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1 Department of Radiology, Beth Israel Deaconess Medical Center and Harvard
Medical School, 330 Brookline Ave., Boston, MA 02215.
2 Department of Radiology, Jackson Memorial Hospital and the University of Miami
School of Medicine, Miami, FL 33136.
Received April 14, 2003;
accepted after revision May 30, 2003.
Address correspondence to P. M. Boiselle.
Abstract
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MATERIALS AND METHODS. Surveys were mailed electronically to the 403 members of the Society of Thoracic Radiology (403 addresses). Respondents were asked to send one response from each institution or department. Information gathered included use of CT angiography in relation to ventilation–perfusion imaging in pregnant patients, written policies, informed consent procedures, and modifications of standard protocols for dose reduction.
RESULTS. Fifty-seven members responded; 43 (75%) reported that they perform CT angiography in pregnant patients suspected of having pulmonary embolism. Of the 43 respondents who perform CT angiography in pregnant patients, 23 (53%) generally perform CT angiography as the initial study rather than ventilation–perfusion scanning, 26 (60%) require informed consent from the patient, seven (16%) have a written policy concerning CT angiography in pregnant patients, and 17 (40%) modify standard imaging protocols for pregnant patients. The most common modification for dose reduction is decreasing the scanning area along the z-axis.
CONCLUSION. Most respondents perform CT angiography in pregnant patients suspected of having pulmonary embolism, but their policies and practices vary considerably.
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Ventilation–perfusion scanning has historically been the primary screening study for pulmonary embolism during pregnancy [2, 3]. Since its first description approximately a decade ago [4], helical CT has been used with increasing frequency as a first-line test to diagnose pulmonary embolism in the general population. To date, however, the role of CT angiography in the evaluation of pregnant patients with suspected pulmonary embolism has received little attention. The purpose of this study was to assess the practices and policies of the radiology departments of the Society of Thoracic Radiology members regarding the use of CT pulmonary angiography in pregnant patients suspected of having pulmonary embolism.
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The specific survey questions are listed in Appendix 1. The initial question asked whether the respondent's department performs pulmonary CT angiography in pregnant patients with suspected pulmonary embolism. Those who answered no to this question were directed to the final portion of the survey, which asked the respondents to identify their type of practice and to state the name of their hospital or institution. For those respondents who answered yes to the first question, subsequent questions gathered information about their usual method of evaluation for diagnosing pulmonary embolism in pregnant patients, written policies and use of informed consent, use of dose-reduction methods, estimated frequency with which CT angiography was performed in pregnant patients at their institution in the last year, and whether a chest X ray is usually obtained before CT angiography. Finally, the respondents were asked to identify their practice setting and the name of their hospital or institution.
Question 8 was used to divide the respondents into two groups: those who performed CT angiography in pregnant patients five times or fewer in the last year and those who performed it more frequently. The two groups were compared regarding written policies and use of informed consent forms. Fisher's exact test was used to assess statistical significance.
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Of the 57 respondents, 43 (75%) reported that they perform CT angiography in pregnant patients suspected of having pulmonary embolism. Of the 14 respondents who stated that they do not perform CT angiography in pregnant patients, nine reported that they do not work with pregnant patients (six reported working in an adult hospital with no pregnant patients and three reported working at a pediatric facility). Of the remaining five respondents who reported that they do not perform CT angiography in pregnant patients, two reported performing ventilation–perfusion imaging instead of CT angiography to decrease the radiation dose, one reported performing conventional pulmonary angiography instead of CT angiography to decrease the contrast dose and prevent fetal hypothyroidism, and two did not give a reason.
When asked how pregnant patients are generally imaged for suspected pulmonary embolism at their institution, 23 (53%) of the 43 respondents who perform CT angiography in pregnant patients reported that CT angiography is generally performed as the initial study and 13 (30%) reported that ventilation–perfusion scanning is generally performed as the initial study. Seven (16%) of 43 respondents selected "other" as a choice to this question. Their responses included "depends on chest radiograph findings" (n = 2), "depends on the trimester of the pregnancy" (n = 2), "decided on a case-bycase basis" (n = 2), and "performed perfusion scanning only" (n = 1).
When asked which factor generally determines whether CT angiography or ventilation–perfusion imaging is performed in a pregnant patient with suspected pulmonary embolism at their institution, 16 (38%) of 42 respondents reported that the clinician's preference is the major factor, 15 (36%) reported that radiologist's preference is the major factor, and none reported patient's preference as the determining factor. Eleven (26%) of 42 respondents selected a response of "other" to this question. Their responses included "depends on the chest radiographs" (n = 4), "clinician and radiologist team approach" (n = 4), "algorithm" (n = 1), "depends on availability" (n = 1), and "no policy" (n = 1). One respondent did not answer this question.
Only seven (17%) of 42 respondents who perform CT angiography in pregnant patients reported that their department has a written policy concerning performing this procedure in pregnant patients, and one respondent did not answer this question. With regard to consent, 26 (60%) of 43 reported that their department requires written informed consent by a pregnant patient, 17 (40%) of 43 reported that their department requires written authorization by the patient's attending clinician, and five (12%) of 43 reported that their department requires written authorization by the radiologist. Table 1 compares policies between responding institutions that perform CT angiography in pregnant patients frequently and those that do not. The rates of written policies and requirements for informed consent between the two groups were not statistically significantly different.
