Pub Date : 1996-06-01DOI: 10.1109/NSSMIC.1995.504327
J. Lauter, A. Forster, H. Luth, K. D. Muller, R. Reinartz
We report on the first realization of 2/spl times/2 detector arrays based on an aluminum gallium arsenide/gallium arsenide (AlGaAs/GaAs) heterostructure avalanche photodiodes. These structures consists of a GaAs absorption layer and an AlGaAs/GaAs avalanche layer which acts as an multiplication region. The samples were grown by molecular beam epitaxy (MBE) and processed into p-i-n diodes of different diameters. Dark current densities were as low as 200 pA/mm/sup 2/ at 90% of the breakdown voltage as determined by I-V measurements. The avalanche gain of the devices have been measured with optical pulses. Gains up to a factor of M=1000 have been determined before breakdown. Additionally the excess noise factor F(M) has been derived for gains between M=1 and M=300. The ionization rates ratio of the structure is k=/spl alpha///spl beta/=3.4/spl plusmn/0.3. In connection to a fast electronic readout chain the time response of the detectors to 14.4 keV X-ray photons has been tested at the ESRF (Grenoble). The time resolution was found to be 200 ps (FWHM) using standard timing electronics.
{"title":"AlGaAs/GaAs avalanche detector array -1 GBit/s X-ray receiver for timing measurements","authors":"J. Lauter, A. Forster, H. Luth, K. D. Muller, R. Reinartz","doi":"10.1109/NSSMIC.1995.504327","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.504327","url":null,"abstract":"We report on the first realization of 2/spl times/2 detector arrays based on an aluminum gallium arsenide/gallium arsenide (AlGaAs/GaAs) heterostructure avalanche photodiodes. These structures consists of a GaAs absorption layer and an AlGaAs/GaAs avalanche layer which acts as an multiplication region. The samples were grown by molecular beam epitaxy (MBE) and processed into p-i-n diodes of different diameters. Dark current densities were as low as 200 pA/mm/sup 2/ at 90% of the breakdown voltage as determined by I-V measurements. The avalanche gain of the devices have been measured with optical pulses. Gains up to a factor of M=1000 have been determined before breakdown. Additionally the excess noise factor F(M) has been derived for gains between M=1 and M=300. The ionization rates ratio of the structure is k=/spl alpha///spl beta/=3.4/spl plusmn/0.3. In connection to a fast electronic readout chain the time response of the detectors to 14.4 keV X-ray photons has been tested at the ESRF (Grenoble). The time resolution was found to be 200 ps (FWHM) using standard timing electronics.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130345090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1996-06-01DOI: 10.1109/NSSMIC.1995.510371
I. Ajinenko, K. Beloous, J. Chudoba, S. Czellár, H. Herr, N. Jouravlev, N. Khovansky, P. Kluit, Z. Zrumstein, K. Kurvinen, V. Lapin, R. Leitner, J. Masik, A. Olchevski, J. Řídký, Y. Sedykh, P. Sicho, O. Smirnova, O. Solovianov, O. Tchikilev, L. Tkatchev, Z. Tomsa, V. Vrba, W. Williams, A. Wetherell, J. Zaslavsky
The DELPHI Hadron Calorimeter was conceived more than ten years ago, as an instrument to measure the energy of hadrons and hadronic jets from e/sup +/e/sup -/ collisions at the CERN collider LEP. In addition it was expected to provide a certain degree of discrimination between pions and muons. The detector is a rather simple and relatively inexpensive device consisting of around 20,000 limited streamer plastic tubes, with inductive pad read-out, embedded in the iron yoke of the 1.2 T DELPHI magnet. Its depth is at minimum 6.6 nuclear lengths. The electronics necessary for the pad read-out was designed to have an adequate performance for a reasonable cost. This detector has proved over six years of operation to have an entirely satisfactory performance and great reliability, for example less than 1% of the streamer tubes have failed and electronic problems remain at the per mil level. During the past two years an improvement programme has been under way. It has been found possible to use the streamer tubes as strips, hence giving better granularity and particle tracking, by reading out the cathode of individual tubes. The constraints on this were considerable because of the inaccessibility of the detectors in the magnet yoke. However a cheap and viable solution has been found. The cathode read-out leads to an improved energy resolution, better /spl mu/ identification, a better /spl pi///spl mu/ separation and to possibilities of neutral particle separation. The simultaneous anode read-out of several planes of the endcaps of the detector will provide a fast trigger in the forward/backward direction which is an important improvement for LEP200. On the barrel the system will provide a cosmic trigger which is very useful for calibration as counting rates at LEP200 will be very low.
