A new algorithm for variance reduction on random coincidences (VRR) has been validated for the HR... more A new algorithm for variance reduction on random coincidences (VRR) has been validated for the HRRT. VRR is crucial to achieve quantitation for low statistics dynamic studies reconstructed with iterative methods based on ordinary Poisson model. On HRRT, VRR cannot be performed in projection space since individual LOR's are mixed after histogramming in parallel projection space using nearest neighbor approximation and axial compression. The proposed algorithm uses the classical random rate equation on the 4.5 109LOR's. However, crystal singles are registered at block level and have lower deadtime than coincidences. Variations in layer identification with countrate were reported biasing random estimation from block singles. Our method overcomes these problems by estimating the singles per crystal from delayed coincidences. A singles map is created histogramming every delayed event into 2 singles. Each element represents the number of coincidences between that crystal and the ones in the 5 opposite coincident heads. The algorithm finds iteratively the crystal singles rates compatible with the delayed coincidence events. The method has been validated on decaying phantoms. We compared estimated and measured block singles to identify deadtime difference between singles and coincidences
... Judson P. Jones, Member, IEEE, William F. Jones, Senior Member, IEEE, Frank Kehren, Danny F. ... more ... Judson P. Jones, Member, IEEE, William F. Jones, Senior Member, IEEE, Frank Kehren, Danny F. Newport, Member, IEEE, Johnny H. Reed, Mark W. Lenox, Ken Baker, Member, IEEE, Larry G. Byars, Christian Michel, Member, IEEE, Michael E. Casey, Senior Member, IEEE F ...
IEEE Symposium Conference Record Nuclear Science 2004., 2004
The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS In... more The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS Innovations using LSO panel detectors. Transmission is measured using a 137 Cs point source, which is moved axially and rotated to cover the FOV. The point source is collimated axially and transaxially to illuminate only a few planes on the heads opposite to the point source location. Pseudo-coincidence events are generated using a given crystal and the source location. The transmission system was previously validated for cold transmissions. For post-injection (hot) transmission, it is not possible to eliminate the emission contamination by raising the lower energy threshold. Since real mock scan is unpractical on HRRT and fake mock scan requires additional data, we developed a new technique to simultaneously measure the transmission and the mock scans. The technique uses a virtual source, axially located at a distance equal to the half of the axial FOV and illuminates a fan separated from the real transmission fan. We validated the shifted-mock scan technique by comparing it to real mock scan one with a 68 Ge phantom and examined its effectiveness with a hot 20 cm phantom filled with 18 F decaying over several half-lives. Local residual bias in µ-map was attributed to transmission scatter and corrected by using partial segmentation in the MAP-TR algorithm. µ-maps from cold and hot transmissions were compared on several clinical patients and a Hoffman brain phantom for which their influence on emission quantification was studied.
Abstract In previous work we compared two parallel algorithms for calculating 3D forward and bac... more Abstract In previous work we compared two parallel algorithms for calculating 3D forward and backprojection on a distributed-memory cluster computer. These two methods were used to develop an implementation of fully three-dimensional Ordered Subset Expectation Maximization ...
European Journal of Nuclear Medicine and Molecular Imaging, 1997
Spatial transformations of positron emission tomographic data for aligning images or transforming... more Spatial transformations of positron emission tomographic data for aligning images or transforming to standard anatomical space are usually performed with reconstructed images. However, they can also be performed during the reconstruction process, thereby interpolating the raw data fewer times. We investigated the performance of spatial transformations during reconstruction, implemented it in a standard 3D reconstruction algorithm, and tested it on phantom and patient H215O activation studies for the application of aligning both transmission and emission scans. Performing the transformations during reconstruction was shown to be equivalent to performing the transformations with reconstructed images for this particular application.
Abstract A dedicated whole human brain positron emission tomograph (PET), the High Resolution Res... more Abstract A dedicated whole human brain positron emission tomograph (PET), the High Resolution Research Tomograph (ECAT HRRT) is utilized to evaluate attenuation correction using single photon based transmission scanning. The patented transmission procedure ...