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Seventeen (40%) of 43 respondents reported that they make modifications to reduce radiation exposure for pregnant patients. The most common modification, reported by 12 (71%) of 17 respondents, was to decrease the scanning area along the z-axis. Other modifications included increasing pitch (n = 3), reducing field of view (n = 2), eliminating frontal and lateral scout images (n = 2), reducing milliampere-seconds (n = 1), reducing peak kilovoltage (n = 1), and thickening detector collimation (n = 1). No respondents reported choosing to use a single-detector helical CT scanner rather than a multidetector scanner to limit dose. Other responses to this question included "no scan of pelvis or legs" (n = 2) and "lead shielding of the abdomen" (n = 1). When asked whether chest radiographs were usually obtained before CT angiography, 33 (80%) of 41 respondents reported that they routinely obtain chest radiographs, and eight (20%) of 41 respondents reported that they do not. Two respondents did not answer this question.
With regard to the frequency with which CT angiography is performed in pregnant patients each year, 10 (24%) of 41 respondents reported a single performance, 20 (49%) reported two to five times, five (12%) reported six to 10 times, and six (15%) reported more than 10 times per year. Two respondents did not answer this question.
Concerning the practice settings of the 57 respondents who completed the survey, 44 (77%) work in a primarily academic setting, three (5%) work in a primarily private practice setting, and 10 (18%) work in a combined academic and private practice setting.
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Only a small minority (5%) of respondents reported that CT angiography is not performed because of concerns about either radiation dose or use of IV contrast material. With regard to radiation dose considerations, Winer-Muram et al. [5] have reported that CT angiography is associated with a lower average fetal radiation dose than ventilation–perfusion imaging during all trimesters—the mean fetal dose was less than 6 mrad (0.00006 Gy) for 20 of 23 study patients. With a standard dose of 37–74 MBq of technetium-99m macroaggregates of human serum albumin, the fetal dose from ventilation–perfusion scanning is approximately 10–37 mrad (0.0001–0.00037 Gy) [6, 7]. However, the fetal dose for both techniques is well below the 5-rad (0.05-Gy) limit that is considered safe for fetal exposure [6–8].
Nearly half of all respondents who perform CT angiography in pregnant patients report that they modify their CT protocols to reduce the dose, usually by decreasing the scanning area along the z-axis. In contrast, a previous survey [3] of nuclear medicine facilities regarding ventilation–perfusion scanning in pregnant patients reported that dose-reduction methods were used by 82% of respondents. The reason for this difference is uncertain but may in part reflect the longer experience with ventilation–perfusion imaging compared with CT angiography for this indication.
CT angiography has other advantages over ventilation–perfusion imaging besides dose levels. It can reveal thrombus directly, rather than relying on indirect evidence; it also yields fewer indeterminate results and can be used to identify other causes of symptoms if no embolism is present [9, 10]. A relative disadvantage of CT angiography is the small risk of reaction to the contrast media.
Although a general consensus in the medical literature indicates imaging studies for the evaluation of pregnant patients with suspected pulmonary embolism, radiologists should recognize that imaging patients during pregnancy involves a medical–legal risk [2, 3, 11]. For example, in an article on radiation exposure during pregnancy, Berlin [11] listed several recommendations for successful risk management. Among his recommendations were that radiology facilities should have a process to evaluate patients who are pregnant, radiologists should be knowledgeable about radiation effects and be accessible to patients and patients' referring physicians, and radiology reports should document all discussions with patients about the risks of radiation exposure. Our results suggest that many radiology departments are performing CT angiography in pregnant patients without careful attention to these factors. For example, only a slight majority (60%) of responding institutions reported that they require informed consent from the patient before scheduling CT angiography. This finding is comparable to findings of an earlier survey of nuclear medicine departments [3] showing that only 52% required informed consent before ventilation–perfusion imaging in pregnant patients. Interestingly, institutions performing CT angiography in pregnant patients more than five times per year were no more likely to have a written policy or to require informed consent than those institutions performing the procedure less frequently.
Our survey has several limitations. Only a small fraction (5%) of our respondents practice in a primarily private practice setting. Although this in part reflects the fact that the Society of Thoracic Radiology comprises mostly radiologists who practice in an academic setting, it also probably reflects a component of response bias among academic radiologists. Thus, our results are more indicative of the current state of pulmonary embolism imaging of pregnant patients in academic environments than in private practice settings. However, those who practice in an academic setting are more likely to encounter complicated obstetric cases (such as pregnant patients with suspected pulmonary embolism) than those in private practice [3].
A second potential limitation of our study is that only one response was allowed from each location. Although this prevented giving disproportionate weight to any single institution, it does not account for the possibility that practice patterns in the same institution could vary. A third limitation, which is shared by most physician survey studies, is that our survey was completed by only a minority of those to whom it was disseminated. However, our 25% response rate is similar to response rates for other surveys that have been published in the radiology literature concerning practice patterns of radiologists and nuclear medicine physicians [3, 12].
In summary, CT angiography is widely used for imaging pregnant patients with suspected pulmonary embolism, and it is often preferred to ventilation–perfusion scanning as a first-line study for this indication. However, practices and policies vary considerably among our respondents. Our results suggest the need for a multi-disciplinary task force to formulate explicit guidelines for the imaging of pregnant patients with suspected pulmonary embolism. In the meantime, the results of this survey may help radiologists in conducting their work. However, radiologists should not feel compelled to adhere to the practice of the majority until more scientific studies have been carried out.
Regardless of which test is performed (CT angiography or ventilation–perfusion scanning), risk management and patient care can be positively influenced by adhering to the following recommendations. Radiology departments should formulate a general written policy for radiologic imaging in pregnant patients and should design protocols for specific tests such as CT angiography or ventilation–perfusion scanning that may be indicated in pregnancy. Radiologists should be knowledgeable about radiation risks and exposures, and they should be accessible to pregnant patients and their physicians. Finally, informed consent should be obtained before the procedure and recorded in the patient's chart [3, 11].
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Acknowledgments
We thank Alexis Potemkin for administrative assistance and Larry Barbaras
for computer assistance.
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