David Townsend | National University of Singapore (original) (raw)

Papers by David Townsend

Journal of Oral and Maxillofacial Surgery, Dec 31, 2007

To investigate the role of 18-fluorine-fluorodeoxyglucose positron emission tomography/ computeri... more To investigate the role of 18-fluorine-fluorodeoxyglucose positron emission tomography/ computerized tomography ( 18 F-FDG PET/CT) in the preoperative prediction of the presence and extent of neck disease in patients with oral/head and neck cancer. Patients and Methods: Seventy patients were enrolled in the study, 47 of whom had a clinically negative neck (N0), 19 of whom had a clinically positive unilateral neck (Nϩ), and 4 of whom were negative on 1 side of the neck and positive on the other. Each patient underwent a PET/CT study before undergoing selective neck dissection for N0 disease or modified radical neck dissection for Nϩ disease. Tissues were submitted for histopathologic examination and were oriented for the pathologist as to the oncologic levels so as to permit correlation between histopathologic findings and the imaging results. Results: The sensitivity and specificity of the PET/CT procedure were 79% and 82% for the N0 neck, and 95% and 25% for the Nϩ neck. One hundred ninety-two (11.4%) of the 1,678 nodes identified at histopathology were positive for metastases. The overall nodal sensitivity and specificity were 48% and 99%, respectively. Conclusion: In patients with clinically negative necks, a negative test would not help the surgeon in the management strategy of the patient because of the rate of false-negative results, but a positive test can diagnose metastatic deposits with a high positive predictive value. In patients with clinically positive necks, a positive test will confirm the presence of disease, although false-negative lymph nodes were additionally identified in these clinically positive necks. With respect to nodes, the sensitivity of the imaging procedure is such that the results could not help the surgeon in deciding which level to dissect and which to spare. In the final analysis, the head and neck oncologic surgeon should not depend on the results of the PET/CT scan to determine which patients will benefit from neck dissection. Rather, time-honored principles of neck surgery should be followed, particularly with regard to the liberal execution of prophylactic neck dissections in patients with clinically N0 necks.

In the two decades since the introduction of the X-ray scanner into radiology, medical imaging te... more In the two decades since the introduction of the X-ray scanner into radiology, medical imaging techniques have become widely established as essential tools in the diagnosis of disease. As a consequence of recent technological and mathematical advances, the non invasive, three-dimensional imaging of internal organs such as the brain and the heart is now possible, not only for anatomical investigations using X-rays but also for studies which explore the functional status of the body using positron-emitting radioisotopes. This report reviews the historical and physical basis of medical imaging techniques using positron-emitting radioisotopes. Mathematical methods which enable three-dimensional distributions of radioisotopes to be reconstructed from projection data (sinograms) acquired by detectors suitably positioned around the patient are discussed. The extension of conventional twodimensional tomographic reconstruction algorithms to fully three-dimensional reconstruction is described in detail. © Parallel projection Eqn. (3.1), <\> = 0 p(s, 0 = 0) © Filtering Eqn. (3.2) Two disks equal concentrations À © Backprojection Eqn. (3.5)

Learning Memory, Oct 1, 2008

and general activity are associated with disparities in working memory, body weight, Age-related ... more and general activity are associated with disparities in working memory, body weight, Age-related declines in general cognitive abilities of Balb/C mice References http://learnmem.cshlp.org/cgi/content/full/15/10/733#References A defining characteristic of age-related cognitive decline is a deficit in general cognitive performance. Here we use a testing and analysis regimen that allows us to characterize the general learning abilities of young (3-5 mo old) and aged (19-21 mo old) male and female Balb/C mice. Animals' performance was assessed on a battery of seven diverse learning tasks. Aged animals exhibited deficits in five of the seven tasks and ranked significantly lower than their young counterparts in general learning abilities (aggregate performance across the battery of tasks). Aging added variability to common core performance (i.e., general learning ability), which translated into increased variability on the individual cognitive tasks. Relatedly, general learning abilities did not differ between the two ages among the best quartile of learners (i.e., cognitive abilities were spared in a subsample of the aged animals). Additionally, working memory capacity (resistance to interference) and duration (resistance to decay) accounted for significantly more of the variability in general learning abilities in aged relative to young animals. Tests of 15 noncognitive performance variables indicated that an increase in body weight (and an associtaed decrease in general activity) was characteristic of those aged animals which exhibited deficient general learning abilities. These results suggest the possibility that general cognitive deficits in aged animals reflect a failure of specific components of the working memory system, and may be related to variations in body weight and an associated decrease in activity. ; fax (732) 445-2263. Article is online at

