In this contribution, large SiPM arrays (8 x 8 elements of 6 x 6 mm(2) each) are processed with an ASIC-based readout and coupled to a monolithic LYSO crystal to explore their potential use for TOF-PET applications. The aim of this work is to study the integration of this technology in the development of clinical PET systems reaching sub-300 ps coincidence resolving time (CRT). The SiPM and readout electronics have been evaluated first, using a small size 1.6 mm (6 mm height) crystal array (32 x 32 elements). All pixels were well resolved and they exhibited an energy resolution of about 20% (using Time-over-Threshold methods) for the 511 keV photons. Several parameters have been scanned to achieve the optimum readout system performance, obtaining a CRT as good as 330 +/- 5 ps FWHM. When using a black-painted monolithic block, the spatial resolution was measured to be on average 2.6 +/- 0.5 mm, without correcting for the source size. Energy resolution appears to be slightly above 20%. CRT measurements with the monolithic crystal detector were also carried out. Preliminary results as well as calibration methods specifically designed to improve timing performance, are being analyzed in the present manuscript. (C) 2017 Elsevier B.V. All rights reserved.

Organ dedicated PET devices provide improved imaging performance when compared to whole body systems. The present study summarizes the test carried out to study a new detector block designed for an organ dedicated PET system. This block includes three novel components namely the scintillator geometry and a retroreflector layer coupled to the entrance face, the photosensor and the readout electronics. We used arrays of 12 x 12 SiPM photosensors with 3 x 3 mm(2) active area each and a pitch of 4.2 mm. We are proposing a new readout electronics that permits to reduce the 12 row and columns signals to only 8 without significant detector performance degradation. This approach also allows for resolving radioactive sources in the whole volume of the proposed crystal, significantly reducing the edge effect that typically rejects these events. An overall spatial resolution of about 1.8 mm FWHM is obtained for the whole scintillation volume, with an average energy resolution of 13% FWHM and a photon depth of interaction resolution (FWHM) of 3.7 mm. (C) 2018 Elsevier B.V. All rights reserved.

A direct ray tracing algorithm has been proposed under the development of a dedicated brain PET insert scanner, called MindView. The presented method takes advantage of the quasi- continuum nature of the impact coordinates provided by detectors composed by of monolithic scintillation crystals (LYSO material). This method requires a two-step filtering process: first, a Butterworth filter, multiplied by a ramp filter, is applied on the reconstructed image to wipe out the low oversampled frequencies after performing a backprojection, and second, an adaptive median filter is applied to the image for the noise to be reduced. Our algorithm, has been evaluated with simulation and real data, and compared with some of the gold-standard algorithms, in terms of image spatial resolution, such as the Filtered Backprojection 3D Reprojected (FBP3DRP) or the List Mode Ordered Subset (LMOS). Data obtained with a Derenzo-like phantom was used showing the 1.6 mm rods and a mean peak-to-Svalley ratio of 2.4 with the proposed algorithm, while in the FBP and LMOS depicted 1.3 and 1.4, respectively.

In this work we are describing a novel approach to the scintillator crystal configuration as used in nuclear medicine imaging. Our design is related to the coupling in one PET module of the two separate crystal configurations used so far there: monolithic and crystal arrays. The particular design we have studied is based on a two-layer scintillator approach (hybrid) composed of a monolithic LYSO crystal (5–6 mm thickness) and a LYSO crystal array with 4–5 mm height (0.8 and 1 mm pixels). We show here the detector block performance, in terms of spatial, energy and DOI information, to be used as a module in the design of PET scanners. The design we propose allows one to achieve accurate three-dimensional spatial resolution (including DOI information) while assuring high detection efficiency at reasonable cost. Moreover, the proposed design improves the spatial response uniformity across the whole detector module, and especially at the edge region. The crystal arrays are mounted in the front and were well resolved. The monolithic crystal inserted between crystal array and the photosensor, provided measured FWHM resolution as good as 1.5–1.7 mm including the 1 mm source size. The monolithic block achieved a DOI resolution (FWHM) nearing 3 mm. We compared these results with an approach in which we use a single monolithic block with total volume equals to the hybrid approach. In general, comparable performances were obtained.

