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The GE Discovery MI PET/CT system has a modular digital detector design allowing three, four, or five detector block rings that extend the axial field-of-view (FOV) from 15 to 25 cm in 5 cm increments. This study investigated the performance of the 5-ring system and compared it to 3- and 4-ring systems; the GE Discovery IQ system that uses conventional photomultiplier tubes; and the GE Signa PET/MR system that has a reduced transaxial FOV. Methods PET performance was evaluated at three different institutions. Spatial resolution, sensitivity, counting rate performance, accuracy, and image quality were measured in accordance with National Electrical Manufacturers Association NU 2-2012 standards. The mean energy resolution, mean timing resolution, and PET/CT subsystem alignment were also measured. Phantoms were used to determine the effects of varying acquisition time and reconstruction parameters on image quality. Retrospective patient scans were reconstructed with various scan durations to evaluate the impact on image quality. Results Results from all three institutions were similar. Radial/tangential/axial full width at half maximum spatial resolution measurements using the filtered back projection algorithm were 4.3/4.3/5.0 mm, 5.5/4.6/6.5 mm, and 7.4/5.0/6.6 mm at 1, 10, and 20 cm from the center of the FOV, respectively. Measured sensitivity at the center of the FOV (20.84 cps/kBq) was significantly higher than systems with reduced axial FOV. The peak noise-equivalent counting rate was 266.3 kcps at 20.8 kBq/ml, with a corresponding scatter fraction of 40.2%. The correction accuracy for count losses up to the peak noise-equivalent counting rate was 3.6%. For the 10-, 13-, 17-, 22-, 28-, and 37-mm spheres, contrast recoveries in the image quality phantom were measured to be 46.2%, 54.3%, 66.1%, 71.1%, 85.3%, and 89.3%, respectively. The mean energy and timing resolution were 9.55% and 381.7 ps, respectively. Phantom and patient images demonstrated excellent image quality, even at short acquisition times or low injected activity. Conclusion Compared to other PET/CT models, the extended axial FOV improved the overall PET performance of the 5-ring GE Discovery MI scanner. This system offers the potential to reduce scan times or injected activities through increased sensitivity.

Time-of-flight (TOF) PET uses very fast detectors to improve localization of events along coincidence lines-of-response. This information is then utilized to improve the tomographic reconstruction. This work evaluates the effect of TOF upon an observer's performance for detecting and localizing focal warm lesions in noisy PET images.An advanced anthropomorphic lesion-detection phantom was scanned 12 times over 3 days on a prototype TOF PET/CT scanner (Siemens Medical Solutions). The phantom was devised to mimic whole-body oncologic (18)F-FDG PET imaging, and a number of spheric lesions (diameters 6-16 mm) were distributed throughout the phantom. The data were reconstructed with the baseline line-of-response ordered-subsets expectation-maximization algorithm, with the baseline algorithm plus point spread function model (PSF), baseline plus TOF, and with both PSF+TOF. The lesion-detection performance of each reconstruction was compared and ranked using localization receiver operating characteristics (LROC) analysis with both human and numeric observers. The phantom results were then subjectively compared to 2 illustrative patient scans reconstructed with PSF and with PSF+TOF.Inclusion of TOF information provides a significant improvement in the area under the LROC curve compared to the baseline algorithm without TOF data (P = 0.002), providing a degree of improvement similar to that obtained with the PSF model. Use of both PSF+TOF together provided a cumulative benefit in lesion-detection performance, significantly outperforming either PSF or TOF alone (P0.002). Example patient images reflected the same image characteristics that gave rise to improved performance in the phantom data.Time-of-flight PET provides a significant improvement in observer performance for detecting focal warm lesions in a noisy background. These improvements in image quality can be expected to improve performance for the clinical tasks of detecting lesions and staging disease. Further study in a large clinical population is warranted to assess the benefit of TOF for various patient sizes and count levels, and to demonstrate effective performance in the clinical environment.

In this work a comparison between experimental and simulated data using GATE and PeneloPET Monte Carlo simulation packages is presented. All simulated setups, as well as the experimental measurements, followed exactly the guidelines of the NEMA NU 4-2008 standards using the microPET R4 scanner. The comparison was focused on spatial resolution, sensitivity, scatter fraction and counting rates performance. Both GATE and PeneloPET showed reasonable agreement for the spatial resolution when compared to experimental measurements, although they lead to slight underestimations for the points close to the edge. High accuracy was obtained between experiments and simulations of the system's sensitivity and scatter fraction for an energy window of 350-650 keV, as well as for the counting rate simulations. The latter was the most complicated test to perform since each code demands different specifications for the characterization of the system's dead time. Although simulated and experimental results were in excellent agreement for both simulation codes, PeneloPET demanded more information about the behavior of the real data acquisition system. To our knowledge, this constitutes the first validation of these Monte Carlo codes for the full NEMA NU 4-2008 standards for small animal PET imaging systems.

