X-ray Fluorescence Computed Tomography (XFCT) Imaging with a Superfine Pencil Beam X-ray Source

Ignacio O Romero,Changqing Li,Michael Lun,Yile Fang

doi:10.3390/photonics8070236

Ignacio O Romero, Changqing Li + Show 2 more

Open Access

https://doi.org/10.3390/photonics8070236

Copy DOI

Journal: Photonics	Publication Date: Jun 25, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: University of California, Merced

Abstract

X-ray fluorescence computed tomography (XFCT) is a molecular imaging technique that can be used to sense different elements or nanoparticle (NP) agents inside deep samples or tissues. However, XFCT has not been a popular molecular imaging tool because it has limited molecular sensitivity and spatial resolution. We present a benchtop XFCT imaging system in which a superfine pencil-beam X-ray source and a ring of X-ray spectrometers were simulated using GATE (Geant4 Application for Tomographic Emission) Monte Carlo software. An accelerated majorization minimization (MM) algorithm with an L1 regularization scheme was used to reconstruct the XFCT image of molybdenum (Mo) NP targets. Good target localization was achieved with a DICE coefficient of 88.737%. The reconstructed signal of the targets was found to be proportional to the target concentrations if detector number, detector placement, and angular projection number are optimized. The MM algorithm performance was compared with the maximum likelihood expectation maximization (ML-EM) and filtered back projection (FBP) algorithms. Our results indicate that the MM algorithm is superior to the ML-EM and FBP algorithms. We found that the MM algorithm was able to reconstruct XFCT targets as small as 0.25 mm in diameter. We also found that measurements with three angular projections and a 20-detector ring are enough to reconstruct the XFCT images.

Highlights

X-ray fluorescence computed tomography (XFCT) is a molecular imaging technique of X-ray photons that can be used to sense different elements or nanoparticle agents inside deep samples or tissues
Compton scattering is a prevalent source of noise in XFCT imaging
The physics lists enabled in GATE consisted of the photoelectric effect, Compton scattering, and Rayleigh scattering, which are the primary physics processes accounted for in XFCT imaging

Summary

Introduction

X-ray fluorescence computed tomography (XFCT) is a molecular imaging technique of X-ray photons that can be used to sense different elements or nanoparticle agents inside deep samples or tissues. Many XFCT benchtop systems employ a cone-beam source geometry, with pinhole detector collimation to reduce the imaging time and dose [1,2,3]. Multiple spectral detectors are configured to optimize the detected X-ray fluorescent signal, reduce scatter detection, and reduce the scan time and dose delivered to the imaging object [4,5]. Compton scattering is a prevalent source of noise in XFCT imaging. Compton scattering does not have a fixed energy and does not have isotropic emissions. The scattered signal can significantly hinder the fluorescent signal if the detector placement is not optimized in an orthogonal configuration or in a backscatter configuration [5]

Methods

Results

Discussion

Conclusion