This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D... more This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D) positron emission tomography (PET) data. A rebinning algorithm is one that first sorts the 3-D data into an ordinary two-dimensional (2-D) data set containing one sinogram for each transaxial slice to be reconstructed; the 3-D image is then recovered by applying to each slice a 2-D reconstruction method such as filtered-backprojection. This approach allows a significant speedup of 3-D reconstruction, which is particularly useful for applications involving dynamic acquisitions or whole-body imaging. The first new algorithm is obtained by discretizing an exact analytical inversion formula. The second algorithm, called the Fourier rebinning algorithm (FORE), is approximate but allows an efficient implementation based on taking 2-D Fourier transforms of the data. This second algorithm was implemented and applied to data acquired with the new generation of PET systems and also to simulated data for a scanner with an 18 axial aperture. The reconstructed images were compared to those obtained with the 3-D reprojection algorithm (3DRP) which is the standard "exact" 3-D filteredbackprojection method. Results demonstrate that FORE provides a reliable alternative to 3DRP, while at the same time achieving an order of magnitude reduction in processing time.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
In order to characterize physiological cerebral activation or tissue response to a treatment, at ... more In order to characterize physiological cerebral activation or tissue response to a treatment, at least two FDG-PET studies are mandatory. In this work, a study of one hour duration with two injections at 30 min apart is reported. The separation of the two input curves (IC) consisted of fitting the blood curve corresponding to the first injection using spectral analysis,
The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated w... more The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated with functional activity of the neural cells. The present work reports a comparison study between rCBF and rCMRGlc in a normal population as a function of age. 10 young (25.965.6 years) and 10 old (65.466.1 years) volunteers were similarly studied at rest. In each subject, rCBF and rCMRGlc were measured in sequence, during the same session. Both rCBF and rCMRGlc values were found to decrease from young (mean rCBF543.7 ml / 100 g per min; mean rCMRGlc540.6 mmol / 100 g per min) to old age (mean rCBF537.3 ml / 100 g per min; mean rCMRGlc535.2 mmol / 100 g per min), resulting in a drop over 40 years of 14.8% (0.37% / year) and 13.3% (0.34% / year), respectively. On a regional basis, the frontal and the visual cortices were observed to have, respectively, the highest and the lowest reduction in rCBF, while, for rCMRGlc, these extremes were observed in striatum and cerebellum. Despite these differences, the ratio of rCBF to rCMRGlc was found to have a similar behavior in all brain regions for young and old subjects as shown by a correlation coefficient of 88%. This comparative study indicates a decline in rCBF and rCMRGlc values and a coupling between CBF and CMRGlc as a function of age.
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
THE Siemens HRRT scanner is a complex PET tomograph, using 8 LSO/LYSO panel detectors and Depth O... more THE Siemens HRRT scanner is a complex PET tomograph, using 8 LSO/LYSO panel detectors and Depth Of Interaction(DOI) with a total of 119908 detector crystals. The Direct Normalization (DN) is the standard method used for sinogram-mode reconstruction. This paper investigates the use of an improved component-based normalization method for HRRT sinogram reconstruction. This method is originally used for MOLAR LOR
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. Aft... more Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. After injection, a large amount of the compound is excreted via the urinary tract, while a variable part is trapped in the tumour(s), allowing the curative effect. Unfortunately, the compound may also be trapped in critical tissues such as kidney or bone marrow. As a consequence, a method for assessment of individual biodistribution and pharmacokinetics is required to predict the maximum dose that can be safely injected into patients. However, (90)Y, a pure beta(-)particle emitter, cannot be used for quantitative imaging. Yttrium-86 is a positron emitter that allows imaging of tissue uptake using a PET camera. In addition to the positron, (86)Y also emits a multitude of prompt single gamma-rays, leading to significant overestimation of uptake when using classical reconstruction methods. We propose a patient-dependent correction method based on sinogram tail fitting using an (86)Y point spread function library. When applied to abdominal phantom acquisition data, the proposed correction method significantly improved the accuracy of the quantification: the initial overestimation of background activity by 117% was reduced to 9%, while the initial error in respect of kidney uptake by 84% was reduced to 5%. In patient studies, the mean discrepancy between PET total body activity and the activity expected from urinary collections was reduced from 92% to 7%, showing the benefit of the proposed correction method.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
... The second algorithm, FOREX, is an exact rebinning algorithm which was first suggested, but n... more ... The second algorithm, FOREX, is an exact rebinning algorithm which was first suggested, but not implemented, ... 4). The exact reconstruction algorithm FOREX has been shown to have similar accuracy as 3DRP and is about 6 times faster. ...