Surgical Endoscopy, 1997

This report describes our initial experience using positron emission tomography (PET) scanning in... more This report describes our initial experience using positron emission tomography (PET) scanning in esophageal cancer patients. In two patients PET identified distant metastatic disease missed by conventional staging. Laparoscopic biopsy provided histological confirmation of metastases. In the third patient, locoregional lymph nodes were identified by PET and confirmed by surgical staging. In this preliminary report, PET appears to be a promising new noninvasive modality for staging patients with esophageal cancer.

Society of Nuclear Medicine Annual Meeting Abstracts, May 1, 2007

Aps Meeting Abstracts, 2008

The Standardized Uptake Value (SUV) is often used in positron emission tomography (PET) to differ... more The Standardized Uptake Value (SUV) is often used in positron emission tomography (PET) to differenciate malignant from benign tumors, and to monitor the progress of the patient response to therapy. Despite its name, SUV may depend on both PET scanner hardware and software details, and will depend on the imaging protocol. In this paper, we present a study of the SUV variability according to these external factors. To study the influence of the PET device, phantom studies were performed on two different combined PET/CT scanners. SUVs were obtained using several reconstruction algorithms and different reconstruction matrix sizes. To study the influence of the imaging protocol, patients were injected with 370 MBq of 18F-FDG and scanned at 60 and 90 min post-injection. SUVs were obtained applying several clinical image reconstruction algorithms. Significant differences in SUVs were obtained depending on the PET scanner, reconstruction method, and imaging protocol. It is essential, therefore, to follow a strict protocol in order to reliably compare FDG uptake with SUVs. Our results may have a significant clinical impact in order to provide an unbiased SUV thereshold to determine malignancy.

1993 IEEE Conference Record Nuclear Science Symposium and Medical Imaging Conference, 1993

Two methods for attenuation correction in 3D positron emission tomography have been compared. The... more Two methods for attenuation correction in 3D positron emission tomography have been compared. The first method, which is referred to here as the direct method, estimates the attenuation correction factors from the ratio of the blank and transmission scan. The second method, referred to here as the reconstruction-reprojection method is based on the reconstruction and forward projection of a transmission

Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference, 1991

Following previous reports of the NEC gain for a PET (positron emission tomography) scanner with ... more Following previous reports of the NEC gain for a PET (positron emission tomography) scanner with retractable septa (Siemens-CTI 953B), methods for 3-D normalization and attenuation correction from 2-D datasets were developed. Physical performance and system calibration were reevaluated for 3-D reconstructed data for this scanner. Normalization is performed by measuring the direct plane sinograms (no cross-plane contribution) with septa in

Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference, 1991

A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtendi... more A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtending two opposing arcs of 60° and mounted on a circular support was developed. Projection data at all angles are acquired by rotating the detector assembly. The scanner has no septa, and data from the equivalent of 16 full rings of detectors are collected and sorted

Continental shelf waters from the Labrador Sea to the Mid-Atlantic Bight experienced significant ... more Continental shelf waters from the Labrador Sea to the Mid-Atlantic Bight experienced significant freshening in the late 1990s, likely caused by increasing glacial melting and enhanced precipitation and river runoff at higher latitudes (as a result of climate change). The freshening of the ocean can alter circulation and stratification of shelf waters and may influence the phytoplankton dynamics and ecosystem

