Applicability of [18F]FDG/PET for investigating rosmarinic acid preconditioning efficacy in a global stroke model in mice

ABSTRACT Positron emission tomography (PET) is a non-invasive nuclear imaging technique that uses radiotracers to track cell activity. The radiopharmaceutical 18F-fluoro-2-deoxyglucose ([18F] FDG) is most commonly used in nuclear medicine for the diagnosis of various diseases, including stroke. A stroke is a serious condition with high mortality and morbidity rates. Rosmarinic acid (RA) is a promising therapeutic agent that exerts neuroprotective effects against various neurological diseases. Therefore, this study aimed to evaluate the applicability of [18F]FDG/PET for investigating the neuroprotective effects of RA in case of a global stroke model in mice. The [18F]FDG/PET technique facilitates the observation of ischemia and reperfusion injuries in the brain. Moreover, the recovery of glucose metabolism in three specific brain regions, the striatum, superior colliculus, and inferior colliculus, was observed after preconditioning with RA. It was concluded that the [18F]FDG/PET technique may be useful for stroke diagnosis and the assessment of treatment response. In addition, a long-term longitudinal study using biochemical analysis in conjunction with functional imaging may provide further conclusive results regarding the effect of RA on cerebral ischemia.

Uso del filtro hidrofóbico estéril de 0, 2 micras para fraccionamiento y dispensación de fludesoxiglucosa (18f-fdg) en el dispensador automático con celda caliente de flujo laminar blindada con filtro hepa / Use of sterile 0, 2 micron hydrophobic filter for fractionation and dispensing of fludeoxyglucose (18f-fdg) in the automatic dispenser with laminar flow hot cell shielded with hepa filter

INTRODUCCIÓN: La tomografía por emisión de positrones (PET) es un examen imagenológico que a través de un scanner para PET, la inyección intravenosa de un radiomarcador o radiosonda nos permite realizar exploraciones para detectar cáncer o determinar si hubo metástasis, evaluar la efectividad del tratamiento contra el cáncer o su recurrencia y evaluar pronóstico. Dentro de los radiomarcadores utilizados para el uso de PET la fludesoxiglucosa (18F-FDG) es un análogo de la glucosa y se acumula en células que utilizan glucosa como fuente primaria de energía y sobre todo las células que tienen un alto intercambio de glucosa como las células oncológicas. Su síntesis se lleva a cabo a través de un equipo especial que requiere de otros insumos para poder lograr en la fase final el fraccionamiento y dispensación exacta de este marcador. Para ello se utilizan filtros hidrofóbicos los cuales son individuales y se colocan en la celda caliente del equipo. En INEN durante el 2021 se estuvieron realizando diariamente PETs en la nueva torre cuya inversión incluyó la adquisición del equipo para la síntesis, fraccionamiento y dispensación del 18F-FDG; sin embargo, actualmente ya no se cuenta con el filtro hidrofóbico que se coloca en el equipo y logra la fase final del procedimiento de obtención de 18F-FDG. Para el correcto funcionamiento se requerirían según lo coordinado con el área usuaria un promedio de 400 filtros adquiridos anualmente. METODOLOGÍA: Se realizó una búsqueda sistemática de la información y una búsqueda dirigida en las principales entidades que elaboran tecnologías sanitarias y guías relacionadas al tema. Con respecto a la búsqueda dirigida se encontró 02 guías de entidades reconocidas a nivel internacional, en una de ellas no se encontró información sobre el procedimiento de síntesis, pero en otra si se encontró y se especificaban las características y la importancia de contar con un filtro hidrofóbico que permita obtener una muestra estéril y fraccionada en cantidades exactas para el paciente. En la búsqueda sistemática se encontró 02 revisiones narrativas que mencionan la importancia de utilizar los filtros hidrofóbicos como parte de la calidad del procedimiento de síntesis del radiofármaco para PET. A pesar de que sean revisiones narrativas, en ambos casos se brinda información con respecto al fraccionamiento, dispensación, esterilidad y la necesidad de filtros hidrofóbicos para la protección del personal de salud que realiza el procedimiento. DISCUSIÓN: Se agregó información sobre el uso de tomografía por emisión de positrones. Este ambiente que incluye el equipo entro en funcionamiento cuando se apertura la torre nueva en INEN. Por ello, la adquisición de los equipos que participan para lograr un adecuado uso del TEM formaron parte del presupuesto del proyecto de la torre nueva y ello incluyo el equipo de celda caliente que tiene como dificultad la necesidad de usar un filtro exclusivo que permita el fraccionamiento y dispensación del radiofármaco usado para el TEM. Durante los primeros meses como se disponía del dispositivo se ha venido trabajando de manera normal; sin embargo, a la actualidad solamente se está usando el TEM cuando el paciente cuenta de manera personal con el radiofármaco (18F-FDG) ya fraccionado y en dosis exactas individualizadas. Por otro lado, si el INEN adquiriera el radiomarcador fraccionado el precio se eleva comparado a adquirirlo para fraccionar a nivel institucional y el fraccionar a nivel institucional permite un uso más racional de las dosis que vienen en un vial. CONCLUSIONES: Finalmente; a pesar de que no se cuente con evidencia de alta calidad con respecto a la utilidad de los filtros hidrofóbicos, la evidencia encontrada aboga por la necesidad de que se apruebe su adquisición debido a que es un dispositivo necesario dentro de la última etapa de dispensación y fraccionamiento del FDG18 y el correcto funcionamiento del equipo de celda caliente en INEN.

