Seungman Yun, Abstract Co-Author: Nothing to Disclose

Jesse Tanguay, Abstract Co-Author: Nothing to Disclose

Ho Kyung Kim, Abstract Co-Author: Nothing to Disclose

Ian A. Cunningham PhD, Presenter: Founder, DQE Instruments Inc

The development of theoretical models of x-ray interaction physics is a critical step in optimal detector design and assessment. While cascaded-systems analyses (CSA) are often used to describe image signal and noise in many systems, past work has considered detectors consisting of a single element (single Z) even though most commonly used and promising candidates are compound materials. In addition, the effects of coherent and incoherent scattering on image quality are usually ignored which can be a poor assumption in low-Z materials.

A parallel-cascade approach is used to describe photoelectric, coherent and incoherent interactions in low-Z, high-Z and double-Z detectors. This is achieved using an “energy-labeled reabsorption” process introduced to describe incoherent scatter and allowing for reabsorption of the high-Z characteristic emission by the low-Z atom. Analytic expressions of signal and noise transfer are developed to describe the detective quantum efficiency (DQE) in terms of the modulation transfer function (MTF) and Wiener noise power spectrum (NPS). The model was validated using Monte Carlo calculations for Si, Se, CsI and PbI2, and by experimental measurements of the DQE using narrow spectra above and below the K-edge energies with a high-resolution CMOS-based CsI detector. Results were compared with a simpler single-Z model to determine the need for the complex double-Z model in each case.

Excellent agreement was obtained with both Monte Carlo and experimental results for all conditions tested. It is shown that a combination of two single-Z models, weighted by the atomic weight of each material, gave equivalent results to the comprehensive double-Z model within a few percent. Incoherent interactions have the potential to produce a substantial low-frequency drop in the MTF and DQE of low-Z detectors.

These results show that combining two simple single-Z models is adequate for a description of the double-Z detectors and the effect of incoherent scatter must be considered for low-Z materials. We believe that this CSA model of the DQE is useful for an optimal design of conventional radiography detectors and the estimation of x-ray imaging performance of novel photoconductor materials.

Development of comprehensive models of the DQE is necessary to ensure high quality images and low patient exposures with new detector designs.

Yun, S, Tanguay, J, Kim, H, Cunningham, I, Cascaded-systems Analyses for Describing the DQE of Low-Z, High-Z and Double-Z Detectors.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13029035.html