Merck Manual

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Comparing Radiation Doses For Different Tests*

Comparing Radiation Doses For Different Tests*

Imaging Test

Approximate Number of Chest X-Rays Needed to Get the Same Dose

Approximate Environmental Exposure Equivalent to the Dose†

1

10 days

10

25 days

An x-ray series of the lumbar spine

75

180 days

CT of the head

100

243 days

CT of the abdomen/pelvis

300–400

2–2.7 years

350–750

2.3–4.9 years

* These doses account for how much radiation is delivered and how susceptible the body part exposed to radiation is to radiation damage.

† People are exposed constantly to low levels of naturally occurring radiation but the amount varies in different geographic locations.

CT = computed tomography.