title: Three-dimensional x-ray fluorescence mapping of a gold nanoparticle-loaded phantom.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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 goldin 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 Kα fluorescence x-rays (65.99 -69.80 keV) acquired after background subtraction are well calibrated, and finally the unattenuated Kα fluorescence counts are used to realize mapping reconstruction and to describe the linear relationship between gold fluorescence counts and corresponding concentration of gold solutions.
  
  
  RESULTS
  The penetration results show that the goldKα 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019.
authors.forename: Liqiang
authors.initials: L
authors.lastname: Ren
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019.
authors.forename: Di
authors.initials: D
authors.lastname: Wu
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Li
authors.affiliation: Biomedical Imaging Cluster and Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180.
authors.forename: Ge
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Radiology, University of Alabama, Birmingham, Alabama 35233.
authors.forename: Xizeng
authors.initials: X
authors.lastname: Wu
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019.
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D002138:Calibration; D005260:Female; D006046:Gold / Q000737:chemistry*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D053768:Metal Nanoparticles / Q000737:chemistry; D053758:Nanoparticles; D036103:Nanotechnology / Q000379:methods*; D019047:Phantoms, Imaging; D011859:Radiography; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation / Q000379:methods*
chemical_list: D006046:Gold