Experimental validation of a radiographic simulation code using breast phantom for X-ray imaging

Abstract

Computer models and simulations of X-ray imaging systems are becoming a very precious tool during the development and evaluation of new X-ray imaging techniques. To provide, however, a faithful simulation of a system, all components must be accurately modelled and tested, followed by verification through experimental measurements. This paper presents a validation study of the XRayImagingSimulator, an in-house developed X-ray imaging simulator, which is extensively used as a basic tool in carrying out complex breast imaging simulations. The approach followed compares results obtained via an experimental setup for breast phantom (CIRS 011A) imaging, using synchrotron radiation (SYRMEP beamline at ELETTRA), with those from its simulated setup under the same conditions. The study demonstrated a very good agreement between experimental and simulated images compared both in terms of subjective and objective criteria. The combination of the XRayImagingSimulator with our BreastSimulator provides a powerful tool for in silico testing of new X-ray breast imaging approaches.

Introduction

Computer modelling and simulation is extensively used in the development of new diagnostic imaging modalities. The use of such tools is becoming of critical importance in designing, testing and predicting the performance of forthcoming X-ray breast imaging systems, prior to their manufacturing and before being accepted for clinical use. Among these are the advanced applications of full field digital mammography systems, especially those that provide three-dimensional images of the breast like digital breast tomosynthesis, cone beam breast Computed Tomography (CT) and breast CT.

To provide a faithful simulation of these systems, all components must be accurately modelled, followed by verification through experimental trials. A traditional approach consists of modelling the breast and a computer code simulating the radiation transport in the model. The breast is usually modelled using regular geometrical structures and with little or no real tissue texture. In mammography, this approach has been used to evaluate scatter to primary ratio [1], to investigate the effect of glandularity on the mean glandular dose and the relationship between glandularity and breast size [2], or to test novel methods for noise reduction [3]. Similarly, this approach was preferred in evaluating the feasibility of breast CT [4], digital breast tomosynthesis [5] and cone beam breast CT [6].

Complex phantoms, on the other hand, are valuable tools that can be used in complicated X-ray imaging studies. The use of realistic patient simulations has wide applications in the field of X-ray imaging and has been reported in the field of mammography [7], [8], [9], [10], breast dosimetry [11], dual energy mammography [12], or to study simulation of the internal structure under compressed conditions [13], [14]. However, validation of such simulators still remains a challenge.

An advanced computer model of the breast [8] that allows simulation of the internal structure under normal and compressed conditions [8], [13], has already been used to predict the performance of dual energy mammography [12], digital breast tomosynthesis and cone beam breast CT [15], [16], [17]. In these investigations, images were obtained using the X-ray imaging simulation module of the in-house developed radiographic simulator XRayImagingSimulator [18]. The aim of this study is to validate this X-ray projection module by comparing simulated and experimentally acquired data. Experiments were performed on a breast phantom, using monochromatic radiation to obtain experimental images. Exposure times varied from 14 to 300 s at an energy of 19 keV. Simulations of the experimental setup were performed with the XRayImagingSimulator. Images obtained experimentally and via simulation were compared subjectively and image characteristics were evaluated quantitatively in terms of mean signal values, signal to noise ratio and profile comparison.