An accurate, low noise estimate of photon attenuation in the subject is required for quantitative microPET studies of molecular tracer distributions in vivo. In this work, several transmission-based ...measurement techniques were compared, including coincidence mode with and without rod windowing, singles mode with two different energy sources ((68)Ge and (57)Co), and postinjection transmission scanning. In addition, the effectiveness of transmission segmentation and the propagation of transmission bias and noise into the emission images were examined. The (57)Co singles measurements provided the most accurate attenuation coefficients and superior signal-to-noise ratio, while (68)Ge singles measurements were degraded due to scattering from the object. Scatter correction of (68)Ge transmission data improved the accuracy for a 10 cm phantom but over-corrected for a mouse phantom. (57)Co scanning also resulted in low bias and noise in postinjection transmission scans for emission activities up to 20 MBq. Segmentation worked most reliably for transmission data acquired with (57)Co but the minor improvement in accuracy of attenuation coefficients and signal-to-noise may not justify its use, particularly for small subjects. We conclude that (57)Co singles transmission scanning is the most suitable method for measured attenuation correction on the microPET Focus 220 animal scanner.
Band 1. Birgitta Fuchs: Geschichte des pädagogischen Denkens. ISBN 978-3-8252-5270-0. Band 2. Peter Vogel: Grundbegriffe der Erziehungs- und Bildungswissenschaft. ISBN 978-3-8252-5271-7. Band 3. ...Heinz-Hermann Krüger: Erziehungs- und Bildungswissenschaft als Wissenschaftsdisziplin. ISBN 978-3-8252-5272-4. Band 4. Arnd-Michael Nohl: AdressatInnen und Handlungsfelder der Pädagogik. ISBN 978-3-8252-5273-1.
Lightweight PET Calibration Source Hamill, James J.; Siegel, Stefan
2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC),
2019-Oct.
Conference Proceeding
PET scanners are commonly calibrated with cylindrical sources, about 20 cm in diameter, in which positron-emitting radioactivity is mixed. The sources are heavy and may require massive shielding for ...storage. In this work we ask if scanner setup can instead be based on hollow, lightweight sources based on small beta sources and positron flight across the air, reducing the shielding requirements, and providing a nearly scatter-free source with negligible photon attenuation. A set of two positron-emitting (beta) sources was created by depositing a 0.7-mm layer of polyurethane resin, containing a total of 42.6 MBq 68 Ge on two copper plates. We also created a second set of sources by depositing a 6-mm spot of 68 Ge DTPA on each of two steel plates. These were positioned inside a hollow polyethylene cylinder with 21.3 cm outer diameter, 32 cm length and 7 mm wall thickness. The sources were at the cylinder's two flat ends. Depending on the positrons' direction after beta decay, the positrons either stopped in the beta source or flew across the air until they encountered the cylinder's walls, causing the emission of annihilation radiation. The cylinder was positioned in an SiPM-based PET/CT scanner. PET scans and a time of flight (TOF) calibration were performed. Fused PET/CT images showed that positrons stopped both in the cylinder's inner wall (33% and 18% of all positrons emitted by the first source and sets of sources, respectively) and in the air inside the cylinder (5% and 2%). Standard software was used to measure 211 ps TOF resolution, comparable to the value derived from traditional extended sources. Because the positron sources are small, they can be easily shielded, eliminating the need for more than 100 kg of shielding. A lightweight, hollow, scatter and attenuation-free source appears to be a practical alternative to the current state of the art.
Performance Evaluation of the microPET registered -FOCUS-F120 Richard Laforest, Richard Laforest; Desmond Longford, Desmond Longford; Stefan Siegel, Stefan Siegel ...