Validation technique and improvements introduced in a new dedicated brain positron emission tomograph (CareMiBrain).

The goal of developing a PET dedicated to the brain (CareMiBrain) has evolved from its initial approach to diagnosis and monitoring of dementias, to the more ambitious of creating a revolutionary clinical pathway for the knowledge and personalized treatment of multiple neurological diseases. The main innovative feature of CareMiBrain is the use of detectors with continuous crystals, which allow a high resolution determination of the depth of annihilation photons interaction within the thickness of the scintillation crystal. The technical validation phase of the equipment consisted of a pilot, prospective and observational study whose objective was to obtain the first images (40 patients), analyze them and make adjustments in the acquisition, reconstruction and correction parameters, comparing the image quality of the CareMiBrain equipment with that of the whole-body PET/CT. Thanks to the team meetings and the joint analysis of the images, it was possible to detect its weak points and some of its causes. The calibration, acquisition and processing processes, as well as the reconstruction, were optimized, the number of iterations was set to achieve the best signal-to-noise ratio, the random correction was optimized and a post-processing algorithm was included in the reconstruction algorithm. The main technical improvements implemented in this phase of technical validation carried out through collaboration of the Services of Nuclear Medicine and Neurology of the Hospital Clínico San Carlos with the Spanish company Oncovision will be exposed in a project financed with funds from the European Union (Horizon 2020 innovation program, 713323).

Photon quantum entanglement in the MeV regime and its application in PET imaging.

Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Imaging of the radiotracer is obtained from the detected hit positions of the two positron annihilation photons in a detector array. The image is degraded by backgrounds from random coincidences and in-patient scatter events which require correction. In addition to the geometric information, the two annihilation photons are predicted to be produced in a quantum-entangled state, resulting in enhanced correlations between their subsequent interaction processes. To explore this, the predicted entanglement in linear polarisation for the two photons was incorporated into a simulation and tested by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. Adapted apparati also enabled correlation measurements where one of the photons had undergone a prior scatter process. We show that the entangled simulation describes the measured correlations and, through simulation of a larger preclinical PET scanner, illustrate a simple method to quantify and remove the unwanted backgrounds in PET using the quantum entanglement information alone.

Study of two-layer tapered depth of interaction PET detector.

Improving detection efficiency in small animal PET scanners without degrading spatial resolution is one of the main problems of these scanners. Commercial small animal PET scanners use different methods to achieve desirable levels of sensitivity and spatial resolution. GE Healthcare eXplore VISTA PET scanner uses double layer (LYSO-GSO) depth-of-interaction (DOI) capable cuboid detector modules. In this work, the design of GE Healthcare eXplore VISTA PET scanner is improved using tapered detector geometry instead of cuboid geometry. Using tapered detector geometry, the gaps between adjacent modules are filled and the sensitive volume has increased about 11.5%. The new designed PET scanner sensitivity and spatial resolution are studied for different crystal layer configurations (LYSO-GSO and GSO-LYSO with different thicknesses). As expected, average sensitivity over FOV is improved. Spatial resolution is slightly degraded but it is still uniform over FOV.

