In humans, action errors and perceptual novelty elicit activity in a shared frontostriatal brain ... more In humans, action errors and perceptual novelty elicit activity in a shared frontostriatal brain network, allowing them to adapt their ongoing behavior to such unexpected action outcomes. Healthy and pathologic aging reduces the integrity of white matter pathways that connect individual hubs of such networks and can impair the associated cognitive functions. Here, we investigated whether structural disconnection within this network because of small-vessel disease impairs the neural processes that subserve motor slowing after errors and novelty (post-error slowing, PES; post-novel slowing, PNS). Participants with intact frontostriatal circuitry showed increased right-lateralized beta-band (12-24 Hz) synchrony between frontocentral and frontolateral electrode sites in the electroencephalogram after errors and novelty, indexing increased neural communication. Importantly, this synchrony correlated with PES and PNS across participants. Furthermore, such synchrony was reduced in participants with frontostriatal white matter damage, in line with reduced PES and PNS. The results demonstrate that behavioral change after errors and novelty result from coordinated neural activity across a frontostriatal brain network and that such cognitive control is impaired by reduced white matter integrity.
Medical Imaging 2011: Physics of Medical Imaging, 2011
Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (... more Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (CT) as they have the potential to overcome some of the most significant limitations of current CT with energy integrating detectors. Among these are: insufficient tissue contrast, relatively high radiation dose, tissue non-specificity, and the non-quantitative nature. In contrast, CT with PCXDs has shown promise in producing higher contrast, tissue specific, quantitative images at lower dose. Novel applications for PCXDs include k-edge and functional imaging and material decomposition. A limiting factor, however, is the high photon flux that occurs in clinical applications resulting in signal pulse pile up in the detector. Faster detectors and new strategies for data corrections and image reconstruction algorithms are needed to overcome these limitations. A research tabletop x-ray CT scanner was developed with the following aims: 1) to characterize and calibrate the PCXD; 2) to acquire CT projection data under conditions similar to those of clinical CT; and 3) to reconstruct images using correction schemes specific for PCXDs. The scanner employs a commercial clinical x-ray tube, a PCXD with two energy thresholds, and allows scanning of objects of up to 40 cm in diameter. This paper presents measurements of detector quantities crucial for data corrections and calibration, such as energy response, deadtime, and count rates. Reconstructed CT images are presented and qualitative results from material decomposition are shown.
ABSTRACT A calibration technique as well as measurement results for a 7 GHz Biosensor are present... more ABSTRACT A calibration technique as well as measurement results for a 7 GHz Biosensor are presented. It is shown that the applied sensor structure can be calibrated by adjusting the phase of a sensing element's transmission S21. This is realized by slowing down the wave traveling a microstrip line serving as a reference in the differential sensor structure. The dielectric properties along with certain physical boundaries of an obstacle covering parts of the microstrip line evoke that effect. Measurements with an ethanol serious along with simulation results showed that sensitivity can be increased substantially with this calibration technique. A change of the real part of the sample's permittivity of 48 leads to a 18 MHz frequency shift.
Experimental results of contactless and label-free characterization techniques of cell cultivatio... more Experimental results of contactless and label-free characterization techniques of cell cultivation are presented. The two demonstrated approaches are compared at two frequencies, 7 GHz and 240 GHz in terms of sensitivity and applicability. At 7 GHz, measurements have been performed using a rat-race based characterizing system. Furthermore, the sensitivity of spectroscopy measurements at 240 GHz has been compared for two extracted parameters: phase and amplitude. The conducted experiments demonstrate that by selecting the proper characterization parameter, the presented techniques are suitable for cell cultivation monitoring in a pipe based microfluidic system with PTFE tubes. Especially, the use of higher frequencies enables a higher compactness.
Developments in room temperature cadmium telluride (CdTe) based solid state imaging arrays for en... more Developments in room temperature cadmium telluride (CdTe) based solid state imaging arrays for energy-resolved photon-counting in medical x-ray imaging are discussed. A number of x-ray imaging applications can benefit from these developments including mammography, radiography, and computed tomography (CT). Energy-resolved photon-counting can provide reduced dose through optimal energy weighting, compositional analysis through multiple basis function material decomposition, and contrast enhancement through spectroscopic x-ray imaging of metal nanoparticles. Extremely high flux can occur in x-ray imaging and energy integrating detectors have been conventionally used. To achieve the benefits of energy resolved photon counting, imaging arrays with a large count rate range and good detection efficiency are required. Compound semiconductor radiation detectors with pixellated anode arrays electrically connected to application specific integrated circuits (ASICs) can provide fast, efficient, low-noise performance with adequate energy resolution however this can only be achieved with a careful optimization of the CdTe sensors and ASICs together. We have designed and constructed CdTe imaging arrays, 3 mm thick with a grid of electrical contacts inter-connected to a multi-channel channel ASICs. Arrays with a pixel pitch of 0.5 mm have achieved a counting range up to 20 million counts per second per square mm. Additionally, ASICs with a two dimensional array of pads has been fabricated and tested by connecting the inputs to 1 mm pitch CdTe sensors demonstrating 7 keV full width at half maximum energy resolution across a dynamic range of 30 keV to 140 keV for clinical CT.
