Diagnosis of acute pulmonary embolism in outpatients: comparison of thin-collimation multi-detector row spiral CT and planar ventilation-perfusion scintigraphy

Computed tomography pulmonary angiography: an assessment of the radiology report

RATIONALE AND OBJECTIVE

The aim of this study was to evaluate the uncertainty in computed tomographic pulmonary angiography (CTPA) radiology reports, manifested by descriptions of report limitations and image quality.

MATERIALS AND METHODS

CTPA reports between 2004 and 2006 were reviewed for patient demographic data (age, gender, pregnancy state), radiologist data (years of experience, subspecialty, final dictation by an attending radiologist vs a resident being present and dictating the report), the presence of pulmonary embolism (PE), and key words describing examination quality and limitations.

RESULTS

There were 2151 CTPA reports. Patterns of reporting CTPA in the impression sections of radiology reports were as follows: (1) PE conclusively positive (10%), (2) PE conclusively negative (29%), (3) PE negative to segmental arteries (27%), (4) PE negative to central pulmonary arteries (21%), (5) PE negative but suboptimal examination (8%), and (6) nondiagnostic examination (5%). Among the last three categories, seven PEs were not initially diagnosed but were found on subsequent imaging examinations. Limitations in image quality, respiratory motion artifact, and contrast enhancement were most frequently mentioned as limitations in image quality (62% and 28% of all reports, respectively). Radiologists tended to report limitations in image quality if they were thoracic radiology subspecialists, had >10 years of experience, or worked independently (P < .001).

CONCLUSION

Different patterns of reporting CTPA exist and vary on the basis of individual radiologists' subspecialties, experience, and whether they work independently or with residents. Certain wording regarding the presence of PE may falsely imply negativity of PE in a limited examination.

Pulmonary MR angiography techniques and applications

This article discusses the role of magnetic resonance angiography (MRA) in evaluating the pulmonary arterial system. For depiction of pulmonary arterial anatomy and morphology, MRA techniques are compared with CT angiography and digital subtraction x-ray angiography. Perfusion, flow, and function are emphasized, as the integrated MR examination offers a comprehensive assessment of vascular morphology and function. Advances in MR technology that improve spatial and temporal resolution and compensate for potential artifacts are reviewed as they pertain to pulmonary MRA. Current and emerging gadolinium contrast-enhanced and non-contrast-enhanced MRA techniques are discussed. The role of pulmonary MRA, clinical protocols, imaging findings, and interpretation pitfalls are reviewed for clinical indications.

Diagnostic management of clinically suspected acute pulmonary embolism

Current diagnostic management of hemodynamically stable patients with clinically suspected acute pulmonary embolism (PE) consists of the accurate and rapid distinction between the approximate 20-25% of patients who have acute PE and require anticoagulant treatment, and the overall majority of patients who do not have the disease in question. Clinical outcome studies have demonstrated that, using algorithms with sequential diagnostic tests, PE can be safely ruled out in patients with a clinical probability indicating PE to be unlikely and a normal D-dimer test result. This obviates the need for additional radiological imaging tests in 20-40% of patients. CT pulmonary angiography (CTPA) has become the first line tool to confirm or exclude the diagnosis of PE in patients with a likely probability of PE or an elevated D-dimer blood concentration. While single-row-detector technology CTPA has a low sensitivity for PE and bilateral compression ultrasound (CUS) of the lower limbs is considered necessary to rule out PE, multi-row-detector CTPA is safe to exclude PE without the confirmatory use of CUS.

Performance of the Wells and Revised Geneva scores for predicting pulmonary embolism

OBJECTIVE

The objective of the study was to compare two scoring methods to predict the risk of pulmonary embolism (PE) as diagnosed with computed tomography angiography (CTA) and/or CT venography (CTV).

METHODS

Prospectively over a 8-month period, emergency department patients and hospital inpatients with suspected PE were consecutively examined and their Wells and Revised Geneva scores calculated to stratify them into a risk group for PE probability. Then all patients were examined with CTA and CTV to determine the presence or absence of PE, as diagnosed by experienced radiology staff physicians.

RESULTS

During the study period, 167 patients were suspected of having a PE and were interviewed for the calculation of their Wells and Revised Geneva scores. All patients underwent CTA or CTV, but the images of only 148 patients were adequate enough to make a certain diagnosis regarding PE. The data of these 148 patients were used for the study. The rates of PE in high, moderate, and low PE risk groups determined according to the Wells score and the Revised Geneva score were 89.6, 26.4, 7.8 and 83.3, 25.6, 0%, respectively. Among both inpatients and ED patients the area under the Wells score receiver operating characteristic curve was higher (P=0.04). When data from only ED patients were analyzed (104 patients) the scoring systems was not significantly different (P=0.07).

