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PE Workup: Official Guidelines of the Fleischner Society

January 11, 2009
Written by: , Filed in: Breast Imaging, Chest Radiology, Safety Issues
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Background
Computed tomographic (CT) angiography using multidetector CT with high spatial and temporal resolution for imaging the pulmonary vasculature has achieved recognition as the preferred diagnostic imaging method for pulmonary embolism. This is largely because CT leads to diagnosis of alternative causes for the patient’s symptoms.

But as result of the well-documented high-radiation exposure associated with CT, there are serious concerns regarding radiation dose. In most protocols for spiral CT for PE, the effective dose is between 3 and 5 mSv, equivalent to 1 to 2 years of exposure to background radiation.

Women are also more sensitive to the radiation exposure of spiral CT for PE, owing to the presence of breast tissue in the radiated field. This is substantial radiation exposure, especially in children and young adults.

Scintigraphy is safe, technically easy, and widely available. Scintigraphy may be particularly important for reproductive-age female patients whose chest radiograph is likely to be normal and for whom the breast irradiation dose from CT angiography can be minimized by using a perfusion scan as the first imaging test.

Another application could be in the follow-up of patients with proven PE and undergoing anticoagulation.

Methodology
A recent study showed that patients with persistent perfusion abnormalities are at risk of chronic thromboembolic pulmonary hypertension. In patients with allergy to iodinated contrast material or impaired renal function, pulmonary scintigraphy is a useful alternative.

For reproductive-age women, breast radiation exposure is a concern. The average absorbed dose to the breast from CT angiography has been calculated as 10-70 mGy. The absorbed dose to the breast with a perfusion lung scan has been estimated to be 0.28 mGy.

In pregnant patients, besides radiation, the use of iodinated contrast medium is a cause of concern because of the reluctance to expose a fetus to any drugs. Free iodine in radiographic contrast medium given to the mother has the potential to depress fetal and neonatal thyroid function.

Reviewer’s Comments
CT angiography seems to be the Fleischner Society’s preferred method of PE detection, but V/Q scintigraphy is preferred in many circumstances, especially in patients with poor kidney function and perhaps those of baby-bearing or breast-feeding age. Our volume of V/Q scans remains substantial despite a first-rate CT section.

As to the basic assumption that CT beats scintigraphy for PE management, I am not yet willing to concede. For example, I wonder whether some tiny PEs detected by CT would not be better off left untreated.

There is good evidence that our low-probability lung scans identify patients who need not be anticoagulated–even though 5% to 19% of them actually have PE on angiogram.
Take-Home Pearl
Scintigraphy may be particularly important for reproductive-age female patients whose chest radiograph is likely to be normal and for whom the breast irradiation dose from CT angiography can be minimized by using a perfusion scan as the first imaging test.
Author: C. Richard Goldfarb, MD

Reference:
Remy-Jardin M, Pistolesi M, et al. Management of Suspected Acute Pulmonary Embolism in the Era of CT Angiography: A Statement from the Fleischner Society. Radiology; 2007; 245 (November): 315-329

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