Mass estimates by computed tomography: physical density from CT numbers.

Area of Science:

• Medical Imaging
• Radiology
• Biophysics

Background:

• Computed Tomography (CT) scanning traditionally uses CT numbers to represent tissue attenuation.
• CT numbers are scanner-specific and susceptible to variations like beam hardening, limiting direct physical interpretation.
• Accurate in vivo mass estimation of organs and tumors is crucial for clinical assessment and treatment planning.

Purpose of the Study:

• To propose expressing CT attenuation in terms of physical density instead of CT numbers.
• To establish a method for calculating in vivo organ and tumor mass using CT-derived physical density.
• To demonstrate the added value of physical density information from routine CT scans.

Main Methods:

• A calibration experiment was conducted to create a physical density versus CT number curve for a specific CT scanner.
• This calibration accounts for scanner-specific variations including beam hardening.
• Physical density values were derived from CT numbers using the established calibration curve.

Main Results:

• A unique calibration curve relating physical density to CT number was successfully established for the tested scanner.
• The method allows for the calculation of organ or tumor mass in grams directly from CT scan data (volume and derived density).
• Physical density information, such as that of bone, can be obtained as supplementary data from existing CT scans.

Conclusions:

• Expressing CT attenuation in physical density offers a more universally applicable and interpretable metric than CT numbers.
• This approach enables non-invasive, in vivo mass determination of biological tissues and pathologies.
• Physical density quantification from CT scans provides valuable diagnostic information, enhancing the utility of routine imaging.