CONCLUSION

The Wells rule seems to be more accurate among both inpatients and emergency department patients. The Revised Geneva score can be used in emergency department patients with high reliability.

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.

Ventilation/perfusion lung scintigraphy: what is still needed? A review considering technetium-99m-labeled macro-aggregates of albumin

Lung perfusion scintigraphy (LPS) with technetium-99m-labeled macro-aggregates of albumin (Tc-99m-MAA) is well established in the diagnostic of pulmonary embolism (PE). In the last decade, it was shown that single-photon emission computer tomography (SPECT) acquisition of LPS overcame static scintigraphy. Furthermore, there are rare indications for LPS, such as preoperative quantification of regional lung function prior to lung resection or transplantation, optimization of lung cancer radiation therapy, quantification of right-left shunt, planning of intra-arterial chemotherapy, and several rare indications in pediatrics. Moreover, LPS with Tc-99m-MAA is a safe method with low radiation exposure. PE can also be diagnosed by spiral computer tomography (CT), ultrasound, magnetic resonance angiography, or pulmonary angiography (PA, former gold standard). The present review considers all these methods, especially spiral CT, and compares them with LPS with respect to sensitivity and specificity and gives an overview of established and newer publications. It shows that LPS with Tc-99m-MAA represents a diagnostic method of continuing value for PE. In comparison with spiral CT and/or PA, LPS is not to be defeated as mentioned also by the most actual Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II reports. This applies in particular to chronic or recurring embolisms, whereas currently spiral CT may be of greater value for major or life-threatening embolisms. At present, LPS cannot be replaced by other methods in some applications, such as pediatrics or in the quantification of regional pulmonary function in a preoperative context or prior to radiation therapy. LPS still has a place in the diagnostics of PE and is irreplaceable in several rare indications as described earlier.

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.

Imaging of pulmonary thromboembolism

Pulmonary thromboembolism usually results from deep venous thrombi originating in the lower extremities. Therefore, imaging of venous thromboembolism includes evaluation of the pulmonary arteries and the deep veins of the lower extremities. The introduction of helical CT and multidetector row CT into daily use has enabled direct visualization of pulmonary arteries. CT venography, performed 3 minutes after CT pulmonary angiography (without additional contrast administration), adds the ability to evaluate the veins of the lower extremities and pelvis. The modalities currently used in the diagnostic workup of venous thromboembolic disease and their advantages and disadvantages are discussed in this article.

Computer-aided diagnosis of lung cancer and pulmonary embolism in computed tomography-a review

Computer-aided detection (CADe) and computer-aided diagnosis (CADx) have been important areas of research in the last two decades. Significant progress has been made in the area of breast cancer detection, and CAD techniques are being developed in many other areas. Recent advances in multidetector row computed tomography have made it an increasingly common modality for imaging of lung diseases. A thoracic examination using thin-section computed tomography contains hundreds of images. Detection of lung cancer and pulmonary embolism on computed tomographic (CT) examinations are demanding tasks for radiologists because they have to search for abnormalities in a large number of images, and the lesions can be subtle. If successfully developed, CAD can be a useful second opinion to radiologists in thoracic CT interpretation. In this review, we summarize the studies that have been reported in these areas, discuss some challenges in the development of CAD, and identify areas that deserve particular attention in future research.

Computed tomography pulmonary angiography in the diagnosis of acute pulmonary embolism in the emergency department

This study was undertaken to evaluate the use of computed tomography pulmonary angiography (CTPA) in patients with pulmonary embolism (PE) who were followed in the emergency department (ED). The files and computer records of 850 patients older than 16 years of age who were seen in the Hacettepe University Hospital ED between April 10, 2001, and December 1, 2005, and who required CTPA for PE prediagnosis and/or another diagnosis, were studied retrospectively. PE was identified by CTPA in 9.4% of 416 women and in 5.8% of 434 men. A significant difference (P<.05) was noted in the women and men in whom PE was detected. The mean age of the patients was 58.13+/-17.88 y (range, 16-100 y). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for clinical susceptibility to PE among patients who underwent CTPA were assessed at 95.3%, 48.2%, 13%, and 99.2%, respectively. CTPA was done for different reasons: aortic aneurysm dissection (n=1), cough distinctive diagnosis (n=1), dyspnea distinctive diagnosis (n=6), chest pain distinctive diagnosis (n=3), PE prediagnosis (n=51), and other reasons (n=2). Also, sensitivity, specificity, PPV, and NPV were found to be 95.4%, 16.2%, 14.4%, and 96%, respectively, for D-dimer. CTPA, which is accessible on a 24-h basis in the ED, is a valuable tool for the diagnosis of PE.