Valor adicional de la tecnología híbrida de PET/RM frente a la RM y la PET en la enfermedad cardiovascular / Additional value of hybrid PET/MR imaging versus MR or PET performed separately to assess cardiovascular disease

Introducción y objetivos Los sistemas híbridos de tomografía por emisión de positrones (PET) y resonancia magnética (RM) son una tecnología prometedora para el diagnóstico por imagen, pero su aplicación cardiovascular en nuestro entorno clínico es desconocida. Nuestro objetivo es evaluar el valor de los equipos integrados de PET/RM frente a la RM y la PET por separado. Métodos Se incluyó prospectivamente a 49 pacientes, 30 para valoración de viabilidad miocárdica (grupo coronario) y 19 para estudio de enfermedad inflamatoria, infecciosa y tumoral (grupo no coronario), a los que se realizó una PET/RM cardiaca con 18F-fluorodesoxiglucosa, incluyendo secuencias de corrección de atenuación y, simultáneamente a la PET, secuencias de cine, caracterización tisular o realce tardío de RM, según indicación clínica. Resultados El 87,8% de los estudios de PET/RM fueron inicialmente interpretables. La PET/RM mejoró el diagnóstico en el 42,1% de los pacientes del grupo coronario respecto a la PET o la RM por separado, y en el 88,9% del grupo no coronario. De los casos no concluyentes según la RM o la PET, la PET/RM reclasificó a estudio diagnóstico al 87,5% de los pacientes del grupo coronario y el 70% de los del no coronario. Conclusiones En nuestra serie, la tecnología multimodal de PET/RM añade valor diagnóstico en algunos pacientes con enfermedad cardiovascular, sobre todo en enfermedad no coronaria y con hallazgos no concluyentes por RM o PET, y complementa cada técnica por separado. Los principales beneficios incluyen la adquisición simultánea, la integración de imágenes anatómicas, funcionales y metabólicas y la interacción entre distintos profesionales expertos en imagen. (AU)

Introduction and objectives Hybrid positron emission tomography (PET) and magnetic resonance (MR) imaging is an emerging technology in the diagnosis of cardiovascular disease; however, there have been no reports of its use in the national clinical setting. Our objective was to evaluate the additional value of integrated PET/MR systems compared with MR and PET performed separately in this setting. Methods We prospectively included 49 patients, 30 to assess myocardial viability (coronary group) and 19 to assess inflammatory, infectious, and tumoral diseases (noncoronary heart disease group). All patients underwent cardiac 18F-fluorodeoxyglucose PET/MR. PET/MR studies included attenuation correction sequences, followed by simultaneous cardiac PET and cardiac MR acquisition, with protocols adapted to the clinical indication (cine, tissue characterization and/or late enhancement imaging). Results Most (87.8%) PET/MR studies were initially interpretable. Use of PET/MR improved diagnosis vs PET or MR performed separately in 42.1% of coronary cases and 88.9% of noncoronary cases. PET/MR enabled reclassification of 87.5% of coronary cases initially classified as showing inconclusive results on MR or PET and 70% of noncoronary cases. Conclusions In our series, multimodality PET/MR technology provided additional diagnostic value in some patients with cardiovascular disease compared with MR and PET performed separately, especially in cases of noncoronary heart disease and in those with inconclusive results on MR or PET. In our experience, the main benefits of PET/MR include the possibility of simultaneous acquisition, the in vivo integration of anatomical/functional/metabolic aspects, and the interaction of different experts in imaging modalities. (AU)

A thick semi-monolithic scintillator detector for clinical PET scanners.

