Peak Noise Equivalent Count Rate Research Articles

Characterization and Pilot Human Trial of Dedicated Breast Ring Positron Emission Tomography (BRPET) System

We describe the design and performance of BRPET, a novel dedicated breast PET (dbPET) scanner designed to maximize visualization of posterior regions of the breast. BRPET uses prone imaging geometry and a 12-module detector ring built from pixelated LYSO crystals coupled to position sensitive photomultiplier tubes (PSPMTs). Optical coupling via slanted plastic fiber optic light guides permits partial insertion of the crystals into the exam table’s breast aperture. Image quality testing procedures were adapted from the NEMA NU4-2008 protocol. Two additional phantom tests quantified the posterior extent of the usable volume of view (VoV). BRPET axial, radial, and tangential FWHM spatial resolutions at the isocenter were 1.8, 1.7, and 1.9 mm, respectively. The peak absolute system sensitivity was 0.97% using an energy window of 460–562 keV. The peak noise equivalent counting rate was 5.33 kcps at 21.6 MBq. The scanner VoV extends to within ~6 mm of the plane defining the location of the chest wall. A pilot human study (n = 10) compared the diagnostic performance of FDG-BRPET to that of contrast enhanced MRI (CEMRI), with biopsy as ground truth. Averaged over three expert human observers, the sensitivity/specificity for BRPET was 0.93/1.0, compared to 1.0/0.25 for CEMRI.

Technical Note: Performance evaluation of a small‐animal PET/CT system based on NEMA NU 4–2008 standards

The MetisTM PET/CT is a self-developed, silicon photomultiplier (SiPM) detector-based, rodent PET/CT system. The objective of this study was to evaluate the performance of the system using the National Electrical Manufacturers Association (NEMA) NU 4-2008 standard protocol. Energy resolution, spatial resolution, sensitivity, scatter fraction (SF), noise-equivalent count rate (NECR), and image quality (IQ) characteristics were measured. A micro Derenzo phantom experiment was performed to evaluate the spatial resolution using three-dimensional ordered-subsets expectation maximization (3D-OSEM) and maximum likelihood expectation maximization (MLEM) reconstructed images. In addition, the CT imaging agent Ioverol 350 was mixed with fluorine-18 (18 F)-fluorodeoxyglucose (FDG) and then injected into the micro Derenzo phantom to evaluate the PET/CT imaging. In vivo PET/CT imaging studies were also conducted in a healthy mouse and rat using 18 F-FDG. The mean energy resolution of the system was 15.3%. The tangential resolution was 0.82mm full-width half-maximum (FWHM) at the center of the field of the view (FOV), and the radial and axial resolution were generally lower than 2.0mm FWHM. The spatial resolution was significantly improved when using 3D-OSEM, especially the axial FWHM could be improved by up to about 57%. The system absolute sensitivity was 7.7% and 6.8% for an energy window of 200-750 and 350-750keV respectively. The scatter fraction was 8.2% and 12.1% for the mouse- and rat-like phantom respectively. The peak NECR was 1343.72kcps at 69MBq and 640.32kcps at 53MBq for the mouse- and rat-like phantom respectively. The 1-mm fillable rod in the IQ phantom can be clearly observed. We can identify the 0.6-mm aperture of the micro Derenzo phantom image clearly using 3D-OSEM (10 subsets, 5 iterations). We also performed the fusion of the PET and CT images of the mouse and the brain imaging of the rat. The results show that the system has the characteristics of high-resolution, high-sensitivity, and excellent IQ and is suitable for rodent imaging-based research.

Performance Characteristics of the Biograph Vision Quadra PET/CT System with a Long Axial Field of View Using the NEMA NU 2-2018 Standard.

