pulmonary angiography, and recently, spiral computed tomography (CT) and magnetic resonance imaging (MRI). Chest radiographic findings in acute PE include focal oligemia, vascular enlargement, atelectasis, pleural effusions, and air space opacities representing pulmonary hemorrhage or infarction. The chest radiograph can occasionally be suggestive of PE but is more often nonspecifically abnormal. The main use of the chest radiograph in the evaluation of suspected PE is to exclude entities that may simulate PE and to assist in the interpretation of V/Q scintigraphy. Lower extremity venous compression ultrasonography (CU) is both sensitive and specific for the diagnosis of femoropopliteal DVT, and the value of negative CU results has been established in outcomes studies. However, the reliability of CU for the detection of isolated calf vein thrombosis is not well established, and the clinical significance of such thrombi is debatable. Additional methods such as color and spectral Doppler analysis are also useful in the diagnostic evaluation of DVT but are best considered as adjuncts to the conventional CU examination rather than as primary diagnostic modalities themselves. Compression ultrasonography and Doppler techniques are useful in the evaluation of suspected upper extremity DVT; spectral Doppler waveform analysis is particularly useful to assess for the patency of veins that cannot be directly visualized and compressed with conventional gray-scale sonography. V/Q scintigraphy has been the initial modality obtained in patients suspected of PE for a number of years. Although many studies have investigated the role of V/Q scintigraphy in the evaluation of VTE, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study has provided the most useful information regarding the utility of V/Q scintigraphy in this setting. A high probability scan interpretation is sufficient justification to institute anticoagulation, and a normal perfusion scan effectively excludes the diagnosis of PE. A normal/near normal scan interpretation also carries a sufficiently low prevalence of angiographically proven PE to withhold anticoagulation. Although the prevalence of PE in the setting of low probability scan interpretations is low and several outcomes studies have demonstrated a benign course in untreated patients with low probability scan results, patients with inadequate cardiopulmonary reserve do not necessarily have good outcomes. Such patients deserve more aggressive evaluation. Patients with intermediate probability scan results have a 20% to 40% prevalence of angiographically proven PE and thus require further investigation. The radionuclide investigation of DVT includes such techniques as radionuclide venography and thrombus-avid scintigraphy. Although these methods have not been as thoroughly evaluated as CU, studies thus far have indicated encouraging results, and further investigations are warranted. Pulmonary angiography has been the gold standard for the diagnosis of PE for decades. Studies have indicated that angiography has probably been underutilized by referring physicians for the evaluation of suspected PE, likely because of the perception of significant morbidity and mortality associated with the procedure. (ABSTRACT TRUNCATED)

Clinical follow-up of patients after a negative digital subtraction pulmonary arteriogram in the evaluation of pulmonary embolism

PURPOSE

This study was designed to examine the clinical course of patients following digital subtraction pulmonary arteriography (DSPA) interpreted as negative for pulmonary emboli (PE).

MATERIALS AND METHODS

Sixty-three patients underwent DSPA interpreted as negative for PE over a 27-month period. Follow-up data were collected by means of medical and diagnostic radiology record review, interviews of referring physicians, and patient telephone interviews.

RESULTS

Of 63 patients, two were excluded and seven were lost to follow-up, leaving a study population of 54 patients. Mean follow-up was 12.1 months (range, 0-28.5 months). Thirty-one reported no symptoms of PE. Of 13 patients reporting intermittent chest pain and/or dyspnea during their mean follow-up of 13.6 months, 10 had a history of cardiac, nonthrombotic pulmonary, or gastroesophageal reflux disease. There were no subsequent positive angiograms or ventilation/perfusion scans. Comorbid conditions in the 10 patients who died included cardiac events (n = 4), advanced cancer (n = 2), sepsis/pneumonia (n = 2), sarcoidosis (n = 1), and cerebrovascular accident (n = 1). No documented PE was identified.

CONCLUSION

The technique of DSPA is sufficiently sensitive to exclude clinically significant PE. The advantages of image post-processing, in addition to the savings in cost, time, and contrast media, support its use in the angiographic diagnosis of PE.