The role of x-ray Swank factor in energy-resolving photon-counting imaging

Journal Article · Wed Dec 15 04:00:00 EST 2010 · Medical Physics

DOI:https://doi.org/10.1118/1.3512794· OSTI ID:22096833

Tanguay, Jesse; Kim, Ho Kyung; Cunningham, Ian. A. ^[1]

---

1. Imaging Research Laboratories, Robarts Research Institute, 100 Perth Drive, London, Ontario N6A 5K8 (Canada) and Department of Medical Biophysics, The University of Western Ontario, 100 Perth Drive, London, Ontario N6A 5C1 (Canada)

Purpose: Energy-resolved x-ray imaging has the potential to improve contrast-to-noise ratio by measuring the energy of each interacting photon and applying optimal weighting factors. The success of energy-resolving photon-counting (EPC) detectors relies on the ability of an x-ray detector to accurately measure the energy of each interacting photon. However, the escape of characteristic emissions and Compton scatter degrades spectral information. This article makes the theoretical connection between accuracy and imprecision in energy measurements with the x-ray Swank factor for a-Se, Si, CdZnTe, and HgI{sub 2}-based detectors. Methods: For a detector that implements adaptive binning to sum all elements in which x-ray energy is deposited for a single interaction, energy imprecision is shown to depend on the Swank factor for a large element with x rays incident at the center. The response function for each converter material is determined using Monte Carlo methods and used to determine energy accuracy, Swank factor, and relative energy imprecision in photon-energy measurements. Results: For each material, at energies below the respective K edges, accuracy is close to unity and imprecision is only a few percent. Above the K-edge energies, characteristic emission results in a drop in accuracy and precision that depends on escape probability. In Si, and to some extent a-Se, Compton-scatter escape also degrades energy precision with increasing energy. The influence of converter thickness on energy accuracy and imprecision is modest for low-Z materials but becomes important when using high-Z materials at energies greater than the K-edge energies. Conclusions: Accuracy and precision in energy measurements by EPC detectors are determined largely by the energy-dependent x-ray Swank factor. Modest decreases in the Swank factor (5%-15%) result in large increases in relative imprecision (30%-40%).

• OSTI ID: 22096833
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 12 Vol. 37; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
62 RADIOLOGY AND NUCLEAR MEDICINE
ACCURACY
COMPTON EFFECT
EMISSION
ENERGY DEPENDENCE
MERCURY IODIDES
MONTE CARLO METHOD
PHOTONS
PROBABILITY
RESPONSE FUNCTIONS
SI SEMICONDUCTOR DETECTORS
X RADIATION
X-RAY DETECTION
X-RAY SPECTROSCOPY