Quantitative estimation of brain glucose metabolism (rCMRGlc) with positron emission tomography a... more Quantitative estimation of brain glucose metabolism (rCMRGlc) with positron emission tomography and fluorodeoxyglucose involves arterial blood sampling to estimate the delivery of radioactivity to the brain. Usually, for an intravenous injection of 30 s duration, an accurate input curve requires a frequency of one sample every 5 s or less to determine the peak activity in arterial plasma during the first 2 min after injection. In this work, 13 standardized sampling times were shown to be sufficient to accurately define the input curve. This standardized input curve was subsequently fitted by a polynomial function for its rising part and by spectral analysis for its decreasing part. Using the measured, the standardized, and the fitted input curves, rCMRGlc was estimated in 32 cerebral regions of interest in 20 normal volunteers. Comparison of rCMRGlc values obtained with the measured and the fitted input curves showed that both procedures gave consistent results, with a maximal relative error in mean rCMRGlc of 1% when using the autoradiographic method and 2% using kinetic analysis of dynamic data. This input-curve-fitting technique, which is not dependent on the peak time occurrence, allows an accurate determination of the input-curve shape from reduced sampling schemes.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
In order to examine the importance of preserving the Poisson characteristics of Positron Emission... more In order to examine the importance of preserving the Poisson characteristics of Positron Emission Tomography data when using Ordered Subset Expectation Maximization iterative reconstruction, we have examined several data weighting schemes with increasing complexity which progressively account for attenuation, normalization, random coincidences and Compton scatter with both ordinary and shifted Poisson models. All schemes have first been tested on 2D dynamic data from a decaying phantom filled with H 2 15 O. The images produced by the various OSEM weighting schemes were compared to the ones obtained by filtered backprojection reconstruction. Small positive bias (1%) could not be excluded for the last 2 schemes considered. The impact of these reconstruction methods on physiological parameters is illustrated with clinical protocols measuring myocardial blood flow with ammonia and Standard Uptake Values from a wholebody study with 18 FDG. Despite the high random rate in cardiac studies, no positive bias was detected in the images when using scans precorrected for random and scatter. Similarly, for whole body studies, at low random rates, the attenuation and normalization weighting scheme produces high quality images with correct quantification. That scheme is likely the best choice for obtaining unbiased high quality emission images in most situations on current 2D scanners.
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. Aft... more Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. After injection, a large amount of the compound is excreted via the urinary tract, while a variable part is trapped in the tumour(s), allowing the curative effect. Unfortunately, the compound may also be trapped in critical tissues such as kidney or bone marrow. As a consequence, a method for assessment of individual biodistribution and pharmacokinetics is required to predict the maximum dose that can be safely injected into patients. However, (90)Y, a pure beta(-)particle emitter, cannot be used for quantitative imaging. Yttrium-86 is a positron emitter that allows imaging of tissue uptake using a PET camera. In addition to the positron, (86)Y also emits a multitude of prompt single gamma-rays, leading to significant overestimation of uptake when using classical reconstruction methods. We propose a patient-dependent correction method based on sinogram tail fitting using an (86)Y point spread function library. When applied to abdominal phantom acquisition data, the proposed correction method significantly improved the accuracy of the quantification: the initial overestimation of background activity by 117% was reduced to 9%, while the initial error in respect of kidney uptake by 84% was reduced to 5%. In patient studies, the mean discrepancy between PET total body activity and the activity expected from urinary collections was reduced from 92% to 7%, showing the benefit of the proposed correction method.