IEEE Symposium Conference Record Nuclear Science 2004., 2004

Evaluation and follow up of small pulmonary nodules has become commonplace with advancing PET and... more Evaluation and follow up of small pulmonary nodules has become commonplace with advancing PET and CT technology. Limits in system resolution, recovery coefficient estimations and transaxial ROI determinations often make obtaining useful SUV data difficult. We demonstrate a method which may be more accurate for making these determinations. It is assumed that the nodule can be distinguished clearly on CT

1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019), 1999

We present a 3D whole-body PET simulator that generates multiple, yet statistically accurate, rea... more We present a 3D whole-body PET simulator that generates multiple, yet statistically accurate, realizations of projection data within a computation time that is short enough to enable the measurement of the task performance of image reconstruction algorithms. The whole-body simulator takes into account the following effects: the seperate amounts of statistical noise contributed by true, scattered, and random coincidences, activity outside the field of view, activity decay between bed positions, detector efficiencies and resolution, and noise arising from the transmission scan. The principle of the simulation is to analytically calculate projections based on the geometrical specification of the emission and attenuation objects that comprise the MCAT phantom. A pre-determined level of statistical noise is then added to the projection data, which is then inputted to the same data correction and image reconstruction procedures used in practice.

Proceedings of 1994 IEEE Nuclear Science Symposium - NSS'94, 1995

The use of X-ray CT for Attenuation Correction of PET Data ... Thomas Beyer, Paul E. Kinahan, Dav... more The use of X-ray CT for Attenuation Correction of PET Data ... Thomas Beyer, Paul E. Kinahan, David W. Townsend, and Donald Sashin Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213-2582 ... This paper presents the results of evaluating ...

1990 IEEE Nuclear Science Symposium Conference Record, 1990

Performance characteristics of a new commercial design of positron tomograph with retractable sep... more Performance characteristics of a new commercial design of positron tomograph with retractable septa for brain imaging have been studied. The device, composed of block BGO detectors (8 x 8 elements per block), has a ring diam of 76cm and an axial FOV of 10.8cm (slice thickness 4.3&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; with septa). The in-plane resolution is less than 5mm with wobble sampling. Its

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 2000

The availability of accurately aligned, whole-body anatomical (CT) and functional (PET) images co... more The availability of accurately aligned, whole-body anatomical (CT) and functional (PET) images could have a significant impact on diagnosing and staging malignant disease and on identifying and localizing metastases. Computer algorithms to align CT and PET images acquired on different scanners are generally successful for the brain, whereas image alignment in other regions of the body is more problematic. A combined PET/CT tomograph with the unique capability of acquiring accurately aligned functional and anatomical images for any part of the human body has been designed and built. The PET/CT scanner was developed as a combination of a Siemens Somatom AR.SP spiral CT and a partial-ring, rotating ECAT ART PET scanner. All components are mounted on a common rotational support within a single gantry. The PET and CT components can be operated either separately, or in combined mode. In combined mode, the CT images are used to correct the PET data for scatter and attenuation. Fully quanti...

2008 IEEE Nuclear Science Symposium Conference Record, 2008

The physical PET performance of the first prototype of the recently introduced Biograph mCT TOF P... more The physical PET performance of the first prototype of the recently introduced Biograph mCT TOF PET/CT scanner (Siemens Molecular Imaging) has been evaluated. The PET component incorporates 192 detector blocks, 5.4 cm x 5.4 cm in cross-section; each block comprises a 13 x 13 matrix of 4 x 4 x 20 mm3 crystal elements. The four detector block rings cover

Journal of Neuroradiology, 2006

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.

1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019), 1999

... Blank and transmission data were acquired in standard 2D (ring difference 5, span of 11) and ... more ... Blank and transmission data were acquired in standard 2D (ring difference 5, span of 11) and true modes, using 3 rotating %e rod sources (activity around 10 mCi), and a 7 bin wide rod mask, which produced scatter free 2D attenuation correction. B. Experimental protocols ...

