Dual-energy index

Fig. 5.2. Dual-Energy Index of atoms in relation to their element number (z). The relation is unique, but only reversible up to a value of 55...

On the other hand, the object that is to be analyzed with dual-energy techniques has to have properties that allow a diagnostically useful differentiation. In order to quantify the spectral behavior of different materials, a Dual-Energy Index can be calculated independently from the mere CT density as the relation of attenuations of the same voxel divided by its mean attenuation at the different tube potentials (Eq. 5.1) ... 

As Hounsfield units should be related hnearly with attenuation, the calculation can be performed based on CT density values measured for the respective substance. However, as the definition of Hounsfield units implies that an attenuation of 0 is reflected by a value of -1,000 for air, the formula for the Dual-Energy Index resolves to (Eq. 5.2) ... 

Abbreviations CLA, conjugated linoleic add BMI, body mass index BC, body composition % BF, percentage of body fat M, men W, women DEXA, dual energy X-ray absorptiometry TOBEC, total body electrical conductivity BIS, bioimpedance spectroscopy NR, not reported SAD, sagittal abdominal diameter. 

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