IEEE Symposium Conference Record Nuclear Science 2004., 2004
The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS In... more The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS Innovations using LSO panel detectors. Transmission is measured using a 137 Cs point source, which is moved axially and rotated to cover the FOV. The point source is collimated axially and transaxially to illuminate only a few planes on the heads opposite to the point source location. Pseudo-coincidence events are generated using a given crystal and the source location. The transmission system was previously validated for cold transmissions. For post-injection (hot) transmission, it is not possible to eliminate the emission contamination by raising the lower energy threshold. Since real mock scan is unpractical on HRRT and fake mock scan requires additional data, we developed a new technique to simultaneously measure the transmission and the mock scans. The technique uses a virtual source, axially located at a distance equal to the half of the axial FOV and illuminates a fan separated from the real transmission fan. We validated the shifted-mock scan technique by comparing it to real mock scan one with a 68 Ge phantom and examined its effectiveness with a hot 20 cm phantom filled with 18 F decaying over several half-lives. Local residual bias in µ-map was attributed to transmission scatter and corrected by using partial segmentation in the MAP-TR algorithm. µ-maps from cold and hot transmissions were compared on several clinical patients and a Hoffman brain phantom for which their influence on emission quantification was studied.
IEEE Symposium Conference Record Nuclear Science 2004., 2004
High spatial resolution dynamic brain PET imaging with the ECAT HRRT scanner with short frame dur... more High spatial resolution dynamic brain PET imaging with the ECAT HRRT scanner with short frame durations is characterized by very few counts per sinogram bin due to the small size of the crystal surface. The use of various weighting schemes for OSEM-3D can result in significantly different results. In particular, the correction for random and scattered coincidences prior to the reconstruction can lead to a systematic positive bias in the reconstructed image. We show that the use of Ordinary Poisson OSEM-3D, where all corrections are applied during the iterative steps, allows to avoid this bias without compromising spatial resolution, at a price of a lower convergence rate.
During the first years of life, the human brain undergoes repetitive modifications in its anatomi... more During the first years of life, the human brain undergoes repetitive modifications in its anatomical, functional, and synaptic construction to reach the complex functional organization of the adult central nervous system. As an attempt to gain further insight in those maturation processes, the evolution of cerebral metabolic activity was investigated as a function of age in epileptic infants, children and adolescents. The regional cerebral metabolic rates for glucose (rCMRGlc) were measured with positron emission tomography (PET) in 60 patients aged from 6 weeks to 19 years, who were affected by complex partial epilepsy. They were scanned at rest, without premedication, in similar conditions to 20 epileptic adults and in 49 adult controls. The distribution of brain metabolic activity successively extended from sensorimotor areas and thalamus in epileptic newborns to temporo-parietal and frontal cortices and reached the adult pattern after 1 year of age. The measured rCMRGlc in the cerebral cortex, excluding the epileptic lesions, increased from low values in infants to a maximum between 4 and 12 years, before it declined to stabilize at the end of the second decade of life. Similar age-related changes in glucose metabolic rates were not observed in the adult groups. Despite the use of medications, the observed variations of rCMRGlc with age in young epileptic humans confirm those previously described in pediatric subjects. These metabolic changes are in full agreement with the current knowledge of the synaptic density evolution in the human brain.
