Purpose: To simultaneously image three clinically-relevant contrast agents (iodine, gadolinium, and gold) in a small animal phantom using K-edge subtraction on a table-top spectral computed tomography (sCT) imaging system.
Methods: The table-top sCT imaging system consisted of a diagnostic x-ray tube, phantom rotation stage, a translation stage to enable detector motion and a 330Î¼m pitch cadmium zinc telluride (CZT) detector of 8mm x 12mm in size capable of discriminating six energy levels. The detector energy bins were set to match the contrast agent K-edges. The 3D-printed 3cm-diameter cylindrical plastic phantom contained seven 6mm-diameter vials with water, 1% and 5% iodine in water, 2% and 5% gadolinium in hexane, and 0.4% and 2% gold chloride in water solutions. The phantom was imaged with 120kVp, 1mm Al-filtered cone beam x-rays at 1 mA using 180 rotation steps in 2-degree intervals to a mean dose of 344mGy. K-edge images for each contrast agent were obtained from the sCT data, which were reconstructed using the Feldkamp-David-Kress (FDK) algorithm. The contrast-to-noise ratio (CNR) was evaluated to find the imaging sensitivity of each contrast agent in its K-edge image.
Results: In the respective K-edge images, the CNR of the 5% iodine, 5% gadolinium, and 2% gold vials were 149.4, 26.5, and 22.4. All vials in the K-edge images were detectable (CNR>4). K-edge images had higher sensitivity compared to CT data reconstructed with summed bins mimicking standard photon-integrating CT scanning. The K-edge imaging sensitivity for iodine and gold was considered biologically relevant at 0.15% and 0.36%, respectively, but not for gadolinium at 0.75%.
Conclusion: This work demonstrated the first multiplexed sCT imaging of three contrast agents in one scan. In the clinic, multiplexed sCT will potentially enable visualization of different processes in a disease pathway tagged with contrast agents in a single scan.
Funding Support, Disclosures, and Conflict of Interest: Redlen Technologies partially funded this work by providing the detector.