Kenta Tokumoto, Presenter: Nothing to Disclose

Yoichi Yamazaki PhD, Abstract Co-Author: Nothing to Disclose

Naohiro Toda PhD, Abstract Co-Author: Nothing to Disclose

Shuji Koyama PhD, Abstract Co-Author: Nothing to Disclose

The effects of scattered radiation on dual-energy X-ray CT (DECT) reconstruction have not yet been investigated. In general, the number of scattered photons increases with increasing width of the X-ray beam. Recently, CT devices have witnessed a transition from fan-beam methods to cone-beam methods, and the influence of scattered radiation is becoming too great. The purpose here was to show that scattered radiation may produce large artifacts in the DE reconstructed image when cone-beam geometry is used by carrying out a Monte Carlo simulation implemented in EGS5.

Some iterative reconstruction algorithms for DECT have been proposed, including models for statistical fluctuation of intensity. However, scattering is ignored in these algorithms. The existence of scattered radiation may hinder good DE reconstruction in cone-beam CT. In order to determine this effect beforehand, we carried out a Monte Carlo simulation implemented in EGS5. We prepared two sets of projection data: one with scattered radiation and the other without. For each dataset, tomographic images were reconstructed using conventional CT and the DE method.

In the case without scattering, few artifacts were recognized in the image reconstructed by the DE method. However, in the case with scattered radiation, artifacts occurred for both conventional CT and the DE method. In particular, the quality of reconstruction for the DE method was significantly influenced by scattering. We evaluated these images from the viewpoint of tissue characterization. In all cases, the scattered radiation was found to cause a large bias in the distribution in the feature space. This means that the presence of scattered radiation makes clustering difficult. 

We analyzed the influence of scattered radiation on the DE method by carrying out a Monte Carlo simulation implemented in EGS5. The following problems were identified: (1) Scattered radiation produces large artifacts. (2) In the presence of scattered radiation, large biases arise when estimating the combination coefficients of basis functions of energy dependency. Therefore, a method is required to overcome such problems caused by scattered radiation.

The influence of scattered radiation may become a serious problem for cone-beam DECT. This study provides a base for constructing methods to extract energy-dependent information from patients.

Tokumoto, K, Yamazaki, Y, Toda, N, Koyama, S, Evaluation of Scattered Radiation in Cone-Beam Dual-Energy X-ray CT with Monte Carlo Simulation.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12031282.html