M. Dupont

First K-Edge Imaging With a Micro-CT Based on the XPAD3 Hybrid Pixel Detector

We investigate the capability to perform K-edge imaging with the newly developed micro-CT PIXSCAN based on the XPAD3 hybrid pixel detector. The XPAD3 detector surface of 8 cm ×11 cm makes it possible to perform whole body mouse imaging. We present a proof of principle of K-edge imaging of mouse-size phantoms filled with Silver and Iodine solutions. Results are compared with standard X-ray absorption tomography for several solution densities.

K-edge imaging with the XPAD3 hybrid pixel detector, direct comparison of CdTe and Si sensors

We investigate the improvement from the use of high-Z CdTe sensors for pre-clinical K-edge imaging with the hybrid pixel detectors XPAD3. We compare XPAD3 chips bump bonded to Si or CdTe sensors in identical experimental conditions. Image performance for narrow energy bin acquisitions and contrast-to-noise ratios of K-edge images are presented and compared. CdTe sensors achieve signal-to-noise ratios at least three times higher than Si sensors within narrow energy bins, thanks to their much higher detection efficiency. Nevertheless Si sensors provide better contrast-to-noise ratios in K-edge imaging when working at equivalent counting statistics, due to their better estimation of the attenuation coefficient of the contrast agent. Results are compared to simulated data in the case of the XPAD3/Si detector. Good agreement is observed when including charge sharing between pixels, which have a strong impact on contrast-to-noise ratios in K-edge images.

Comparison of the performance of the photon counting hybrid pixel camera XPAD3 versus the CCD camera DALSA XR-4 for cone-beam micro-CT

Hybrid pixel detectors represent a new generation of digital X-ray camera working in a photon counting mode that can replace conventional charge integration in 2D detectors. We compare cone-beam CT using either the hybrid pixel camera XPAD3 or the CCD camera DALSA XR-4 within the newly developed micro-CT irradiation setup PIXSCAN within a range of total integrated doses from 30 to 900 mGy. Detector stability, image uniformity, spatial resolution, noise power spectrum, and detectability at low contrast were studied for both cameras. The results we obtained confirmed the absence of dark current for the hybrid pixel photon counting camera XPAD3, although the two detectors are virtually equivalent in standard conditions. The linearity of the CT value is demonstrated for both cameras, but the achieved contrast and spatial resolution are noticeably better with the hybrid pixel camera than with the CCD camera.

Development of K-edge spectral tomography using XPAD3 composite pixels

Hybrid pixel cameras are new devices in which photon counting replaces charge integration used in standard radiography systems. This novel approach involves several advantages, in particular the absence of dark noise integration and the ability to set an energy threshold on each pixel of the detected photons. This ability is of uppermost importance for the development of K-edge imaging approaches, which exploit spectral information on the counted photons. We investigate the capability to perform K-edge imaging by using the hybrid pixel camera XPAD3 with 500,000 pixels of (130 × 130) μm2 integrated in the micro-CT demonstrator PIXSCAN II. K-edge images are obtained from three sets of projections acquired from the same subject under three different energy threshold conditions around the K-shell binding energy of a contrast agent. To minimize the time dependent changes of the biological samples between the three acquisitions, we have developed a composite pixel protocol allowing simultaneous acquisitions of the projections for three different energy thresholds. This methodology reduces the acquisition duration by a factor three at the expense of a corresponding loss of spatial resolution. We nevertheless demonstrate the validity of the method on different phantoms and finally on mice.

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

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.

The ClearPET/XPAD prototype: Development of a simultaneous PET/CT scanner for mice

We developed the ClearPET/XPAD prototype: the first simultaneous PET/CT mouse scanner combining on the same rotating gantry ClearPET modules and the hybrid pixel camera XPAD3 facing an X-ray source. To demonstrate the capabilities of the new machine, we present the first simultaneous PET/CT scans of 68Ge and 22Na point sources, of a micro Derenzo phantom and of a live mouse injected in the tail vein with [18F]FDG.

A large surface X-ray camera based on XPAD3/CdTe single chip hybrids

The XPAD3 chip bump-bonded to a Si sensor has been widely used in preclinical microcomputed tomography and in synchrotron experiments. Although the XPAD3 chip is linear up to 60 keV, the performance of the XPAD3/Si hybrid detector is limited to energies below 30 keV, for which detection efficiencies remain above 20%. To overcome this limitation on detection efficiency in order to access imaging at higher energies, we decided to develop a camera based on XPAD3 single chips bump-bonded to high-Z CdTe sensors. We will first present the construction of this new camera, from the first tests of the single chip hybrids to the actual mechanical assembly. Then, we will show first images and stability tests performed on the D2AM beam line at ESRF synchrotron facility with the fully assembled camera.

Component separation for spectral X-ray imaging using the hybrid pixel camera XPAD3

Hybrid pixel cameras are new devices for which photon counting replaces charge integration, which have the capability to acquire spectral information on the counted photons. This ability is of uppermost importance for the development of new polychromatic X-ray imaging for which one goal is to separate images in several components of physical and biological interest. For instance, the photoelectric and Compton contributions can be separated while several contrast agents can be simultaneously localized. In this paper, we investigate the capability to perform component separation by using the newly developed hybrid pixel camera XPAD3 incorporated in the microCT demonstrator PIXSCAN. Several experiments have been led on data simulated analytically and by Monte Carlo, showing the great interest of component separation to enhance the contrast of materials when compared to classical X-ray data processing in microCT, and to cancel beam hardening artifacts. Results obtained on real data acquired with PIXSCAN on a phantom including Aluminium, water and Yttrium, the latter being treated as a contrast agent, show that the photoelectric, Compton and Yttrium components can be clearly separated and that each of them carries information allowing for the identification of different structures within the phantom.

Comparison of K-edge versus standard absorption imaging using the XPAD3 hybrid pixel detector

We investigate the capability to perform K-edge imaging by using the newly developed micro-CT PIXSCAN based on the XPAD3 hybrid pixel detector. K-edge tomography of Silver and Iodine is compared with standard X-ray absorption for several solution densities.