Journal of Oral and Maxillofacial Surgery, Dec 31, 2007

To investigate the role of 18-fluorine-fluorodeoxyglucose positron emission tomography/ computeri... more To investigate the role of 18-fluorine-fluorodeoxyglucose positron emission tomography/ computerized tomography ( 18 F-FDG PET/CT) in the preoperative prediction of the presence and extent of neck disease in patients with oral/head and neck cancer. Patients and Methods: Seventy patients were enrolled in the study, 47 of whom had a clinically negative neck (N0), 19 of whom had a clinically positive unilateral neck (Nϩ), and 4 of whom were negative on 1 side of the neck and positive on the other. Each patient underwent a PET/CT study before undergoing selective neck dissection for N0 disease or modified radical neck dissection for Nϩ disease. Tissues were submitted for histopathologic examination and were oriented for the pathologist as to the oncologic levels so as to permit correlation between histopathologic findings and the imaging results. Results: The sensitivity and specificity of the PET/CT procedure were 79% and 82% for the N0 neck, and 95% and 25% for the Nϩ neck. One hundred ninety-two (11.4%) of the 1,678 nodes identified at histopathology were positive for metastases. The overall nodal sensitivity and specificity were 48% and 99%, respectively. Conclusion: In patients with clinically negative necks, a negative test would not help the surgeon in the management strategy of the patient because of the rate of false-negative results, but a positive test can diagnose metastatic deposits with a high positive predictive value. In patients with clinically positive necks, a positive test will confirm the presence of disease, although false-negative lymph nodes were additionally identified in these clinically positive necks. With respect to nodes, the sensitivity of the imaging procedure is such that the results could not help the surgeon in deciding which level to dissect and which to spare. In the final analysis, the head and neck oncologic surgeon should not depend on the results of the PET/CT scan to determine which patients will benefit from neck dissection. Rather, time-honored principles of neck surgery should be followed, particularly with regard to the liberal execution of prophylactic neck dissections in patients with clinically N0 necks.

In the two decades since the introduction of the X-ray scanner into radiology, medical imaging te... more In the two decades since the introduction of the X-ray scanner into radiology, medical imaging techniques have become widely established as essential tools in the diagnosis of disease. As a consequence of recent technological and mathematical advances, the non invasive, three-dimensional imaging of internal organs such as the brain and the heart is now possible, not only for anatomical investigations using X-rays but also for studies which explore the functional status of the body using positron-emitting radioisotopes. This report reviews the historical and physical basis of medical imaging techniques using positron-emitting radioisotopes. Mathematical methods which enable three-dimensional distributions of radioisotopes to be reconstructed from projection data (sinograms) acquired by detectors suitably positioned around the patient are discussed. The extension of conventional twodimensional tomographic reconstruction algorithms to fully three-dimensional reconstruction is described in detail. © Parallel projection Eqn. (3.1), <\> = 0 p(s, 0 = 0) © Filtering Eqn. (3.2) Two disks equal concentrations À © Backprojection Eqn. (3.5)

Learning Memory, Oct 1, 2008

and general activity are associated with disparities in working memory, body weight, Age-related ... more and general activity are associated with disparities in working memory, body weight, Age-related declines in general cognitive abilities of Balb/C mice References http://learnmem.cshlp.org/cgi/content/full/15/10/733#References A defining characteristic of age-related cognitive decline is a deficit in general cognitive performance. Here we use a testing and analysis regimen that allows us to characterize the general learning abilities of young (3-5 mo old) and aged (19-21 mo old) male and female Balb/C mice. Animals' performance was assessed on a battery of seven diverse learning tasks. Aged animals exhibited deficits in five of the seven tasks and ranked significantly lower than their young counterparts in general learning abilities (aggregate performance across the battery of tasks). Aging added variability to common core performance (i.e., general learning ability), which translated into increased variability on the individual cognitive tasks. Relatedly, general learning abilities did not differ between the two ages among the best quartile of learners (i.e., cognitive abilities were spared in a subsample of the aged animals). Additionally, working memory capacity (resistance to interference) and duration (resistance to decay) accounted for significantly more of the variability in general learning abilities in aged relative to young animals. Tests of 15 noncognitive performance variables indicated that an increase in body weight (and an associtaed decrease in general activity) was characteristic of those aged animals which exhibited deficient general learning abilities. These results suggest the possibility that general cognitive deficits in aged animals reflect a failure of specific components of the working memory system, and may be related to variations in body weight and an associated decrease in activity. ; fax (732) 445-2263. Article is online at