IEEE Nuclear Science Symposuim & Medical Imaging Conference, 2010
Page 1. Photon-counting energy-resolving CdTe detectors for high-flux x-ray imaging William C. Ba... more Page 1. Photon-counting energy-resolving CdTe detectors for high-flux x-ray imaging William C. Barber, Member, IEEE, Einar Nygard, Jan C. Wessel, Nail Malakhov, Neal E. Hartsough, Member, IEEE, Thulasi Gandhi, Member ...
2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications (ANIMMA), 2013
ABSTRACT We have fabricated fast room-temperature energy dispersive photon counting x-ray imaging... more ABSTRACT We have fabricated fast room-temperature energy dispersive photon counting x-ray imaging arrays using pixellated cadmium zinc (CdTe) and cadmium zinc telluride (CdZnTe) semiconductors. We have also fabricated fast application specific integrated circuits (ASICs) with a two dimensional (2D) array of inputs for readout from the CdZnTe sensors. The new CdTe and CdZnTe sensors have a 2D array of pixels with a 0.5 mm pitch and can be tiled in 2D. The new 2D ASICs have four energy discriminators per pixel with a linear energy response across the entire dynamic range for clinical CT. The ASICs can also be tiled in 2D and are designed to fit within the active area of the 2D sensors. We have measured several important performance parameters including; an output count rate (OCR) in excess of 20 million counts per second per square mm, an energy resolution of 7 keV full width at half maximum (FWHM) across the entire dynamic range, and a noise floor less than 20 keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdTE and CdZnTe sensors incurring very little additional capacitance. We present a comparison of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, and noise floor.
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
Semiconductor radiation detectors are a promising technology for single photon counting detectors... more Semiconductor radiation detectors are a promising technology for single photon counting detectors. Unlike scintillator-based indirect radiation detectors, semiconductor detectors directly convert absorbed photons to charge, thereby reducing energy spreading and signal loss that can occur in scintillator-based detectors. Cadmium telluride (CdTe) has attracted research interest due to its higher stopping power compared to other semiconductors such as germanium and silicon as well as its room-temperature operating capability. A CdTe photon-counting, energy-resolving detector system has been developed for x-ray and radionuclide imaging, and is capable of discriminating incident photon energy using multiple voltage thresholds per detector element with fast signal formation. Using this CdTe detector, a reproducible method of generating energy spectra was developed for a given incident radiation source. The energy resolution of the CdTe detector was determined by generating the energy spectra of three radiation sources.
Medical Imaging 2009: Physics of Medical Imaging, 2009
We report on a characterization study of a multi-row direct-conversion x-ray detector used to gen... more We report on a characterization study of a multi-row direct-conversion x-ray detector used to generate the first photon counting clinical x-ray computed tomography (CT) patent images. In order to provide the photon counting detector with adequate performance for low-dose CT applications, we have designed and fabricated a fast application specific integrated circuit (ASIC) for data readout from the pixellated CdTe detectors that comprise the photon counting detector. The cadmium telluride (CdTe) detector has 512 pixels with a 1 mm pitch and is vertically integrated with the ASIC readout so it can be tiled in two dimensions similar to those that are tiled in an arc found in 32-row multi-slice CT systems. We have measured several important detector parameters including the maximum output count rate, energy resolution, and noise performance. Additionally the relationship between the output and input rate has been found to fit a non-paralyzable detector model with a dead time of 160 nsec. A maximum output rate of 6 × 10 6 counts per second per pixel has been obtained with a low output x-ray tube for CT operated between 0.01 mA and 6 mA at 140 keV and different source-to-detector distances. All detector noise counts are less that 20 keV which is sufficiently low for clinical CT. The energy resolution measured with the 60 keV photons from a 241 Am source is ~12%. In conclusion, our results demonstrate the potential for the application of the CdTe based photon counting detector to clinical CT systems. Our future plans include further performance improvement by incorporating drift structures to each detector pixel.
