Monte Carlo simulation of a CsI-based flat-panel imager for mammography

Abstract

The development of new digital mammography techniques such as dual-energy imaging, tomosynthesis and CT mammography often requires investigating optimal camera design parameters and imaging techniques. One tool that is useful for this purpose is Monte Carlo simulation. This paper presents a methodology for generating simulated images from a CsI-based, flat-panel imager by using the Geant 3 Monte Carlo code to model x-ray transport and absorption within the CsI scintillator, and the DETECT-II code to track optical photon spread within a columnar model of the CsI scintillator. The Monte Carlo modeling of x-ray transport and absorption within the CsI was validated by comparing to previously published values for the probability of a K-shell interaction, the fluorescent yield, the probability of a Kfluorescent emission, and the escape fraction describing the probability of a K x-ray escaping the scintillator. To validate the combined (Geant coupled with DETECT-II) Monte Carlo approach to form simulated images, comparison of modulation transfer functions (MTFs) and system sensitivity (electrons/mR/pixel) obtained from simulations were compared to empirical measurements obtained with different x-ray spectra and imagers with varying CsI thicknesses. By varying the absorption and reflective properties of the columnar CsI used in the DETECT-II code, good agreement between simulated MTFs and system sensitivity and empirically measured values were observed.

A theoretical and experimental evaluation of the microangiographic fluoroscope: A high‐resolution region‐of‐interest x‐ray imager

“…A soft spectrum with 50 kVp was taken for the MTF measurements to avoid the contribution from the K-edge blurring. The MTF measurement agrees with the published results from other groups 56,61 who measured the 300 lm thick HL CsI supplied by Hamamatsu Corp. Bridgewater, NJ.…”

“…For the parallel branching parameters of the linear cascade model, the fluorescence yield of the K-alpha photoelectric interaction n, the probability of K shell interaction x in the CsI, the probability of K-edge re-absorption f k and the probability of K-photon ejection I k was used from the works by Others [55][56][57] and from NIST data sheets. 58 The values of these parameters are listed in the Table II. The mean gain for branches A, B and C was calculated with the values of average energy and the K-edge energy of the CsI using Eqs.…”

Lubberts effect in columnar phosphors

“…For instance, an x-ray/ electron Monte Carlo transport code could be used to determine the three-dimensional distribution of energy deposition in the phosphor, and light generated at these locations could be followed with DETECT-II to obtain simulated images (see, for instance, Ref. 38).…”