The rise in the incidence of pulmonary embolus after joint arthroplasty: is modern imaging to blame?

In recent years, there has been an apparent increase in the incidence of pulmonary embolus after joint arthroplasty at our institution. We hypothesized the use of sophisticated imaging modalities such as the multidetector computed tomography scan, with better sensitivity, resulted in an apparent increase in the incidence of pulmonary embolus. We studied all patients with pulmonary embolus after joint arthroplasty between 2000 and 2005. The incidence of pulmonary embolus increased from 0.21% (six of 2859) when VQ scan was the modality of choice to 0.98% (50 of 5095) during the time spiral computed tomography was used to 1.72% (89 of 5179) in recent years when multidetector computed tomography was used. Despite the apparent increase in pulmonary embolus, we observed no change in mortality during the study period. Surgeons should be aware of the challenges sophisticated imaging modalities in general and modern imaging introduce for pulmonary embolus in particular. Extremely sensitive imaging tests with unknown specificity have resulted in an increase in diagnosed pulmonary embolus. However, diagnosing pulmonary embolus generates implications for further treatment such as prolonged anticoagulation and/or inferior vena cava filter insertion with potential for catastrophic complications. The challenge is to distinguish which require treatment and which do not.

Influence of age on the cost-effectiveness of diagnostic strategies for suspected pulmonary embolism

BACKGROUND

Age has a marked effect on the diagnostic yield of D-dimer measurement and lower limb compression ultrasonography (CUS) in patients with suspected pulmonary embolism (PE), suggesting that specific diagnostic strategies may be needed in elderly patients.

OBJECTIVE

To evaluate the cost-effectiveness of including D-dimer and CUS in the workup of PE, with particular attention to patient age.

SUBJECTS AND METHODS

We analyzed data from two recent outcome studies that enrolled 1721 consecutive outpatients with suspected PE. Both studies used a sequential diagnostic strategy that included assessment of clinical probability, D-dimer measurement, CUS, and helical computed tomography (hCT). A decision analysis model was created for analyzing cost-effectiveness according to six classes of age. The main outcome measures were 3-month quality-adjusted expected survival and costs per patient managed.

RESULTS

All strategies were equally safe, with variations in the 3-month survival never exceeding 0.5% as compared to the most effective strategy. D-dimer measurement was highly cost-saving under the age of 80 years. Above 80 years, the cost-sparing effect of D-dimer was diminished, but not completely abolished. Inclusion of CUS increased the costs of diagnostic strategies irrespective of age. Results were unchanged over a wide range of the variables of interest (costs, sensitivity, and specificity of the tests).

CONCLUSIONS

Diagnostic strategies using D-dimer are less expensive. The cost-sparing effect of D-dimer is reduced but not abolished above 80 years, suggesting that adapting specific diagnostic strategies in elderly outpatients is not mandatory. CUS is costly, and only marginally improves the safety of diagnostic strategies for PE.

Comprehensive cardiovascular ECG-gated MDCT as a standard diagnostic tool in patients with acute chest pain

Acute myocardial infarction, pulmonary embolism, and aortic dissection are diseases associated with acute chest pain and may lead to severe morbidity and mortality. These diseases may not be trivial to diagnose in the settings of emergency room. ECG-gated multi-detector computed tomography (MDCT), already established for the assessment of pulmonary embolism and aortic dissection, provides reliable information regarding the triage of patients with acute coronary syndrome in the emergency room. MDCT recently appeared to be logistically feasible and a promising comprehensive method for the evaluation of cardiac and non-cardiac chest pain in emergency department patients. The possibility to scan the entire thorax visualizing the thoracic aorta, the pulmonary arteries, and the coronary arteries could provide a new approach to the triage of acute chest pain. The inherent advantage of MDCT with cardiac state-of-the-art capabilities is the rapid investigation of the main sources of acute chest pain with a high negative predictive value. Recent studies also reports an advantage in terms of costs. With current evidence, the selection of patients with acute chest pain candidates to MDCT should remain restricted to avoid unjustified risk of ionizing radiation.