Medical Imaging 2010: Physics of Medical Imaging, 2010
We report results from the development of a second-generation CdTe direct-conversion compound-sem... more We report results from the development of a second-generation CdTe direct-conversion compound-semiconductor x-ray detector for photon-counting clinical CT. The first-generation detector has 512 pixels with a 1 mm pitch and is vertically integrated with the readout. A 32-row multi-slice CT system using first-generation detectors has been used for clinical low-dose CT applications. To provide adequate performance for whole-body diagnostic CT
We have fabricated a fast energy-resolved photon-counting x-ray imaging array using pixellated ca... more We have fabricated a fast energy-resolved photon-counting x-ray imaging array using pixellated cadmium telluride (CdTe) semiconductor sensors and have achieved an output count rate (OCR) exceeding 20 million counts per second per square mm (Mcps/mm2) measured with a clinical computed tomography (CT) x-ray source. We have also fabricated a fast application specific integrated circuit (ASIC) with a two dimensional (2D)
Medical Applications of Radiation Detectors II, 2012
ABSTRACT Developments in room temperature solid state imaging arrays for energy-resolved single p... more ABSTRACT Developments in room temperature solid state imaging arrays for energy-resolved single photon counting in medical x-ray imaging are discussed. A number of x-ray imaging applications can benefit from these developments including mammography which requires very good spatial resolution. Energy resolved photon counting can provide reduced dose through optimal energy weighting and compositional analysis through multiple basis function material decomposition. Extremely high flux can occur in x-ray imaging and energy integrating detectors with a large dynamic range and good detection efficiency have been conventionally used. To achieve the benefits of energy resolved photon counting, imaging arrays with a large count rate range and good detection efficiency are required. Si based semiconductor radiation detectors with strip anode arrays electrically connected to application specific integrated circuits (ASICs) can provide fast, efficient, low-noise performance with good energy and spatial resolution for use in mammography however this can only be achieved with a careful optimization of the Si sensors and ASICs together. We have designed and constructed a Si imaging array, with a 1 x 1024 grid of electrical 100 micron wide strip contacts inter connected to multi channel ASICs, with a counting range up to 1 x 106 counts per second per pixel.
Medical Applications of Radiation Detectors III, 2013
ABSTRACT We report on our efforts toward the development of silicon (Si) strip detectors for ener... more ABSTRACT We report on our efforts toward the development of silicon (Si) strip detectors for energy-resolved clinical breast imaging. Typically, x-ray integrating detectors based on scintillating cesium iodide CsI(Tl) or amorphous selenium (a- Se) are used in most commercial systems. Recently, mammography instrumentation has been introduced based on photon counting silicon Si strip detectors. Mammography requires high flux from the x-ray generator, therefore, in order to achieve energy resolved single photon counting, a high output count rate (OCR) for the detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel, provided that the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions. We present our methods and results from the optimization of prototype detectors based on Si strip structures. We describe the detector optimization and the development of ASIC readout electronics that provide the required spatial resolution, low noise, high count rate capabilities and minimal power consumption.
We report on methods for optimizing room temperature semi-conductor detectors for energy-resolved... more We report on methods for optimizing room temperature semi-conductor detectors for energy-resolved x-ray imaging in radiology including applications such as computed tomography (CT), dual-energy x-ray absorptiometry (DEXA), and mammography. These applications produce high input count rates from an x-ray generator delivered to the detector. Room temperature semiconductors, operating as direct conversion x-ray sensors, can provide the required photon counting speed
According to recent accounts, the processing of errors and generally infrequent, surprising (nove... more According to recent accounts, the processing of errors and generally infrequent, surprising (novel) events share a common neuroanatomical substrate. Direct empirical evidence for this common processing network in humans is, however, scarce. To test this hypothesis, we administered a hybrid error-monitoring/novelty-oddball task in which the frequency of novel, surprising trials was dynamically matched to the frequency of errors. Using scalp electroencephalographic recordings and event-related functional magnetic resonance imaging (fMRI), we compared neural responses to errors with neural responses to novel events. In Experiment 1, independent component analysis of scalp ERP data revealed a common neural generator implicated in the generation of both the error-related negativity (ERN) and the novelty-related frontocentral N2. In Experiment 2, this pattern was confirmed by a conjunction analysis of event-related fMRI, which showed significantly elevated BOLD activity following both types of trials in the posterior medial frontal cortex, including the anterior midcingulate cortex (aMCC), the neuronal generator of the ERN. Together, these findings provide direct evidence of a common neural system underlying the processing of errors and novel events. This appears to be at odds with prominent theories of the ERN and aMCC. In particular, the reinforcement learning theory of the ERN may need to be modified because it may not suffice as a fully integrative model of aMCC function. Whenever course and outcome of an action violates expectancies (not necessarily related to reward), the aMCC seems to be engaged in evaluating the necessity of behavioral adaptation.