Our purpose was to evaluate the performance of the Biograph Vision Quadra PET/CT system. This new system is based on the Biograph Vision 600, using the same silicon photomultiplier-based detectors with 3.2 × 3.2 × 20 mm lutetium-oxoorthosilicate crystals. The 32 detector rings of the Quadra provide a 4-fold larger axial field of view (AFOV) of 106 cm, enabling imaging of major organs in 1 bed position. Methods: The physical performance of the scanner was evaluated according to the National Electrical Manufacturers Association NU 2-2018 standard, with additional experiments to characterize energy resolution. Image quality was assessed with foreground-to-background ratios of 4:1 and 8:1. Additionally, a clinical 18F-FDG PET study was reconstructed with varying frame durations. In all experiments, data were acquired using the maximum ring distance of 322 crystals (MRD 322), whereas image reconstructions could be performed with a maximum ring distance of only 85 crystals (MRD 85). Results: The spatial resolution at full width at half maximum in the radial, tangential, and axial directions was 3.3, 3.4, and 3.8 mm, respectively. The sensitivity was 83 cps/kBq for MRD 85 and 176 cps/kBq for MRD 322. The noise-equivalent count rates (NECRs) at peak were 1,613 kcps for MRD 85 and 2,956 kcps for MRD 322, both at 27.49 kBq/mL. The respective scatter fractions at peak NECR equaled 36% and 37%. The time-of-flight resolution at peak NECR was 228 ps for MRD 85 and 230 ps for MRD 322. Image contrast recovery ranged from 69.6% to 86.9% for 4:1 contrast ratios and from 77.7% to 92.6% for 8:1 contrast ratios reconstructed using point-spread function time of flight with 8 iterations and 5 subsets. Thirty-second frames provided readable lesion detectability and acceptable noise levels in clinical images. Conclusion: The Biograph Vision Quadra PET/CT device has spatial and time resolution similar to those of the Biograph Vision 600 but exhibits improved sensitivity and NECR because of its extended AFOV. The reported spatial resolution, time resolution, and sensitivity make it a competitive new device in the class of PET scanners with an extended AFOV.

Performance Evaluation and Compatibility Studies of a Compact Preclinical Scanner for Simultaneous PET/MR Imaging at 7 Tesla

We present the design and performance of a new compact preclinical system combining positron emission tomography (PET) and magnetic resonance imaging (MRI) for simultaneous scans. The PET contains sixteen SiPM-based detector heads arranged in two octagons and covers an axial field of view (FOV) of 102.5 mm. Depth of interaction effects and detector's temperature variations are compensated by the system. The PET is integrated in a dry magnet operating at 7 T. PET and MRI characteristics were assessed complying with international standards and interferences between both subsystems during simultaneous scans were addressed. For the rat size phantom, the peak noise equivalent count rates (NECR) were 96.4 kcps at 30.2 MBq and 132.3 kcps at 28.4 MBq respectively with and without RF coil. For mouse, the peak NECR was 300.0 kcps at 34.5 MBq and 426.9 kcps at 34.3 MBq respectively with and without coil. At the axial centre of the FOV, spatial resolutions expressed as full width at half maximum / full width at tenth maximum (FWHM/FWTM) ranged from 1.69/3.19 mm to 2.39/4.87 mm. The peak absolute sensitivity obtained with a 250-750 keV energy window was 7.5% with coil and 7.9% without coil. Spill over ratios of the NEMA NU4-2008 image quality (NEMA-IQ) phantom ranged from 0.25 to 0.96 and the percentage of non-uniformity was 5.7%. The image count versus activity was linear up to 40 MBq. The principal magnetic field variation was 0.03 ppm/mm over 40 mm. The qualitative and quantitative aspects of data were preserved during simultaneous scans.

Design and performance of SIAT aPET: a uniform high-resolution small animal PET scanner using dual-ended readout detectors

In this work, a small animal PET scanner named SIAT aPET was developed using dual-ended readout depth encoding detectors to simultaneously achieve high spatial resolution and high sensitivity. The scanner consists of four detector rings with 12 detector modules per ring; the ring diameter is 111 mm and the axial field of view (FOV) is 105.6 mm. The images are reconstructed using an ordered subset expectation maximization (OSEM) algorithm. The spatial resolution of the scanner was measured by using a 22Na point source at the center axial FOV with different radial offsets. The sensitivity of the scanner was measured at center axis of the scanner with different axial positions. The count rate performance of the system was evaluated by scanning mouse-sized and rat-sized phantoms. An ultra-micro hot-rods phantom and two mice injected with 18F-NaF and 18F-FDG were scanned on the scanner. An average depth of interaction (DOI) resolution of 1.96 mm, energy resolution of 19.1% and timing resolution of 1.20 ns were obtained for the detector. Average spatial resolutions of 0.82 mm and 1.16 mm were obtained up to a distance of 30 mm radially from the center of the FOV when reconstructing a point source in 1% and 10% warm backgrounds, respectively, using OSEM reconstruction with 16 subsets and 10 iterations. Sensitivities of 16.0% and 11.9% were achieved at center of the scanner for energy windows of 250–750 keV and 350–750 keV respectively. Peak noise equivalent count rates (NECRs) of 324 kcps and 144 kcps were obtained at an activity of 26.4 MBq for the mouse-sized and rat-sized phantoms. Rods of 1.0 mm diameter can be visually resolved from the image of the ultra-micro hot-rods phantom. The capability of the scanner was demonstrated by high quality in-vivo mouse images.