[Value of multislice CT for the work-up of pulmonary embolism]

Multislice computed tomography (MSCT) of the pulmonary arteries has overcome the limitations of single-slice CT and is accepted as the sole reference standard for imaging pulmonary embolism (PE) in many institutions. This technique provides the opportunity of efficient risk stratification to enable adequate differential therapy. With a low or intermediate pretest probability and a negative CT angiography (CTA), relevant PE can be ruled out safely. In >30% further diagnoses other than pulmonary embolism, e.g., pneumonia or aortic aneurysm, can be established on the basis of thoracic CTA. This article discusses the present role of MSCT in diagnostic imaging of PE and provides optimized acquisition protocols as well as practical aspects for secondary image reconstruction. Examples of typical imaging features of PE are shown. Diagnostic algorithms for daily emergency practice are discussed with respect to artifacts and pitfalls in image interpretation.

MDCT for suspected pulmonary embolism: multi-institutional survey of 16-MDCT data acquisition protocols

The purpose of this study was to determine the extent to which a consensus exists on multidetector row computed tomography (MDCT) protocol parameters for suspected pulmonary embolism (PE). In August of 2004, a questionnaire addressing a number of body MDCT protocols was mailed to 99 fellows of the Society of Computed Body Tomography, representing a total of 46 institutions. In May 2005, this was followed up with a second mailing. The survey requested details pertaining to protocols for the most advanced MDCT scanner in the department. The overall survey response rate of 37% (17/46) yielded 15 protocols for 16-MDCT imaging of suspected PE. This data was tabulated and revealed a consensus for the use of bolus tracking, rapid contrast infusion, caudo-cranial scanning, the narrowest detector row collimation, and thin (<2 mm) reconstruction sections. However, contrast infusion timing, contrast concentration, and implementation of radiation dose modulation were variable. This compilation of protocols reflects recently published studies advocating the use of narrow acquisition collimation and reconstruction sections for MDCT of suspected PE. Future studies are necessary to elucidate the optimal intravenous contrast infusion parameters and further assess the efficacy of reduced radiation dose protocols.

Pulmonary Embolism: Radiation Dose with Multi–Detector Row CT and Digital Angiography for Diagnosis

PURPOSE

To compare radiation dose delivered at four- and 16-detector row computed tomography (CT) with a dose-modulation program and that delivered at digital angiography for evaluation of pulmonary embolism (PE).

MATERIALS AND METHODS

The part of the study involving patients (seven women, four men; mean age, 62 years +/- 16 [standard deviation]; range, 41-85 years) was approved by the institutional review board. Patients gave written informed consent. Exposure was performed with an anthropomorphic phantom with thermoluminescent dosimeters for four-detector row CT without the dose-modulation program and 16-detector row CT without and with the dose-modulation program with standard protocols for pulmonary CT angiography (120 kV, 144 mAs, four and 16 detector rows with 1.00- and 0.75-mm section thickness, respectively). Digital angiograms were acquired with four standard projections at 80 kV. For digital angiography, radiation dose was calculated according to phantom measurements and adapted to acquisition and fluoroscopy times. Distribution of dose was compared for CT and digital angiography.

RESULTS

During pulmonary CT angiography, mean radiation dose delivered at middle of chest was 21.5, 19.5, and 18.2 mGy for four-detector row CT and for 16-detector row CT without and with dose-modulation program, respectively. At the same level, a mean dose of 91 mGy was delivered with digital angiography. The dose adjusted to clinical conditions was 139.0 mGy for digital angiography and could be reduced after technical adjustment. Ratios of maximum dose to mean dose were 1.15 and 2.96 for CT and digital angiography, respectively. With application of the dose-modulation program at 16-detector row CT, radiation dose was reduced 15%-20% at the upper chest.

CONCLUSION

Multi-detector row CT delivers a lower radiation dose, with better spatial distribution of dose, than does pulmonary digital [corrected] angiography. With 16-detector row CT and a dose-modulation program, radiation dose is decreased during PE work-up.

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.

The Undiagnosed Pleural Effusion

The most common causes for undiagnosed transudative effusions are congestive heart failure and hepatic hydrothorax. Pleural fluid N terminal pro-brain natriuretic peptide levels higher than 1500 pg/mL are virtually diagnostic of congestive heart failure. The most common causes for undiagnosed exudative pleural effusions are malignancy, pulmonary embolism, and tuberculosis. Clinical characteristics of patients with a malignant pleural effusion are symptoms for more than 1 month, absence of fever, blood-tinged pleural fluid, and CT findings suggestive of malignancy. Thoracoscopy is useful to establish the diagnosis of malignancy and tuberculosis.

Scanning systems and protocols used during imaging for acute pulmonary embolism: how much do our clinical colleagues know?