An arrow version of the Eriksen flanker task was employed to investigate the influence of conflic... more An arrow version of the Eriksen flanker task was employed to investigate the influence of conflict on the error-related negativity (ERN). The degree of conflict was modulated by varying the distance between flankers and the target arrow (CLOSE and FAR conditions). Error rates and reaction time data from a behavioral experiment were used to adapt a connectionist model of this task. This model was based on the conflict monitoring theory and simulated behavioral and event-related potential data. The computational model predicted an increased ERN amplitude in FAR incompatible (the low-conflict condition) compared to CLOSE incompatible errors (the high-conflict condition). A subsequent ERP experiment confirmed the model predictions. The computational model explains this finding with larger postresponse conflict in far trials. In addition, data and model predictions of the N2 and the LRP support the conflict interpretation of the ERN.
Using a microfluidic system based on PTFE tubes, experimental results of contactless and label-fr... more Using a microfluidic system based on PTFE tubes, experimental results of contactless and label-free characterization techniques of yeast cell cultivation are presented. The PTFE tube has an inner diameter of 0.5 mm resulting in a sample volume of 2 µl for 1 cm sample length. Two approaches (at frequencies around 7 GHz and 240 GHz) are presented and compared in terms of sensitivity and applicability. These frequency bands are particularly interesting to gain information on the permittivity of yeast cells in Glucose solution. Measurements from 240 GHz to 300 GHz were conducted with a continuous wave spectrometer from Toptica. At 7 GHz band, measurements have been performed using a ratrace based characterizing system realized on a printed circuit board. The conducted experiments demonstrate that by selecting the phase as characterization parameter, the presented contactless and label-free techniques are suitable for cell cultivation monitoring in a PTFE pipe based microfluidic system.
The differences between erroneous actions that are consciously perceived as errors and those that... more The differences between erroneous actions that are consciously perceived as errors and those that go unnoticed have recently become an issue in the field of performance monitoring. In EEG studies, error awareness has been suggested to influence the error positivity (Pe) of the response-locked event-related brain potential, a positive voltage deflection prominent approximately 300 msec after error commission, whereas the preceding error-related negativity (ERN) seemed to be unaffected by error awareness. Erroneous actions, in general, have been shown to promote several changes in ongoing autonomic nervous system (ANS) activity, yet such investigations have only rarely taken into account the question of subjective error awareness. In the first part of this study, heart rate, pupillometry, and EEG were recorded during an antisaccade task to measure autonomic arousal and activity of the CNS separately for perceived and unperceived errors. Contrary to our expectations, we observed differences in both Pe and ERN with respect to subjective error awareness. This was replicated in a second experiment, using a modified version of the same task. In line with our predictions, only perceived errors provoke the previously established post-error heart rate deceleration. Also, pupil size yields a more prominent dilatory effect after an erroneous saccade, which is also significantly larger for perceived than unperceived errors. On the basis of the ERP and ANS results as well as brain-behavior correlations, we suggest a novel interpretation of the implementation and emergence of error awareness in the brain. In our framework, several systems generate input signals (e.g., ERN, sensory input, proprioception) that influence the emergence of error awareness, which is then accumulated and presumably reflected in later potentials, such as the Pe.
The development of an innovative detector technology for photon-counting in X-ray imaging is repo... more The development of an innovative detector technology for photon-counting in X-ray imaging is reported. This new generation of detectors, based on pixellated cadmium telluride (CdTe) and cadmium zinc telluride (CZT) detector arrays electrically connected to application specific integrated circuits (ASICs) for readout, will produce fast and highly efficient photon-counting and energydispersive X-ray imaging. There are a number of applications that can greatly benefit from these novel imagers including mammography, planar radiography, and computed tomography (CT). Systems based on this new detector technology can provide compositional analysis of tissue through spectroscopic X-ray imaging, significantly improve overall image quality, and may significantly reduce X-ray dose to the patient. A very high X-ray flux is utilized in many of these applications. For example, CT scanners can produce ~100 Mphotons/mm 2 /s in the unattenuated beam. High flux is required in order to collect sufficient photon statistics in the measurement of the transmitted flux (attenuated beam) during the very short time frame of a CT scan. This high count rate combined with a need for high detection efficiency requires the development of detector structures that can provide a response signal much faster than the transit time of carriers over the whole detector thickness. We have developed CdTe and CZT detector array structures which are 3 mm thick with 16×16 pixels and a 1 mm pixel pitch. These structures, in the two different implementations presented here, utilize either a small pixel effect or a drift phenomenon. An energy resolution of 4.75% at 122 keV has been obtained with a 30 ns peaking time using discrete electronics and a 57 Co source. An output rate of 6×10 6 counts per second per individual pixel has been obtained with our ASIC readout electronics and a clinical CT X-ray tube. Additionally, the first clinical CT images, taken with several of our prototype photon-counting and energy-dispersive detector modules, are shown.