Monte Carlo Simulations of the GE Signa PET/MR for Different Radioisotopes.

NEMA characterization of PET systems is generally based on 18F because it is the most relevant radioisotope for the clinical use of PET. 18F has a half-life of 109.7 min and decays into stable 18O via β+ emission with a probability of over 96% and a maximum positron energy of 0.633 MeV. Other commercially available PET radioisotopes, such as 82Rb and 68Ga have more complex decay schemes with a variety of prompt gammas, which can directly fall into the energy window and induce false coincidence detections by the PET scanner.MethodsAim of this work was three-fold: (A) Develop a GATE model of the GE Signa PET/MR to perform realistic and relevant Monte Carlo simulations (B) Validate this model with published sensitivity and Noise Equivalent Count Rate (NECR) data for 18F and 68Ga (C) Use the validated GATE-model to predict the system performance for other PET isotopes including 11C, 15O, 13N, 82Rb, and 68Ga and to evaluate the effect of a 3T magnetic field on the positron range.ResultsSimulated sensitivity and NECR tests performed with the GATE-model for different radioisotopes were in line with literature values. Simulated sensitivities for 18F and 68Ga were 21.2 and 19.0/kBq, respectively, for the center position and 21.1 and 19.0 cps/kBq, respectively, for the 10 cm off-center position compared to the corresponding measured values of 21.8 and 20.0 cps/kBq for the center position and 21.1 and 19.6 cps/kBq for the 10 cm off-center position. In terms of NECR, the simulated peak NECR was 216.8 kcps at 17.40 kBq/ml for 18F and 207.1 kcps at 20.10 kBq/ml for 68Ga compared to the measured peak NECR of 216.8 kcps at 18.60 kBq/ml and 205.6 kcps at 20.40 kBq/ml for18F and 68Ga, respectively. For 11C, 13N, and 15O, results confirmed a peak NECR similar to 18F with the effective activity concentration scaled by the inverse of the positron fraction. For 82Rb, and 68Ga, the peak NECR was lower than for 18F while the corresponding activity concentrations were higher. For the higher energy positron emitters, the positron range was confirmed to be tissue-dependent with a reduction of the positron range by a factor of 3 to 4 in the plane perpendicular to the magnetic field and an increased positron range along the direction of the magnetic field.ConclusionMonte-Carlo simulations were used to predict sensitivity and NECR performance of GE Signa PET/MR for 18F, 15O, 13N, 11C, 82Rb, and 68Ga radioisotopes and were in line with literature data. Simulations confirmed that sensitivity and NECR were influenced by the particular decay scheme of each isotope. As expected, the positron range decreased in the direction perpendicular to the 3T magnetic field. However, this will be only partially improving the resolution properties of a clinical PET/MR system due to the limiting spatial resolution of the PET detector.

SimPET: a Preclinical PET Insert for Simultaneous PET/MR Imaging.

SimPET/M7 system is a small-animal dedicated simultaneous positron emission tomography and magnetic resonance imaging (PET/MRI) scanner. The SimPET insert has been upgraded from its prototype with a focus on count rate performance and sensitivity. The M7 scanner is a 1-T permanent magnet-based compact MRI system without any cryogens. Here, we present performance evaluation results of SimPET along with the results of mutual interference evaluation and simultaneously acquired PET/MR imaging. Following NEMA NU 4-2008 standard, we evaluated the performance of the SimPET system. The M7 MRI compatibility of SimPET was also assessed by analyzing MRI images of a uniform phantom under different PET conditions and PET count rates with different MRI pulse sequences. Mouse imaging was performed including a whole-body 18F-NaF PET scan and a simultaneous PET/MRI scan with 64Cu-NOTA-ironoxide. The spatial resolution at center based on 3D OSEM without and with warm background was 0.7mm and 1.45mm, respectively. Peak sensitivity was 4.21% (energy window = 250-750keV). The peak noise equivalent count rate with the same energy window was 151kcps at 38.4MBq. The uniformity was 4.42%, and the spillover ratios in water- and air-filled chambers were 14.6% and 12.7%, respectively. In the hot rod phantom image, 0.75-mm-diameter rods were distinguishable. There were no remarkable differences in the SNR and uniformity of MRI images and PET count rates with different PET conditions and MRI pulse sequences. In the whole-body 18F-NaF PET images, fine skeletal structures were well resolved. In the simultaneous PET/MRI study with 64Cu-NOTA-ironoxide, both PET and MRI signals changed before and after injection of the dual-modal imaging probe, which was evident with the exact spatiotemporal correlation. We demonstrated that the SimPET scanner has a high count rate performance and excellent spatial resolution. The combined SimPET/M7 enabled simultaneous PET/MR imaging studies with no remarkable mutual interference between the two imaging modalities.