德尔菲强子量热计是十多年前构想出来的，用于测量欧洲核子研究中心对撞机LEP上e/sup +/e/sup -/碰撞产生的强子和强子射流的能量。此外，它还被期望在介子和介子之间提供一定程度的区别。检测器是一种相当简单和相对便宜的设备，由大约20,000个有限的拖带塑料管组成，带有感应板读出，嵌入在1.2 T DELPHI磁铁的铁轭中。它的深度至少有6.6个核长度。pad读出所需的电子设备设计为以合理的成本具有足够的性能。经过六年的运行证明，该探测器具有完全令人满意的性能和很高的可靠性，例如，只有不到1%的拖缆管失效，电子问题仍然保持在每密尔的水平。在过去两年中，一直在执行一项改进方案。已经发现可以使用拖缆管作为条带，因此通过读出单个管的阴极来提供更好的粒度和颗粒跟踪。这方面的限制是相当大的，因为磁铁轭中的探测器是不可接近的。然而，已经找到了一种廉价可行的解决方案。阴极读出可以提高能量分辨率，更好的/spl mu/识别，更好的/spl pi///spl mu/分离以及中性粒子分离的可能性。探测器端盖的多个平面的同时阳极读出将提供正向/反向的快速触发，这是LEP200的一个重要改进。在枪管上，系统将提供一个宇宙触发器，这对于校准非常有用，因为LEP200的计数率将非常低。
{"title":"The performance of the DELPHI Hadron Calorimeter at LEP","authors":"I. Ajinenko, K. Beloous, J. Chudoba, S. Czellár, H. Herr, N. Jouravlev, N. Khovansky, P. Kluit, Z. Zrumstein, K. Kurvinen, V. Lapin, R. Leitner, J. Masik, A. Olchevski, J. Řídký, Y. Sedykh, P. Sicho, O. Smirnova, O. Solovianov, O. Tchikilev, L. Tkatchev, Z. Tomsa, V. Vrba, W. Williams, A. Wetherell, J. Zaslavsky","doi":"10.1109/NSSMIC.1995.510371","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.510371","url":null,"abstract":"The DELPHI Hadron Calorimeter was conceived more than ten years ago, as an instrument to measure the energy of hadrons and hadronic jets from e/sup +/e/sup -/ collisions at the CERN collider LEP. In addition it was expected to provide a certain degree of discrimination between pions and muons. The detector is a rather simple and relatively inexpensive device consisting of around 20,000 limited streamer plastic tubes, with inductive pad read-out, embedded in the iron yoke of the 1.2 T DELPHI magnet. Its depth is at minimum 6.6 nuclear lengths. The electronics necessary for the pad read-out was designed to have an adequate performance for a reasonable cost. This detector has proved over six years of operation to have an entirely satisfactory performance and great reliability, for example less than 1% of the streamer tubes have failed and electronic problems remain at the per mil level. During the past two years an improvement programme has been under way. It has been found possible to use the streamer tubes as strips, hence giving better granularity and particle tracking, by reading out the cathode of individual tubes. The constraints on this were considerable because of the inaccessibility of the detectors in the magnet yoke. However a cheap and viable solution has been found. The cathode read-out leads to an improved energy resolution, better /spl mu/ identification, a better /spl pi///spl mu/ separation and to possibilities of neutral particle separation. The simultaneous anode read-out of several planes of the endcaps of the detector will provide a fast trigger in the forward/backward direction which is an important improvement for LEP200. On the barrel the system will provide a cosmic trigger which is very useful for calibration as counting rates at LEP200 will be very low.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121199437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.510431
S. Glick
Photon attenuation and the limited non-stationary spatial resolution of the detector can reduce both qualitative and quantitative image quality in SPECT. Here, the authors describe a reconstruction approach which can compensate for both of these degradations. The approach involves processing the projection data with Bellini's method for attenuation compensation followed by an iterative deconvolution technique which uses the frequency distance principle (FDP) to model the distance-dependent camera blur. Modelling of the camera blur with the FDP allows an efficient implementation using FFT methods. After processing of the projection data, reconstruction is performed using filtered backprojection. Simulation studies using the Hoffman brain phantom show that this approach gives reconstructions with low bias and no visually undesirable noise artifact with a low computational overhead.