1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, 1995
A set of applications has been developed for volumic medical image display and analysis in PET an... more A set of applications has been developed for volumic medical image display and analysis in PET and MRI. Although the set may appear at first glance, as a implementation in X-Windows of a package previously developed at CTI under SunView, major improvements have been added to its functionality. All graphical user interfaces have been developed with InterViews, a public domain
A new algorithm for variance reduction on random coincidences (VRR) has been validated for the HR... more A new algorithm for variance reduction on random coincidences (VRR) has been validated for the HRRT. VRR is crucial to achieve quantitation for low statistics dynamic studies reconstructed with iterative methods based on ordinary Poisson model. On HRRT, VRR cannot be performed in projection space since individual LOR's are mixed after histogramming in parallel projection space using nearest neighbor approximation and axial compression. The proposed algorithm uses the classical random rate equation on the 4.5 109LOR's. However, crystal singles are registered at block level and have lower deadtime than coincidences. Variations in layer identification with countrate were reported biasing random estimation from block singles. Our method overcomes these problems by estimating the singles per crystal from delayed coincidences. A singles map is created histogramming every delayed event into 2 singles. Each element represents the number of coincidences between that crystal and the ones in the 5 opposite coincident heads. The algorithm finds iteratively the crystal singles rates compatible with the delayed coincidence events. The method has been validated on decaying phantoms. We compared estimated and measured block singles to identify deadtime difference between singles and coincidences
... Judson P. Jones, Member, IEEE, William F. Jones, Senior Member, IEEE, Frank Kehren, Danny F. ... more ... Judson P. Jones, Member, IEEE, William F. Jones, Senior Member, IEEE, Frank Kehren, Danny F. Newport, Member, IEEE, Johnny H. Reed, Mark W. Lenox, Ken Baker, Member, IEEE, Larry G. Byars, Christian Michel, Member, IEEE, Michael E. Casey, Senior Member, IEEE F ...
IEEE Symposium Conference Record Nuclear Science 2004., 2004
The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS In... more The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS Innovations using LSO panel detectors. Transmission is measured using a 137 Cs point source, which is moved axially and rotated to cover the FOV. The point source is collimated axially and transaxially to illuminate only a few planes on the heads opposite to the point source location. Pseudo-coincidence events are generated using a given crystal and the source location. The transmission system was previously validated for cold transmissions. For post-injection (hot) transmission, it is not possible to eliminate the emission contamination by raising the lower energy threshold. Since real mock scan is unpractical on HRRT and fake mock scan requires additional data, we developed a new technique to simultaneously measure the transmission and the mock scans. The technique uses a virtual source, axially located at a distance equal to the half of the axial FOV and illuminates a fan separated from the real transmission fan. We validated the shifted-mock scan technique by comparing it to real mock scan one with a 68 Ge phantom and examined its effectiveness with a hot 20 cm phantom filled with 18 F decaying over several half-lives. Local residual bias in µ-map was attributed to transmission scatter and corrected by using partial segmentation in the MAP-TR algorithm. µ-maps from cold and hot transmissions were compared on several clinical patients and a Hoffman brain phantom for which their influence on emission quantification was studied.
Abstract In previous work we compared two parallel algorithms for calculating 3D forward and bac... more Abstract In previous work we compared two parallel algorithms for calculating 3D forward and backprojection on a distributed-memory cluster computer. These two methods were used to develop an implementation of fully three-dimensional Ordered Subset Expectation Maximization ...
European Journal of Nuclear Medicine and Molecular Imaging, 1997
Spatial transformations of positron emission tomographic data for aligning images or transforming... more Spatial transformations of positron emission tomographic data for aligning images or transforming to standard anatomical space are usually performed with reconstructed images. However, they can also be performed during the reconstruction process, thereby interpolating the raw data fewer times. We investigated the performance of spatial transformations during reconstruction, implemented it in a standard 3D reconstruction algorithm, and tested it on phantom and patient H215O activation studies for the application of aligning both transmission and emission scans. Performing the transformations during reconstruction was shown to be equivalent to performing the transformations with reconstructed images for this particular application.
Abstract A dedicated whole human brain positron emission tomograph (PET), the High Resolution Res... more Abstract A dedicated whole human brain positron emission tomograph (PET), the High Resolution Research Tomograph (ECAT HRRT) is utilized to evaluate attenuation correction using single photon based transmission scanning. The patented transmission procedure ...
