U. Pietrzyk

GATE: a simulation toolkit for PET and SPECT.

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. This paper gives a detailed description of the design and development of GATE by the OpenGATE collaboration, whose continuing objective is to improve, document and validate GATE by simulating commercially available imaging systems for PET and SPECT. Large effort is also invested in the ability and the flexibility to model novel detection systems or systems still under design. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at http:/www-lphe.epfl.ch/GATE/. Two benchmarks developed for PET and SPECT to test the installation of GATE and to serve as a tutorial for the users are presented. Extensive validation of the GATE simulation platform has been started, comparing simulations and measurements on commercially available acquisition systems. References to those results are listed. The future prospects towards the gridification of GATE and its extension to other domains such as dosimetry are also discussed.

The ECAT EXACT HR: Performance of a new high resolution positron scanner

Objective The ECAT EXACT HR is a newly designed CTI–Siemens PET scanner with high spatial resolution. Its physical performance with respect to resolution, count rate efficiency, and scatter was investigated and evaluated with phantom studies. Materials and Methods The new tomograph consists of three rings of 112 BGO block detectors (50 mm x 23 mm x 30 mm deep) each, covering an axial field of view of 15 cm with a patient port of 56 cm diameter. Each block is sawed into an 8 x 7 matrix giving 24 detector rings with 784 crystals each. Results Total sensitivity for a 20 cm cylinder phantom is 177 kcps/μCi/ml in two-dimensional (2D) mode and increases to 1.46 Mcps/μCi/ml in 3D mode. Count rate performance was investigated for different low energy discriminator thresholds. Smaller detector blocks improve noise equivalent counts by ∼50% compared with the EXACT system both in 2D and in 3D mode. Scatter fractions vary in 2D from 0.09 to 0.13 for energy thresholds from 450 to 250 keV for line sources in a 20 cm diameter phantom. In 3D mode an increase of scatter by a factor of 3 is observed. Transaxial spatial resolution varies from 3.6 mm full width at half-maximum (FWHM) at the center to 4.5 mm FWHM tangentially and 7.4 mm FWHM radially at R = 20 cm. Average axial resolution changes from 4.0 mm FWHM at center to 6.7 mm FWHM at R = 20 cm. Conclusion Due to its special properties, the EXACT HR can be equally applied to routine clinical brain and whole-body imaging and to noninvasive experimental studies of regional tracer concentrations in medium-sized animals.

AN INVESTIGATION OF THE SPIN STRUCTURE OF THE PROTON IN DEEP INELASTIC SCATTERING OF POLARISED MUONS ON POLARISED PROTONS

An investigation of the spin structure of the proton in deep inelastic scattering of polarised muons on polarised protons

The ratio of the nucleon structure functions

Abstract Using the data on deep inelastic muon scattering on iron and deuterium the ratio of the nucleon structure functions F 2 N ( Fe )/ F 2 N ( D ) is presented. The observed x -dependence of this ratio is in disagreement with existing theoretical predictions.

F^N_2

Sixteen patients were studied by multitracer positron emission tomography (PET) within 6–48 (mean of 23) h of onset of a hemispheric ischemic stroke and again 13–25 (mean of 15.6) days later. Cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral metabolic rate of glucose (CMRglc) were measured each time by standard methods, and the sets of brain slices obtained at the two studies were matched using a three-dimensional alignment procedure. On matched brain slices, regions of interest (ROIs) for infarct and peri-infarct tissue, contralateral mirror regions, and major brain structures were outlined. In the core of infarction, blood flow and metabolism were significantly lower than in the corresponding contralateral regions at the first study, and did not change during the observation period. In the peri-infarct tissue, CMRO2 was moderately decreased at the first measurement; over time, the CMRO2 deteriorated progressively while flow did not change. When peri-infarct regions were selected on the basis of increased OEF (25 ± 29.8% above corresponding contralateral regions) on the early scans, the CBF was significantly decreased (23 ± 6.6%) while the CMRO2 showed only a slight difference from the mirror region. Within the observation period, the CBF improved but the CMRO2, OEF, and CMRglc deteriorated. Only in a few regions with increased OEF and slightly impaired CMRO2 was metabolism preserved close to normal values. These data from repeat PET studies in reproducibly defined tissue compartments furnish evidence of viable tissue in the border zone of ischemia up to 48 h after stroke. While this viable peri-infarct tissue exhibits some potential for effective treatment of ischemic stroke, therapeutic routines available today cannot prevent subsequent metabolic derangement and progression to necrosis. Multitracer PET studies identifying viable tissue could be of value in the development of effective treatment of ischemic stroke.