Both monolithic and semi-monolithic scintillator positron emission tomography (PET) detectors can measure the depth of interaction with single-ended readout. Usually scintillators with a thickness of 10 mm or less are used since the position resolutions of the detectors degrade as the scintillator thickness increases. In this work, the performance of a 20 mm thick long rectangular semi-monolithic scintillator PET detector was measured by using both single-ended and dual-ended readouts with silicon photomultiplier (SiPM) arrays to provide a high detection efficiency. The semi-monolithic scintillator detector consists of nine lutetium-yttrium oxyorthosilicate slices measuring 1.37 × 51.2 × 20 mm3 with erythrocyte sedimentation rate foils of 0.065 mm thickness in between the slices. The SiPM array at each end of the scintillator detector consists of 16 × 4 SiPMs with a pixel size of 3.0 × 3.0 mm2 and a pitch of 3.2 mm. The 64 signals of each SiPM array are processed by using the TOFPET2 application-specific integrated circuit individually. All but the edge slices can be clearly resolved for the detectors with both single-ended and dual-ended readouts. The single-ended readout detector provides an average full width at half maximum (FWHM) Y (continuous direction) position resolution of 2.43 mm, Z (depth direction) position resolution of 4.77 mm, energy resolution of 25.7% and timing resolution of 779 ps. The dual-ended readout detector significantly improves the Y and Z position resolutions, slightly improves the energy and timing resolution at the cost of two photodetectors required for one detector module and provides an average FWHM Y position resolution of 1.97 mm, Z position resolution of 2.60 mm, energy resolution of 21.7% and timing resolution of 718 ps. The energy and timing resolution of the semi-monolithic scintillator detector in this work are worse than those of the segmented scintillator array detector and need to be further improved. The semi-monolithic scintillator detector described in this work reduces costs as compared to the traditional segmented scintillator array detector and reduces the edge effect as compared to the monolithic scintillator detector.

Performance Evaluation of SimPET-X, a PET Insert for Simultaneous Mouse Total-Body PET/MR Imaging.

PURPOSE: In this study, a small animal PET insert (SimPET-X, Brightonix Imaging Inc.) for simultaneous PET/MR imaging studies is presented. This insert covers an 11-cm-long axial field-of-view (FOV) and enables imaging of mouse total-bodies and rat heads. PROCEDURES: SimPET-X comprises 16 detector modules to yield a ring diameter of 63 mm and an axial FOV of 110 mm. The detector module supports four detector blocks, each comprising two 4 × 4 SiPM arrays coupled with a 20 × 9 array of LSO crystals (1.2 × 1.2 × 10 mm3). The physical characteristics of SimPET-X were measured in accordance with the NEMA NU4-2008 standard protocol. In addition, we assessed the compatibility of SimPET-X with a small animal-dedicated MRI (M7, Aspect Imaging) and conducted phantom and animal studies. RESULTS: The radial spatial resolutions at the center based on 3D OSEM without and with the warm background were 0.73 mm and 0.99 mm, respectively. The absolute peak sensitivity of the system was 10.44% with an energy window of 100-900 keV and 8.27% with an energy window of 250-750 keV. The peak NECR and scatter fraction for the mouse phantom were 348 kcps at 26.2 MBq and 22.1% with an energy window of 250-750 keV, respectively. The standard deviation of pixel value in the uniform region of an NEMA IQ phantom was 4.57%. The spillover ratios for air- and water-filled chambers were 9.0% and 11.0%, respectively. In the hot-rod phantom image reconstructed using 3D OSEM-PSF, all small rods were resolved owing to the high spatial resolution of the SimPET-X system. There was no notable interference between SimPET-X and M7 MRI. SimPET-X provided high-quality mouse images with superior spatial resolution, sensitivity, and counting rate performance. CONCLUSION: SimPET-X yielded a remarkably improved sensitivity and NECR compared with SimPETTM.

Quantitative and qualitative evaluation of sequential PET/MRI using a newly developed mobile PET system for brain imaging.

