K-edge ratio method for identification of multiple nanoparticulate contrast agents by spectral CT imaging

Abstract

Objective: Recently introduced energy-sensitive X-ray CT makes it feasible to discriminate different nanoparticulate contrast materials. The purpose of this work is to present a K-edge ratio method for differentiating multiple simultaneous contrast agents using spectral CT. Methods: The ratio of two images relevant to energy bins straddling the K-edge of the materials is calculated using an analytic CT simulator. In the resulting parametric map, the selected contrast agent regions can be identified using a thresholding algorithm. The K-edge ratio algorithm is applied to spectral images of simulated phantoms to identify and differentiate up to four simultaneous and targeted CT contrast agents. Results: We show that different combinations of simultaneous CT contrast agents can be identified by the proposed K-edge ratio method when energy-sensitive CT is used. In the K-edge parametric maps, the pixel values for biological tissues and contrast agents reach a maximum of 0.95, whereas for the selected contrast agents, the pixel values are larger than 1.10. The number of contrast agents that can be discriminated is limited owing to photon starvation. For reliable material discrimination, minimum photon counts corresponding to 140 kVp, 100 mAs and 5-mm slice thickness must be used. Conclusion: The proposed K-edge ratio method is a straightforward and fast method for identification and discrimination of multiple simultaneous CT contrast agents. Advances in knowledge: A new spectral CT-based algorithm is proposed which provides a new concept of molecular CT imaging by non-iteratively identifying multiple contrast agents when they are simultaneously targeting different organs.Despite remarkable advances in diagnostic and therapeutic procedures during the past two decades, annual reports still indicate that cancer remains a challenging disease all over the world. To reduce the morbidity and mortality caused by cancer and many other diseases, endeavours spanning technological innovations in imaging systems to the development of nanoparticulate (NP) materials aim at improving clinical diagnosis and therapy planning. Numerous high-atomic-number agents have been investigated for X-ray imaging applications, such as bismuth [1] [11]. Moreover, NP CT contrast agents proved to be promising in the context of molecular imaging owing to their higher diagnostic efficacy than current contrast agents [12][13][14]. Targetability and high circulation time in vivo make it possible to use multiple contrast agents simultaneously and integrate multiple phases of diagnostic imaging in a single scan. This may decrease CT radiation dose, drug dose and diagnosis time, with higher sensitivity and specificity [12].Although the use of multiple high-atomic-number contrast agents may improve the efficiency of clinical diagnosis, it would require differentiation of the contrast agents used simultaneously. However, owing to the wide range of atomic numbers and concentrations in the body, conventional CT that uses an integrating detection system is unlike...

CT Image Contrast of High-ZElements: Phantom Imaging Studies and Clinical Implications

“…It is possible to simulate the expected CT image contrast produced by a given material by using x-ray spectrum and material attenuation estimation tools (12,25,30). However, spectral models are difficult to validate, and nonideal effects, such as x-ray scatter, are difficult to model.…”

Spectral diffusion: an algorithm for robust material decomposition of spectral CT data

“…Being generic to the number of materials and energies is important for the future development of passively and actively targeted nanoprobes based on different high atomic number elements for functional CT imaging (Ghadiri et al 2013). Being generic to the number of input energies also enables investigation of over-constrained material decompositions which are of potential interest for increasing material sensitivity, particularly in the case of photon counted data (Faby et al 2014).…”

“…Being generic to the number of input energies also enables investigation of over-constrained material decompositions which are of potential interest for increasing material sensitivity, particularly in the case of photon counted data (Faby et al 2014). The most significant point, being robust in the presence of noise , is of critical importance for performing material decomposition in small animal micro-CT data, which is typically an order of magnitude noisier than clinical CT data, for improving the limits of detectability for each material, for application to low dose scanning with an energy integrating detector, and for application to photon-starved, K-edge imaging with a photon counting detector (Ghadiri et al 2013). …”

Evaluation of image quality and radiation dose using gold nanoparticles and other clinical contrast agents in dual-energy Computed Tomography (CT): CT abdomen phantom

“…This finding contradicts from other studies due to lower concentration of the gold nanoparticles used. The concentration of gold nanoparticles from other studies 10,17,18 were between 2.0 mg/ml to 13.6 mg/ml while this study used 2.15 x 10 -7 g/ml. This low concentration reduced the x-ray attenuating atom per agent as low particles number found in gold nanoparticles 7 .…”

“…The use of multiple contrast agents simultaneously are possible in diagnostic imaging which may reduce the drug dose, diagnosis time, radiation dose, and improve specificity and sensitivity. Nevertheless, the conventional CT is unable to differentiate between the multiple contrast agents with wide range of concentrations and atomic numbers when they use simultaneously [8][9][10] . This limitation can be overcome by using DECT as two different energies are applied which can differentiate the contrast agents with different atomic numbers.…”