NEMA-2008 and In-Vivo Animal and Plant Imaging Performance of the Large FOV Preclinical Digital PET/CT System Discoverist 180

The RAYCAN Discoverist 180 (RAYCAN D180) is a novel preclinical positron emission tomography (PET) and computed tomography (CT) integrated system for the imaging of small- and medium-sized animals and plants. We measured a system resolution of (2.56±0.04) mm (radial), (2.46±0.05) mm (transverse), and (1.67 ± 0.03) mm (axial) at the center of the field of view using a filtered backprojection reconstruction algorithm. An OSEM-PSF-3D reconstruction algorithm improves the spatial resolution to (1.34±0.04) mm (radial), (1.35±0.05) mm (transverse), and (1.64±0.04) mm (axial). The peak noise equivalent count rate of the system is (713 ± 2) kcps, (207 ± 2) kcps, and (47 ± 1) kcps reached at approximately 97 MBq for the mouse-, rat- and monkey-like phantoms, respectively. This result is approximately $2\times $ higher and is reached at approximately $3\times $ higher activity in comparison with most of the existing commercial and research scanners. The peak absolute system sensitivity is (4.00±0.02)% and is competitive with state-of-the-art preclinical PET scanners. We found an image uniformity of (4.86±0.04)%. Finally, we report the static PET/CT scan of a mouse and of a leaf of Epipremnum aureum, and the time-activity curves of the [18F]-FDG metabolism in mouse left myocardial ventricle and kidneys obtained with a PET/CT scan in dynamic modality.

Performance evaluation of HiPET, a high sensitivity and high resolution preclinical PET tomograph

HiPET is a recently developed prototype preclinical PET scanner dedicated to high sensitivity and high resolution molecular imaging. The HiPET system employs a phoswich depth of interaction (DOI) detector design, which also allows identification of the large majority of the cross layer crystal scatter (CLCS) events. This work evaluates its performance characteristics following the National Electrical Manufacturers Association (NEMA) NU4-2008 protocol.The HiPET consists of twenty flat panel type detectors arranged in two rings. The inner diameter is 160 mm and the axial field of view (FOV) is 104 mm. Each detector is comprised of two layers of phoswich scintillator crystal arrays, a tapered, pixelated glass lightguide and a multi anode photomultiplier tube (MAPMT). The front (gamma ray entrance) layer is a 48 × 48 pixelated cerium doped lutetium yttrium orthosilicate (LYSO) scintillator array with individual crystals measuring 1.01 × 1.01 × 6.1 mm. The back (towards the PMT) layer is a 32 × 32 pixelated bismuth germanate (BGO) scintillator array with individual crystals measuring 1.55 × 1.55 × 8.9 mm.For energy windows of 250–650 keV and 350–650 keV, the peak absolute sensitivity at the center of the FOV was 13.5% and 10.4% including CLCS events, and 11.8% and 8.9% excluding CLCS events, respectively. The average detector energy resolution derived by averaging the individual crystal spectra was 11.7% ± 1.4% for LYSO and 17.0% ± 1.4% for BGO. The 3D ordered-subsets expectation maximization (OSEM) reconstructed image of a point source in air, ranged from 0.73 mm to 1.19 mm, with an average value of 0.93 ± 0.09 mm at all measured locations. The peak noise equivalent count rate (NECR) and scatter fraction were 179 kcps at 12.4 MBq and 6.9% for the mouse-sized phantom, and 63 kcps at 11.3 MBq and 18.3% for the rat-sized phantom. For the NEMA image quality phantom, the uniformity was 5.8%, and the spillover ratios measured in the water- and air-filled cold region chambers were 0.047 and 0.044, respectively. The recovery coefficients (RC) ranged from 0.31 to 0.92.These results and in vivo evaluation demonstrate that the HiPET can achieve high quality molecular imaging for biomedical applications.

Performance characteristic evaluation of a bismuth germanate-based high-sensitivity 5-ring discovery image quality positron emission tomography/computed tomography system as per National Electrical Manufacturers Association NU 2-2012.

