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Radiation from CT and perfusion scanning in pregnancy

BMJ 2005; 331 doi: (Published 04 August 2005) Cite this as: BMJ 2005;331:350

This article has a correction. Please see:

  1. J Valmai Cook, consultant radiologist (Valmai.cook{at},
  2. John Kyriou, radiation protection adviser (John.kyriou{at}
  1. Epsom and St Helier University NHS Trust, Carshalton, Surrey SM5 1AA
  2. Radiological Protection Centre, St George's Hospital, London SW17 0QT

    EDITOR—In her news article Eaton notes that most of the rise in medical radiation exposure is due to computed tomography.1 However, the whole body effective dose given for computed tomography may not reflect the increased risk to individual exposed body areas.

    Last year we assessed the risks for pregnant women undergoing investigation for possible pulmonary embolism.2 The British Thoracic Society guidelines 2003 recommend computed tomography for pulmonary angiography as the modality of choice for non-massive pulmonary emboli.3 It is also recommended for pregnant women because of the low fetal dose compared with low dose (50 milliBequerel) technetium-99m perfusion lung scans.

    According to our local data, the maternal whole body effective dose for computed tomography for pulmonary angiography was 2 milliSievert (mSv) compared with 0.6 mSv for a low dose perfusion scan. The absorbed doses to the fetus were 0.01 milliGray (mGy; risk of fatal cancer to the age of 15 years is < 1/1 000 000) for computed tomography for pulmonary angiography and 0.12 mGy (risk of 1/280 000) for the perfusion scan. This shows a distinct advantage to the fetus of performing computed tomography for pulmonary angiography.

    However, the absorbed doses to the breast were 10 mGy for computed tomography for pulmonary angiography and 0.28 mGy for a perfusion scan, about 40 times the dose to the breast at a time when proliferating, pregnant breast tissue would be expected to be at greater risk.

    When available and appropriate, lung perfusion scans should be considered the investigation of first choice for any young woman. Pregnant women with a family history of breast cancer or who have had previous computed tomography for pulmonary angiography may wish to elect for lung perfusion scans, despite the slightly higher risk to the fetus.

    Computed tomography is a valuable, but high dose, investigation. Although the overall risk is very small and usually completely outweighed by the benefits of obtaining a prompt diagnosis, it is still important to choose the technique that entails the least risk.


    • Competing interests None declared.


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