Characterization of the imaging performance of a micro-CT system based on the photon counting XPAD3/Si hybrid pixel detectors

Abstract

We characterize the imaging performance of the micro computed tomography (micro-CT) prototype PIXSCAN equipped with an x-ray photon counting camera based on XPAD3/Si hybrid pixel detectors. The camera, which is composed of eight distinctive horizontal modules, permits the performance of whole-body mouse scans. Photon counting supplied by hybrid pixels guarantees acquisitions at a Poisson noise level exclusively determined by the detected photon statistics. First, we characterize the performance of the imaging system while assessing its linearity, noise, spatial resolution and low contrast detectability estimated from scans of appropriate phantoms. Then, we show CT images of mice data acquired either in vivo or post mortem, without or with an injection of iodine as a contrast agent. Although hybrid pixels guarantee a minimal noise to the images, the limited detection efficiency of Si sensors impairs detected photon statistics and therefore the improvement in contrast-to-noise ratio for standard tomographic imaging. Indeed, the most innovative potential of the PIXSCAN prototype is its capacity to perform spectral tomographic imaging and fast dynamic imaging. The first is thanks to the possibility of setting an energy threshold on the detected photons, and the second is thanks to its fast acquisition rate (till 500 images/s). We present some examples of these imaging methods applied to mice and discuss their main limiting factors.

Tracking Dynamics of Spontaneous Tumors in Mice Using Photon-Counting Computed Tomography

“…Hence, hybrid pixels provide PC instead of integrating the overall signal charge generated by the X-ray beam. This feature allowed a linear detector response free from electronic noise (Cassol et al., 2009), thus minimizing the X-ray flux and the dose delivered to the animal (Cassol et al., 2016). We optimized the scanner acquisition parameters (50 kV/500 μA, 0.6 mm Al filtering, 720 projections) to reach a low radiation dose (180 mGy/scan), thus preventing radiobiological effects along repeated scans and maximizing contrast-to-noise ratio observed for a contrast phantom QRM-microCT-HA (QRM GmbH, Germany).…”

“…Consequently, the Alb-R26 Met model allows detecting endogenous tumors at initiation stages and following their progression overtime, in contrast to other models previously used for longitudinal micro-CT imaging based on the HCC cell implantation into the liver. Small tumor detectability is affected by the noise of the system (Cassol et al., 2016, Hanson, 1979), which in the case of PC is only related to the counting statistics, and hence to the delivered dose. Moreover, it depends on the intrinsic contrast of the lesion and on its dimension.…”

“…In the present study, we report the development of a micro-CT scanner prototype named PIXSCAN-FLI based on hybrid pixel detectors (Ballabriga et al, 2016, Cassol et al., 2009, Delpierre, 2014, Wermes, 2005) to perform photon-counting (PC)-CT scans of mice (Cassol et al., 2016, Taguchi and Iwanczyk, 2013). PC-CT allows reducing the required dose of radiation received by the mice, thus limiting the damaging effects after multiple scans that might affect tissue homeostasis and the mouse life.…”

X-ray-based virtual slicing of TB-infected lungs

“…However, these techniques are usually only feasible with synchrotron light sources 43–48 , which are only available in 73 facilities worldwide, thus preventing their use in high-throughput studies. Cutting-edge spectral systems are expected to demonstrate superior image quality, even with larger voxel sizes than standard CT systems, provided that the attenuation of subjects under study is enhanced 30,49 , which could be achieved by contrast-enhancing preparations such as the one we proposed.…”

Accuracy and Precision of Iodine Quantification in Subtracted Micro-Computed Tomography: Effect of Reconstruction and Noise Removal Algorithms

“…The fFBP and fSIRT images were obtained after applying the corresponding BF to the reconstructed images. The 2D and 1D NPS were evaluated from images of a water phantom, and the 1D MTF was evaluated in the transverse plane from images of an acrylic semi-cylinder phantom, following guidelines for the assessment of image quality in CT scanners [ 24 , 25 ]. Figure 1 shows the water and acrylic phantoms.…”