National Electrical Manufacturers Association (NEMA) provides guidelines to assess the performance of Positron Emission Tomography (PET). A PET/CT scanner, Discovery IQ, GE Medical systems, Milwaukee, USA was installed in our department which has high a sensitivity PET component. We have performed the NEMA NU-2 2012 quality control tests to evaluate this system on site before clinical use. Performance measurements of the PET scanner were made using the NEMA NU2-2012 procedures for spatial resolution, scatter fraction, sensitivity, count rate loss and random coincidence estimation, Noise Equivalent Count Rate (NECR) and image quality. As per NU2 2012, spatial resolution was measured at 1 cm, 10 cm and 20 cm vertically from the centre and at each of these points resolution was measured at tangential, radial and axial directions. Sensitivity was measured at centre and 10 cm off center vertically from the center. The system sensitivity is reported as an average of the two measured values. Scatter fraction and NECR measurements, Image quality test was also performed. The tangential, radial and axial FWHM were 4.99 mm, 4.20 mm and 4.79 mm at 1 cm off centre, 5.49 mm, 4.69 mm and 4.81 mm at 10 cm off centre and 7.99 mm, 5.07 mm and 4.95 mm at 20 cm off centre respectively. The absolute sensitivity of this scanner was found to be 20.1 cps/kBq. The scatter fraction calculated from the decay method was 37.94% and NECR was 125 kcps. The peak NECR was achieved at activity concentration of 8.7 KBq/ml and the count loss below the peak NECR was found to be 0.68%. Image quality test for, contrast recovery, background variability and lung error residual mean met all specifications. Overall PET performance of Discovery IQ whole-body scanner was satisfactory and the scanner met all the performance specifications required by NEMA 2012.

NEMA NU 2\u20132007 performance characteristics of GE Signa integrated PET/MR for different PET isotopes

BackgroundFully integrated PET/MR systems are being used frequently in clinical research and routine. National Electrical Manufacturers Association (NEMA) characterization of these systems is generally done with 18F which is clinically the most relevant PET isotope. However, other PET isotopes, such as 68Ga and 90Y, are gaining clinical importance as they are of specific interest for oncological applications and for follow-up of 90Y-based radionuclide therapy. These isotopes have a complex decay scheme with a variety of prompt gammas in coincidence. 68Ga and 90Y have higher positron energy and, because of the larger positron range, there may be interference with the magnetic field of the MR compared to 18F. Therefore, it is relevant to determine the performance of PET/MR for these clinically relevant and commercially available isotopes.MethodsNEMA NU 2–2007 performance measurements were performed for characterizing the spatial resolution, sensitivity, image quality, and the accuracy of attenuation and scatter corrections for 18F, 68Ga, and 90Y. Scatter fraction and noise equivalent count rate (NECR) tests were performed using 18F and 68Ga. All phantom data were acquired on the GE Signa integrated PET/MR system, installed in UZ Leuven, Belgium.Results18F, 68Ga, and 90Y NEMA performance tests resulted in substantially different system characteristics. In comparison with 18F, the spatial resolution is about 1 mm larger in the axial direction for 68Ga and no significative effect was found for 90Y. The impact of this lower resolution is also visible in the recovery coefficients of the smallest spheres of 68Ga in image quality measurements, where clearly lower values are obtained. For 90Y, the low number of counts leads to a large variability in the image quality measurements. The primary factor for the sensitivity change is the scale factor related to the positron emission fraction. There is also an impact on the peak NECR, which is lower for 68Ga than for 18F and appears at higher activities.ConclusionsThe system performance of GE Signa integrated PET/MR was substantially different, in terms of NEMA spatial resolution, image quality, and NECR for 68Ga and 90Y compared to 18F. But these differences are compensated by the PET/MR scanner technologies and reconstructions methods.

Performance evaluation of the 5‐Ring GE Discovery MI PET/CT system using the national electrical manufacturers association NU 2‐2012 Standard

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 from all three institutions were similar. Radial/tangential/axial full width at half maximum spatial resolution measurements using the filtered back projection algorithm were 4.3/4.3/5.0mm, 5.5/4.6/6.5mm, and 7.4/5.0/6.6mm at 1, 10, and 20cm from the center of the FOV, respectively. Measured sensitivity at the center of the FOV (20.84cps/kBq) was significantly higher than systems with reduced axial FOV. The peak noise-equivalent counting rate was 266.3kcps at 20.8kBq/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 381.7ps, respectively. Phantom and patient images demonstrated excellent image quality, even at short acquisition times or low injected activity. 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.

NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging system

The RAYCAN Trans-PET/CT X5 is a preclinical positron emission tomography and computed tomography (PET/CT) system intended for in vivo imaging of rats and mice, featuring all-digital readout electronics for PET data acquisition.The National Electrical Manufacturers Association (NEMA) NU 4-2008 performance evaluation was conducted on the RAYCAN Trans-PET/CT X5 in addition to assessing in vivo imaging performance of the system on live animals. The performance characteristics of the system were evaluated, including system spatial resolution, count rate performance, sensitivity and image quality. The system imaging performance is assessed in dynamic in vivo PET imaging.The system resolution defined as full width half maximum (FWHM) was 2.07 mm, 2.11 mm and 1.31 mm for the tangential, radial and axial resolution, respectively, at the center of the field of view. The peak noise equivalent count rate (NECR) values measured were 61 kcps at 0.19 MBq ml−1 for the rat size phantom and 126 kcps at 1.53 MBq ml−1 for the mouse size phantom. Scatter fractions were 24% and 14% for the rat and mouse phantom. The measured peak sensitivity of the system was 1.70%. Image quality in static imaging was deemed sufficient based on the image quality phantom study, with average activity concentration of 155 ± 8.6 kBq ml−1 and image uniformity of 5.57% when using two-dimensional filtered backprojection algorithm (2D-FBP). Rods in the image quality phantom were visualized easily up to 2 mm in size. In dynamic in vivo PET imaging, time-activity-curves from several regions were successfully measured, characterizing the radioactivity distribution in myocardial blood pool, liver, left ventricle and the lung.In conclusion, the RAYCAN Trans-PET/CT X5 system can be considered a suitable option for basic imaging needs in preclinical imaging.

Performance characteristics of silicon photomultiplier based 15-cm AFOV TOF PET/CT

BackgroundThis paper describes the National Electrical Manufacturers Association (NEMA) system performance of the Discovery MI 3-ring PET/CT (GE Healthcare) installed in Bruges, Belgium. This time-of-flight (TOF) PET camera is based on silicon photomultipliers instead of photomultiplier tubes.MethodsThe NEMA NU2-2012 standard was used to evaluate spatial resolution, sensitivity, image quality (IQ) and count rate curves of the system. Timing and energy resolution were determined.ResultsFull width at half maximum (FWHM) of spatial resolution in radial, tangential and axial direction was 4.69, 4.08 and 4.68 mm at 1 cm; 5.58, 4.64 and 5.83 mm at 10 cm; and 7.53, 5.08 and 5.47 mm at 20 cm from the centre of the field of view (FOV) for the filtered backprojection reconstruction. For non-TOF ordered subset expectation maximization (OSEM) reconstruction without point spread function (PSF) correction, FWHM was 3.87, 3.69 and 4.15 mm at 1 cm; 4.80, 3.81 and 4.87 mm at 10 cm; and 7.38, 4.16 and 3.98 mm at 20 cm. Sensitivity was 7.258 cps/kBq at the centre of the FOV and 7.117 cps/kBq at 10-cm radial offset. Contrast recovery (CR) using the IQ phantom for the TOF OSEM reconstruction without PSF correction was 47.4, 59.3, 67.0 and 77.0% for the 10-, 13-, 17- and 22-mm radioactive spheres and 82.5 and 85.1% for the 28- and 37-mm non-radioactive spheres. Background variability (BV) was 16.4, 12.1, 9.1, 6.6, 5.1 and 3.8% for the 10-, 13-, 17-, 22-, 28- and 37-mm spheres. Lung error was 8.5%. Peak noise equivalent count rate (NECR) was 102.3 kcps at 23.0 kBq/ml with a scatter fraction of 41.2%. Maximum accuracy error was 3.88%. Coincidence timing resolution was 375.6 ps FWHM. Energy resolution was 9.3% FWHM. Q.Clear reconstruction significantly improved CR and reduced BV compared with OSEM.ConclusionSystem sensitivity and NECR are lower and IQ phantom’s BV is higher compared with larger axial FOV (AFOV) scanners like the 4-ring discovery MI, as expected from the smaller solid angle of the 3-ring system. The other NEMA performance parameters are all comparable with those of the larger AFOV scanners.

