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†


10 days


25 days

An x-ray series of the lumbar spine


180 days

CT of the head


243 days

CT of the abdomen/pelvis


2–2.7 years


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.