Surgical Endoscopy, 1997

This report describes our initial experience using positron emission tomography (PET) scanning in... more This report describes our initial experience using positron emission tomography (PET) scanning in esophageal cancer patients. In two patients PET identified distant metastatic disease missed by conventional staging. Laparoscopic biopsy provided histological confirmation of metastases. In the third patient, locoregional lymph nodes were identified by PET and confirmed by surgical staging. In this preliminary report, PET appears to be a promising new noninvasive modality for staging patients with esophageal cancer.

Society of Nuclear Medicine Annual Meeting Abstracts, May 1, 2007

Aps Meeting Abstracts, 2008

The Standardized Uptake Value (SUV) is often used in positron emission tomography (PET) to differ... more The Standardized Uptake Value (SUV) is often used in positron emission tomography (PET) to differenciate malignant from benign tumors, and to monitor the progress of the patient response to therapy. Despite its name, SUV may depend on both PET scanner hardware and software details, and will depend on the imaging protocol. In this paper, we present a study of the SUV variability according to these external factors. To study the influence of the PET device, phantom studies were performed on two different combined PET/CT scanners. SUVs were obtained using several reconstruction algorithms and different reconstruction matrix sizes. To study the influence of the imaging protocol, patients were injected with 370 MBq of 18F-FDG and scanned at 60 and 90 min post-injection. SUVs were obtained applying several clinical image reconstruction algorithms. Significant differences in SUVs were obtained depending on the PET scanner, reconstruction method, and imaging protocol. It is essential, therefore, to follow a strict protocol in order to reliably compare FDG uptake with SUVs. Our results may have a significant clinical impact in order to provide an unbiased SUV thereshold to determine malignancy.

1993 IEEE Conference Record Nuclear Science Symposium and Medical Imaging Conference, 1993

Two methods for attenuation correction in 3D positron emission tomography have been compared. The... more Two methods for attenuation correction in 3D positron emission tomography have been compared. The first method, which is referred to here as the direct method, estimates the attenuation correction factors from the ratio of the blank and transmission scan. The second method, referred to here as the reconstruction-reprojection method is based on the reconstruction and forward projection of a transmission

Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference, 1991

Following previous reports of the NEC gain for a PET (positron emission tomography) scanner with ... more Following previous reports of the NEC gain for a PET (positron emission tomography) scanner with retractable septa (Siemens-CTI 953B), methods for 3-D normalization and attenuation correction from 2-D datasets were developed. Physical performance and system calibration were reevaluated for 3-D reconstructed data for this scanner. Normalization is performed by measuring the direct plane sinograms (no cross-plane contribution) with septa in

Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference, 1991

A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtendi... more A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtending two opposing arcs of 60° and mounted on a circular support was developed. Projection data at all angles are acquired by rotating the detector assembly. The scanner has no septa, and data from the equivalent of 16 full rings of detectors are collected and sorted

Continental shelf waters from the Labrador Sea to the Mid-Atlantic Bight experienced significant ... more Continental shelf waters from the Labrador Sea to the Mid-Atlantic Bight experienced significant freshening in the late 1990s, likely caused by increasing glacial melting and enhanced precipitation and river runoff at higher latitudes (as a result of climate change). The freshening of the ocean can alter circulation and stratification of shelf waters and may influence the phytoplankton dynamics and ecosystem