NEMA NU-4 performance evaluation of a non-human primate animal PET

The Eplus-260 primate PET is an animal PET imaging system developed by the Institute of High Energy Physics, Chinese Academy of Sciences, which is designed to image non-human primates, especially the brain of large non-human primates. The system consists of 48 block detectors arranged in two 24-sided rings with a ring diameter of 263 mm and an axial extent of 64 mm. Each block detector is composed of a 16 × 16 cerium-doped lutetium–yttrium orthosilicate crystal array with a pixel size of 1.9 × 1.9 × 10 mm3. This article presents a performance evaluation of the PET scanner according to the National Electrical Manufacturers Association NU-4 2008 standards. All measurements were made for an energy window of 360–660 keV and a coincidence timing window of 2 ns. In terms of the FWHM, the FBP reconstructed spatial resolution results in all three directions at the radial position of 5 mm were better than or approached to 2 mm, and remained below 3.0 mm within the central 5 cm diameter of the FOV. The peak absolute sensitivity of the scanner was measured 1.80%. For a monkey-sized phantom, the scatter fraction was 34.2% and the peak noise equivalent count rate (NECR) was 26.5 kcps at 64.3 kBq/cc. The overall imaging capabilities of the scanner were also assessed using in vivo imaging study of a rhesus macaque. The performance measurements demonstrate that the Eplus-260 primate PET scanner has the potential ability to obtain good quality and high-contrast images for non-human primates, especially the brain of large non-human primates and could be considered as one technologically advanced dedicated non-human primate PET scanner available today.

Performance evaluation of a whole-body prototype PET scanner with four-layer DOI detectors

Parallax error caused by the detector crystal thickness degrades spatial resolution at the peripheral regions of the field-of-view (FOV) of a scanner. To resolve this issue, depth-of-interaction (DOI) measurement is a promising solution to improve the spatial resolution and its uniformity over the entire FOV. Even though DOI detectors have been used in dedicated systems with a small ring diameter such as for the human brain, breast and small animals, the use of DOI detectors for a large bore whole-body PET system has not been demonstrated yet. We have developed a four-layered DOI detector, and its potential for a brain dedicated system has been proven in our previous development. In the present work, we investigated the use of the four-layer DOI detector for a large bore PET system by developing the world’s first whole-body prototype. We evaluated its performance characteristics in accordance with the NEMA NU 2 standard. Furthermore, the impact of incorporating DOI information was evaluated with the NEMA NU 4 image quality phantom. Point source images were reconstructed with a filtered back projection (FBP), and an average spatial resolution of 5.2 ± 0.7 mm was obtained. For the FBP image, the four-layer DOI information improved the radial spatial resolution by 48% at the 20 cm offset position. The peak noise-equivalent count rate (NECR) was 22.9 kcps at 7.4 kBq ml−1 and the scatter fraction was 44%. The system sensitivity was 5.9 kcps MBq−1. For the NEMA NU 2 image quality phantom, the 10 mm sphere was clearly visualized without any artifacts. For the NEMA NU 4 image quality phantom, we measured the phantom at 0, 10 and 20 cm offset positions. As a result, we found the image with four-layer DOI could visualize the 2 mm-diameter hot cylinder although it could not be recognized on the image without DOI. The average improvements in the recovery coefficients for the five hot rods (1–5 mm) were 0.3%, 4.4% and 26.3% at the 0, 10 and 20 cm offset positions, respectively (except for the 1 mm-diameter rod at the 20 cm offset position). Although several practical issues (such as adding end-shields) remain to be addressed before the scanner is ready for clinical use, we showed that the four-layer DOI technology provided higher and more uniform spatial resolution over the FOV and improved contrast for small uptake regions located at the peripheral FOV, which could improve detectability of small and distal lesions such as nodal metastases, especially in obese patients.

Mini EXPLORER II: a prototype high-sensitivity PET/CT scanner for companion animal whole body and human brain scanning

As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner, which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. The detector modules are composed of arrays of lutetium (yttrium) oxyorthosilicate (LYSO) crystals of dimensions 2.76 × 2.76 × 18.1 mm3 coupled to silicon photomultipliers (SiPMs) for read-out. The CT component is a 24 detector row CT scanner with a 50 kW x-ray tube. PET system time-of-flight resolution was measured to be 409 ± 39 ps and average system energy resolution was 11.7% ± 1.5% at 511 keV. The NEMA NU2-2012 system sensitivity was found to be 52–54 kcps MBq−1. Spatial resolution was 2.6 mm at 10 mm from the center of the FOV and 2.0 mm rods were clearly resolved on a mini-Derenzo phantom. Peak noise-equivalent count (NEC) rate, using the NEMA NU 2-2012 phantom, was measured to be 314 kcps at 9.2 kBq cc−1. The CT scanner passed the technical components of the American College of Radiology (ACR) accreditation tests. We have also performed scans of a Hoffman brain phantom and we show images from the first canine patient imaged on this device.