PURPOSE: To evaluate the clinical feasibility of a newly developed mobile PET system with MR-compatibility (flexible PET; fxPET), compared with conventional PET (cPET)/CT for brain imaging. METHODS: Twenty-one patients underwent cPET/CT with subsequent fxPET/MRI using 18F-FDG. As qualitative evaluation, we visually rated image quality of MR and PET images using a four-point scoring system. We evaluated overall image quality for MR, while we evaluated overall image quality, sharpness and lesion contrast. As quantitative evaluation, we compared registration accuracy between two modalities [(fxPET and MRI) and (cPET and CT)] measuring spatial coordinates. We also examined the accuracy of regional 18F-FDG uptake. RESULTS: All acquired images were of diagnostic quality and the number of detected lesions did not differ significantly between fxPET/MR and cPET/CT. Mean misregistration was significantly larger with fxPET/MRI than with cPET/CT. SUVmax and SUVmean for fxPET and cPET showed high correlations in the lesions (R = 0.84, 0.79; P < 0.001, P = 0.002, respectively). In normal structures, we also showed high correlations of SUVmax (R = 0.85, 0.87; P < 0.001, P < 0.001, respectively) and SUVmean (R = 0.83, 0.87; P < 0.001, P < 0.001, respectively) in bilateral caudate nuclei and a moderate correlation of SUVmax (R = 0.65) and SUVmean (R = 0.63) in vermis. CONCLUSIONS: The fxPET/MRI system showed image quality within the diagnostic range, registration accuracy below 3 mm and regional 18F-FDG uptake highly correlated with that of cPET/CT.

H2RSPET: a 0.5 mm resolution high-sensitivity small-animal PET scanner, a simulation study.

With the goal of developing a total-body small-animal PET system with a high spatial resolution of ∼0.5 mm and a high sensitivity >10% for mouse/rat studies, we simulated four scanners using the graphical processing unit-based Monte Carlo simulation package (gPET) and compared their performance in terms of spatial resolution and sensitivity. We also investigated the effect of depth-of-interaction (DOI) resolution on the spatial resolution. All the scanners are built upon 128 DOI encoding dual-ended readout detectors with lutetium yttrium oxyorthosilicate (LYSO) arrays arranged in 8 detector rings. The solid angle coverages of the four scanners are all ∼0.85 steradians. Each LYSO element has a cross-section of 0.44 × 0.44 mm2 and the pitch size of the LYSO arrays are all 0.5 mm. The four scanners can be divided into two groups: (1) H2RS110-C10 and H2RS110-C20 with 40 × 40 LYSO arrays, a ring diameter of 110 mm and axial length of 167 mm, and (2) H2RS160-C10 and H2RS160-C20 with 60 × 60 LYSO arrays, a diameter of 160 mm and axial length of 254 mm. C10 and C20 denote the crystal thickness of 10 and 20 mm, respectively. The simulation results show that all scanners have a spatial resolution better than 0.5 mm at the center of the field-of-view (FOV). The radial resolution strongly depends on the DOI resolution and radial offset, but not the axial resolution and tangential resolution. Comparing the C10 and C20 designs, the former provides better resolution, especially at positions away from the center of the FOV, whereas the latter has 2× higher sensitivity (∼10% versus ∼20%). This simulation study provides evidence that the 110 mm systems are a good choice for total-body mouse studies at a lower cost, whereas the 160 mm systems are suited for both total-body mouse and rat studies.

Positron range-free and multi-isotope tomography of positron emitters.

Despite improvements in small animal PET instruments, many tracers cannot be imaged at sufficiently high resolutions due to positron range, while multi-tracer PET is hampered by the fact that all annihilation photons have equal energies. Here we realize multi-isotope and sub-mm resolution PET of isotopes with several mm positron range by utilizing prompt gamma photons that are commonly neglected. A PET-SPECT-CT scanner (VECTor/CT, MILabs, The Netherlands) equipped with a high-energy cluster-pinhole collimator was used to image 124I and a mix of 124I and 18F in phantoms and mice. In addition to positrons (mean range 3.4 mm) 124I emits large amounts of 603 keV prompt gammas that-aided by excellent energy discrimination of NaI-were selected to reconstruct 124I images that are unaffected by positron range. Photons detected in the 511 keV window were used to reconstruct 18F images. Images were reconstructed iteratively using an energy dependent matrix for each isotope. Correction of 18F images for contamination with 124I annihilation photons was performed by Monte Carlo based range modelling and scaling of the 124I prompt gamma image before subtracting it from the 18F image. Additionally, prompt gamma imaging was tested for 89Zr that emits very high-energy prompts (909 keV). In Derenzo resolution phantoms 0.75 mm rods were clearly discernable for 124I, 89Zr and for simultaneously acquired 124I and 18F imaging. Image quantification in phantoms with reservoirs filled with both 124I and 18F showed excellent separation of isotopes and high quantitative accuracy. Mouse imaging showed uptake of 124I in tiny thyroid parts and simultaneously injected 18F-NaF in bone structures. The ability to obtain PET images at sub-mm resolution both for isotopes with several mm positron range and for multi-isotope PET adds to many other unique capabilities of VECTor's clustered pinhole imaging, including simultaneous sub-mm PET-SPECT and theranostic high energy SPECT.