{"title":"Iterative restoration of SPECT projection images","authors":"S. Glick","doi":"10.1109/NSSMIC.1995.510431","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.510431","url":null,"abstract":"Photon attenuation and the limited non-stationary spatial resolution of the detector can reduce both qualitative and quantitative image quality in SPECT. Here, the authors describe a reconstruction approach which can compensate for both of these degradations. The approach involves processing the projection data with Bellini's method for attenuation compensation followed by an iterative deconvolution technique which uses the frequency distance principle (FDP) to model the distance-dependent camera blur. Modelling of the camera blur with the FDP allows an efficient implementation using FFT methods. After processing of the projection data, reconstruction is performed using filtered backprojection. Simulation studies using the Hoffman brain phantom show that this approach gives reconstructions with low bias and no visually undesirable noise artifact with a low computational overhead.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117058095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.504181
F. Doty, J. F. Butler, P. Hink, J. Macri
We report results of a study undertaken to experimentally determine the achievable spatial resolution of monolithic cadmium zinc telluride (CZT) arrays. It was demonstrated that CZT arrays can produce direct electronic X-ray images with fine spatial resolution and high detection efficiency. For low X-ray energies useful for imaging soft tissue such as the breast, 50 micron resolution with virtually 100% detection efficiency were demonstrated, while for higher energy X-rays where fluorescence dominates the signal spreading, 100 micron resolution was demonstrated. Due to electrostatic effects of small anodes, improved charge deficit tailing and pulse rise time results are observed for strips as well as pixels.
{"title":"Performance of submillimeter CdZnTe strip detectors","authors":"F. Doty, J. F. Butler, P. Hink, J. Macri","doi":"10.1109/NSSMIC.1995.504181","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.504181","url":null,"abstract":"We report results of a study undertaken to experimentally determine the achievable spatial resolution of monolithic cadmium zinc telluride (CZT) arrays. It was demonstrated that CZT arrays can produce direct electronic X-ray images with fine spatial resolution and high detection efficiency. For low X-ray energies useful for imaging soft tissue such as the breast, 50 micron resolution with virtually 100% detection efficiency were demonstrated, while for higher energy X-rays where fluorescence dominates the signal spreading, 100 micron resolution was demonstrated. Due to electrostatic effects of small anodes, improved charge deficit tailing and pulse rise time results are observed for strips as well as pixels.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117119394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.500261
M. Gambaccini, A. Taibi, A. Del Guerra, F. Frontera
X-ray imaging with low-energy, narrow-band, and tunable radiation offers the possibility of reducing dose and improving image contrast. We investigate the production of narrow energy band X-ray beams with a standard X-ray tube by using Bragg diffraction on mosaic crystals for mammography application. Quasi-monochromatic X-ray beams (/spl Delta/E/E/spl sim/0.1) have been produced in the mammography energy range. Small-field (1.1/spl times/3.0 cm/sup 2/) radiographs of a plexiglas phantom 3.6 cm thick were obtained with 18, 20, and 22 keV quasi-monochromatic beams and a conventional film/screen combination for mammography. Images showed a nonuniformity in the irradiation field. A digital detector was used as imaging system to correct the phantom radiographs for this uneven illumination across the image. The overall contrast of the images decreases with increasing energy of the beam from 18 keV to 22 keV. A measurement of the resolving power of the reflected beam has shown an asymmetric unsharpness along the two dimensions of the image plane. The actual focal spot has a size of about 0.2/spl times/0.05 cm/sup 2/.
