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Why do different body parts show up as different colors on a CT scan?

Different body parts show up as different colors on a computerized tomography (CT) scan, also called a computed tomography or CAT scan, because different parts of the body absorb different amounts of x-rays.

The CT scanner works by sending a beam of x-rays through the body and onto electronic "film." Some of the x-rays pass through the body and some are absorbed. Harder parts of the body, like bones, absorb more x-rays and show up white. Where there’s little or nothing to stop the x-rays (like lungs), it shows up as black. Softer parts of the body—like the brain, muscles and skin—absorb less of the x-rays and show up as shades of gray.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.