The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Sibylle Ziegler - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the attenuation properties of mr equipment for its use in a whole body pet mr scanner
Physics in Medicine and Biology, 2010Co-Authors: Gaspar Delso, Axel Martinezmoller, Ralph A Bundschuh, Ralf Ladebeck, Y Candidus, David Faul, Sibylle ZieglerAbstract:The combination of magnetic resonance imaging (MR) and positron emission tomography (PET) scanners can provide a powerful tool for clinical diagnosis and investigation. Among the challenges of developing a combined scanner, obtaining attenuation maps for PET reconstruction is of critical importance. This requires accounting for the presence of MR hardware in the field of view. The attenuation introduced by this hardware cannot be obtained from MR data. We propose the creation of attenuation models of MR hardware, to be registered into the MR-based attenuation map prior to PET reconstruction. Two steps were followed to assess the viability of this method. First, transmission and emission measurements were performed on MR components (RF coils and medical probes). The severity of the artifacts in the reconstructed PET images was evaluated. Secondly, a high-exposure computed tomography (CT) scan was used to obtain a model of a head coil. This model was registered into the attenuation map of PET/CT scans of a uniform phantom fitted with the coil. The resulting PET images were compared to the PET/CT reconstruction in the absence of coils. The artifacts introduced by misregistration of the model were studied. The transmission scans revealed 17% count loss due to the presence of head and neck coils in the field of view. Important sources of attenuation were found in the Lock, Signal cables and connectors. However, the worst source of attenuation was the casing between both coils. None of the measured medical probes introduced a significant amount of attenuation. Concerning the attenuation model of the head coil, reconstructed PET images with model-based correction were comparable to the reference PET/CT reconstruction. However, inaccuracies greater than 1-2 mm in the axial positioning of the model led to important artifacts. In conclusion, the results show that model-based attenuation correction is possible. Using a high-exposure scan to create an attenuation model of the coils has been proved feasible. However, adequate registration of the model is mandatory.
A Kumarakrishnan - One of the best experts on this subject based on the ideXlab platform.
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characterization and applications of auto Locked vacuum sealed diode lasers for precision metrology
Review of Scientific Instruments, 2019Co-Authors: H C Beica, Alex Pouliot, A Carew, A Vorozcovs, N Afkhamijeddi, T Vacheresse, G Carlse, P Dowling, B Barron, A KumarakrishnanAbstract:We demonstrate the performance characteristics of a new class of vacuum-sealed, autoLocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autoLocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autoLocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the Lock Signal. We find that the ADEV floor of 2 × 10−12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducing the current noise and cavity pressure decreases the ADEV floor and increases the averaging time at which the floor occurs, which is a signature of long-term stability. We also show that evacuating the cavity to ∼1 Torr reduces the range of the correction Signal of the feedback loop by approximately one order of magnitude, thereby increasing the Lock range of the controller. The long-term stability allows the laser to be incorporated into a commercial gravimeter for accurate measurements of gravitational acceleration at the level of a few parts-per-billion, which are comparable to values obtained with an iodine-stabilized He–Ne laser. The autoLocking and pattern-matching features of the controller allow the laser to be tuned and stabilized with respect to a temperature tunable transmission spectrum of a fiber-Bragg grating. This capability may be suitable for the development of a differential absorption LIDAR transmitter that can generate data at both on-line and off-line Lock points using a single laser.We demonstrate the performance characteristics of a new class of vacuum-sealed, autoLocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autoLocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autoLocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the Lock Signal. We find that the ADEV floor of 2 × 10−12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducin...
Barron B. - One of the best experts on this subject based on the ideXlab platform.
