| 1. |
- Fröjdh, Erik, 1984-, et al.
(författare)
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Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
- 2012
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Ingår i: 2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC). - : IEEE conference proceedings. - 9781467320306 - 9781467320283 ; , s. 4233-4236
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-threshold mode. The time-over-threshold mode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects and indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out in the Extreme Conditions Beamline I15 at Diamond Light Source.
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| 2. |
- Holmberg, Daniel, et al.
(författare)
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Reducing scanning time to 50% for In-111 pentetreotide SPECT when using model-based compensation
- 2012
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Ingår i: 2012 IEEE nuclear science symposium and medical imaging conference record (NSS/MIC). - : IEEE. - 9781467320306 - 9781467320283 ; , s. 2946-2949
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Konferensbidrag (refereegranskat)abstract
- In In-111-pentetreotide SPECT, it can be difficult to detect small tumors because of high noise levels and low spatial resolution. The aim of this study was to perform optimization of tumor detection in the liver, with regards to the acquisition and reconstruction protocol for In-111-pentetreotide SPECT with model-based compensation included in the OSEM reconstruction. We were also interested in the effect of performing the examination in half of the time or with half the administered activity. Image reconstruction without model-based compensation was also included for comparison. The study concentrates on the acquired number of projections and the subset size in the OSEM reconstruction, and evaluates contrast as a function of noise for a range of OSEM iterations. The raw-data projections are produced using Monte Carlo simulations of a patient-like anthropomorphic phantom with realistic In-111 pentetreotide uptake, including spherical tumors in the liver. Two collimators are evaluated, the extended low-energy general-purpose (ELEGP) and the medium-energy general-purpose (MEGP) collimator. ELEGP proved to be a better collimator when using model-based compensation. The results also indicate that a relatively low number of subsets is advantageous, and that 60 projection angles or even lower is a better choice than 120. For both collimators the time-reduced scan including model-based compensation was better compared to the full-time reconstructions without model-based compensation.
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| 3. |
- Häggström, Ida, et al.
(författare)
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The influence of time sampling scheme on kinetic parameters obtained from compartmental modeling of a dynamic PET study : a Monte Carlo study
- 2012
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Ingår i: IEEE Nuclear Science Symposium Conference Record. - Anaheim : IEEE conference proceedings. - 9781467320306 ; , s. 3101-3107
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Konferensbidrag (refereegranskat)abstract
- Compartmental modeling of dynamic PET data enables quantification of tracer kinetics in vivo, through the obtained model parameters. The dynamic data is sorted into frames during or after the acquisition, with a sampling interval usually ranging from 10 s to 300 s. In this study we wanted to investigate the effect of the chosen sampling interval on kinetic parameters obtained from a 2-tissue model, in terms of bias and standard deviation, using a complete Monte Carlo simulated dynamic F-18-FLT PET study. The results show that the bias and standard deviation in parameter K-1 is small regardless of sampling scheme or noise in the time-activity curves (TACs), and that the bias and standard deviation in k(4) is large for all cases. The bias in V-a is clearly dependent on sampling scheme, increasing for increased sampling interval. In general, a too short sampling interval results in very noisy images and a large bias of the parameter estimate, and a too long sampling interval also increases bias. Noise in the TACs is the largest source of bias.
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| 4. |
- Klamra, Wlodzimierz, et al.
(författare)
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Study of undoped CeF3 scintillators at room and liquid nitrogen temperature
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference record (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 315-317
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Konferensbidrag (refereegranskat)abstract
- In this paper properties of various undoped CeF3 scintillators were investigated at room and liquid nitrogen (LN2) temperature. The study was focused on measurements of radioluminescence spectra, decay time, non-proportional response on X- and γ-rays and energy resolution at different temperature environment. Surprisingly, the pure CeF3 crystals show comparable non-proportionality curves, which are very similar to that presented by inorganic scintillators. The investigation of the phenomenon occurring in CeF3 scintillators would be another step to get a better knowledge of the scintillators nature, which still haven't been entirely understood.
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| 5. |
- Pearce, Mark, et al.
(författare)
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Balloon-borne hard X-ray polarimetry with PoGOLite
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 1885-1892
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Konferensbidrag (refereegranskat)abstract
- PoGOLite is a hard X-ray polarimeter operating in the 25-100 keV energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-X1. The polarisation of incoming photons is determined using coincident Compton scattering and photo-absorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.
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| 6. |
- Ren, Wuwei, et al.
(författare)
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Stationary SPECT with multi-layer multiple-pinhole-arrays
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 2594-2597
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Konferensbidrag (refereegranskat)abstract
- The potential of Multiple Pinhole Arrays (MPA) collimators for developing a Single Photon Emission Computer Tomography (SPECT) system without rotating or moving elements is investigated. A four layer arrangement is proposed and the system performance is evaluated using the simulation toolkit GATE [1]. For a camera with a field of view (FOV) of the order of a human brain (a sphere of radius 100 mm), a sensitivity of 86, 0 cps/MBq and an overall resolution of 5 mm have been estimated, indicating that performances comparable to traditional parallel-hole-collimator cameras can be achieved.
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| 7. |
- Turco, Anna, et al.
(författare)
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Modular miniPET : A comparison between 10 and 12 detector modules
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 2598-2602
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Konferensbidrag (refereegranskat)abstract
- By means of computer simulations, scatter fraction, spatial resolution and sensitivity of two 10-detector-module small-animal PET (r77-miniPET and r106-miniPET), are analyzed and compared to the performance of the 12-detector-module PET scanner miniPET II [1]. All simulations have been performed with the well validated Geant4 Application for Emission Tomography (GATE) [2]. Sensitivity and scatter fraction speak in favor of the 10-module scanner: a clear improvement in count rate and scatter fraction was found. Moreover, steeper slopes of noise equivalent count rate curves at low levels of activity was found. Spatial resolution instead was found to be better in the 12-module scanner.
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| 8. |
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| 9. |
- Valastyán, Iván, et al.
(författare)
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Novel time over threshold based readout method for MRI compatible small animal PET detector
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 1295-1299
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Konferensbidrag (refereegranskat)abstract
- Combined PET-MRI scanners start a new era in medical imaging. However the development of MRI compatible PET detector module is a challenging task. SiPM sensors are insensitive to magnetic field and constitute a promising solution. A drawback is the high dark current. A readout concept for SiPM based small animal PET detector module is presented in this paper. The results show that the readout of the SiPM is possible using only four ADC channels and the position map is comparable to the ideal solution. The detector modules based on the method are feasible solution for MRI compatible PET scanners.
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