A Method to Improve Electron Density Measurement of Cone-Beam CT Using Dual Energy Technique

Abstract

Purpose: To develop a dual energy imaging method to improve the accuracy of electron density measurement with a cone-beam CT (CBCT) device.

Materials and methods: The imaging system is the XVI CBCT system on Elekta Synergy linac. Projection data were acquired with the high and low energy X-ray, respectively, to set up a basis material decomposition model. Virtual phantom simulation and phantoms experiments were carried out for quantitative evaluation of the method. Phantoms were also scanned twice with the high and low energy X-ray, respectively. The data were decomposed into projections of the two basis material coefficients according to the model set up earlier. The two sets of decomposed projections were used to reconstruct CBCT images of the basis material coefficients. Then, the images of electron densities were calculated with these CBCT images.

Results: The difference between the calculated and theoretical values was within 2% and the correlation coefficient of them was about 1.0. The dual energy imaging method obtained more accurate electron density values and reduced the beam hardening artifacts obviously.

Conclusion: A novel dual energy CBCT imaging method to calculate the electron densities was developed. It can acquire more accurate values and provide a platform potentially for dose calculation.

Figure 1

The flowchart of the proposed method.

Figure 2

Basis material phantom.

Figure 3

The transaxial arrangement of the virtual phantom.

Figure 4

The CTP 486 module within Catphan 500 phantom. (a) Catphan 500 phantom. (b) Schematic drawing of CTP 486 module.

Figure 5

The CIRS phantom.

Figure 6

CBCT images of the CTP 486 module in Catphan 500 phantom: (a) 70 kVp, (b) 120 kVp, and (c) dual energy imaging. (d) Profiles through the region of interest, indicated by the white solid line in (a).

Figure 7

CBCT images of the CIRS phantom: (a) 70 kVp, (b) 120 kVp, and (c) dual energy imaging. (d) Profiles through the horizontal axis of (a), (b), and (c) and the theoretical curves. (e) Electron densities obtained by conventional and dual energy method.