RATIONALE AND OBJECTIVES

The imaging systems and protocols used during ventilation-perfusion lung (V-P) scintigraphy and computed tomographic (CT) pulmonary angiography (CTPA) can affect diagnostic performance. We investigated the level of awareness of these factors among US clinicians who refer patients for imaging for suspected acute pulmonary embolism.

MATERIALS AND METHODS

Between September 2004 and February 2005, we conducted a mail survey of 855 physicians selected at random from three professional organizations. We asked participants how important the availability of state-of-the-art equipment was in their imaging decisions, whether V-P scintigraphy was performed with planar or single-photon emission CT (SPECT) equipment in their communities, to identify the most advanced type of CT scanner used for CTPA, and whether CT venography (CTV) was performed routinely after CTPA.

RESULTS

We received completed surveys from 240 (29.8%) physicians practicing in 44 states. One hundred sixty-six respondents (70.9%) indicated that state-of-the-art equipment was an extremely or very important factor when they made imaging decisions. However, 191 clinicians (80.3%) did not know whether SPECT equipment was used for V-P scintigraphy, and 119 (50.6%) did not know the type of CT scanner used for CTPA in their communities. Of respondents, 39.2% reported access to multidetector row CT technology for CTPA, whereas 10.2% referred patients to facilities using single-detector CT. Only 9.3% of respondents indicated that CTV was performed routinely after CTPA.

CONCLUSION

Although state-of-the-art equipment is important to them, clinicians practicing in the United States have limited knowledge of the equipment being used during CTPA and V-P scintigraphy scanning in their communities. Radiologists should intensify efforts to familiarize their clinical colleagues with the equipment they use.

Multidetector computed tomography for acute pulmonary embolism

BACKGROUND

The accuracy of multidetector computed tomographic angiography (CTA) for the diagnosis of acute pulmonary embolism has not been determined conclusively.

METHODS

The Prospective Investigation of Pulmonary Embolism Diagnosis II trial was a prospective, multicenter investigation of the accuracy of multidetector CTA alone and combined with venous-phase imaging (CTA-CTV) for the diagnosis of acute pulmonary embolism. We used a composite reference test to confirm or rule out the diagnosis of pulmonary embolism.

RESULTS

Among 824 patients with a reference diagnosis and a completed CT study, CTA was inconclusive in 51 because of poor image quality. Excluding such inconclusive studies, the sensitivity of CTA was 83 percent and the specificity was 96 percent. Positive predictive values were 96 percent with a concordantly high or low probability on clinical assessment, 92 percent with an intermediate probability on clinical assessment, and nondiagnostic if clinical probability was discordant. CTA-CTV was inconclusive in 87 of 824 patients because the image quality of either CTA or CTV was poor. The sensitivity of CTA-CTV for pulmonary embolism was 90 percent, and specificity was 95 percent. CTA-CTV was also nondiagnostic with a discordant clinical probability.

CONCLUSIONS

In patients with suspected pulmonary embolism, multidetector CTA-CTV has a higher diagnostic sensitivity than does CTA alone, with similar specificity. The predictive value of either CTA or CTA-CTV is high with a concordant clinical assessment, but additional testing is necessary when the clinical probability is inconsistent with the imaging results.

CT pulmonary angiography is the first-line imaging test for acute pulmonary embolism: a survey of US clinicians

RATIONALE AND OBJECTIVES

Our aim is to document current imaging practices for diagnosing acute pulmonary embolism (PE) among physicians practicing in the United States and explore factors associated with these practices.

MATERIALS AND METHODS

Between September 2004 and February 2005, we surveyed by mail 855 physicians selected at random from membership lists of three professional organizations. Physicians reported their imaging practices and experiences in managing patients with suspected acute PE during the preceding 12 months.

RESULTS

Completed questionnaires were received from 240 of 806 eligible participants (29.8%) practicing in 44 states: 86.7% of respondents believed that computed tomographic pulmonary angiography (CTPA) was the most useful imaging procedure for patients with acute PE compared with 8.3% for ventilation-perfusion (V-P) scintigraphy and 2.5% for conventional pulminary angiography (PA). After chest radiography, CTPA was the first imaging test requested 71.4% of the time compared with V-P scintigraphy (19.7%) and lower-limb venous ultrasound (5.8%). Participants received indeterminate or inconclusive results 46.4% of the time for V-P scintigraphy, 10.6% of the time for CTPA, and 2.2% of the time for PA. CTPA was available around the clock to 88.3% of participants compared with 53.8% for V-P scintigraphy and 42.5% for PA. A total of 68.6% of respondents received CTPA results in 2 hours or less (vs 37.5% for V-P scintigraphy and 22.9% for PA). CTPA also provided an alternative diagnosis to PE or showed other significant abnormalities 28.5% of the time, and these findings frequently altered management.