GATE Simulation Study of the Siemens Biograph mCT 20 Excel PET/CT System

Abstract We used GATE simulation to study the effect of the coincidence time window (CTW) along with the block gap and the intercrystal gap on the count rate performance and the spatial resolution of the Biograph™ mCT 20 Excel. We ran simulations on our local cluster to reduce computation time. The task was split into several jobs that were then triggered simultaneously on the cluster nodes. The BiographTM mCT 20 Excel was validated using the NEMA NU 2-2012 protocol. Our results showed good agreement with experimental data. The simulated sensitivity, peak true count rate, peak noise equivalent count rate (NECR), and scatter fraction showed agreement within 3.62%, 5.77%, 0.6%, and 2.69%, respectively. In addition, the spatial resolution agreed within <0.51 mm. The results showed that a decrease in the coincidence time window and the block gap and an increase in the intercrystal gap increase the count rate performance and improve the spatial resolution. The results also showed that decreasing the coincidence time window increased the NECR by 27.37%. Changing the intercrystal gap from 0 to 0.2 mm and the block gap and from 4 to 0.4 mm increased the NECR by 5.53% and improved the spatial resolution at 1 cm by 2.91% and that at 10 cm by 3.85%. The coincidence time window, crystal gap, and block gap are important parameters with respect to improving the spatial resolution.

Performance evaluation of a small animal PET scanner a high level of multiplexing and charge-signal transmission

Small animal positron emission tomography (PET) is a noninvasive imaging modality that enables in vivo imaging and quantification of the biological processes of small experimental animals. We have developed a small animal PET that utilizes a high-resolution multiplexed readout and charge signal transmission (CST) method. The small animal PET was composed of six detector blocks consisting of SiPMs and LYSO arrays. Six detector blocks were mounted on a PET gantry having an inner diameter of 76 mm, outer diameter of 112 mm, and axial length of 40.8 mm. The charge signals of SiPM output were transmitted to the input of multiplexed readout using 4 m flexible flat cables. The multiplexed readout was composed of six main boards, each of which included 36 detector boards, to reduce the number of readout channels by a factor of 36, with a multiplexing ratio of 144:4. The performance of the small animal PET was evaluated using NEMA NU 4-2008 standards, and its imaging capability was demonstrated by in vivo mouse imaging studies. The average energy and time resolutions were 13.2% ± 0.3% and 3.8 ns, respectively. The spatial resolution at the center of the transaxial FOV was 1.1 mm, and the peak sensitivity at the center of the axial FOV was 1.5%. The peak noise equivalent count (NEC) rate and scatter fraction were 21.1 kcps at 18.2 MBq and 21%, respectively. The acquired images demonstrated high quality tracer uptake patterns of small experimental animals. The results of performance evaluation and animal imaging indicate that the small animal PET developed in this study can provide high-quality small animal imaging with cost-effectiveness and compactness.

Evaluation of Hamamatsu PET imaging modules for dedicated TOF-capable scanners.

Time-of-flight (TOF) capability is becoming an important capability offered in both commercial and research PET scanners. Often commercial vendors and laboratory researchers develop and utilize proprietary electronics for their devices. Consequently, it is challenging for independent research groups to develop their own TOF-PET scanners. In this investigation, we tested a prototype scanner consisting of commercially available TOF-capable modules from Hamamatsu Photonics that can be used as building blocks for PET scanners. The scanner consists of a ring of 16 modules, for a total diameter of 26.7 cm. Testing demonstrated that the scanner is capable of sustaining ~1 MHz single counting rate with a peak noise equivalent count rate (NECR) of 117.5 kHz at 75.25 MBq measured with NEMA NU-4 "rat" phantom. Spatial resolution of 2.3 mm 5 mm from the center of the scanner was measured. Energy resolution of 17.2% at 511 keV was measured. Peak sensitivity of 1.28% is reported. All the measurements were performed with energy cuts from 350 to 700 keV Finally, scanner timing resolution was found to be 462 ps. Results from testing of a prototype scanner constructed using newly released TOF-capable detector modules produced by Hamamatsu demonstrated the promise for these devices to create high performance PET system with TOF capabilities.