{"title":"Small-field imaging properties of narrow energy band X-ray beams for mammography","authors":"M. Gambaccini, A. Taibi, A. Del Guerra, F. Frontera","doi":"10.1109/NSSMIC.1995.500261","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.500261","url":null,"abstract":"X-ray imaging with low-energy, narrow-band, and tunable radiation offers the possibility of reducing dose and improving image contrast. We investigate the production of narrow energy band X-ray beams with a standard X-ray tube by using Bragg diffraction on mosaic crystals for mammography application. Quasi-monochromatic X-ray beams (/spl Delta/E/E/spl sim/0.1) have been produced in the mammography energy range. Small-field (1.1/spl times/3.0 cm/sup 2/) radiographs of a plexiglas phantom 3.6 cm thick were obtained with 18, 20, and 22 keV quasi-monochromatic beams and a conventional film/screen combination for mammography. Images showed a nonuniformity in the irradiation field. A digital detector was used as imaging system to correct the phantom radiographs for this uneven illumination across the image. The overall contrast of the images decreases with increasing energy of the beam from 18 keV to 22 keV. A measurement of the resolving power of the reflected beam has shown an asymmetric unsharpness along the two dimensions of the image plane. The actual focal spot has a size of about 0.2/spl times/0.05 cm/sup 2/.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121049498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.504226
T. Zimmerman, M. Sarraj
A second generation charge integrator and encoder ASIC (QIE5) has been designed for the KTeV experiment at Fermilab. It is intended to be used in conjunction with a FADC (typically eight bits) to digitize photomultiplier tube (PMT) current pulses at a fast rate, with variable resolution over a 16 bit dynamic range. QIE5 integrates pulses of up to 30 ma peak on eight nonoverlapping binary scaled ranges. A system clock of up to 53 MHz controls the integration period and readout rate. The device is pipelined so that there is no signal deadtime. For each clock period, one range is selected depending on the signal magnitude, and the output of that range is routed to the QIE5 analog output and fed to the FADC to form the mantissa. The selected range is encoded and output as a three bit digital exponent. With this method, the measurement resolution is a relatively constant fraction of the signal over a large dynamic range. Previous reports have described a single ended device (QIE2) which had inherent limitations. The QIE5 is a fully differential design and contains numerous other features which provide significant performance improvements. The new design philosophy and test results are presented for the first time.
{"title":"A second generation charge integrator and encoder ASIC","authors":"T. Zimmerman, M. Sarraj","doi":"10.1109/NSSMIC.1995.504226","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.504226","url":null,"abstract":"A second generation charge integrator and encoder ASIC (QIE5) has been designed for the KTeV experiment at Fermilab. It is intended to be used in conjunction with a FADC (typically eight bits) to digitize photomultiplier tube (PMT) current pulses at a fast rate, with variable resolution over a 16 bit dynamic range. QIE5 integrates pulses of up to 30 ma peak on eight nonoverlapping binary scaled ranges. A system clock of up to 53 MHz controls the integration period and readout rate. The device is pipelined so that there is no signal deadtime. For each clock period, one range is selected depending on the signal magnitude, and the output of that range is routed to the QIE5 analog output and fed to the FADC to form the mantissa. The selected range is encoded and output as a three bit digital exponent. With this method, the measurement resolution is a relatively constant fraction of the signal over a large dynamic range. Previous reports have described a single ended device (QIE2) which had inherent limitations. The QIE5 is a fully differential design and contains numerous other features which provide significant performance improvements. The new design philosophy and test results are presented for the first time.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124965527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.504189
H. B. Barber, F. Augustine, H. Barrett, E. Dereniak, J. Eskin, D. G. Marks, K. Matherson, J. Venzon, J. Woolfenden, E. Young
We are developing an imaging technique for nuclear medicine that makes use of semiconductor arrays having a large number of separate pixels on a single slab that are read out by a monolithic integrated circuit called a multiplexer. The device is similar to a focal-plane array used for infrared imaging. Here we present results verifying the concept by using a Hughes 48/spl times/48 Ge PIN focal-plane array as a gamma-ray imaging system. The performance of this device as an imaging spectrometer was extraordinary, with a spatial resolution of 125 /spl mu/m at 30 keV and an energy resolution of 2 keV FWHM (25-140 keV). The device performed well over a temperature range of 136-200 K. It is concluded that semiconductor detector arrays with multiplexer readout are a very attractive approach for a new generation of nuclear medicine imaging systems.
