A new method to measure electron density and effective atomic number using dual-energy CT images

Abstract

The purpose of this work is to present a new method to extract the electron density ([Formula: see text]) and the effective atomic number (Z eff) from dual-energy CT images, based on a Karhunen-Loeve expansion (KLE) of the atomic cross section per electron. This method was used to calibrate a Siemens Definition CT using the CIRS phantom. The predicted electron density and effective atomic number using 80 kVp and 140 kVp were compared with a calibration phantom and an independent set of samples. The mean absolute deviations between the theoretical and calculated values for all the samples were 1.7 % ± 0.1 % for [Formula: see text] and 4.1 % ± 0.3 % for Z eff. Finally, these results were compared with other stoichiometric method. The application of the KLE to represent the atomic cross section per electron is a promising method for calculating [Formula: see text] and Z eff using dual-energy CT images.

Dual-Energy CT: New Horizon in Medical Imaging

“…Effective atomic number (Z eff ) and electron density (ρ e ) can be calculated from dual-energy CT data with small errors of 1.7 and 4.1%, respectively (16). Effective atomic number map is a quantitative approach in material differentiation by analyzing attenuation changes as a function of energy.…”

A simple formulation for deriving effective atomic numbers via electron density calibration from dual-energy CT data in the human body

“…Currently, the latter is more commonly used since it is easier to handle and can be implemented on most DECT scanners without any constraint on consistent projection data. So far, several image domain procedures to decompose DECT images into ρ e and Z eff images have been proposed . Although they differ widely in their computational complexity, all these approaches can achieve similar absolute errors in the estimation of ρ e and Z eff for calibration phantoms, of less than 1% and several percent, respectively.…”

“…So far, several image domain procedures to decompose DECT images into q e and Z eff images have been proposed. [2][3][4][8][9][10] Although they differ widely in their computational complexity, all these approaches can achieve similar absolute errors in the estimation of q e and Z eff for calibration phantoms, of less than 1% and several percent, respectively. Those methods that use a calibration phantom with known q e and Z eff are of special practical interest because they do not require prior knowledge of the CT scanner spectra, which are not always readily available.…”

On the equivalence of image-based dual-energy CT methods for the determination of electron density and effective atomic number in radiotherapy

“…The determination of these tissue parameters is of particular interest for the improvement of dose calculation in particle therapy treatment planning: they can be used either directly (e.g., electron density) or as proxy for other quantities (e.g., the effective atomic number as a proxy for the mean excitation energy) to calculate stopping-power ratios via the Bethe formula [3,4]. Since the introduction of dedicated clinical dualenergy CT (DECT) scanners [5], an increasing number of algorithms for DECT-basedn /Z eff determination is found in literature [6][7][8][9][10][11][12][13][14][15][16].…”