DEXA (DXA) or Dual Energy X-Ray Absorptiometry is a non-invasive imaging modality based on exploiting the difference in the X-Ray attenuation of tissue and bone at different X- ray energies. Calcified tissues such as bone absorb X-Rays a lot more than soft or low density tissues such as lean tissue, fat, and organs (Figure 1). Using mathematical algorithms based on extracting the amount of X-Rays that were absorbed by either tissue, bone information OR tissue information can be eliminated in the resulting radiograph (Figure 2).
In clinical DEXA, scans are used to evaluate bone quality by assessing Bone Mineral Density (BMC) and Bone Mineral Content (BMC). Focus on the patient’s hips and spine are predominant. Values are graded based on a “T-score.” Based on that value, a patient can be considered to have healthy bone quality, osteopenic, or osteoporotic.
In pre-clinal DEXA, whole body scans of mice or rats can be used to extract not only BMD and BMC information, but whole body composition. Questions such as how much fat or lean tissue a particular genotype mouse has or the effects from a particular pharmaceutical intervention can be answered.
Sources for images:
https://en.wikibooks.org/wiki/File:MacBoneTissue.jpg
https://en.wikibooks.org/wiki/Basic_Physics_of_Nuclear_Medicine/Dual-Energy_Absorptiometry