Implementation and detection optimisation of gold nanoparticles as contrast media in diagnostic radiology
Creators: name: Jackson, Price
Publisher: name: RMIT University
Year: 2024

description: This project has focused on identifying any interesting properties, particularly from a physics perspective, that gold nanoparticles offer as the basis for a contrast agent in diagnostic radiology. The use of colloid, or nanoparticulate, contrast agents is not a new proposition (for example: early thorium-based contrast media), but in the last several decades iodinated compounds have become the standard due to their safety and relatively high radiopacity. Accordingly, contrast-aided procedures employing iodine are set to exposure parameters designed to optimally enhance the K-edge of that particular element (33.2 keV).<br><br>With improvements in chemical engineering, understanding of protein-cell interactions, and the ability to record measurements on a nanometre scale, there has been renewed interest in the use of nanoparticles for biological applications. Gold nanoparticles suspension represents a particularly attractive candidate for use in radiographic imaging. There are well documented synthesis procedures for gold nanoparticles. The element has a relatively large atomic number and is subsequently highly radiopaque. Gold particles can be bound to cell-specific targeting molecules. Gold as an element is bioinert and while the toxicity of nanoparticles is still debatable, gold is expected to have markedly lower toxicity than most other heavy elements.<br>In this project I have sought to determine the most practical X-ray imaging modalities for use of gold nanoparticle contrast media. Special emphasis has been placed on optimally detecting attenuated photons above the K-edge of gold (80.7 keV). The optimal energy spectrum to maximise relative contrast of gold nanoparticles with respect to normal tissues and conventional contrast media has been investigated by phantom study with radiographic images. These results are supported by quantitative simulations by Monte Carlo technique which further identify that the optimal tube potential for visualisation of gold nanoparticles is in the range of 120 to 140 kilovolts for most applications. Further study has considered the implementation of a combined, double-layer detector system to capture simultaneous subtraction images which would benefit from the relatively high K-edge of Au. Finally, experiments designed to shape the X-ray energy spectra transmitted from a source were conducted and applied to a novel subtraction imaging technique. Results from those experiments showed particular promise for maximising the detection of small quantities of Au in dual-energy subtraction imaging.<br><br>Attention has been given to nanoparticle-specific size-effects. These quantum confinement effects can subtly alter the attenuation of X-ray photons by very small clusters of atoms compared to bulk crystal structures. Measurements were completed using X-ray Absorption Spectroscopy and also in radiographic imaging with the aim of determining whether an optimal particle size should be selected to maximise image contrast in a radiographic image.