A layered single-side readout depth of interaction time-of-flight-PET detector.

We are exploring a scintillator-based PET detector with potential of high sensitivity, depth of interaction (DOI) capability, and timing resolution, with single-side readout. Our design combines two previous concepts: (1) multiple scintillator arrays stacked with relative offset, yielding inherent DOI information, but good timing performance has not been demonstrated with conventional light sharing readout. (2) Single crystal array with one-to-one coupling to the photodetector, showing superior timing performance compared to its light sharing counterparts, but lacks DOI. The combination, where the first layer of a staggered design is coupled one-to-one to a photodetector array, may provide both DOI and timing resolution and this concept is here evaluated through light transport simulations. Results show that: (1) unpolished crystal pixels in the staggered configuration yield better performance across all metrics compared to polished pixels, regardless of readout scheme. (2) One-to-one readout of the first layer allows for accurate DOI extraction using a single threshold. The number of multi pixel photon counter (MPPC) pixels with signal amplitudes exceeding the threshold corresponds to the interaction layer. This approach was not possible with conventional light sharing readout. (3) With a threshold of 2 optical photons, the layered approach with one-to-one coupled first layer improves timing close to the MPPC compared to the conventional one-to-one coupling non-DOI detector, due to effectively reduced crystal thickness. Single detector timing resolution values of 91, 127, 151 and 164 ps were observed per layer in the 4-layer design, to be compared to 148 ps for the single array with one-to-one coupling. (4) For the layered design with light sharing readout, timing improves with increased MPPC pixel size due to higher signal per channel. In conclusion, the combination of straightforward DOI determination, good timing performance, and relatively simple design makes the proposed concept promising for DOI-Time-of-Flight PET detectors.

Field-programable-gate-array-based distributed coincidence processor for high count-rate online positron emission tomography coincidence data acquisition.

For positron emission tomography (PET) online data acquisition, a centralized coincidence processor (CCP) with single-thread data processing has been used to select coincidence events for many PET scanners. A CCP has the advantages of highly integrated circuit, compact connection between detector front-end and system electronics and centralized control of data process and decision making. However, it also has the drawbacks of data process delay, difficulty in handling very high count-rates of single and coincidence events and complicated algorithms to implement. These problems are exacerbated when implementing a CCP on a field-programable-gate-array (FPGA) due to increased routing congestion and reduced data throughput. Industry companies have applied non-centralized or distributed data processing to solve these problems, but those solutions remain either proprietary or lack full disclosure of technical details that make the techniques unclear and difficult to adapt for most research communities. In this study, we investigated the use of a set of distributed coincidence processors (DCP) that can address the CCP problems and be implemented relatively easily. Each coincidence processor exclusively connects one detector pair and selects coincidence events from this detector pair only, which breaks a centralized coincidence process to a collection of independent and parallel processes. DCP can significantly minimize the data process delay, maximize count-rates of coincidence events and simplify implementation by implementing a single coincidence processor with one detector pair and replicating it to the rest. A prototype DCP with 42 coincidence processors was implemented on an off-the-shelf FPGA development board for a small PET with 12 detectors configured with 42 detector pairs. DCP performances were tested with both pulsed signals and gamma ray interactions. There was no coincidence data loss up to the detector's maximum singles count-rate (250 k s-1). Approximately 1.2 k registers were utilized for each coincidence processor and the FPGA resource utilization was proportional to the number of coincidence processors. Coincidence timing spectra showed the results from accurately acquired coincidence events. In conclusion: complementary to CCP, DCP can provide high count-rate capability, with a simplified algorithm for implementation and potentially a practical solution for online acquisition of a PET with a larger number of detector pairs or for ultrahigh-throughput imaging.

Further investigations of a radiation detector based on ionization-induced modulation of optical polarization.

