Instrumentation research in small animal Positron Emission Tomography (PET) imaging is driven by improving timing, spatial resolution and sensitivity. Conventional PET scanners are built of multiple detectors placed in a cylindrical geometry with gaps between them in both the transaxial and axial planes. These gaps decrease sensitivity and degrade spatial resolution towards the edges of the system field of view (FOV). To mitigate these problems, we have designed and validated an edgeless pre-clinical PET system based on a single LYSO annulus with an inner diameter of 62 mm and 10 outer facets of 26 × 52 mm2 each. The scintillation light is read out using the row and columns of Silicon Photomultipliers (SiPMs) mounted in magnetic-field compatible PCBs. The objective of this work is to provide a calibration method for this system. The particular design of the annulus produces some undesirable effects in the light distributions (LD) at the module joints, which needs to be addressed. Nevertheless, after calibration, the system allows one to properly retrieve both, the energy and 3D photon impact positions.

Abstract Background Prostate cancer (PCa) represents one of the most common types of cancers facing the male population. Nowadays, to confirm PCa, systematic or multiparametric MRI-targeted transrectal or transperineal biopsies of the prostate are required. However, due to the lack of an accurate imaging technique capable to precisely locate cancerous cells in the prostate, ultrasound biopsies sample random parts of the prostate and, therefore, it is possible to miss regions where those cancerous cells are present. In spite of the improvement with multiparametric MRI, the low reproducibility of its reading undermines the specificity of the method. Recent development of prostate-specific radiotracers has grown the interest on using positron emission tomography (PET) scanners for this purpose, but technological improvements are still required (current scanners have resolutions in the range of 4–5 mm). Results The main goal of this work is to improve state-of-the-art PCa imaging and diagnosis. We have focused our efforts on the design of a novel prostate-dedicated PET scanner, named ProsPET. This system has small scanner dimensions defined by a ring of just 41 cm inner diameter. In this work, we report the design, implementation, and evaluation (both through simulations and real data) of the ProsPET scanner. We have been able to achieve < 2 mm resolution in reconstructed images and high sensitivity. In addition, we have included a comparison with the Philips Gemini-TF scanner, which is used for routine imaging of PCa patients. The ProsPET exhibits better contrast, especially for rod sizes as small as 4.5 mm in diameter. Finally, we also show the first reconstructed image of a PCa patient acquired with the ProsPET. Conclusions We have designed and built a prostate specific PET system, with a small footprint and improved spatial resolution when compared to conventional whole-body PET scanners. The gamma ray impact within each detector block includes accurate DOI determination, correcting for the parallax error. The potential role of combined organ-dedicated prostate-specific membrane antigen (PSMA) PET and ultrasound devices, as a prebiopsy diagnostic tool, could be used to guide sampling of the most aggressive sites in the prostate.

3123 Objectives: Multimodal PET/MR imaging is a powerful molecular imaging tool widely used in research and clinical practice for a broad variety of applications. Small animal PET inserts are an instrumentation tool that can be used in combination with already installed MRI systems. This work shows the initial performance and MRI compatibility of a small animal PET insert for mouse applications, based on monolithic LYSO scintillation crystals. Methods: The PET system is based on LYSO cuboids of 25x33x10 mm, laterally black painted and include a retroreflector layer at the entrance face. This layer improves the detectability of the gamma ray position interaction. The crystals are coupled to custom made 10x8 SiPM arrays with 3x3 mm active area each. 24 crystals are distributed in 3 rings defining an axial and transaxial FOV of 100 mm and 40 mm, respectively. The SiPM photosensor and readout electronics are mounted on high performance boards that avoid the generation of eddy current by the switching gradient fields.This work shows the results carried out within a Bruker BioSpec 94/20 MRI imaging instrument using a 35 mm volume RF coil. The PET insert includes an RF shielding based on carbon fiber structures. We report here the average performance of the detector blocks, and some of the most important parameters regarding PET imagingand MR compatibility. Results: After calibration of each detector block using a novel approach based on Voronoi diagrams [1], the average energy resolution of the whole system is about 13.5%, together with an impact precision determination in 2D below 1.5 mm, and about 2 mm depth of interaction (DOI) resolution.Regarding MR compatibility, the PET insert has been run under several MRI sequences including EPI with high duty cycles. No significant change in MRI performance was observed when compared to the case without the PET. The PET detector performance is not affected by interferences that could arise from different MRI imaging sequences, concerning impact determination, energy or any other parameter [2,3]. Therefore, the reconstructed images did not exhibit any degradation.The initial performance evaluation resulted in a peak sensitivity of nearly 12% at CFOV, and a NECR mouse peak of 481 kcps at 25.7 MBq . The PSF-corrected spatial resolution has been determined to be about 0.7 mm FWHM for all three space components. Using DOI allows to reach similar spatial resolution performance for the entire FOV. The good spatial resolution of the device allows to distinguish 0.8mm rods of a micro-Derenzo phantom when using 0.25 mm voxels, 1 mm virtual pixels and 25 iterations (MLEM). Conclusions: This works provides design principles needed for the realization of small PET/MR inserts for mice. The initial study has shown that the requirements for simultaneous PET/MR mouse imaging applications can be reached, thus high spatial PET imaging resolution and the absence of any interference effects for PET and MRI.The PET insert reaches an unprecedented image performance resolving well 0.8 mm Derenzo rods while simultaneously imaging MRI with EPI sequences. The high spatial resolution is obtained across the entire PET FOV, thus helping researchers for a more reliable quantification during their investigations. Bibliography: [1] M. Freire, IEEE TRPMS, 2019, doi: 0.1109/TRPMS.2019.2947716. [2] A.J. Gonzalez, IEEE TRPMS 3, 343, 2019. [3] W. Gsell, to be submitted to EJNMMI, 2020.