This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D... more This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D) positron emission tomography (PET) data. A rebinning algorithm is one that first sorts the 3-D data into an ordinary two-dimensional (2-D) data set containing one sinogram for each transaxial slice to be reconstructed; the 3-D image is then recovered by applying to each slice a 2-D reconstruction method such as filtered-backprojection. This approach allows a significant speedup of 3-D reconstruction, which is particularly useful for applications involving dynamic acquisitions or whole-body imaging. The first new algorithm is obtained by discretizing an exact analytical inversion formula. The second algorithm, called the Fourier rebinning algorithm (FORE), is approximate but allows an efficient implementation based on taking 2-D Fourier transforms of the data. This second algorithm was implemented and applied to data acquired with the new generation of PET systems and also to simulated data for a scanner with an 18 axial aperture. The reconstructed images were compared to those obtained with the 3-D reprojection algorithm (3DRP) which is the standard "exact" 3-D filteredbackprojection method. Results demonstrate that FORE provides a reliable alternative to 3DRP, while at the same time achieving an order of magnitude reduction in processing time.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
In order to characterize physiological cerebral activation or tissue response to a treatment, at ... more In order to characterize physiological cerebral activation or tissue response to a treatment, at least two FDG-PET studies are mandatory. In this work, a study of one hour duration with two injections at 30 min apart is reported. The separation of the two input curves (IC) consisted of fitting the blood curve corresponding to the first injection using spectral analysis,
The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated w... more The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated with functional activity of the neural cells. The present work reports a comparison study between rCBF and rCMRGlc in a normal population as a function of age. 10 young (25.965.6 years) and 10 old (65.466.1 years) volunteers were similarly studied at rest. In each subject, rCBF and rCMRGlc were measured in sequence, during the same session. Both rCBF and rCMRGlc values were found to decrease from young (mean rCBF543.7 ml / 100 g per min; mean rCMRGlc540.6 mmol / 100 g per min) to old age (mean rCBF537.3 ml / 100 g per min; mean rCMRGlc535.2 mmol / 100 g per min), resulting in a drop over 40 years of 14.8% (0.37% / year) and 13.3% (0.34% / year), respectively. On a regional basis, the frontal and the visual cortices were observed to have, respectively, the highest and the lowest reduction in rCBF, while, for rCMRGlc, these extremes were observed in striatum and cerebellum. Despite these differences, the ratio of rCBF to rCMRGlc was found to have a similar behavior in all brain regions for young and old subjects as shown by a correlation coefficient of 88%. This comparative study indicates a decline in rCBF and rCMRGlc values and a coupling between CBF and CMRGlc as a function of age.
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
THE Siemens HRRT scanner is a complex PET tomograph, using 8 LSO/LYSO panel detectors and Depth O... more THE Siemens HRRT scanner is a complex PET tomograph, using 8 LSO/LYSO panel detectors and Depth Of Interaction(DOI) with a total of 119908 detector crystals. The Direct Normalization (DN) is the standard method used for sinogram-mode reconstruction. This paper investigates the use of an improved component-based normalization method for HRRT sinogram reconstruction. This method is originally used for MOLAR LOR
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. Aft... more Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. After injection, a large amount of the compound is excreted via the urinary tract, while a variable part is trapped in the tumour(s), allowing the curative effect. Unfortunately, the compound may also be trapped in critical tissues such as kidney or bone marrow. As a consequence, a method for assessment of individual biodistribution and pharmacokinetics is required to predict the maximum dose that can be safely injected into patients. However, (90)Y, a pure beta(-)particle emitter, cannot be used for quantitative imaging. Yttrium-86 is a positron emitter that allows imaging of tissue uptake using a PET camera. In addition to the positron, (86)Y also emits a multitude of prompt single gamma-rays, leading to significant overestimation of uptake when using classical reconstruction methods. We propose a patient-dependent correction method based on sinogram tail fitting using an (86)Y point spread function library. When applied to abdominal phantom acquisition data, the proposed correction method significantly improved the accuracy of the quantification: the initial overestimation of background activity by 117% was reduced to 9%, while the initial error in respect of kidney uptake by 84% was reduced to 5%. In patient studies, the mean discrepancy between PET total body activity and the activity expected from urinary collections was reduced from 92% to 7%, showing the benefit of the proposed correction method.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
... The second algorithm, FOREX, is an exact rebinning algorithm which was first suggested, but n... more ... The second algorithm, FOREX, is an exact rebinning algorithm which was first suggested, but not implemented, ... 4). The exact reconstruction algorithm FOREX has been shown to have similar accuracy as 3DRP and is about 6 times faster. ...
