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Experimental demonstration of direct L ‐shell x‐ray fluorescence imaging of gold nanoparticles using a benchtop x‐ray source
Author(s) -
Manohar Nivedh,
Reynoso Francisco J.,
Cho Sang Hyun
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4816297
Subject(s) - imaging phantom , calibration curve , materials science , calibration , optics , detector , collimator , x ray fluorescence , dosimetry , nuclear medicine , detection limit , fluorescence , physics , chemistry , medicine , chromatography , quantum mechanics
Purpose: To develop a proof‐of‐principle L ‐shell x‐ray fluorescence (XRF) imaging system that locates and quantifies sparse concentrations of gold nanoparticles (GNPs) using a benchtop polychromatic x‐ray source and a silicon (Si)‐PIN diode x‐ray detector system.Methods: 12‐mm‐diameter water‐filled cylindrical tubes with GNP concentrations of 20, 10, 5, 0.5, 0.05, 0.005, and 0 mg/cm 3 served as calibration phantoms. An imaging phantom was created using the same cylindrical tube but filled with tissue‐equivalent gel containing structures mimicking a GNP‐loaded blood vessel and approximately 1 cm 3 tumor. Phantoms were irradiated by a 3‐mm‐diameter pencil‐beam of 62 kVp x‐rays filtered by 1 mm aluminum. Fluorescence/scatter photons from phantoms were detected at 90° with respect to the beam direction using a Si‐PIN detector placed behind a 2.5‐mm‐diameter lead collimator. The imaging phantom was translated horizontally and vertically in 0.3‐mm steps to image a 6 mm × 15 mm region of interest (ROI). For each phantom, the net L ‐shell XRF signal from GNPs was extracted from background, and then corrected for detection efficiency and in‐phantom attenuation using a fluorescence‐to‐scatter normalization algorithm.Results: XRF measurements with calibration phantoms provided a calibration curve showing a linear relationship between corrected XRF signal and GNP mass per imaged voxel. Using the calibration curve, the detection limit (at the 95% confidence level) of the current experimental setup was estimated to be a GNP mass of 0.35 μ g per imaged voxel (1.73 × 10 −2 cm 3 ). A 2D XRF map of the ROI was also successfully generated, reasonably matching the known spatial distribution as well as showing the local variation of GNP concentrations.Conclusions: L ‐shell XRF imaging can be a highly sensitive tool that has the capability of simultaneously imaging the spatial distribution and determining the local concentration of GNPs presented on the order of parts‐per‐million level within subcentimeter‐sized ex vivo samples and superficial tumors during preclinical animal studies.