Optimization of K-edge imaging for vulnerable plaques using gold nanoparticles and energy resolved photon counting detectors: a simulation study

• Published in: Physics in medicine & biology 2014-01, Vol.59 (1), p.135-152
• Main Authors: Alivov, Yahya, Baturin, Pavlo, Le, Huy Q, Ducote, Justin, Molloi, Sabee
• Format: Article
• Language: English
• Subjects: Cadmium; Gold - chemistry; Gold - metabolism; Metal Nanoparticles; Models, Theoretical; Phantoms, Imaging; Photons; Plaque, Atherosclerotic - diagnostic imaging; Polymethyl Methacrylate; Scintillation Counting - methods; Signal-To-Noise Ratio; Tellurium; Tomography, X-Ray Computed - methods; Zinc
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/59/1/135

We investigated the effect of different imaging parameters, such as dose, beam energy, energy resolution and the number of energy bins, on the image quality of K-edge spectral computed tomography (CT) of gold nanoparticles (GNP) accumulated in an atherosclerotic plaque. A maximum likelihood technique was employed to estimate the concentration of GNP, which served as a targeted intravenous contrast material intended to detect the degree of the plaque's inflammation. The simulation studies used a single-slice parallel beam CT geometry with an x-ray beam energy ranging between 50 and 140 kVp. The synthetic phantoms included small (3 cm in diameter) cylinder and chest (33 × 24 cm2) phantoms, where both phantoms contained tissue, calcium and gold. In the simulation studies, GNP quantification and background (calcium and tissue) suppression tasks were pursued. The x-ray detection sensor was represented by an energy resolved photon counting detector (e.g., CdZnTe) with adjustable energy bins. Both ideal and more realistic (12% full width at half maximum (FWHM) energy resolution) implementations of the photon counting detector were simulated. The simulations were performed for the CdZnTe detector with a pixel pitch of 0.5-1 mm, which corresponds to a performance without significant charge sharing and cross-talk effects. The Rose model was employed to estimate the minimum detectable concentration of GNPs. A figure of merit (FOM) was used to optimize the x-ray beam energy (kVp) to achieve the highest signal-to-noise ratio with respect to the patient dose. As a result, the successful identification of gold and background suppression was demonstrated. The highest FOM was observed at the 125 kVp x-ray beam energy. The minimum detectable GNP concentration was determined to be approximately 1.06 µmol mL−1 (0.21 mg mL−1) for an ideal detector and about 2.5 µmol mL−1 (0.49 mg mL−1) for a more realistic (12% FWHM) detector. The studies show the optimal imaging parameters at the lowest patient dose using an energy resolved photon counting detector to image GNP in an atherosclerotic plaque.