Optical property modulation induced by ionizing radiation is a promising approach for ultra-fast, lower time jitter detection of photon arrival time. If successful, this method can be utilized in time-of-flight positron emission tomography to achieve a coincidence time resolution approaching 10 ps. In this work, the optical property modulation based method is further developed with focus on a detection setup based on two crossed polarizers. Previous work demonstrated that such an optical setup could be utilized in radiation detection, though its detection sensitivity needed improvement. This work investigates the angle between polarizers and electric field distribution within the detection crystal to understand and improve the detection sensitivity of an optical polarization modulation based method. For this work, cadmium telluride (CdTe) was studied as the detector crystal . The 'magic' angle (i.e. optimal working angle) of the two crossed polarizers based optical setup with CdTe were explored theoretically and experimentally. The experimental results show that the detection sensitivity could be improved by around 10% by determining the appropriate 'magic' angle. We then studied the dependence of detection sensitivity on electric field distribution as well as on the bias voltage across the detector crystal using CdTe crystals. The experimental results show that a smaller electrode on the detector crystal, or a more concentrated electric field distribution could improve detection sensitivity. For CdTe, a detector crystal sample with 2.5 mm × 2.5 mm square electrode has twice the detection sensitivity of a detector crystal with 5 mm × 5 mm square electrode. Increasing the bias voltage before saturation for CdTe could further enhance the modulation strength and thus, the sensitivity. Our investigations demonstrated that by determining the proper working angle of polarizers and bias electrical distribution to the detector, we could improve the sensitivity of the proposed optical setup.

Novel dietary protocol prior to 18F-fluorodeoxyglucose positron emission tomography to evaluate for cardiac sarcoidosis.

The diagnosis of cardiac sarcoidosis (CS) is challenging. Recently, guidelines incorporated cardiac positron emission tomography (PET) with 18F-Fluorodeoxyglucose (F18-FDG) as a non-invasive diagnostic modality for the detection and follow-up of CS. However, this technique is dependent of patient dietary preparation to suppress physiological myocardial F18-FDG uptake. We present a case of possible CS which highlights a novel preparation protocol that facilitated appropriate myocardial suppression.

Update on the PennPET Explorer: A Whole-body Imager with Scalable Axial Field-of-View.

Following successful performance testing and human imaging of a prototype PennPET Explorer, the scanner has been expanded to a current axial field of view of 1.12 m. Initial studies on this instrument have demonstrated encouraging results for total-body positron emission tomography imaging. Planned studies will test the capabilities of the PennPET Explorer further and inform the design of further human imaging protocols.

Scanner Design Considerations for Long Axial Field-of-View PET Systems.

This article describes aspects of PET scanner design for long axial field-of-view systems and how these choices have an impact on scanner performance.

A validated Geant4 model of a whole-body PET scanner with four-layer DOI detectors.

The purpose of this work is to develop a validated Geant4 simulation model of a whole-body prototype PET scanner constructed from the four-layer depth-of-interaction detectors developed at the National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Japan. The simulation model emulates the behaviour of the unique depth of interaction sensing capability of the scanner without needing to directly simulate optical photon transport in the scintillator and photodetector modules. The model was validated by evaluating and comparing performance metrics from the NEMA NU 2-2012 protocol on both the simulated and physical scanner, including spatial resolution, sensitivity, scatter fraction, noise equivalent count rates and image quality. The results show that the average sensitivities of the scanner in the field-of-view were 5.9 cps kBq-1 and 6.0 cps kBq-1 for experiment and simulation, respectively. The average spatial resolutions measured for point sources placed at several radial offsets were 5.2± 0.7 mm and 5.0± 0.8 mm FWHM for experiment and simulation, respectively. The peak NECR was 22.9 kcps at 7.4 kBq ml-1 for the experiment, while the NECR obtained via simulation was 23.3 kcps at the same activity. The scatter fractions were 44% and 41.3% for the experiment and simulation, respectively. Contrast recovery estimates performed in different regions of a simulated image quality phantom matched the experimental results with an average error of -8.7% and +3.4% for hot and cold lesions, respectively. The results demonstrate that the developed Geant4 model reliably reproduces the key NEMA NU 2-2012 performance metrics evaluated on the prototype PET scanner. A simplified version of the model is included as an advanced example in Geant4 version 10.5.