The aim of this work is to show the potential capabilities of monolithic-based LYSO crystals, coupled to large SiPM arrays to be considered as detector blocks for TOF-PET scanners. An ASIC read-out with accurate timing capabilities is used to independently process each SIPM element. Several studies have been carried out using both crystal arrays and monolithic blocks showing an overall good performance. The most relevant parameters evaluated in this work are: spatial, energy and time resolutions. We obtained coincidence resolving times as good as 340 ps FWHM for one to one coupling in crystal arrays and 1.2 ns FWHM using a monolithic block in coincidence with a 1 pixel reference detector.

Gradient coils are a main part of a Magnetic Resonance Imaging (MRI) system. The aim of gradient coils in a MRI system is to encode spatially the Field of View (FoV). Different gradient coil design methods have been presented in the last years. Some factors such as linearity, inductance and resistance must be taken in account to obtain an optimized design for the gradient coils. A combinatorial method to design the MRI gradient coils is presented. The method developed uses very simple shapes to obtain the coil path patternand it allows finding the best coil design in a time less than 2 minutes. Path combination which generates the highest gradient field is chosen for the X/Y gradient coil, and also the most homogeneous magnetic field is considered to select the Z-gradient path combination. Efficiencies values of 93 and 19.4 mT/m/A are obtained for X/Y and Z gradient coil, respectively. The gradient system has been tested in a biplanar permanent magnet (PM) system. Experimental gradient coil evaluation shows the ability to generate a strong gradient field (0.56 and 0.75 T/m for X/Y and Z gradient coil, respectively). A preliminary 2D MRI image with 1mm accuracy is obtained.

The main aim of this work is to provide a method to retrieve the intrinsic resolution of detector blocks based on monolithic crystals in a fully assembled scanner. This method suggests a software collimation to the original data. The results are compared with the traditional approach of separating two detector blocks far enough, resulting in geometrical collimation.An empirical equation has been deduced to fit the experimental data in which the detector intrinsic resolution follows a Gaussian distribution and the contribution of the source, given the small size of 0.25 mm in diameter, follows a Lorentzian profile. The experiments resulted in an average detector intrinsic spatial resolution of 0.6 mm FWHM, with a standard deviation error of 0.1 mm. These tests show a method to determine the intrinsic resolution of monolithic-based detector blocks, once assembled in the PET system, with high accuracy.

Current PET detectors have a very low sensitivity, of the order of a few percent. One of the reasons is that Compton events are being rejected. In this work we aim to prove that Compton events are a very rich source of additional information that can play a crucial role in the image reconstruction process. With this additional data, the detector sensitivity will be substantially improved and thus, the applied dose on the patient can also be reduced. This could be a really breaking point for PET detector technology as one should be able to obtain better image quality with less patient radiation. By means of Compton cone matching (the Compton cones coming from the same event should be compatible) one should be able to better recognize matching events and discard randoms and even events that have previously suffered scattering within the patient's body.

Detectors for current PET scanners are based on the detection of the photoelectric energy peak while information from Compton scattering is being rejected. If an event involves multiple Compton scattering and the total energy deposited lays within the photoelectric peak, then a energy-weighted average is given for the interaction point. This technique introduces blurring in the image reconstruction process. We show that one can drastically improve the quality of the final reconstructed image, by precisely knowing the coordinates of the first interaction point. Compton events are rich source of information and one can also use them in order to discard random, single or even patient scattered events by means of reconstructing the Compton cones and require them to be compatible (Compton cones for photons that come from the same event must intersect in a line of response). In order to fully benefit experimentally from Compton events using monolithic scintillators a multi layer configuration is needed.