In humans, action errors and perceptual novelty elicit activity in a shared frontostriatal brain ... more In humans, action errors and perceptual novelty elicit activity in a shared frontostriatal brain network, allowing them to adapt their ongoing behavior to such unexpected action outcomes. Healthy and pathologic aging reduces the integrity of white matter pathways that connect individual hubs of such networks and can impair the associated cognitive functions. Here, we investigated whether structural disconnection within this network because of small-vessel disease impairs the neural processes that subserve motor slowing after errors and novelty (post-error slowing, PES; post-novel slowing, PNS). Participants with intact frontostriatal circuitry showed increased right-lateralized beta-band (12-24 Hz) synchrony between frontocentral and frontolateral electrode sites in the electroencephalogram after errors and novelty, indexing increased neural communication. Importantly, this synchrony correlated with PES and PNS across participants. Furthermore, such synchrony was reduced in participants with frontostriatal white matter damage, in line with reduced PES and PNS. The results demonstrate that behavioral change after errors and novelty result from coordinated neural activity across a frontostriatal brain network and that such cognitive control is impaired by reduced white matter integrity.
Medical Imaging 2011: Physics of Medical Imaging, 2011
Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (... more Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (CT) as they have the potential to overcome some of the most significant limitations of current CT with energy integrating detectors. Among these are: insufficient tissue contrast, relatively high radiation dose, tissue non-specificity, and the non-quantitative nature. In contrast, CT with PCXDs has shown promise in producing higher contrast, tissue specific, quantitative images at lower dose. Novel applications for PCXDs include k-edge and functional imaging and material decomposition. A limiting factor, however, is the high photon flux that occurs in clinical applications resulting in signal pulse pile up in the detector. Faster detectors and new strategies for data corrections and image reconstruction algorithms are needed to overcome these limitations. A research tabletop x-ray CT scanner was developed with the following aims: 1) to characterize and calibrate the PCXD; 2) to acquire CT projection data under conditions similar to those of clinical CT; and 3) to reconstruct images using correction schemes specific for PCXDs. The scanner employs a commercial clinical x-ray tube, a PCXD with two energy thresholds, and allows scanning of objects of up to 40 cm in diameter. This paper presents measurements of detector quantities crucial for data corrections and calibration, such as energy response, deadtime, and count rates. Reconstructed CT images are presented and qualitative results from material decomposition are shown.
ABSTRACT A calibration technique as well as measurement results for a 7 GHz Biosensor are present... more ABSTRACT A calibration technique as well as measurement results for a 7 GHz Biosensor are presented. It is shown that the applied sensor structure can be calibrated by adjusting the phase of a sensing element's transmission S21. This is realized by slowing down the wave traveling a microstrip line serving as a reference in the differential sensor structure. The dielectric properties along with certain physical boundaries of an obstacle covering parts of the microstrip line evoke that effect. Measurements with an ethanol serious along with simulation results showed that sensitivity can be increased substantially with this calibration technique. A change of the real part of the sample's permittivity of 48 leads to a 18 MHz frequency shift.
Experimental results of contactless and label-free characterization techniques of cell cultivatio... more Experimental results of contactless and label-free characterization techniques of cell cultivation are presented. The two demonstrated approaches are compared at two frequencies, 7 GHz and 240 GHz in terms of sensitivity and applicability. At 7 GHz, measurements have been performed using a rat-race based characterizing system. Furthermore, the sensitivity of spectroscopy measurements at 240 GHz has been compared for two extracted parameters: phase and amplitude. The conducted experiments demonstrate that by selecting the proper characterization parameter, the presented techniques are suitable for cell cultivation monitoring in a pipe based microfluidic system with PTFE tubes. Especially, the use of higher frequencies enables a higher compactness.
Developments in room temperature cadmium telluride (CdTe) based solid state imaging arrays for en... more Developments in room temperature cadmium telluride (CdTe) based solid state imaging arrays for energy-resolved photon-counting in medical x-ray imaging are discussed. A number of x-ray imaging applications can benefit from these developments including mammography, radiography, and computed tomography (CT). Energy-resolved photon-counting can provide reduced dose through optimal energy weighting, compositional analysis through multiple basis function material decomposition, and contrast enhancement through spectroscopic x-ray imaging of metal nanoparticles. Extremely high flux can occur in x-ray imaging and energy integrating detectors have been conventionally used. To achieve the benefits of energy resolved photon counting, imaging arrays with a large count rate range and good detection efficiency are required. Compound semiconductor radiation detectors with pixellated anode arrays electrically connected to application specific integrated circuits (ASICs) can provide fast, efficient, low-noise performance with adequate energy resolution however this can only be achieved with a careful optimization of the CdTe sensors and ASICs together. We have designed and constructed CdTe imaging arrays, 3 mm thick with a grid of electrical contacts inter-connected to a multi-channel channel ASICs. Arrays with a pixel pitch of 0.5 mm have achieved a counting range up to 20 million counts per second per square mm. Additionally, ASICs with a two dimensional array of pads has been fabricated and tested by connecting the inputs to 1 mm pitch CdTe sensors demonstrating 7 keV full width at half maximum energy resolution across a dynamic range of 30 keV to 140 keV for clinical CT.
