Multicolor spectral photon-counting computed tomography: in vivo dual contrast imaging with a high count rate scanner

Abstract

A new prototype spectral photon-counting computed tomography (SPCCT) based on a modified clinical CT system has been developed. SPCCT analysis of the energy composition of the transmitted x-ray spectrum potentially allows simultaneous dual contrast agent imaging, however, this has not yet been demonstrated with such a system. We investigated the feasibility of using this system to distinguish gold nanoparticles (AuNP) and an iodinated contrast agent. The contrast agents and calcium phosphate were imaged in phantoms. Conventional CT, gold K-edge, iodine and water images were produced and demonstrated accurate discrimination and quantification of gold and iodine concentrations in a phantom containing mixtures of the contrast agents. In vivo experiments were performed using New Zealand White rabbits at several times points after injections of AuNP and iodinated contrast agents. We found that the contrast material maps clearly differentiated the distributions of gold and iodine in the tissues allowing quantification of the contrast agents' concentrations, which matched their expected pharmacokinetics. Furthermore, rapid, repetitive scanning was done, which allowed measurement of contrast agent kinetics with high temporal resolution. In conclusion, a clinical scale, high count rate SPCCT system is able to discriminate gold and iodine contrast media in different organs in vivo.

Figure 1

(A) Schematic depiction of SPCCT image formation. The transmitted spectrum (a) is divided by photon-counting detectors into multiple bins (b). These datasets are jointly processed to provide conventional images, and specific material decomposition images, e.g. water, iodine and gold images (c). (B) Photograph of the spectral photon-counting CT system used in this study. (C) Schematic depiction of the in vivo imaging protocol.

Figure 2

(A) Schematic representation of the gold nanoparticle used in this report. (B) TEM of the gold nanoparticles.

Figure 3

(A) Schematic of the phantom with unmixed solutions. (B) Conventional, gold, iodine, water and overlay images are depicted. (C) Graph of the expected and the measured concentrations.

Figure 4

(A) Schematic of the phantom with mixed solutions. (B) Conventional, gold, iodine, water and overlay images are depicted. (C) Comparison of the expected and the measured concentrations.

Figure 5

Photon-counting CT images of the chest of a rabbit. Conventional, gold, iodine, water and overlay images are shown for the three different time points. Arrowheads indicate bones, white arrows indicate the heart, black arrows indicate the aorta and stars indicate the lungs.

Figure 6

Photon-counting CT images of the abdomen of a rabbit. Conventional, gold, iodine, water and overlay images are shown for the three different time points. Arrowheads indicate aorta, white arrows indicate the spleen and black arrows indicate the kidney.

Figure 7

Concentrations of contrast agents in (A) the blood compartment and (B) the renal pelvis.

Figure 8

Conventional, gold k-edge and iodine material decomposition images at the level of the heart of a rabbit injected with AuNP and an iodine contrast agent at various timepoints (left). Quantification of the signal in various organs at the different timepoints (right).