Yoichi Yamazaki PhD, Presenter: Nothing to Disclose

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

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

We previously proposed an implementation method for dual-energy computed tomography (DECT) with an asymmetrical absorption filter (AF) using fan-beam geometry, which we call the asymmetric filter method (AFM). The advantage of this method is its simple implementation since only the absorption filters are replaced. Furthermore, this method performs the measurement required by DECT in one time scan. Recently, cone-beam CT has become more widespread for high-speed measurements as it has a measuring range wider than fan-beam CT. Our purpose was to present an extended version of AFM for cone-beam CT.

When extending AFM to cone-beam CT, it is important to note that the two time measurements strictly required in the original DECT are not done for cone-beam CT as they are for fan-beam AFM. First, we found that any point in the object space is exposed to two kinds of X-rays—namely, hard and soft— by three-dimensional step-type AF, which is an extended version of two-dimensional AF in the direction of the body axis. This fact allowed us to employ an iterative reconstruction algorithm introduced by Fessler et al. because this algorithm does not require the strict condition of two time measurements at each beam line. We propose a method that combines the above elements; we examined whether the reconstruction was correctly performed by numerical simulation. We also considered the filter installation accuracy to propose a method named pixel size relaxing in which the pixel size around the origin is enlarged. This method was also examined through numerical simulations.

We confirmed that the image error became sufficiently small and that artifacts were not recognizable in the reconstruction images. We also confirmed that pixel size relaxing effectively reduced the artifacts in cases where the error was included in the filter installation.

We proposed AFM for cone-beam CT and evaluated the proposed method numerically. The results showed that the proposed method can accurately perform DECT reconstruction. In addition, pixel size relaxing recovered errors in the filter installation position.

Due to the spread of DECT, an implementation method with a suitable introductory cost for utility value is needed. The proposed method is a strong candidate to meet this need.

Yamazaki, Y, Toda, N, Koyama, S, Simple Implementation Method of Cone-Beam Dual-Energy CT Using an Asymmetric Filter.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12026943.html