We report on benchmark tests of a 3 TW/50 fs, table-top laser system specifically developed for proton acceleration with an intrinsic pump rate up to 100 Hz. In two series of single-shot measurements differing in pulse energy and contrast the successful operation of the diode pumped laser is demonstrated. Protons have been accelerated up to 1.6 MeV in interactions of laser pulses focused on aluminium and mylar foils between 0.8 and 25 μm thickness. Their spectral distributions and maximum energies are consistent with former experiments under similar conditions. These results show the suitability of our system and provide a reference for studies of laser targets at high repetition rate and possible applications.

Developing front-end electronics to improve charge detection and time resolution in gamma-ray detectors is one of the main tasks to improve performance in new multimodal imaging systems that merge information of Magnetic Resonance Imaging and Gamma Camera or PET tomographs.The aim of this work is to study the behaviour and to optimize the performance of an ASIC for PET and Gamma Camera applications based on SiPMs detectors. PETIROC2 is a commercial ASIC developed by Weeroc to provide accurate charge and time coincidence resolutions. It has 32 analog input channels that are independently managed. Each channel is divided into two signals, one for time stamping using a TDC and another for charge measurement. In this work, PETIROC2 is evaluated in an experimental setup composed of two pixelated LYSO crystals based detectors, each coupled to a Hamamatsu 4 x 4 SiPM array. Both detectors are working in coincidence with a separation distance between them that can be modified.In the present work, an energy resolution of 13 : 6% FWHM and a time coincidence resolution of 815 ps FWHM have been obtained. These results will be useful to optimize and improve PETIROC2 based PET and Gamma Camera systems.

Clinical and organ-dedicated PET systems typically require a high efficiency imposing the use of thick scintillators, normally through crystal arrays. To provide depth of interaction (DOI) information, two or more layers are sometimes mounted in the staggered or phoswich approach. In this paper, we are proposing an alternative using thick and large monolithic crystals. We have tested two surface treatments for a 50 mm x 50 mm x 20 mm LYSO block. We provide data in this paper as close as 5 mm to the lateral walls. We left those walls black painted and the exit face coupled to the photosensor (12 x 12 SiPM array) polished. The entrance face was: 1) black painted or 2) coupled to a retroreflector (RR) layer. These configurations keep a good DOI linearity and, on average, reached 4 mm DOI resolution, measured as the full width at half of the maximum. Approaches using RR layers return constant and good energy resolutions nearing 12%, compared to a range of 15%-16% in the case of totally black painted blocks. The best result concerning the detector spatial resolution was obtained when one of the smallest RR was used (120 um corner cube size), being 1.7 mm at the entrance crystal layer and 0.7 mm in the layer closest to the photosensor. These values worsen at least 30% for the black treatment case.

In PET systems with a geometry different from a closed ring, the Time of Flight (TOF) of the annihilation photons appears to be relevant. Such a system capability helps to compensate the missing angular information that generates artifacts on the reconstructed images. In this work, two ASIC designs are evaluated for their use in PET systems having accurate coincidence resolving times (CRT) while preserving both energy and spatial resolutions. One of the ASIC options is the TOFPET1 from PETsys and the other the so-called PETIROC2 from Weeroc. Detection blocks based on scintillation LYSO crystal arrays have been used to first optimize the experiments. Parameters such as spatial, energy and time resolution have been obtained. Promising CRT results were found nearing 350 ps FWHM for a pair of photosensor channels (PETsys) and roughly 800 ps for all 16 against 16 channels (Weeroc). In terms of spatial resolution, 2 mm pixels size are well resolved with energy values approaching 15% have preliminary been measured for both ASICs. With the TOFPET1 ASIC, also tests with monolithic crystals were carried out. Those showed the system to provide depth of interaction (DOI) information. A DOI resolution (FWHM) of about 3 mm was preliminary estimated in a 25×25×10 mm 3 LYSO scintillator. A calibration process for time alignment of the signal paths was carried out to provide accurate CRT results. The time walk error between channels was also compensated. Several methods for the timestamp averaging have been tried, resulting on preliminary CRT values in the 1 ns FWHM range.