In this manuscript, detector blocks for Positron-Emission-Tomography (PET) are being evaluated for their integration in a TOF-PET system. In this contribution, detector concepts based on analog SiPM photosensors have been tested along with different types of scintillation materials. Firstly, pixelated crystals have been evaluated showing accurate results in terms of spatial, energy and timing resolution. Then, monolithic blocks were coupled to large SiPM photosensors arrays to determine their capabilities to resolve the gamma impacts in terms of position and timing. The read-out and the digitation of all signals were performed by a commercially available Application-Specific-Integrated-Circuit (ASIC) named TOFPET2. The obtained results as well as some methodologies that imrove the timing performance of the monolithic blocks, are being described in this paper.

Hybrid molecular and anatomical imaging devices, especially when simultaneously working, have shown to provide advantages over sequential acquisitions. In particular, we present in this preliminary study, the working performance of a brain positron emission tomography (PET) insert, within a 3T magnetic resonance imaging (MRI) system. To our knowledge, this is the largest PET system based on monolithic LYSO blocks. It consists of 60 scintillator blocks of $50\ \text{mm} \times 50\ \text{mm} \times 20\ \text{mm}$ arranged in 3 rings of 20 detector modules each. An effective field of view (FOV) of 240 mm in diameter and 154 mm axially is defined. The crystals included a retroreflector layer at the entrance face, and are coupled to custom arrays of $12 \times 12$ silicon photomultipliers (SiPM), $3\ \text{mm} \times 3\ \text{mm}$ each. Frontend electronics provide ${X}$ and ${Y}$ projections of the scintillation light by sampling each row and column of the SiPM arrays. The insert is thermally stabilized by using temperature-controlled air to about 27 °C. The PET insert has been installed at the Klinikum rechts der Isar (Munich) and tested within the whole-body Siemens biograph mMR, a 3T MRI combined with a PET scanner. A system sensitivity of almost 7% for an energy window of 350–650 keV was measured using a small size source at the center of the FOV (CFOV). Current system evaluation showed a spatial resolution at the CFOV of 1.7 mm using iterative algorithms, being below 2 mm within a centered diameter of 120 mm. Rods of a small Derenzo phantom of 2.5 mm were clearly resolved, independently of all tested MRI sequences including echo-planar imaging, ultrashort time echo, MPrage, and T2-flair or arterial spin labeling. The PET insert did not show any count rate degradation also under those sequences for a variety of MR imaging acquisitions.

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.

In gamma ray imaging, a scintillation crystal is typically used to convert the gamma radiation into visible light. Photosensors are used to transform this light into measurable signals. Several types of photosensors are currently in use depending on the application, most known are Position Sensitive Photomultiplier Tubes (PSPMT) or arrays of Silicon Photomultipliers (SiPMs). There have been investigations towards reducing the number of output signals from those photosensors in order to decrease system costs and complexity without impacting system performance. We propose here two different reduction schemes without degradation of the detector performance, keeping a good spatial, energy and timing resolution, specially well suited for monolithic scintillation crystals based detectors. We have carried out comparative results that will be shown.

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.

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.

RESULTS A multichannel system based on an array of 10 planar coils has been chosen to design the shimming system. This system is composed by two PCBs each containing 5 Planar Coils (see Fig.1b) placed each around the FoV. For the coil design a fingerprint pattern was chosen. Each coil has an outer diameter of 50mm (16 turns) and there is composed of 8 layers and connected in series. For the power supply and control of the shimming system, an in-house system was built (see Figs.1c-d) with each coil can be powered up to 40 W and independently controlled. A driver board controls up to 20 channels independently and is powered by LCM600 power supply [3]. The communication with the PC is performed with a USB-i 2 C adapter. A more detailed description of the control system can be found in [4]. Before manufacturing the shimming array, a system formed by two coils was built and characterized with a magnetic test bench available in the i3M (Fig.1e). Fig.1f shows the MF profile for this proof system using a current I=7A.

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.

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).

In this work, a direct image reconstruction algorithm for PET is proposed. This method follows naturally from the concept of LOR, and easily admits depth of interaction and time of flight information. In addition, this algorithm does not require the computation of sinograms or a system matrix. Thus, it is not restricted in the formation of high pixel density images and allows the image formation in real-time (simultaneously to the data acquisition process). One of the key advantages of this algorithm is the preservation of high frequencies, producing accurate images that can be generated in high resolution, because of the lack of space restrictions imposed by the intermediate generation of sinograms, aside of the native support of real-time image reconstruction. In this work, a C++ implementation of the described algorithm has been developed. Image reconstructions of simulated PET events according to the MindView (a brain dedicated PET insert) scanner geometry and real data measured with the first one ring prototype system have been performed. Results show capability of correct image formation, either with simulated and real data.