IEEE Nuclear Science Symposuim & Medical Imaging Conference, 2010
Page 1. Photon-counting energy-resolving CdTe detectors for high-flux x-ray imaging William C. Ba... more Page 1. Photon-counting energy-resolving CdTe detectors for high-flux x-ray imaging William C. Barber, Member, IEEE, Einar Nygard, Jan C. Wessel, Nail Malakhov, Neal E. Hartsough, Member, IEEE, Thulasi Gandhi, Member ...
2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications (ANIMMA), 2013
ABSTRACT We have fabricated fast room-temperature energy dispersive photon counting x-ray imaging... more ABSTRACT We have fabricated fast room-temperature energy dispersive photon counting x-ray imaging arrays using pixellated cadmium zinc (CdTe) and cadmium zinc telluride (CdZnTe) semiconductors. We have also fabricated fast application specific integrated circuits (ASICs) with a two dimensional (2D) array of inputs for readout from the CdZnTe sensors. The new CdTe and CdZnTe sensors have a 2D array of pixels with a 0.5 mm pitch and can be tiled in 2D. The new 2D ASICs have four energy discriminators per pixel with a linear energy response across the entire dynamic range for clinical CT. The ASICs can also be tiled in 2D and are designed to fit within the active area of the 2D sensors. We have measured several important performance parameters including; an output count rate (OCR) in excess of 20 million counts per second per square mm, an energy resolution of 7 keV full width at half maximum (FWHM) across the entire dynamic range, and a noise floor less than 20 keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdTE and CdZnTe sensors incurring very little additional capacitance. We present a comparison of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, and noise floor.
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
Semiconductor radiation detectors are a promising technology for single photon counting detectors... more Semiconductor radiation detectors are a promising technology for single photon counting detectors. Unlike scintillator-based indirect radiation detectors, semiconductor detectors directly convert absorbed photons to charge, thereby reducing energy spreading and signal loss that can occur in scintillator-based detectors. Cadmium telluride (CdTe) has attracted research interest due to its higher stopping power compared to other semiconductors such as germanium and silicon as well as its room-temperature operating capability. A CdTe photon-counting, energy-resolving detector system has been developed for x-ray and radionuclide imaging, and is capable of discriminating incident photon energy using multiple voltage thresholds per detector element with fast signal formation. Using this CdTe detector, a reproducible method of generating energy spectra was developed for a given incident radiation source. The energy resolution of the CdTe detector was determined by generating the energy spectra of three radiation sources.
Medical Imaging 2009: Physics of Medical Imaging, 2009
We report on a characterization study of a multi-row direct-conversion x-ray detector used to gen... more We report on a characterization study of a multi-row direct-conversion x-ray detector used to generate the first photon counting clinical x-ray computed tomography (CT) patent images. In order to provide the photon counting detector with adequate performance for low-dose CT applications, we have designed and fabricated a fast application specific integrated circuit (ASIC) for data readout from the pixellated CdTe detectors that comprise the photon counting detector. The cadmium telluride (CdTe) detector has 512 pixels with a 1 mm pitch and is vertically integrated with the ASIC readout so it can be tiled in two dimensions similar to those that are tiled in an arc found in 32-row multi-slice CT systems. We have measured several important detector parameters including the maximum output count rate, energy resolution, and noise performance. Additionally the relationship between the output and input rate has been found to fit a non-paralyzable detector model with a dead time of 160 nsec. A maximum output rate of 6 × 10 6 counts per second per pixel has been obtained with a low output x-ray tube for CT operated between 0.01 mA and 6 mA at 140 keV and different source-to-detector distances. All detector noise counts are less that 20 keV which is sufficiently low for clinical CT. The energy resolution measured with the 60 keV photons from a 241 Am source is ~12%. In conclusion, our results demonstrate the potential for the application of the CdTe based photon counting detector to clinical CT systems. Our future plans include further performance improvement by incorporating drift structures to each detector pixel.