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Characterization and applications of auto-Locked vacuum-sealed diode lasers for precision metrology
'AIP Publishing', 2019Co-Authors: Kumarakrishnan Anantharaman, Beica Hermina, Pouliot Alexander, Carew A., Vorozcovs A., Afkhami-jeddi N., Vacheresse T., Carlse G., Dowling P., Barron B.Abstract:We demonstrate the performance characteristics of a new class of vacuum-sealed, autoLocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autoLocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autoLocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the Lock Signal. We find that the ADEV floor of 2 × 10−12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducing the current noise and cavity pressure decreases the ADEV floor and increases the averaging time at which the floor occurs, which is a signature of long-term stability. We also show that evacuating the cavity to ∼1 Torr reduces the range of the correction Signal of the feedback loop by approximately one order of magnitude, thereby increasing the Lock range of the controller. The long-term stability allows the laser to be incorporated into a commercial gravimeter for accurate measurements of gravitational acceleration at the level of a few parts-per-billion, which are comparable to values obtained with an iodine-stabilized He–Ne laser. The autoLocking and pattern-matching features of the controller allow the laser to be tuned and stabilized with respect to a temperature tunable transmission spectrum of a fiber-Bragg grating. This capability may be suitable for the development of a differential absorption LIDAR transmitter that can generate data at both on-line and off-line Lock points using a single laser
Gaspar Delso - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the attenuation properties of mr equipment for its use in a whole body pet mr scanner
Physics in Medicine and Biology, 2010Co-Authors: Gaspar Delso, Axel Martinezmoller, Ralph A Bundschuh, Ralf Ladebeck, Y Candidus, David Faul, Sibylle ZieglerAbstract:The combination of magnetic resonance imaging (MR) and positron emission tomography (PET) scanners can provide a powerful tool for clinical diagnosis and investigation. Among the challenges of developing a combined scanner, obtaining attenuation maps for PET reconstruction is of critical importance. This requires accounting for the presence of MR hardware in the field of view. The attenuation introduced by this hardware cannot be obtained from MR data. We propose the creation of attenuation models of MR hardware, to be registered into the MR-based attenuation map prior to PET reconstruction. Two steps were followed to assess the viability of this method. First, transmission and emission measurements were performed on MR components (RF coils and medical probes). The severity of the artifacts in the reconstructed PET images was evaluated. Secondly, a high-exposure computed tomography (CT) scan was used to obtain a model of a head coil. This model was registered into the attenuation map of PET/CT scans of a uniform phantom fitted with the coil. The resulting PET images were compared to the PET/CT reconstruction in the absence of coils. The artifacts introduced by misregistration of the model were studied. The transmission scans revealed 17% count loss due to the presence of head and neck coils in the field of view. Important sources of attenuation were found in the Lock, Signal cables and connectors. However, the worst source of attenuation was the casing between both coils. None of the measured medical probes introduced a significant amount of attenuation. Concerning the attenuation model of the head coil, reconstructed PET images with model-based correction were comparable to the reference PET/CT reconstruction. However, inaccuracies greater than 1-2 mm in the axial positioning of the model led to important artifacts. In conclusion, the results show that model-based attenuation correction is possible. Using a high-exposure scan to create an attenuation model of the coils has been proved feasible. However, adequate registration of the model is mandatory.
H C Beica - One of the best experts on this subject based on the ideXlab platform.
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characterization and applications of auto Locked vacuum sealed diode lasers for precision metrology
Review of Scientific Instruments, 2019Co-Authors: H C Beica, Alex Pouliot, A Carew, A Vorozcovs, N Afkhamijeddi, T Vacheresse, G Carlse, P Dowling, B Barron, A KumarakrishnanAbstract:We demonstrate the performance characteristics of a new class of vacuum-sealed, autoLocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autoLocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autoLocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the Lock Signal. We find that the ADEV floor of 2 × 10−12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducing the current noise and cavity pressure decreases the ADEV floor and increases the averaging time at which the floor occurs, which is a signature of long-term stability. We also show that evacuating the cavity to ∼1 Torr reduces the range of the correction Signal of the feedback loop by approximately one order of magnitude, thereby increasing the Lock range of the controller. The long-term stability allows the laser to be incorporated into a commercial gravimeter for accurate measurements of gravitational acceleration at the level of a few parts-per-billion, which are comparable to values obtained with an iodine-stabilized He–Ne laser. The autoLocking and pattern-matching features of the controller allow the laser to be tuned and stabilized with respect to a temperature tunable transmission spectrum of a fiber-Bragg grating. This capability may be suitable for the development of a differential absorption LIDAR transmitter that can generate data at both on-line and off-line Lock points using a single laser.We demonstrate the performance characteristics of a new class of vacuum-sealed, autoLocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autoLocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autoLocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the Lock Signal. We find that the ADEV floor of 2 × 10−12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducin...