CONCLUSION

US clinicians unequivocally prefer CTPA in patients with suspected acute PE. Reasons for this preference include availability and timely reporting, a lower rate of inconclusive results, and the additional diagnostic capabilities that CTPA can provide.

Diagnosis and management of subsegmental pulmonary embolism

INTRODUCTION

Although the advent of multi-detector row computed tomography (CT) has enabled better visualization of subsegmental pulmonary (SSP) arteries, SSP embolism is of uncertain clinical significance. We aimed at answering the following questions: Is spiral CT an accurate method to detect SSP embolism? How are subsegmental perfusion defects managed in outcome studies including spiral CT? What are the main characteristics and outcomes of patients in whom CT detects isolated subsegmental defects?

METHODS

We performed a Medline search on July 1, 2004, using the keywords 'pulmonary embolism' and 'computed tomography'. We limited our search to English language prospective studies comparing CT to pulmonary angiography, and to prospective outcome studies including CT in a diagnostic strategy, with at least a 3-month follow-up.

RESULTS

Fourteen studies comparing CT to pulmonary angiography, and five prospective management studies using CT were retrieved. The sensitivity of single-detector CT for detecting subsegmental defects compared with pulmonary angiography was low (25%). The proportion of isolated SSP images was significantly higher in management studies using multi-detector CT (17 of 770 scans, 2.2%) compared with those using single-detector CT (22 of 2232, 1.0%; P = 0.01). No straightforward attitude regarding anticoagulation therapy for isolated subsegmental defects emerged from the available literature. Finally, important clinical differences were found between patients having subsegmental and segmental or more proximal defects.

CONCLUSIONS

These findings underline the uncertainty regarding the clinical significance of SSP embolism, and the management of patients with such findings.

CT lower extremity venography in suspected pulmonary embolism in the ED

The purpose of this study was to evaluate the added benefit of computed tomography lower extremity venography (CTLV)--performed following CT pulmonary angiography (CTPA)--in the emergency department (ED) patient suspected of pulmonary embolism (PE). A retrospective review of 427 consecutive patients having both CTPA and CTLV performed to evaluate patients suspected of PE at two community hospitals was conducted. Three-month follow-up was performed on all patients to ensure that no case of PE or deep venous thrombosis (DVT) was missed. Forty patients were positive for PE, and 11 were positive for DVT. There were 6 CTPA studies read as indeterminate for PE and 11 CTLV studies indeterminate for DVT. Only 1 patient was positive for DVT, who did not have a concurrent PE identified by CTPA. The estimated charges for detecting the single case of isolated DVT was 206,400 US dollars. In our ED setting, the additional benefit of adding CTLV to the standard ED work-up of PE was minimal.

Acute Pulmonary Embolism: Imaging in the Emergency Department

Acute pulmonary embolism (PE) is a life-threatening condition that requires accurate diagnostic imaging. Morbidity and mortality that result from PE can be reduced significantly if appropriate treatment is initiated early; this makes timely diagnosis imperative. Historically, the gold standard for the imaging of PE has been pulmonary angiography. Rapid advances in radiology and nuclear medicine have led to this modality largely being replaced by noninvasive techniques, most frequently multidetector helical CT pulmonary angiography (CTPA). In cases in which CTPA is contraindicated, other modalities for diagnosis of PE include nuclear ventilation perfusion scanning, magnetic resonance pulmonary angiography, duplex Doppler ultrasonography for deep venous thrombosis, and echocardiography. This article reviews the literature on the role of these imaging modalities in the diagnosis of PE.

IV Contrast Selection for MDCT: Current Thoughts and Practice

OBJECTIVE

The purpose of this article is to review studies evaluating how contrast concentration affects MDCT of the body and to report IV contrast infusion protocols from MDCT angiography and MDCT of abdominal tumors.

CONCLUSION

Higher concentrations (350 mg I/mL or greater) may improve visualization of small abdominal arteries. However, preliminary data comparing 300 mg I/mL to higher concentrations for MDCT of hypervascular hepatocellular carcinoma and pancreatic cancer have shown that higher concentrations may not increase tumor conspicuity.