Medical Imaging 2010: Physics of Medical Imaging, 2010
We report results from the development of a second-generation CdTe direct-conversion compound-sem... more We report results from the development of a second-generation CdTe direct-conversion compound-semiconductor x-ray detector for photon-counting clinical CT. The first-generation detector has 512 pixels with a 1 mm pitch and is vertically integrated with the readout. A 32-row multi-slice CT system using first-generation detectors has been used for clinical low-dose CT applications. To provide adequate performance for whole-body diagnostic CT
We have fabricated a fast energy-resolved photon-counting x-ray imaging array using pixellated ca... more We have fabricated a fast energy-resolved photon-counting x-ray imaging array using pixellated cadmium telluride (CdTe) semiconductor sensors and have achieved an output count rate (OCR) exceeding 20 million counts per second per square mm (Mcps/mm2) measured with a clinical computed tomography (CT) x-ray source. We have also fabricated a fast application specific integrated circuit (ASIC) with a two dimensional (2D)
Medical Applications of Radiation Detectors II, 2012
ABSTRACT Developments in room temperature solid state imaging arrays for energy-resolved single p... more ABSTRACT Developments in room temperature solid state imaging arrays for energy-resolved single photon counting in medical x-ray imaging are discussed. A number of x-ray imaging applications can benefit from these developments including mammography which requires very good spatial resolution. Energy resolved photon counting can provide reduced dose through optimal energy weighting and compositional analysis through multiple basis function material decomposition. Extremely high flux can occur in x-ray imaging and energy integrating detectors with a large dynamic range and good detection efficiency have been conventionally used. To achieve the benefits of energy resolved photon counting, imaging arrays with a large count rate range and good detection efficiency are required. Si based semiconductor radiation detectors with strip anode arrays electrically connected to application specific integrated circuits (ASICs) can provide fast, efficient, low-noise performance with good energy and spatial resolution for use in mammography however this can only be achieved with a careful optimization of the Si sensors and ASICs together. We have designed and constructed a Si imaging array, with a 1 x 1024 grid of electrical 100 micron wide strip contacts inter connected to multi channel ASICs, with a counting range up to 1 x 106 counts per second per pixel.
Medical Applications of Radiation Detectors III, 2013
ABSTRACT We report on our efforts toward the development of silicon (Si) strip detectors for ener... more ABSTRACT We report on our efforts toward the development of silicon (Si) strip detectors for energy-resolved clinical breast imaging. Typically, x-ray integrating detectors based on scintillating cesium iodide CsI(Tl) or amorphous selenium (a- Se) are used in most commercial systems. Recently, mammography instrumentation has been introduced based on photon counting silicon Si strip detectors. Mammography requires high flux from the x-ray generator, therefore, in order to achieve energy resolved single photon counting, a high output count rate (OCR) for the detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel, provided that the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions. We present our methods and results from the optimization of prototype detectors based on Si strip structures. We describe the detector optimization and the development of ASIC readout electronics that provide the required spatial resolution, low noise, high count rate capabilities and minimal power consumption.
We report on methods for optimizing room temperature semi-conductor detectors for energy-resolved... more We report on methods for optimizing room temperature semi-conductor detectors for energy-resolved x-ray imaging in radiology including applications such as computed tomography (CT), dual-energy x-ray absorptiometry (DEXA), and mammography. These applications produce high input count rates from an x-ray generator delivered to the detector. Room temperature semiconductors, operating as direct conversion x-ray sensors, can provide the required photon counting speed
According to recent accounts, the processing of errors and generally infrequent, surprising (nove... more According to recent accounts, the processing of errors and generally infrequent, surprising (novel) events share a common neuroanatomical substrate. Direct empirical evidence for this common processing network in humans is, however, scarce. To test this hypothesis, we administered a hybrid error-monitoring/novelty-oddball task in which the frequency of novel, surprising trials was dynamically matched to the frequency of errors. Using scalp electroencephalographic recordings and event-related functional magnetic resonance imaging (fMRI), we compared neural responses to errors with neural responses to novel events. In Experiment 1, independent component analysis of scalp ERP data revealed a common neural generator implicated in the generation of both the error-related negativity (ERN) and the novelty-related frontocentral N2. In Experiment 2, this pattern was confirmed by a conjunction analysis of event-related fMRI, which showed significantly elevated BOLD activity following both types of trials in the posterior medial frontal cortex, including the anterior midcingulate cortex (aMCC), the neuronal generator of the ERN. Together, these findings provide direct evidence of a common neural system underlying the processing of errors and novel events. This appears to be at odds with prominent theories of the ERN and aMCC. In particular, the reinforcement learning theory of the ERN may need to be modified because it may not suffice as a fully integrative model of aMCC function. Whenever course and outcome of an action violates expectancies (not necessarily related to reward), the aMCC seems to be engaged in evaluating the necessity of behavioral adaptation.
