Pulmonary Embolism: A Clinician's Perspective

Reducing computed tomography radiation dose in diagnosing pulmonary embolism

Background and Objective:

Computed tomography angiography plays a major role in the diagnosis of pulmonary embolism. Radiation dose associated with it is a major concern; therefore it is important to optimize protocols and techniques to ensure minimum radiation dose.

Methods:

The study compares two protocols i. Conventional Timing Bolus CT protocol and Delayed Timing Bolus protocol used to assist suspected pulmonary embolism patients.

Results:

A significant reduction in the average effective dose (39%) was noticed when using the delayed timing bolus protocol.

Conclusion:

Delayed timing bolus protocol has a good impact on radiation dose without affecting the value of the computed tomography angiography study.

Pulmonary ventilation/perfusion single photon emission tomography--Initial experience of a Nuclear Medicine Department

INTRODUCTION

Lung ventilation/perfusion scintigraphy with planar images (V/QS-planar) is very useful for the diagnosis and follow-up of pulmonary thromboembolism (PTE). Acquiring tomographic images (V/QS-SPECT) is a recent development with potential to increase the technique's accuracy. The purpose of this work is to evaluate the added benefits of V/QS-SPECT studies as opposed to traditional planar imaging.

PATIENTS AND METHODS

We prospectively revised 53 V/QS-planar and V/QS-SPECT exams, performed according to the European Association of Nuclear Medicine guidelines. We evaluated the exams independently, by consensus of two Nuclear Medicine physicians. For both methods, we gave each lung a score expressing the dimension and extension of perfusion defects with normal ventilation. For each lung, we compared the scores with the paired Wilcoxon test, estimating the 95% confidence interval (95 CI) for the respective difference.

RESULTS

We performed V/QS-SPECT exams without technical difficulties. The paired Wilcoxon test estimated the score difference to be -0.75 (95 CI of -1.0 to -0.5; p-value=9.6 × 10(-7)), expressing a statistically significant difference of about 1 subsegmental defect between both methods, with V/QS-SPECT detecting more defects.

DISCUSSION

The results demonstrate that V/QS-SPECT identifies a slightly larger number of perfusion defects than V/QS-planar, suggesting a higher sensitivity of this technique. However, more studies are necessary to evaluate the clinical meaning of this fact.

CONCLUSION

V/QS-SPECT demonstrates a higher capability to identify perfusion defects. This method looks promising, allowing for a greater role of this exam in pulmonary thromboembolism diagnosis and follow-up.

Interest of chest X-ray in tailoring the diagnostic strategy in patients with suspected pulmonary embolism

Current diagnostic strategies for pulmonary embolism rely on the sequential use of noninvasive diagnostic tests including ventilation-perfusion (V/Q) scan and computed tomography pulmonary angiography (CTPA). V/Q scan remains criticized because of a high proportion of nondiagnostic test results, especially when the chest X-ray (CXR) is abnormal. The present study assesses whether CXR results have an impact on the conclusiveness of a noninvasive diagnostic strategy of pulmonary embolism based on the combination of pretest probability, compression ultrasonography, V/Q scan, and CTPA. Patients suspected of having pulmonary embolism were managed according to a validated diagnostic strategy. All patients underwent a CXR within 24 h of the suspicion of pulmonary embolism. CXR results were correlated to strategy conclusiveness, as assessed by the rate of required CTPA as per the diagnostic algorithm. Two hundred and twenty-three patients were retrospectively analyzed. CXRs were considered as normal in 108 (48%) patients and abnormal in 115 (52%) patients. According to the diagnostic algorithm, a CTPA was required to reach a diagnostic conclusion in 11 (10%) patients of the normal CXR group, and in 14 (12%) patients of the abnormal CXR group (P > 0.05). In this study, the presence of CXR abnormalities did not have an impact on the conclusiveness of a diagnostic strategy of pulmonary embolism based on V/Q scan. CXR abnormalities should likely not be regarded as a contraindication to the use of V/Q scan in patients with suspected pulmonary embolism.

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.