{"title":"High-resolution imaging using a 48/spl times/48 Ge array with multiplexer readout","authors":"H. B. Barber, F. Augustine, H. Barrett, E. Dereniak, J. Eskin, D. G. Marks, K. Matherson, J. Venzon, J. Woolfenden, E. Young","doi":"10.1109/NSSMIC.1995.504189","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.504189","url":null,"abstract":"We are developing an imaging technique for nuclear medicine that makes use of semiconductor arrays having a large number of separate pixels on a single slab that are read out by a monolithic integrated circuit called a multiplexer. The device is similar to a focal-plane array used for infrared imaging. Here we present results verifying the concept by using a Hughes 48/spl times/48 Ge PIN focal-plane array as a gamma-ray imaging system. The performance of this device as an imaging spectrometer was extraordinary, with a spatial resolution of 125 /spl mu/m at 30 keV and an energy resolution of 2 keV FWHM (25-140 keV). The device performed well over a temperature range of 136-200 K. It is concluded that semiconductor detector arrays with multiplexer readout are a very attractive approach for a new generation of nuclear medicine imaging systems.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125823470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.510472
G. L. Zeng, G. Gullberg
In a single photon emission computed tomography (SPECT) study, the projections may be truncated due to the relatively small detector size. The truncation problem is severe in a transmission study especially when a fan-beam collimator is used. It is commonly believed that truncated projections always result in an under-determined reconstruction problem and cause artifacts in the reconstruction. In fact, when the projections are truncated, an exact image can be reconstructed under certain circumstances such as that the image is band-limited and the sinogram is continuously measured. We use the singular value decomposition (SVD) to analyze the imaging system. It is demonstrated that the reconstruction with truncated projections is not always an under-determined problem. However, a fully determined problem can be ill-conditioned, which is characterized by its condition number. One should try to reduce the condition number as much as possible. In practice if we have a situation where truncation is not avoidable, we recommend the following: (1) increase the number of views while acquiring data, (2) decrease the sampling interval on the detector, (3) increase the pixel size of the image, sacrificing resolution for smaller condition number, (4) use constrains such as supports, non-negativity, smoothness, and so on, and (5) use a good projection model with accurate image basis functions to reduce aliasing artifacts.