Quantitative estimation of brain glucose metabolism (rCMRGlc) with positron emission tomography a... more Quantitative estimation of brain glucose metabolism (rCMRGlc) with positron emission tomography and fluorodeoxyglucose involves arterial blood sampling to estimate the delivery of radioactivity to the brain. Usually, for an intravenous injection of 30 s duration, an accurate input curve requires a frequency of one sample every 5 s or less to determine the peak activity in arterial plasma during the first 2 min after injection. In this work, 13 standardized sampling times were shown to be sufficient to accurately define the input curve. This standardized input curve was subsequently fitted by a polynomial function for its rising part and by spectral analysis for its decreasing part. Using the measured, the standardized, and the fitted input curves, rCMRGlc was estimated in 32 cerebral regions of interest in 20 normal volunteers. Comparison of rCMRGlc values obtained with the measured and the fitted input curves showed that both procedures gave consistent results, with a maximal relative error in mean rCMRGlc of 1% when using the autoradiographic method and 2% using kinetic analysis of dynamic data. This input-curve-fitting technique, which is not dependent on the peak time occurrence, allows an accurate determination of the input-curve shape from reduced sampling schemes.
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998
In order to examine the importance of preserving the Poisson characteristics of Positron Emission... more In order to examine the importance of preserving the Poisson characteristics of Positron Emission Tomography data when using Ordered Subset Expectation Maximization iterative reconstruction, we have examined several data weighting schemes with increasing complexity which progressively account for attenuation, normalization, random coincidences and Compton scatter with both ordinary and shifted Poisson models. All schemes have first been tested on 2D dynamic data from a decaying phantom filled with H 2 15 O. The images produced by the various OSEM weighting schemes were compared to the ones obtained by filtered backprojection reconstruction. Small positive bias (1%) could not be excluded for the last 2 schemes considered. The impact of these reconstruction methods on physiological parameters is illustrated with clinical protocols measuring myocardial blood flow with ammonia and Standard Uptake Values from a wholebody study with 18 FDG. Despite the high random rate in cardiac studies, no positive bias was detected in the images when using scans precorrected for random and scatter. Similarly, for whole body studies, at low random rates, the attenuation and normalization weighting scheme produces high quality images with correct quantification. That scheme is likely the best choice for obtaining unbiased high quality emission images in most situations on current 2D scanners.
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. Aft... more Several yttrium-90 labelled somatostatin analogues are now available for cancer radiotherapy. After injection, a large amount of the compound is excreted via the urinary tract, while a variable part is trapped in the tumour(s), allowing the curative effect. Unfortunately, the compound may also be trapped in critical tissues such as kidney or bone marrow. As a consequence, a method for assessment of individual biodistribution and pharmacokinetics is required to predict the maximum dose that can be safely injected into patients. However, (90)Y, a pure beta(-)particle emitter, cannot be used for quantitative imaging. Yttrium-86 is a positron emitter that allows imaging of tissue uptake using a PET camera. In addition to the positron, (86)Y also emits a multitude of prompt single gamma-rays, leading to significant overestimation of uptake when using classical reconstruction methods. We propose a patient-dependent correction method based on sinogram tail fitting using an (86)Y point spread function library. When applied to abdominal phantom acquisition data, the proposed correction method significantly improved the accuracy of the quantification: the initial overestimation of background activity by 117% was reduced to 9%, while the initial error in respect of kidney uptake by 84% was reduced to 5%. In patient studies, the mean discrepancy between PET total body activity and the activity expected from urinary collections was reduced from 92% to 7%, showing the benefit of the proposed correction method.