Eighty-peak kilovoltage 16-channel multidetector computed tomography and reduced contrast-medium doses tailored to body weight to diagnose pulmonary embolism in azotaemic patients

The aim of this study was to assess the feasibility of minimising contrast-medium (CM) doses using 80-peak kilovoltage (kVp) 16-channel multidetector computed tomography (MDCT) with CM dose tailored to body weight, when diagnosing pulmonary embolism (PE) in azotaemic patients. Twenty-nine patients (68-93 years; 38-79 kg) with an estimated glomerular filtration rate of 12-49 ml/min underwent 80 kVp MDCT at a median dose of 200 mg iodine (I)/kg and 15 s injection time. Pulmonary artery (PA) enhancement where compared with our own reference material using 320 mg I/kg at 120 kVp and with reported figures in the literature at 120-140 kVp and a 42 g iodine CM dose. Median (1st and 3rd quartiles) values regarding CM dose were 12.2 (9.9-12.8) g iodine; density of left main and lower lobe segmental PA 339 (275-395) Hounsfield units (HU) and 354 (321-442) HU, respectively. Those enhancement values were similar to those obtained from the reference population at 120 kVp and those reported in the literature at 120-140 kVp. One patient had a transient increase in plasma creatinine. Three months' follow-up revealed deep venous thrombosis among 1/18 patients with negative results from computed tomography (CT). We conclude that 80 kVp 16-channel MDCT to diagnose PE in azotaemic patients may be performed with markedly reduced CM doses, implying a lesser risk for CM-induced nephropathy.

Helical computed tomography and alternative diagnosis in patients with excluded pulmonary embolism

OBJECTIVE

A clinical diagnosis of pulmonary embolism (PE) is confirmed objectively in 20-30% of patients. Helical computed tomography (CT) can allow an alternative diagnosis to be made. The frequency and validity of alternative diagnoses on helical CT in consecutive patients presenting with clinically suspected PE was assessed.

PATIENTS AND METHODS

In all 512 prospectively analyzed patients helical CT scan was performed, and apart from presence or absence of PE, pathologic changes in lung parenchyma, mediastinum, cardiovascular system, pleura and skeleton were recorded. When possible an alternative diagnosis was given and compared with the final diagnosis after 3 months follow-up.

RESULTS

In 130 patients (25.4%) PE was excluded and an alternative diagnosis considered likely. In 123 of the 130 patients (94.6%) this diagnosis was unchanged at 3 months follow-up. The diagnoses included pneumonia (n = 67), malignancy (n = 22), pleural fluid (n = 10), cardiac failure (n = 10), COPD (n = 6) and a variety of other causes (n = 15). The diagnosis changed at follow-up in seven patients (5.4%). An initial diagnosis of pneumonia changed to malignancy in two patients and to pleuritis and cardiac failure in one patient each. In two other patients malignancy and chronic obstructive pulmonary disease (COPD) were ruled out and the diagnosis changed to pneumonia. In one patient the final diagnosis remained unknown after an initial suspicion of malignancy.

CONCLUSION

In clinically suspected PE helical CT allows a reliable alternative diagnosis to be made in 25.4% of patients. This feature is an unique advantage in comparison with other diagnostic tests and supports the decision of taking helical CT as first line test in suspected PE.

The Indeterminate CT Pulmonary Angiogram: Imaging Characteristics and Patient Clinical Outcome

PURPOSE

To retrospectively review imaging characteristics of indeterminate computed tomographic (CT) pulmonary angiograms for pulmonary embolism (PE) and patient outcome.

MATERIALS AND METHODS

Investigational review board approval was obtained, informed consent was waived, and the study was HIPAA compliant. Retrospective review of 3612 CT pulmonary angiography reports created between July 1, 2001, and July 1, 2003, was performed with a keyword search for "indeterminate," "nondiagnostic," or "inadequate" (thereafter, all defined as "indeterminate") and yielded studies from 237 patients (mean age, 57 years; 117 men, 120 women). Randomly selected diagnostic studies were used to form a control group of 25 subjects (mean age, 64 years; eight men, 17 women). Electronic medical records were reviewed for follow-up imaging (repeat CT pulmonary angiography, conventional pulmonary angiography, ventilation-perfusion scintigraphy, or lower-extremity ultrasonography [US]), use of anticoagulation, placement of inferior vena cava (IVC) filters, clinical outcomes, and comments regarding indeterminate reading of CT angiograms. Studies (in patients and control subjects) were reviewed for PE, contrast attenuation in the main pulmonary artery (MPA), motion artifacts, image noise, and flow artifacts. Findings were compared with two-sample t tests assuming unequal variance.