An arrow version of the Eriksen flanker task was employed to investigate the influence of conflic... more An arrow version of the Eriksen flanker task was employed to investigate the influence of conflict on the error-related negativity (ERN). The degree of conflict was modulated by varying the distance between flankers and the target arrow (CLOSE and FAR conditions). Error rates and reaction time data from a behavioral experiment were used to adapt a connectionist model of this task. This model was based on the conflict monitoring theory and simulated behavioral and event-related potential data. The computational model predicted an increased ERN amplitude in FAR incompatible (the low-conflict condition) compared to CLOSE incompatible errors (the high-conflict condition). A subsequent ERP experiment confirmed the model predictions. The computational model explains this finding with larger postresponse conflict in far trials. In addition, data and model predictions of the N2 and the LRP support the conflict interpretation of the ERN.
Using a microfluidic system based on PTFE tubes, experimental results of contactless and label-fr... more Using a microfluidic system based on PTFE tubes, experimental results of contactless and label-free characterization techniques of yeast cell cultivation are presented. The PTFE tube has an inner diameter of 0.5 mm resulting in a sample volume of 2 µl for 1 cm sample length. Two approaches (at frequencies around 7 GHz and 240 GHz) are presented and compared in terms of sensitivity and applicability. These frequency bands are particularly interesting to gain information on the permittivity of yeast cells in Glucose solution. Measurements from 240 GHz to 300 GHz were conducted with a continuous wave spectrometer from Toptica. At 7 GHz band, measurements have been performed using a ratrace based characterizing system realized on a printed circuit board. The conducted experiments demonstrate that by selecting the phase as characterization parameter, the presented contactless and label-free techniques are suitable for cell cultivation monitoring in a PTFE pipe based microfluidic system.
The differences between erroneous actions that are consciously perceived as errors and those that... more The differences between erroneous actions that are consciously perceived as errors and those that go unnoticed have recently become an issue in the field of performance monitoring. In EEG studies, error awareness has been suggested to influence the error positivity (Pe) of the response-locked event-related brain potential, a positive voltage deflection prominent approximately 300 msec after error commission, whereas the preceding error-related negativity (ERN) seemed to be unaffected by error awareness. Erroneous actions, in general, have been shown to promote several changes in ongoing autonomic nervous system (ANS) activity, yet such investigations have only rarely taken into account the question of subjective error awareness. In the first part of this study, heart rate, pupillometry, and EEG were recorded during an antisaccade task to measure autonomic arousal and activity of the CNS separately for perceived and unperceived errors. Contrary to our expectations, we observed differences in both Pe and ERN with respect to subjective error awareness. This was replicated in a second experiment, using a modified version of the same task. In line with our predictions, only perceived errors provoke the previously established post-error heart rate deceleration. Also, pupil size yields a more prominent dilatory effect after an erroneous saccade, which is also significantly larger for perceived than unperceived errors. On the basis of the ERP and ANS results as well as brain-behavior correlations, we suggest a novel interpretation of the implementation and emergence of error awareness in the brain. In our framework, several systems generate input signals (e.g., ERN, sensory input, proprioception) that influence the emergence of error awareness, which is then accumulated and presumably reflected in later potentials, such as the Pe.
The development of an innovative detector technology for photon-counting in X-ray imaging is repo... more The development of an innovative detector technology for photon-counting in X-ray imaging is reported. This new generation of detectors, based on pixellated cadmium telluride (CdTe) and cadmium zinc telluride (CZT) detector arrays electrically connected to application specific integrated circuits (ASICs) for readout, will produce fast and highly efficient photon-counting and energydispersive X-ray imaging. There are a number of applications that can greatly benefit from these novel imagers including mammography, planar radiography, and computed tomography (CT). Systems based on this new detector technology can provide compositional analysis of tissue through spectroscopic X-ray imaging, significantly improve overall image quality, and may significantly reduce X-ray dose to the patient. A very high X-ray flux is utilized in many of these applications. For example, CT scanners can produce ~100 Mphotons/mm 2 /s in the unattenuated beam. High flux is required in order to collect sufficient photon statistics in the measurement of the transmitted flux (attenuated beam) during the very short time frame of a CT scan. This high count rate combined with a need for high detection efficiency requires the development of detector structures that can provide a response signal much faster than the transit time of carriers over the whole detector thickness. We have developed CdTe and CZT detector array structures which are 3 mm thick with 16×16 pixels and a 1 mm pixel pitch. These structures, in the two different implementations presented here, utilize either a small pixel effect or a drift phenomenon. An energy resolution of 4.75% at 122 keV has been obtained with a 30 ns peaking time using discrete electronics and a 57 Co source. An output rate of 6×10 6 counts per second per individual pixel has been obtained with our ASIC readout electronics and a clinical CT X-ray tube. Additionally, the first clinical CT images, taken with several of our prototype photon-counting and energy-dispersive detector modules, are shown.
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Papers by Jan Wessel