The presence of the naturally occurring isotope 176Lu gives rise to background count rates in LSO/LYSO crystals to be used in PET and SPECT systems. The aim of this work is to measure 176Lu background count rates and its spatial distributions in a continuous LYSO block. Our results show that the low energy component of 176Lu background is related to partial energy deposition mainly produced near the crystal edge showing a hot-perimeter artifact. Furthermore, 176Lu background rate is observed to be x10 times lower for a 100-180 keV than for a 411-611 keV energy window. Our findings indicate that when using monolithic LYSO crystal blocks, 176Lu background is not expected to significantly deteriorate the performance of single photon detection systems.

Monte Carlo simulations were carried out in order to evaluate the performance of readout solutions for monolithic LYSO blocks, considering several 2D array configurations of discrete SiPMs. Results were compared to conventional multianode PMT readout. Our findings show that a detector module based on an array of 8×8 discrete SiPM may lead to better energy resolution and comparable spatial resolution. Our work shows the feasibility of using discrete SiPMs as readout for monolithic scintillator-based detector modules.

Positron Emission Tomography (PET) techniques have gained an important role in the diagnosis of human diseases as well as for pharmaceutical and biomedical research. In order to best optimize their capabilities, evaluation of their performance has to be achieved through standardized methodology from specific standards. The aim of this work was to assess the performance evaluation of the microPET R4 system for imaging rodents according to the new NEMA NU 4-2008 standards and compare it against its previous evaluation according the adapted clinical NEMA NU 2-2001. All measurements were made for an energy window of 350-650 keV. Spatial resolution of 2.12 mm FWHM in the radial direction, 2.66 mm FWHM in the tangential direction and 2.23 mm FWHM in the axial direction was measured in the centre of the axial FOV. Scatter fraction for mouse and rat phantoms were found to be 9.5% and 22% respectively. The maximum noise-equivalent count rate (NECR) was 110 kcps at 121.3 MBq for the rat phantom 287 kcp at 129.8 MBq for the mouse phantom. The absolute sensitivity of the scanner was found to be 1.66% at the centre of the field of view.

Monte Carlo simulations were carried out in order to guide the choice of crystal block material and thickness for a small FOV PET/SPECT camera. A continuous crystal block of 50mm x 50mm was simulated considering several thickness (8 mm, 16 mm and 32 mm) and two scintillation crystal types(LSO:Ce and NaI:Tl). Detection module parameters like spatial resolution at centre and border of FOV, efficiency and energy resolution were evaluated. Despite there is a common opinion that LSO is a less valuable material for SPECT detection, our findings demonstrate that LSO crystal blocks have interesting design features for the development of an hybrid SPECT and PET system. Our results show that by adequate corrections of non-linearity of a thick crystal block response, a high detection efficiency can be preserved (nearly 80% for PET and 99.9% for SPECT) without compromising high spatial resolution (about 1.9 mm for PET and 1.45 mm for SPECT).

The LHCb experiment, which is currently under construction at the Large Hadron Collider~(CERN, Geneva), is designed to study $CP$ violation and find rare decays in the $B$ meson system. To achieve the physics goals the LHCb detector must have excellent tracking performance. An important element of the LHCb tracking system is the Silicon Tracker, which covers a sensitive surface of about 12~m$^2$ with silicon microstrip detectors and includes about 272k readout channels. It uses up to 132~cm long detector modules with readout strips of up to 38~cm in length and up to 57~cm long Kapton interconnects in between sensors and readout hybrids. The production of detector modules has been completed recently and the detector is currently under installation. A rigorous quality assurance programme has been performed to ensure that the detector modules meet the mechanical and electrical requirements and study their various characteristics. In this paper, the detector design, the module production steps, and the module quality assurance programme are briefly described.

This paper shows a feasibility study on the use of discrete SiPMs to read out monolithic scintillator-based detectors for use in molecular imaging applications. Monte Carlo simulations are carried out in order to evaluate the basic performance of 8 × 8 arrays of discrete SiPMs with different PDE values and compare it to conventional 64 channel multi-anode PMT (MA-PMT) readout. A detailed optical transport model was incorporated into the Monte Carlo simulation and a detector module based on a monolithic scintillator crystal of 50 × 50 × 4 mm3 coupled to a MA-PMT was built for experimental validation. The effect of the SiPM dynamic range was also investigated by including a model of the saturation effects into the optical transport simulation. The results show that a detector module based on an array of 8 × 8 discrete SiPM devices (3 × 3 mm2 and PDE > 32%) is feasible as a replacement of a 64 channel MA-PMT in order to read out large monolithic crystals for MR-compatible gamma cameras.

LHCb is one of the experiments of the Large Hadron Collider at CERN, dedicated to B-physics and CP-violation measurements. To fully exploit the physics potential, a good tracking performance with high efficiency in a high particle density environment close to the beam pipe is required. Silicon strip detectors with large read-out pitch and long strips will be used for the LHCb Inner Tracker after the magnet and the Trigger Tracker station in front of the magnet. We report here about the design of the Silicon Tracker, test beam results and the electrical tests foreseen during module production.