IEEE Symposium Conference Record Nuclear Science 2004., 2004
The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS In... more The High Resolution Research Tomograph (HRRT) is a brain-dedicated scanner manufactured by CPS Innovations using LSO panel detectors. Transmission is measured using a 137 Cs point source, which is moved axially and rotated to cover the FOV. The point source is collimated axially and transaxially to illuminate only a few planes on the heads opposite to the point source location. Pseudo-coincidence events are generated using a given crystal and the source location. The transmission system was previously validated for cold transmissions. For post-injection (hot) transmission, it is not possible to eliminate the emission contamination by raising the lower energy threshold. Since real mock scan is unpractical on HRRT and fake mock scan requires additional data, we developed a new technique to simultaneously measure the transmission and the mock scans. The technique uses a virtual source, axially located at a distance equal to the half of the axial FOV and illuminates a fan separated from the real transmission fan. We validated the shifted-mock scan technique by comparing it to real mock scan one with a 68 Ge phantom and examined its effectiveness with a hot 20 cm phantom filled with 18 F decaying over several half-lives. Local residual bias in µ-map was attributed to transmission scatter and corrected by using partial segmentation in the MAP-TR algorithm. µ-maps from cold and hot transmissions were compared on several clinical patients and a Hoffman brain phantom for which their influence on emission quantification was studied.
IEEE Symposium Conference Record Nuclear Science 2004., 2004
High spatial resolution dynamic brain PET imaging with the ECAT HRRT scanner with short frame dur... more High spatial resolution dynamic brain PET imaging with the ECAT HRRT scanner with short frame durations is characterized by very few counts per sinogram bin due to the small size of the crystal surface. The use of various weighting schemes for OSEM-3D can result in significantly different results. In particular, the correction for random and scattered coincidences prior to the reconstruction can lead to a systematic positive bias in the reconstructed image. We show that the use of Ordinary Poisson OSEM-3D, where all corrections are applied during the iterative steps, allows to avoid this bias without compromising spatial resolution, at a price of a lower convergence rate.
During the first years of life, the human brain undergoes repetitive modifications in its anatomi... more During the first years of life, the human brain undergoes repetitive modifications in its anatomical, functional, and synaptic construction to reach the complex functional organization of the adult central nervous system. As an attempt to gain further insight in those maturation processes, the evolution of cerebral metabolic activity was investigated as a function of age in epileptic infants, children and adolescents. The regional cerebral metabolic rates for glucose (rCMRGlc) were measured with positron emission tomography (PET) in 60 patients aged from 6 weeks to 19 years, who were affected by complex partial epilepsy. They were scanned at rest, without premedication, in similar conditions to 20 epileptic adults and in 49 adult controls. The distribution of brain metabolic activity successively extended from sensorimotor areas and thalamus in epileptic newborns to temporo-parietal and frontal cortices and reached the adult pattern after 1 year of age. The measured rCMRGlc in the cerebral cortex, excluding the epileptic lesions, increased from low values in infants to a maximum between 4 and 12 years, before it declined to stabilize at the end of the second decade of life. Similar age-related changes in glucose metabolic rates were not observed in the adult groups. Despite the use of medications, the observed variations of rCMRGlc with age in young epileptic humans confirm those previously described in pediatric subjects. These metabolic changes are in full agreement with the current knowledge of the synaptic density evolution in the human brain.
1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, 1995
A set of applications has been developed for volumic medical image display and analysis in PET an... more A set of applications has been developed for volumic medical image display and analysis in PET and MRI. Although the set may appear at first glance, as a implementation in X-Windows of a package previously developed at CTI under SunView, major improvements have been added to its functionality. All graphical user interfaces have been developed with InterViews, a public domain
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Papers by Christian Michel