The Multimodal Imaging of Neurological Disorders (MINDView) project aims to develop a dedicated brain Positron Emission Tomography (PET) scanner with sufficient resolution and sensitivity to visualize neurotransmitter pathways and their disruptions in mental disorders for diagnosis and follow-up treatment. The PET system should be compact and fully compatible with a Magnetic Resonance Imaging (MRI) device in order to allow its operation as a PET brain insert in a hybrid imaging setup with most MRI scanners. The proposed design will enable the currently-installed MRI base to be easily upgraded to PET/MRI systems.The current design for the PET insert consists of a 3-ring configuration with 20 modules per ring and an axial field of view of similar to 15 cm and a geometrical aperture of similar to 33 cm in diameter. When coupled to the new head Radio Frequency (RF) coil, the inner usable diameter of the complete PET-RF coil insert is reduced to 26 cm. Two scintillator configurations have been tested, namely a 3-layer staggered array of LYSO with 1.5 mm pixel size, with 35 x 35 elements (6 mm thickness each) and a black-painted monolithic LYSO block also covering about 50 x 50 mm(2) active area with 20 mm thickness.Laboratory test results associated with the current MINDView PET module concept are presented in terms of key parameters' optimization, such as spatial and energy resolution, sensitivity and Depth of Interaction (DOI) capability. It was possible to resolve all pixel elements from the three scintillator layers with energy resolutions as good as 10%. The monolithic scintillator showed average detector resolutions varying from 3.5 mm in the entrance layer to better than 1.5 mm near the photosensor, with average energy resolutions of about 17%. (C) 2016 Elsevier B.V. All rights reserved.

A new small animal PET based on SiPM and monolithic LYSO crystals has been developed. Eight detector modules form the PET ring, each mounting an array of 12 × 12 SiPMs coupled to a readout providing the summed signals of the pixels on each of the 12 rows and 12 columns of the SiPM array. This design makes it possible to accurately determine the centroid of the scintillation light distribution with about 1.6 mm full width at half maximum (FWHM) resolution without correction for the 1 mm source size, and the photon depth of interaction (DOI) with nearly 2 mm FWHM. This single ring PET system has a homogeneous spatial resolution across the entire 80 mm transaxial field of view (FOV) of about 1 mm FWHM. The noise equivalent count rate (NECR) peak is estimated to occur at around 39.2 MBq with a rate of approximately 82.7 kcps for the mouse-like phantom and 22 kcps at 48.1 MBq for the rat-like phantom. Following the NEMA protocol, the peak absolute sensitivity in the center of the FOV is 2.8% for a 30% peak energy window. A pilot test injecting NaF to a mouse of 20 grams is also presented. Finally, the PET ring has been tested in front of a high field 15.2 T Magnetic Resonance (MR). No significant variation on energy and spatial resolution across the FOV has been observed due to the presence of the magnetic field.

Magnetic Resonance Imaging (MRI) is a widely used technique to obtain images in different applications based on the nuclear magnetic renonance (NMR) phenomenon. Gradient coils are the responsible components for encoding the volume of interest (VOI). Linearity, inductance and resistance are taken in account to perform the gradient coil design. In this work, EM and thermal gradient coil properties are studied and two cooling system are presented to cool them. Finally, the gradient coils are tested in a biplanar permanent magnet system and a 2D phantom image is obtained.

