Guillaume Montemont

This paper compares methods for rejecting in-patient scattered photons in PET instruments, which can degrade image quality by introducing bias and noise. The focus is on events where both annihilation photons interact several times in the detection medium. Compton scattering physics and annihilation photon polarization entanglement are utilized. Events are classified by the number of hits in the detector to assess information quality, and the spatial response from lines of response or Compton cones is analysed. A comparison between methods is made through a simulation of an ideal cylindrical detector with a radius of 15 cm and a thickness of 1 cm, using Geant4. Results from the simulations are used to create histograms for the different observables. Metrics, such as receiver-operating-characteristic (ROC) curves and noise equivalent count (NEC), are used to quantify the efficiency of each method and the influence of hit multiplicity. Alongside this simulation-based investigation, an experiment using a pair of CdZnTe Compton cameras has been set up to validate the entanglement model and its integration simulation. We demonstrate that entanglement information may be considered less valuable, achieving an area under the ROC curve of 52% compared to energy deposition and Compton kinematics, which have an area of 97%. Finally, the obtained detective quantum efficiency (DQE) demonstrates the superiority of Compton cones for low resolution, up to around 0.05 cm-1, followed by the line of response, which achieves a spatial bandwidth of 1.6 cm-1, thus showing the complementarity between the two types of information. This study highlights the importance of Compton kinematics and the limited value of entanglement for rejecting scattered events.

Recent progress with Cadmium Zinc Telluride (CZT) radiation sensors grown by the traveling heater method (THM) at Kromek is reported. Large volume monolithic pixelated detectors, 40×40×15 mm³ have been fabricated with good initial gamma spectroscopy response (< 2.5% energy resolution at 662 keV at room temperature without correction). After depth of interaction (DOI) correction, detector performance with < 1% energy resolution at 662 keV at room temperature has been obtained on pixelated 22×22×15 mm³ CZT detector. For medical imaging applications, 20×20×6 mm³ pixelated detectors exhibits < 3% energy resolution at 122 keV without correction. These results have been achieved via our proprietary THM crystal growth in combination with our robust device fabrication technique. Examples of progress in other areas of CZT development for gamma spectroscopy and imaging applications such as 40×40×5 mm³ cross-strip device for PET and Kromek’s general-purpose SPECT camera will also be presented.

We have recently developed NuVISION, a portable gamma camera based on CZT. It is based on the HiSPECT imaging module architecture featuring IDeFX-HD ASICs [1] and 3D subpixel positioning architecture [2]. This device weights 3 kilograms, is waterproof (IP65) and is fully autonomous: it embeds an hybrid ARM processor/FPGA system on a chip and is powered by a battery allowing 7-hour operation. It can be interfaced to a computer or tablet by wired or wireless local area network.The detector is 40×40×6 mm thick CZT with 2.5 mm anode pitch allowing a overall resolution of 2.5 % at 122 keV and 1.5 % at 662 keV. The system uses coded aperture mask imaging to provide high sensitivity and high resolution in a limited frontal field of view (45°). Compton imaging is used to coarsely localize out of field radiation at the same time. It has been tested on various isotopes from Am-241 to Co-60 and it performs spectrometric imaging with automated isotope recognition. System sensitivity is sufficient to localize a 50 nSv/h Co-57 source in natural background in less than 1 second and a 50 nSv/h Cs-137 source in less than 1 minute. Additionally, processing speed allows to perform real time imaging and to observe mobile sources. We describe CZT detector spectral and imaging performance, the FPGA based 3D positioning and the list-mode image reconstruction technique used.

Single Photon Emission Tomography (SPECT) is mainly limited by the trade-off between spatial resolution and sensitivity determined by the collimation. In this context, CdZnTe detectors enable higher intrinsic spatial resolution compared to previously used scintillators, even improved by using techniques for 3D positioning. Moreover, the compactness of these detectors enables new system architectures. To improve the sensitivity of SPECT systems without degrading their spatial resolution, a possible way is to adapt the field of view depending on the kind of acquisition and the morphology of the patient, using flexible detection heads. That means computing reconstruction fast enough to determine interesting area where to focus detectors. This task is problematic because of the complexity of data to be processed, as the high resolution of detectors makes measurements sparse, and because of the dependency of reconstruction to head position, that must be taken into account. The aim of the present study is to propose new approaches to deal with this massive amount of complex information in real time to dynamically adapt the field of view. Implementation techniques from MLEM algorithm are proposed in order to fasten the reconstruction and adapt the geometrical configuration during the examination, and thus improve the sensitivity of the system without degrading its spatial resolution.