RESULTS

The cause cited for indeterminism was most often motion (74%), followed by poor contrast enhancement (40%). Contrast attenuation in the MPA was 245 HU +/- 80 (standard deviation) in patients and 339 HU +/- 88 in control subjects (P < .001). Only 46% of indeterminate studies met institutional criteria for adequate contrast attenuation in the MPA. Rereview of studies demonstrated five missed PEs. A total of 81 patients (33%) underwent follow-up imaging within 5 days, with one positive pulmonary angiogram and four positive lower-limb US scans. Reread or follow-up images depicted thromboembolic disease in 4.2% of patients. Nineteen patients (8%) with indeterminate final result were treated for thromboembolic disease with either anticoagulation or IVC filters. Reports on 22% of indeterminate studies contained recommendations for follow-up imaging, and those recommendations nonsignificantly increased the rate for those examinations from 13% to 19%. Review of discharge summaries showed 22% of studies are clinically interpreted as negative.

CONCLUSION

The two major causes of indeterminism are motion artifacts and poor contrast enhancement.

CT Depiction of Pulmonary Emboli: Display Window Settings

PURPOSE

To compare computed tomographic (CT) window settings selected by radiologists with those determined by using two alternative approaches for depiction of pulmonary emboli (PE).

MATERIALS AND METHODS

Institutional review board approval was obtained; informed consent was not required. This study was compliant with the Health Insurance Portability and Accountability Act. Twenty-five clinical chest CT studies were obtained with a standardized PE protocol and retrospectively evaluated by five chest and two body CT radiologists. Of these studies, 13 were positive for PE, and 12 were negative. At the main pulmonary artery (PA), mean attenuations (MPA) and standard deviations (SDPA) were measured. Initially, images were displayed with a standard mediastinal window setting (window width, W = 400 HU; window center, C = 30 HU), and each observer adjusted the setting to a personally preferred setting (eg, "personal") for PE detection. Images displayed at this setting were compared in a side-by-side fashion with the "modified" (W = MPA + 2 . SDPA, C = W/2) and "double-half" (W = 2 . MPA, C = MPA/2) window setting. Each observer rated images from 1 (ie, most preferred) to 3 (ie, least preferred). For quantitative analysis, window width and center value of each setting were divided by corresponding MPA to compute a width ratio and a center ratio. Window settings and ratings were compared with repeated-measures analysis of variance, paired t tests, and Wilcoxon signed-rank tests.

RESULTS

Ratings for all three types of window settings were significantly different (P < .001). Observers preferred their personal settings the most and the modified settings the least. Mean ratios for the seven observers were 1.68 +/- 0.20 for window width and 0.47 +/- 0.08 for window center. Window width ratios for all settings were significantly different from each other (P < .001). Window center ratios were significantly higher for the modified setting than for the double-half setting (P = .013). Values for mean PA attenuation were correlated with window width ratios for six (86%) observers (mean r2 value = 0.29 +/- 0.19, P < or = .03) and with window center ratios for four (57%) observers (mean r2 value = 0.16 +/- 0.14, P < or = .02), thus indicating a trend of setting window width and window center higher when contrast enhancement is lower and vice versa.

CONCLUSION

On average, observers selected CT window settings for PE detection at a window width of slightly less than twice the mean PA attenuation and at a window center of about half the mean PA attenuation. Observers tended to use larger window widths and centers as the degree of PA enhancement was lower.

Reproducibility of multi-detector spiral computed tomography in detection of sub-segmental acute pulmonary embolism

The aim of this study was to evaluate the inter-observer and intra-observer agreement of the diagnosis of sub-segmental acute pulmonary embolism (PE) in an inpatient population explored by 16 slice multi-detector spiral computed tomography (MDCT). Four hundred consecutive inpatients were referred for MDCT for the clinical suspicion of acute PE. One hundred and seventy seven (44.2%) had a known cardio-respiratory disease at the time of examination. Inter-observer and intra-observer agreements for the diagnosis of acute PE and of sub-segmental acute PE were assessed blind and independently by three experienced readers and by kappa statistics. Seventy-five patients were diagnosed as having acute PE findings (19.5%), and clots were located exclusively within sub-segmental arteries in nine patients (12%). When clots were limited to sub-segmental or more distal branches of the pulmonary arteries, kappa values were found to be moderate (0.56) to very good (0.85) for the diagnosis of sub-segmental acute PE, whereas for the diagnosis of acute PE in the whole population, kappa values ranged from 0.84 to 0.97. Intra-observer agreement was found to be perfect (kappa=1). MDCT is a reproducible technique for the diagnosis of sub-segmental acute PE as well as for acute PE. In this inpatient population, sub-segmental acute PE was not a rare event.