2641 Objectives Design of a high performance PET subsystem using continuous crystals which can be combined with a MRI system or other imaging modalities. This poses significant design constraints to achieve sensitivity and count rate targets like a large axial FOV, a built-in cooling and fast electronics. Methods A black painted continuous crystal and a SensL 12×12 SiPMs array are enclosed in a detector housing with integrated air cooling. 8 modules are combined to form a detector ring with a 117 mm inner diameter. Three axial arranged rings achieve a 148 mm FOV. Nickel-free PCBs read out the 12 rows and 12 columns of each module. For sampling the signals are transferred to a 2×32 A/D custom board including on-board FPGA processing for 3D position decoding. Novel approaches are used to provide accurate photon impact position with 1 mm FWHM spatial resolution in the XY plane and 1 mm sigma DOI (app. 2 mm FWHM). Several systems have been already mounted and tested in different conditions, such as alone and in front of high field MR (15.2 T). Results The FWHM of the PSF of a Na source shows uniform volumetric values of about 0.9-1.0 mm3 (MLEM reconstruction) across the entire image FOV (148×80 mm: axial×transaxial). The Derenzo-like phantom has also been tested showing the system capabilities to resolve rods with sizes ranging from 2.4 to 0.75 mm. The NEMA NU4-2008 protocol has been applied to evaluate the performance of the new SiPM based PET system in sensitivity and NECR. A peak maximum sensitivity of 9% was determined at the center of the FOV and with a 256-767 keV energy window. Using new DAQ electronics and computer processing capabilities of this SiPM prototype, the NECR peak is determined to occur at a rate of approximately 576 kcps and around 986 uCi with the mouse-like phantom. About 330 kcps at 1275 uCi is observed when using the rat-like phantom. Conclusions The new design for this small animal PET featuring the emerging SiPM based detectors significantly outperforms its PSPMT based predecessor in all tested performance parameters. This PET system exhibits two main improvements that make it especially suitable for small-animal preclinical studies. On one hand, a highly accurate DOI determination of photon impacts within the continuous crystals allowed us to correct for the parallax error even very close to the FOV edge. Thus, a nearly uniform spatial resolution is observed across the entire FOV, avoiding resolution dependent partial volume effects and thus providing more consistent quantification for small structures.

A whole-body PET device is sometimes not suitable for brain studies because the achieved image resolution is typically not sufficient to investigate small size structures. Thus, a dedicated brain PET insert system with high performance would overcome such limitations. Moreover, these functional studies lack of anatomical information. It is shown elsewhere the convenience of simultaneously acquisition of PET and MR data. In this work we show the final design and first pilot evaluation tests of a novel brain PET insert. Each detector block is based on a monolithic scintillation crystal, an array of SiPMs and a readout allowing characterizing the scintillation light distribution in the X and Y detector axes. The scintillators have a parallelepiped geometry with dimensions of 50×50×20 mm 3 . Their lateral walls are black painted and with the entrance face coupled to a retroreflector optical layer. We have determined an average (XYZ) detector spatial resolution through the FWHM of 1.2 mm (whole scintillator volume). The DOI resolution was measured with lateral incidence experiments and found to be about 3.5 mm, also on average for all photons depth of interactions and crystal positions. Thanks to the retroreflector, the energy resolution improves when compared to a case with all surfaces black painted, resulting on an average value of 13%. The tomographic reconstruction of the data was evaluated using different algorithms, including analytical (FBP STIR-3D), iterative (MLEM and List Mode OS) and a novel method that provides images by directly tracing the measured LORs. The minimum pixel/voxel sizes that were tried are 0.8/0.4 mm, 1.0/0.5 mm and 0.16/0.16 mm, respectively. All methods made it possible to show the PET system capabilities to resolve 1.6 mm rods in a Derenzo-like phantom filled with 150 uCi and scanned for 20 minutes. Pilot tests of the PET insert inside a clinical 3T MR showed a good system performance for most of the sequences typically used for brain imaging.

A histological intraoperative analysis of tissue specimen is usually required for evaluation of sentinel lymph node (SLN) and determination of margins of surgical resection. Currently, this analysis is performed by Touch Imprint Cytology (TIC), Frozen Section (FS) analysis, scrape cytology or a combination of these methods. We propose an alternative approach based on Magnetic Resonance Imaging (MRI). In particular, in this contribution we present the development, components, characterization as well as the first images obtained with our tabletop and transportable MRI system. Experiments with our MRI system shown that we can get images with high image spatial resolution (about 100 urn) and good signal-to-noise ratio in only few seconds using fast pulse sequences (fast and spin gradient echo).