The Scintilla FP7 project is ended in December 2014, the fruitful results of 3 years development and tests will be presented. SCINTILLA offers the capacity to finding a reliable alternative to Helium-3 based detection systems since the gas which is predominantly used in nuclear safeguards and security applications has now become very expensive, rare and nearly unavailable. SCINTILLA benchmarks results are based on international standards. Radiation Portal tests were carried out at the Joint Research Centre (JRC) in Ispra (Italy). The scintilla project addresses few mains issues. The first is to develop neutron detectors for Radiation Portal Monitor (RPM) and the second is the need of new wearable integrated solutions for Spectrometric Personal Radiation Monitor (SPRM). The partners which provide technical systems of the scintilla project are INFN-ANSALDO, CEA, SYMETRICA and SAPHYMO. For RPM, the objective is to find reliable alternatives to Helium-3 historical neutron detector and provide technical solutions which cope with tests for reliable mobile and cost effective. For Spectrometric Personal Radiation Monitor (SPRM), SCINTILLA is innovating in technology areas that offer complementary capabilities for detecting and identifying gamma Two CZT (Cadmium Zinc Telluride) addressing contexts of used by first responder technologies, one is a wearable detector and the second is a gamma camera complemented by advanced image processing technologies.

CZT detectors are the basic building block of a variety of new SPECT systems. Their modularity allows adapting system architecture to specific applications such as cardiac, breast, brain or small animal imaging. In semiconductors, a high number of electron-hole pairs is produced by a single interaction. This direct conversion process allows better energy and spatial resolutions than usual scintillation detectors based on NaI(Tl). However, it remains often unclear if SPECT imaging can really benefit of that performance gain. We investigate the system performance of a detection module, which is based on 5 mm thick CZT with a segmented anode having a 2.5 mm pitch by simulation and experimentation. This pitch allows an easy assembly of the crystal on the readout board and limits the space occupied by electronics without significantly degrading energy and spatial resolution.

X-ray diffraction is a powerful technique to provide information on the molecular structure of samples. Energy dispersive X-ray diffraction (EDXRD) spectra are classically measured at one single fixed scattering angle using a polychromatic X-ray source and a spectroscopic detector. In order to remove system blurring and restore material proper information, inversion of the EDXRD spectra is required. This paper proposes to combine EDXRD spectra at different scattering angles to improve reconstruction results. To quantify the improvements, detective quantum efficiency (DQE) calculations are used, which allow to compare the performance of mono-and multi-angle systems, are used. We present a reconstruction method based on multi-angle EDXRD spectra. The algorithm was tested on simulated salt (NaCl) spectra. Finally, advantages of multi-angle over mono-angle spectra are discussed.

The use of energy-dispersive X-ray diffraction (XRD) in security screening applications allows for highest detection and lowest false-alarm rates. So far, only Germanium-detectors have been used in commercially available XRD baggage-scanning systems, limiting the available detection area due to technical and commercial reasons, and as a consequence, the achievable throughput. Morpho Detection has built an innovative X-ray diffraction imaging (XDi) system equipped with 17 pixelated Cadmium-Zinc-Telluride (CZT) detector modules for increased detection-area to alleviate this limitation. A multi-focus X-ray source (MFXS) allows for high X-ray flux and makes any other mechanical movement, except for the bags, obsolete. In conjunction with a dedicated collimation system the detectors measure the scatter from the bag spatially and energetically resolved, allowing for a voxelized reconstruction of the bag's scatter-signature. The detector-array is required to deliver spectra of high quality, calling for very good energy-resolution and efficiencies, which is why signal-corrections are performed on-board. Each module is a completely independent unit to ensure service friendliness, receiving just one voltage, a trigger and Ethernet for control and data-transfer. We will explain the functional principle of the XDi -system, present the performance of the detectors with respect to stability and show spectra of different materials and reconstructed 3-D feature maps.