: X-ray fluorescence (XRF) is a promising technique with sufficient specificity and sensitivity for identifying and quantifying features in small samples containing high atomic number (Z) materials such as iodine, gadolinium, and gold. In this study, the feasibility of applying XRF to early breast cancer diagnosis and treatment is studied using a novel approach for three-dimensional (3D) x-ray fluorescence mapping (XFM) of gold nanoparticle (GNP)-loaded objects in a physical phantom at the technical level.
: All the theoretical analysis and experiments are conducted under the condition of using x-ray pencil beam and a compactly integrated x-ray spectrometer. The penetrability of the fluorescence x-rays from GNPs is first investigated by adopting a combination of BR12 with 70 mm/50 mm in thickness on the excitation/emission path to mimic the possible position of tumor gold in vivo. Then, a physical phantom made of BR12 is designed to translate in 3D space with three precise linear stages and subsequently the step by step XFM scanning is performed. The experimental technique named as background subtraction is applied to isolate the gold fluorescence from each spectrum obtained by the spectrometer. Afterwards, the attenuations of both the incident primary x-ray beam with energies beyond the gold K-edge energy (80.725 keV) and the isolated gold K α fluorescence x-rays (65.99 –69.80 keV) acquired after background subtraction are well calibrated, and finally the unattenuated K α fluorescence counts are used to realize mapping reconstruction and to describe the linear relationship between gold fluorescence counts and corresponding concentration of gold solutions.
: The penetration results show that the gold K α fluorescence x-rays have sufficient penetrability for this phantom study, and the reconstructed mapping results indicate that both the spatial distribution and relative concentration of GNPs within the designed BR12 phantom can be well identified and quantified.
: Although the XFM method in this investigation is still studied at the technical level and is not yet practical for routinein vivo mapping tasks with GNPs, the current penetrability measurements and phantom study strongly suggest the feasibility to establish and develop a 3D XFM system.
This research is supported in part by a grant from the University of Oklahoma Charles and Peggy Stephenson Cancer Center funded by the Oklahoma Tobacco Settlement Endowment Trust. The authors would like to acknowledge the support of the Charles and Jean Smith Chair endowment fund as well. The authors wish to thank Dr. Laurie L. Fajardo (University of Iowa, Iowa City, Iowa) for helpful discussions.
II. MATERIALS AND METHODS
II.A. Measurements for the penetrability of fluorescence x-rays from GNPs
II.A.1. Experimental setup
II.A.2. Measurements for penetrability of fluorescence x-rays
II.B. XFM of a designed phantom containing GNPs
II.B.1. Preparation of phantom containing GNPs and its scanning process
II.B.2. Background subtraction and fluorescence data acquisition
II.B.3. Attenuation analysis and determination of calibration factor (CF)
III.A. Typical spectra and spatial resolution validation
III.B. Background subtraction
III.C. Attenuation calibration and 3D mapping
IV.A. X-ray beam geometry and detector arrays
IV.B. X-ray scanning resolution
IV.C. Attenuation calibration
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