{"title":"Does truncation always result in an under-determined problem? An SVD study","authors":"G. L. Zeng, G. Gullberg","doi":"10.1109/NSSMIC.1995.510472","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.510472","url":null,"abstract":"In a single photon emission computed tomography (SPECT) study, the projections may be truncated due to the relatively small detector size. The truncation problem is severe in a transmission study especially when a fan-beam collimator is used. It is commonly believed that truncated projections always result in an under-determined reconstruction problem and cause artifacts in the reconstruction. In fact, when the projections are truncated, an exact image can be reconstructed under certain circumstances such as that the image is band-limited and the sinogram is continuously measured. We use the singular value decomposition (SVD) to analyze the imaging system. It is demonstrated that the reconstruction with truncated projections is not always an under-determined problem. However, a fully determined problem can be ill-conditioned, which is characterized by its condition number. One should try to reduce the condition number as much as possible. In practice if we have a situation where truncation is not avoidable, we recommend the following: (1) increase the number of views while acquiring data, (2) decrease the sampling interval on the detector, (3) increase the pixel size of the image, sacrificing resolution for smaller condition number, (4) use constrains such as supports, non-negativity, smoothness, and so on, and (5) use a good projection model with accurate image basis functions to reduce aliasing artifacts.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"85 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125853438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.504178
A. Niemela, L. Grodzins
The toxicological effects of lead in humans have been long known. The long-term exposure is best measured by the lead in bone, which is known to contain over 90% of the body's lead burden. We are in the process of developing a faster, more accurate measurement system based on the latest techniques pioneered in astrophysics and synchrotron light source research. We report here on the first phase of the program, which is aimed at determining the parameters for obtaining the maximum sensitivity with L X-ray fluorescence; a further phase will be concerned with K XRF. The studies are being carried out at the National Synchrotron Light Source at Brookhaven National Laboratory (BNL NSLS) using a monochromatic, polarized X-ray beam, tunable over the energy range from 8 keV (well below the L/sub III/ binding energy of 13.035 keV) to 30 keV (well above the L/sub I/ binding energy of 15.86 keV). We used cylindrical bone phantoms made from plaster of paris, doped with 17 ppm and 115 ppm of lead, and covered with 5 mm of Lucite to simulate the overlaying skin tissue. At an excitation energy of 16.5 keV, and with an available planar Ge detector in an XRF geometry that made effective use of the polarized beam, we were immediately able to measure 17 ppm of lead in bone phantom in a few minutes.
{"title":"Design of an XRF system for in vivo measurement of lead in bone","authors":"A. Niemela, L. Grodzins","doi":"10.1109/NSSMIC.1995.504178","DOIUrl":"https://doi.org/10.1109/NSSMIC.1995.504178","url":null,"abstract":"The toxicological effects of lead in humans have been long known. The long-term exposure is best measured by the lead in bone, which is known to contain over 90% of the body's lead burden. We are in the process of developing a faster, more accurate measurement system based on the latest techniques pioneered in astrophysics and synchrotron light source research. We report here on the first phase of the program, which is aimed at determining the parameters for obtaining the maximum sensitivity with L X-ray fluorescence; a further phase will be concerned with K XRF. The studies are being carried out at the National Synchrotron Light Source at Brookhaven National Laboratory (BNL NSLS) using a monochromatic, polarized X-ray beam, tunable over the energy range from 8 keV (well below the L/sub III/ binding energy of 13.035 keV) to 30 keV (well above the L/sub I/ binding energy of 15.86 keV). We used cylindrical bone phantoms made from plaster of paris, doped with 17 ppm and 115 ppm of lead, and covered with 5 mm of Lucite to simulate the overlaying skin tissue. At an excitation energy of 16.5 keV, and with an available planar Ge detector in an XRF geometry that made effective use of the polarized beam, we were immediately able to measure 17 ppm of lead in bone phantom in a few minutes.","PeriodicalId":409998,"journal":{"name":"1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126113769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1995-10-21DOI: 10.1109/NSSMIC.1995.500311
J. Heanue, J.K. Brown, K. Kalki, B. Hasegawa
The authors seek to determine the desired energy resolution for quantitative SPECT imaging. As the energy resolution of the system is improved, the relative error due to scatter decreases. Yet, at some point the improvement becomes inconsequential since the scatter error is small compared to the other physical perturbations in the radionuclide measurement. In order to estimate the energy resolution at which this condition becomes true, the authors used a Monte Carlo code to simulate the emission data from a myocardial perfusion phantom. The data were reconstructed using a maximum likelihood code, and the images were analyzed to determine the relative effects of attenuation correction, collimator response compensation, noise, and scatter rejection on image quantitation. The simulations showed that improving the system energy resolution beyond 5 keV offers little benefit for myocardial perfusion studies. The relevance of this result to other applications is also discussed.
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