The early use of fracking to get at reserves previously thought of as unrecoverable, shortly after the turn of the 21st century, came about after exploration companies began examining geologic formations using x-ray computed tomography, or CT scanners.

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"To put that into context, 20mSv is the same dose you get from three computed tomography (X-ray) scans of your chest, roughly, " she told reporters.

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The technique can provide excellent, detailed images of the body's soft tissue and is an alternative to using X-ray techniques such as computed tomography (CT).

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