X-ray fluorescence computed tomography (XFCT) imaging of gold nanoparticle-loaded objects using 110 kVp x-rays

Abstract

A conventional x-ray fluorescence computed tomography (XFCT) technique requires monochromatic synchrotron x-rays to simultaneously determine the spatial distribution and concentration of various elements such as metals in a sample. However, the synchrotron-based XFCT technique appears to be unsuitable for in vivo imaging under a typical laboratory setting. In this study we demonstrated, for the first time to our knowledge, the possibility of performing XFCT imaging of a small animal-sized object containing gold nanoparticles (GNPs) at relatively low concentrations using polychromatic diagnostic energy range x-rays. Specifically, we created a phantom made of polymethyl methacrylate plastic containing two cylindrical columns filled with saline solution at 1 and 2 wt% GNPs, respectively, mimicking tumors/organs within a small animal. XFCT scanning of the phantom was then performed using microfocus 110 kVp x-ray beam and cadmium telluride (CdTe) x-ray detector under a pencil beam geometry after proper filtering of the x-ray beam and collimation of the detector. The reconstructed images clearly identified the locations of the two GNP-filled columns with different contrast levels directly proportional to gold concentration levels. On the other hand, the current pencil-beam implementation of XFCT is not yet practical for routine in vivo imaging tasks with GNPs, especially in terms of scanning time. Nevertheless, with the use of multiple detectors and a limited number of projections, it may still be used to image some objects smaller than the current phantom size. The current investigation suggests several modification strategies of the current XFCT setup, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-top XFCT system for GNP-based preclinical molecular imaging applications.

Pinhole X-ray fluorescence imaging of gadolinium and gold nanoparticles using polychromatic X-rays: a Monte Carlo study

“…[49][50][51] The pinhole XRF imaging system has an imaging mechanism very similar to SPECT. 38 The model was benchmarked against the design and the dimension of the pinhole, as well as the type and the pixel size of the detector commonly used in preclinical pinhole SPECT. [52][53][54][55][56] A cylindrical water phantom in the middle, as shown in Figure 1A, had a diameter of 5 cm and a height of 5 cm each.…”

“…37 X-ray fluorescence (XRF) computed tomography (XFCT) is one of the promising imaging modalities for in vivo imaging. 38 XFCT was first proposed in 1986 using synchrotron sources. 39 Since polychromatic X-ray sources were made available on the laboratory scale, implementing benchtop fluorescence imaging systems has shown that XFCT could be a potential molecular imaging device similar to positron emission tomography (PET) and single-photon emission computed tomography (SPECT).…”

“…39 Since polychromatic X-ray sources were made available on the laboratory scale, implementing benchtop fluorescence imaging systems has shown that XFCT could be a potential molecular imaging device similar to positron emission tomography (PET) and single-photon emission computed tomography (SPECT). 38 Focusing on K-shell XFCT, 0.5% gold by weight (wt%) was able to be detected using 105 kVp cone-beam X-rays by Jones et al 40 Ahmad et al 41 showed images of 0.25 wt% AuNP using 120 kVp pencil-beam X-rays by optimizing the detector angular configuration. Recently, L-shell imaging of AuNP using a benchtop X-ray source has been developed to improve the detection limit on the order of parts per million (ppm).…”

Development of XFCT imaging strategy for monitoring the spatial distribution of platinum‐based chemodrugs: Instrumentation and phantom validation

“…The XRF photons can be imaged with energy-resolving x-ray photon counting detectors. [9][10][11] This provides a means of quantitatively detecting the change in the distribution and concentration of Pt drugs. The present study represents an important advance in the ability of XRF to image platinum in a tomographic approach.…”

The potential of L-shell X-ray fluorescence CT (XFCT) for molecular imaging

“…2 Concentrations of AuNP and other suitable XFCT imaging agents of up to three orders of magnitude lower than the latter value have been detected in small animals and are expected in human studies. Therefore, in order to apply XFCT imaging clinically and even preclinically (i.e.…”