IEEE Symposium Conference Record Nuclear Science 2004., 2004

Evaluation and follow up of small pulmonary nodules has become commonplace with advancing PET and... more Evaluation and follow up of small pulmonary nodules has become commonplace with advancing PET and CT technology. Limits in system resolution, recovery coefficient estimations and transaxial ROI determinations often make obtaining useful SUV data difficult. We demonstrate a method which may be more accurate for making these determinations. It is assumed that the nodule can be distinguished clearly on CT

1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019), 1999

We present a 3D whole-body PET simulator that generates multiple, yet statistically accurate, rea... more We present a 3D whole-body PET simulator that generates multiple, yet statistically accurate, realizations of projection data within a computation time that is short enough to enable the measurement of the task performance of image reconstruction algorithms. The whole-body simulator takes into account the following effects: the seperate amounts of statistical noise contributed by true, scattered, and random coincidences, activity outside the field of view, activity decay between bed positions, detector efficiencies and resolution, and noise arising from the transmission scan. The principle of the simulation is to analytically calculate projections based on the geometrical specification of the emission and attenuation objects that comprise the MCAT phantom. A pre-determined level of statistical noise is then added to the projection data, which is then inputted to the same data correction and image reconstruction procedures used in practice.

Proceedings of 1994 IEEE Nuclear Science Symposium - NSS'94, 1995

The use of X-ray CT for Attenuation Correction of PET Data ... Thomas Beyer, Paul E. Kinahan, Dav... more The use of X-ray CT for Attenuation Correction of PET Data ... Thomas Beyer, Paul E. Kinahan, David W. Townsend, and Donald Sashin Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213-2582 ... This paper presents the results of evaluating ...

1990 IEEE Nuclear Science Symposium Conference Record, 1990

Performance characteristics of a new commercial design of positron tomograph with retractable sep... more Performance characteristics of a new commercial design of positron tomograph with retractable septa for brain imaging have been studied. The device, composed of block BGO detectors (8 x 8 elements per block), has a ring diam of 76cm and an axial FOV of 10.8cm (slice thickness 4.3&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; with septa). The in-plane resolution is less than 5mm with wobble sampling. Its

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 2000

The availability of accurately aligned, whole-body anatomical (CT) and functional (PET) images co... more The availability of accurately aligned, whole-body anatomical (CT) and functional (PET) images could have a significant impact on diagnosing and staging malignant disease and on identifying and localizing metastases. Computer algorithms to align CT and PET images acquired on different scanners are generally successful for the brain, whereas image alignment in other regions of the body is more problematic. A combined PET/CT tomograph with the unique capability of acquiring accurately aligned functional and anatomical images for any part of the human body has been designed and built. The PET/CT scanner was developed as a combination of a Siemens Somatom AR.SP spiral CT and a partial-ring, rotating ECAT ART PET scanner. All components are mounted on a common rotational support within a single gantry. The PET and CT components can be operated either separately, or in combined mode. In combined mode, the CT images are used to correct the PET data for scatter and attenuation. Fully quanti...

2008 IEEE Nuclear Science Symposium Conference Record, 2008

The physical PET performance of the first prototype of the recently introduced Biograph mCT TOF P... more The physical PET performance of the first prototype of the recently introduced Biograph mCT TOF PET/CT scanner (Siemens Molecular Imaging) has been evaluated. The PET component incorporates 192 detector blocks, 5.4 cm x 5.4 cm in cross-section; each block comprises a 13 x 13 matrix of 4 x 4 x 20 mm3 crystal elements. The four detector block rings cover

Journal of Neuroradiology, 2006

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.

1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019), 1999

... Blank and transmission data were acquired in standard 2D (ring difference 5, span of 11) and ... more ... Blank and transmission data were acquired in standard 2D (ring difference 5, span of 11) and true modes, using 3 rotating %e rod sources (activity around 10 mCi), and a 7 bin wide rod mask, which produced scatter free 2D attenuation correction. B. Experimental protocols ...