Abstract
Spectral photon-counting computed tomography (SPCCT) is a rapidly emerging imaging modality that provides energy-dependent information on individual x-ray photons, leading to accurate material decomposition and simultaneous quantification of multiple contrast generating materials. Development of SPCCT-specific contrast agents is needed to overcome the issues with currently used iodinated contrast agents, such as difficulty in differentiation from calcified structures, and yield SPCCT’s full promise. In this study, the contrast generation of different elements is investigated using a prototype SPCCT scanner based on a modified clinical CT system and suitable elements for novel contrast agent development for SPCCT imaging are identified. Furthermore, nanoparticles were synthesized from tantalum as a proof of concept spectral photon-counting CT agent and tested for their in vitro cytotoxicity and contrast generation to provide insight into the feasibility of nanoparticle contrast agent development from these elements. We found that gadolinium, ytterbium and tantalum generate high contrast in spectral photon-counting CT imaging and may be suitable elements for contrast agent development for this modality. Our proof of concept results with tantalum-based nanoparticles underscore this conclusion due to their detectability with spectral photon-counting CT, as well as their biocompatibility.
Highlights
X-ray computed tomography (CT) is one of the most widely used imaging modalities in medicine due to its broad availability, low cost, high spatial resolution and fast image acquisition[1]
There was an excellent linear correlation between the attenuation observed in conventional CT equivalent images and element concentration used in this study, as is typically the case[6,18,30]
We found that gadolinium had the highest value of Attenuation rate (AR), followed by tantalum, ytterbium, gold, tungsten and bismuth (Fig. 4B)
Summary
X-ray computed tomography (CT) is one of the most widely used imaging modalities in medicine due to its broad availability, low cost, high spatial resolution and fast image acquisition[1]. Besides the advantages of SPCCT in terms of image quality and patient dose, these systems can distinguish multiple contrast generating materials in a single scan via material decomposition by assigning an appropriate number of energy bins and their thresholds[18,19,20,21,22,23] This feature allows differentiation of exogenous contrast agents from soft tissues and calcified structures (e.g. bones and calcified atherosclerotic plaques), which can be especially beneficial in coronary CT angiography. While contrast generation of iodinated contrast agents in SPCCT systems is as effective as contrast generation in conventional and dual energy CT systems, they do not take full advantage of the capability of K-edge imaging in SPCCT since iodine’s K-edge energy (33.2 keV) is too low for material decomposition for most clinical CT applications This is because there are too few photons in CT x-ray beams below this K-edge for accurate data to be gathered. To the best of our knowledge, a systematic study of the contrast generation from different elements in SPCCT imaging has not been reported to date
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