Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

Abstract

Purpose: MANTIS is a Monte Carlo code developed for the detailed simulation of columnar CsI scintillator screens in x-ray imaging systems. Validation of this code is needed to provide a reliable and valuable tool for system optimization and accurate reconstructions for a variety of x-ray applications. Whereas previous validation efforts have focused on matching of summary statistics, in this work the authors examine the complete point response function ͑PRF͒ of the detector system in addition to relative light output values. Methods: Relative light output values and high-resolution PRFs have been experimentally measured with a custom setup. A corresponding set of simulated light output values and PRFs have also been produced, where detailed knowledge of the experimental setup and CsI:Tl screen structures are accounted for in the simulations. Four different screens were investigated with different thicknesses, column tilt angles, and substrate types. A quantitative comparison between the experimental and simulated PRFs was performed for four different incidence angles ͑0°, 15°, 30°, and 45°͒ and two different x-ray spectra ͑40 and 70 kVp͒. The figure of merit ͑FOM͒ used measures the normalized differences between the simulated and experimental data averaged over a region of interest. Results: Experimental relative light output values ranged from 1.456 to 1.650 and were in approximate agreement for aluminum substrates, but poor agreement for graphite substrates. The FOMs for all screen types, incidence angles, and energies ranged from 0.1929 to 0.4775. To put these FOMs in context, the same FOM was computed for 2D symmetric Gaussians fit to the same experimental data. These FOMs ranged from 0.2068 to 0.8029. Our analysis demonstrates that MANTIS reproduces experimental PRFs with higher accuracy than a symmetric 2D Gaussian fit to the experimental data in the majority of cases. Examination of the spatial distribution of differences between the PRFs shows that the main reason for errors between MANTIS and the experimental data is that MANTIS-generated PRFs are sharper than the experimental PRFs. Conclusions: The experimental validation of MANTIS performed in this study demonstrates that MANTIS is able to reliably predict experimental PRFs, especially for thinner screens, and can reproduce the highly asymmetric shape seen in the experimental data. As a result, optimizations and reconstructions carried out using MANTIS should yield results indicative of actual detector performance. Better characterization of screen properties is necessary to reconcile the simulated light output values with experimental data.

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

“…This implies that potential inaccuracies in the analytical estimate of (originally derived for amorphous selenium) are most likely to affect low‐ to mid‐frequency DQE. Further refinement of the estimates of and requires dedicated experimental techniques and more sophisticated scintillator models (e.g., Monte Carlo simulations) that are beyond the scope of this study. In the present work, the impact of these approximations is limited because we are primarily concerned with tasks emphasizing mid‐ to high frequencies (>2 mm −1 ), where the simulation agrees well with measurements.…”

Modelling the transport of optical photons in scintillation detectors for diagnostic and radiotherapy imaging

“…Furthermore, extensive work has been published by Badano et al on modelling indirect X-ray detectors by interfacing PENELOPE with DETECTII routines (Badano and Sempau, 2006; Freed et al , 2009). This open-source model called MANTIS accounts not only for X-ray photon interactions but also for secondary electron interactions and the associated spreading that further degrades detector performance.…”

“…, MTF) might not provide sufficient evidence for model validation (Zhao et al , 2004). Since most models include parameters that can be adjusted to match experimental results, a more sound approach for validating indirect X-ray imager models should compare blur estimates while maintaining the information or Swank factor and light output consistent with previously published data as described in (Freed et al , 2009). …”

“…Indirect imaging systems employing columnar scintillators (e.g., cesium iodide) have been studied in a series of experimentally verified dedicated optical MC codes (Badano and Sempau, 2006; Freed et al , 2009; Sharma et al , 2012; Sharma and Badano, 2013; Dong et al , 2014; Nillius et al , 2015). …”

Effect of Oblique X-ray Incidence in Flat-Panel Computed Tomography of the Breast

“…The three performance parameters we have previously used are the information (Swank) factor , the light output (either in absolute or relative scales depending on the availability of data from the literature), and the spatial detector response. A full report on the validation of the simulation results with measurements of phosphor blur for a variety of screen designs, thicknesses, and X-ray energies will be published elsewhere [35] (preliminary results were included in [7]). …”