Performance characteristics of the Inveon micro-CT scanner in small animal imaging

Abstract

InveonTM is a tri-modality (Siemens Medical Solutions) imaging system designed to image rodents such as mice and rats. The objective of this study was to characterize the performance of the CT component of the scanner in terms of image noise, uniformity, spatial resolution as well as image quality. A clinically relevant water phantom was used for the measurement of image noise and uniformity. Spatial resolution was measured by calculating the modulation transfer function (MTF) using the slanted edge method. Image noise was estimated under several conditions of beam amperage (50–500 μA) and x-ray CT voltages (40–80 kVp) at an exposure time of 200 ms. The CT number for different tissues was measured using a manufacturer-supplied phantom of different densities (0, 50, 250, 750 mg/cc). System linearity was assessed using a wide range of iodine concentrations (Ultravist 370) ranging from 5 to 70 mg/cc. No significant change was noticed for image uniformity across the whole range of tube currents at voltage of 80 kVp. However, a significant reduction of the noise was noticed when the current increased from 50 to 500 μA and also with gradual increment of the tube voltage. The best noise measure was obtained at 500 μA and 80 kVp. Noise or ring reduction feature showed a significant reduction of the noise level. The relationship between noise and the current was shown to be dominated by the photon statistics with less contribution from the system noise. The MTF measurements showed a resolution of 198 μm, 43 μm and 9.52 μm respectively at 10% modulation. A good linear correlation was found between the CT number and iodine concentrations with high statistical significance. The system has shown good CT performance measures in terms of uniformity, spatial resolution, image noise and contrast linearity. Clinical results showed the capability of the system in acquiring high spatial resolution images. One of the shortcomings is disability to perform 4D CT and thus additional engineering work is requested to further enhance the sensitivity and temporal resolution of the scanner.