An apparatus, method, and computer program product for calibrating a CT scan without the use of an external calibration phantom, to enable quantitative assessment of internal body tissues and organs and additionally for any application that would benefit from a calibration of the scan attenuation data, such as viewing CT images in a consistent fashion. Embodiments are described with applications to quantitative assessment of bone density in the spine and hip, mineral content in blood vessels, hepaticfat content in the liver, and gray-to-white matter ratio in the brain. The primary advantages of the method are that it does not require the use of an external calibration phantom, it is robust across different CT machines and scanner settings, and it is also highly precise, lending itself to a high degree of automation.
