G. Hall

Design and performance of a high rate, high angular resolution beam telescope used for crystal channeling studies

A charged particle telescope has been constructed for data taking at high rates in a CERN 400 GeV/c proton beam line. It utilises ten planes of silicon microstrip sensors, arranged as five pairs each measuring two orthogonal coordinates, with an active area of 3.8 × 3.8 cm2. The objective was to provide excellent angular and spatial resolution for measuring the trajectories of incident and outgoing particles. The apparatus has a long baseline, of approximately 10 m in each arm, and achieves an angular resolution in the incoming arm of 2.8 μrad and a total angular resolution on the difference of the two arms of 5.2 μrad, with performance limited by multiple scattering in the sensor layers. The sensors are instrumented by a system based on the CMS Tracker electronic readout chain, including analogue signal readout for optimal spatial resolution. The system profits from modified CMS software and hardware to provide a data acquisition capable of peak trigger rates of at least 7 kHz. We describe the sensor readout, electronic hardware and software, together with the measured performance of the telescope during studies of crystal channeling for the UA9 collaboration. Measurements of a previously unobserved periodic movement of the beam are also presented and the significance of such an effect for precise studies such as for channeling is discussed.

The CBC microstrip readout chip for CMS at the High Luminosity LHC

The CMS Binary Chip (CBC) is designed for readout of silicon microstrips in the CMS Tracker at the High Luminosity LHC (HL-LHC). Binary, unsparsified readout is well suited to the high luminosity environment, where particle fluences and data rates will be much higher than at the LHC. In September 2011, a module comprising a CBC bonded to a silicon microstrip sensor was tested with 400 GeV protons in the H8 beamline at CERN. Performance was in agreement with expectations. The spatial resolution of the sensor and CBC has been shown to be better than pitch/ p 12 due to spatial distribution of one and two strip clusters. Large cluster events show consistency with the production of delta rays. At operating thresholds, the hit efficiency has been shown to be approximately 98%, limited by the resolution of timing apparatus, while the noise occupancy is measured to be below 10 4 . The distribution of charge deposition in the sensor has been reconstructed by measurement of the hit efficiency as a function of comparator threshold; assuming the underlying distribution is a Landau.

A Multi-Element Detector System for Intelligent Imaging: I-ImaS

I-ImaS is a European project aiming to produce new, intelligent X-ray imaging systems using novel APS sensors to create optimal diagnostic images. Initial systems concentrate on mammography and encephalography. Later development will yield systems for other types of radiography such as industrial QA and homeland security. The I-ImaS system intelligence, due to APS technology and FPGAs, allows real-time analysis of data during image acquisition, giving the capability to build a truly adaptive imaging system with the potential to create images with maximum diagnostic information within given dose constraints. A companion paper deals with the DAQ system and preliminary characterization. This paper considers the laboratory X-ray characterization of the detector elements of the I-ImaS system. The characterization of the sensors when tiled to form a strip detector will be discussed, along with the appropriate correction techniques formulated to take into account the misalignments between individual sensors within the array. Preliminary results show that the detectors have sufficient performance to be used successfully in the initial mammographic and encephalographic I-ImaS systems under construction and this paper will further discuss the testing of these systems and the iterative processes used for intelligence upgrade in order to obtain the optimal algorithms and settings.

Adaptive image content-based exposure control for scanning applications in radiography

I-ImaS (Intelligent Imaging Sensors) is a European project which has designed and developed a new adaptive X-ray imaging system using on-line exposure control, to create locally optimized images. The I-ImaS system allows for real-time image analysis during acquisition, thus enabling real-time exposure adjustment. This adaptive imaging system has the potential of creating images with optimal information within a given dose constraint and to acquire optimally exposed images of objects with variable density during one scan. In this paper we present the control system and results from initial tests on mammographic and encephalographic images. Furthermore, algorithms for visualization of the resulting images, consisting of unevenly exposed image regions, are developed and tested. The preliminary results show that the same image quality can be achieved at 30-70% lower dose using the I-ImaS system compared to conventional mammography systems.

Design and Characterization of the I-ImaS Multi-Element X-Ray Detector System

I-ImaS (Intelligent Imaging Sensors) is a European project aiming to produce new, intelligent X-ray imaging systems using novel APS sensors to create optimal diagnostic images. Initial systems have been constructed for medical imaging; specifically mammography and dental encephalography. However, the I-ImaS system concept could be applied to all areas of X-ray imaging, including homeland security and industrial QA. The I-ImaS system intelligence is implemented by the use of APS technology and FPGAs, allowing real-time analysis of data during image acquisition. This gives the system the capability to perform as an on-the-fly adaptive imaging system, with the potential to create images with maximum diagnostic information within given dose constraints. The I-ImaS system uses a scanning linear array of scintillator-coupled 1.5-D CMOS Active Pixel Sensors to create a full 2-D X-ray image of an object. This paper describes the parameters considered when choosing the scintillator elements of the detectors. A study of the positioning of the sensors to form a linear detector is also considered, along with a discussion of the potential losses in image quality associated with creating a linear sensor by tiling many smaller sensors. Preliminary results show that the detectors have sufficient performance to be used successfully in the initial mammographic and encephalographic I-ImaS systems that are currently under construction.

Observation of channeling in bent crystals at the CERN LHC

The feasibility of crystal-assisted collimation is being investigated for improvements of the LHC collimation system, as a part of the future high luminosity upgrade of the CERN LHC (HL-LHC). Two high-accuracy goniometers, each equipped with one bent silicon crystal, were installed in the betatron cleaning insertion of the LHC in 2014. During dedicated tests in 2015, bent crystals were approached to the circulating the beams to test their usage as a first stage in a crystal-based system, both with proton and Pb ion beams. Tests were performed with protons at injection energy (450 GeV/c) and at flat top (6.5 TeV/c), and with ions at injection energy (450 Z GeV/c). A reduction of losses immediately downstream of the crystals was observed in optimum channeling orientation, demonstrating for the first time channeling at these energies. Halo cleaning efficiency of the crystal-based collimation system was also measured.

I-ImaS: intelligent imaging sensors

Conventional x-radiography uniformly irradiates the relevant region of the patient. Across that region, however, there is likely to be significant variation in both the thickness and pathological composition of the tissues present, which means that the x-ray exposure conditions selected, and consequently the image quality achieved, are a compromise. The I-ImaS concept eliminates this compromise by intelligently scanning the patient to identify the important diagnostic features, which are then used to adaptively control the x-ray exposure conditions at each point in the patient. In this way optimal image quality is achieved throughout the region of interest whilst maintaining or reducing the dose. An I-ImaS system has been built under an EU Framework 6 project and has undergone pre-clinical testing. The system is based upon two rows of sensors controlled via an FPGA based DAQ board. Each row consists of a 160 mm ? 1 mm linear array of ten scintillator coated 3T CMOS APS devices with 32 ?m pixels and a readable array of 520 ? 40 pixels. The first sensor row scans the patient using a fraction of the total radiation dose to produce a preview image, which is then interrogated to identify the optimal exposure conditions at each point in the image. A signal is then sent to control a beam filter mechanism to appropriately moderate x-ray beam intensity at the patient as the second row of sensors follows behind. Tests performed on breast tissue sections found that the contrast-to-noise ratio in over 70% of the images was increased by an average of 15% at an average dose reduction of 9%. The same technology is currently also being applied to baggage scanning for airport security.