IEEE transactions on nuclear science,
01/2007, Letnik:
54, Številka:
1
Journal Article
Recenzirano
microPETreg-Focus-F120 is the latest model of dedicated small animal PET scanners from CTI-Concorde Microsystems LLC, (Knoxville, TN). This scanner, based on the geometry of the microPET-R4, takes ...advantage of several detector modifications to the coincidence processing electronics that improve the image resolution, sensitivity, and counting rate performance as compared to the predecessor models. This work evaluates the performance of the Focus-F120 system and shows its improvement over the earlier models. In particular, the spatial resolution is shown to improve from 2.32 to 1.69 mm at 5 mm radial distance and the peak absolute sensitivity increases from 4.1% to 7.1% compared to the microPET-R4. The counting rate capability, expressed in noise equivalent counting rate (NEC-1R), was shown to peak at over 800 kcps at 88 MBq for both systems using a mouse phantom. For this small phantom, the NECR counting rate is limited by the data transmission bandwidth between the scanner and the acquisition console. The rat-like phantom showed peak NEC-1R value at 300 kcps at 140 MBq. Evaluation of image quality and quantitation accuracy was also performed using specially designed phantoms and animal experiments
A new instrument for simultaneous microbeam small‐ and wide‐angle X‐ray scattering and X‐ray fluorescence (SAXS/WAXS/XRF) is presented. The instrument is installed at the microfocus beamline at BESSY ...II and provides a beam of 10 µm size with a flux of about 109 photons s−1. A SAXS resolution up to 500 Åd‐spacing and a range of scattering vectors of almost three orders of magnitude are reached by using a large‐area high‐resolution CCD‐based detector for simultaneous SAXS/WAXS. The instrument is particularly suited for scanning SAXS/WAXS/XRF experiments on hierarchically structured biological tissues. The necessary infrastructure, such as a cryo‐stream facility and an on‐site preparation laboratory for biological specimens, are available.
Plant cystoliths are mineralized objects that are formed by specialized cells in the leaves of certain plants. The main mineral component of cystoliths by volume is amorphous calcium carbonate (ACC) ...and the minor component is silica. We show that the silica stalk is formed first and is essential for ACC formation. Furthermore, the cystolith is shown to be composed of four distinct mineral phases with different chemical properties: an almost pure silica phase grades into a Mg‐rich silica phase. This Mg‐rich silica is overlaid by a relatively stable ACC phase. A bulky and less stable ACC phase encapsulates the first ACC phase. This architecture poses interesting questions about the role of Mg in the silica phase and suggests a strategy for ACC stabilization that takes advantage of a precise regulation of the mineral‐growth microenvironment.
The fantastic four: Cystoliths are mineralized objects that are mainly composed of amorphous calcium carbonate (ACC), which is found in the leaves of several plants. They have a unique composition and architecture of four distinct amorphous phases. A Mg‐rich silica phase is essential for the formation of two distinct ACC phases. The inner ACC phase has inherently higher stability, presumably required by the sequential formation mechanism.
In situ X‐ray diffraction during heating of lobster cuticle reveals three regions of thermally induced transformations: 1)Chitin decomposition, 2) amorphous calcium carbonate (ACC) – calcite ...transformation, and 3) amorphous calcium phosphate (ACP) – hydroxyapatite transformation. These results provide new insights into the stabilization mechanisms of amorphous biominerals based on ACC and ACP.
The microPET Focus is the latest generation microPET system dedicated to high-resolution animal imaging and incorporates several changes to enhance its performance. This study evaluated the basic ...performance of the scanner and compared it with the Primate (P4) and Rodent (R4) models.
The system consists of 168 lutetium oxyorthosilicate (LSO) detectors arranged in 4 contiguous rings, with a 25.8-cm diameter and a 7.6-cm axial length. Each detector consists of a 12 x 12 LSO crystal array of 1.51 x 1.51 x 10.00 mm3 elements. The scintillation light is transmitted to position-sensitive photomultiplier tubes via optical fiber bundles. The system was evaluated for its energy and spatial resolutions, sensitivity, and noise equivalent counting rate. Phantoms and animals of varying sizes were scanned to evaluate its imaging capability.
The energy resolution averages 18.5% for the entire system. Reconstructed image resolution is 1.3-mm full width at half maximum (FWHM) at the center of field of view (CFOV) and remains under 2 mm FWHM within the central 5-cm-diameter FOV in all 3 dimensions. The absolute sensitivity of the system is 3.4% at the CFOV for an energy window of 250-750 keV and a timing window of 10 ns. The noise equivalent counting-rate performance reaches 645 kcps for a mouse-size phantom using 250- to 750-keV and 6-ns settings. Emission images of a micro-Derenzo phantom demonstrate the improvement in image resolution compared with previous models. Animal studies exhibit the capability of the system in studying disease models using mouse, rat, and nonhuman primates.
The Focus has significantly improved performance over the previous models in all areas evaluated. This system represents the state-of-the-art scintillator-based animal PET scanner currently available and is expected to advance the potential of small animal PET.
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