for iron and deuterium

The Cologne Special is a prototype of the ECAT EXACT (model 921), a new generation of Siemens-CTI PET scanners. It consists of three rings of 48 BGO block detectors each, covering an axial field of view of 16.2 cm with a patient port of 56.2 cm diameter. This results in a total of 24 rings with 384 crystals each, giving 47 contiguous image planes in two-dimensional (2D) mode. Total system sensitivity is 216 kcps/μCi/ml for a 20 cm cylinder phantom in 2D. This increases to 1.5 Mcps/μCi/ml in 3D. Data are acquired in the stationary mode only (no wobble motion), resulting in a transaxial spatial resolution of better than 6 mm full width at half-maximum (FWHM) at the center, which degrades to 7.5 mm tangentially and 9.6 mm radially at a radius of 20 cm. Average axial resolution changes from 5.0 mm FWHM at the center to 8.1 mm at R = 20 cm. Count rate performance was investigated at different low energy discriminator settings and found to be linear up to 2.5 μCi/ml with a 20 cm phantom. The magnitude and distribution of scatter were evaluated for both septa-extended and septa-retracted conditions for a range of energy thresholds. Brain, heart, and whole-body studies with the new tomography demonstrate the versatility of its applications without compromising on physical performance.

Progressive Derangement of Periinfarct Viable Tissue in Ischemic Stroke

Examination of the individual functional anatomy of language is of particular interest in clinical neurology to explain the variability of aphasic symptoms after focal lesions and to avoid damage of language-related brain areas by surgery. For a silent verb generation task, we examined whether activation PET with 3D data acquisition, multiple replication of conditions, and coregistration with MRI provides results that are consistent and reproducible enough to be useful clinically. Visual analysis was performed on PET-MRI fusion images, including renderings of the brain surface. Quantitative analysis was based on volumes of interest. In seven right-handed normals, activation of the triangular part of the left inferior frontal cortex [Brodman area (BA) 45] was the most significant finding that was present in each subject. Two subjects showed minor anatomical variants of the ascending or horizontal ramus of the sylvian fissure that were associated with the least activation of BA 45. In the left hemisphere the other frontal gyri, the superior temporal and posterior part of the middle temporal gyrus, and the paracingulate gyrus were also significantly activated. There was significant bilateral cerebellar activation, but it was significantly more intense on the right than on the left side. The consistency and high interindividual reproducibility of these findings suggest that this technique may be useful for clinical assessment of language-related areas.

Performance Evaluation of the Positron Scanner ECAT EXACT

BACKGROUND: The neck lymph nodes are a common site of metastases from carcinoma of unknown primary (CUP syndrome). 2[ 18 F]-fluoro-2-deoxy-D-glucose positron emission tomography (18-FDG-PET) has been shown to be a sensitive tool for detecting primary malignant lesions as well as metastatic spread. We have prospectively investigated the sensitivity of 18-FDG-PET in detecting occult primary carcinomas with manifestation in the head and neck lymph nodes. METHODS: From May 1994 to July 1998, in 723 patients a cancer of the head and neck was diagnosed at the University of Cologne ENT outpatient clinic. The routinely performed staging procedures were chest radiography; full blood count; cervical and liver ultrasound; endoscopy of the nasopharynx, oropharynx, hypopharynx, larynx, and esophagus; and laboratory analyses. After the staging workup, in 27 of 723 patients (3.7%) CUP syndrome had to be presumed because the primary cancer could not be detected. In these patients 18-FDG-PET was performed, and images were reconstructed with a transmission-emission fusion technique. RESULTS: In 7 of 27 patients (26%) 18-FDG-PET revealed an unknown primary: in 2 a bronchial carcinoma, in 2 a nasopharyngeal carcinoma, in 1 a squamous cell carcinoma of the parotid gland, in 1 a squamous cell carcinoma of the hypopharynx, and in 1 a carcinoma of the tonsil. In 4 of 7 patients the occult primary tumor was removed surgically. In 8 of 27 patients therapeutic strategy was changed as a result of the 18-FDG-PET findings. CONCLUSION: 18-FDG-PET should be performed in all patients with CUP syndrome after conventional diagnostic workup fails to identify the primary.

Individual Functional Anatomy of Verb Generation

Positron emission tomography (PET) of 18F-2-fluoro-2-shirlyD-glucose (FDG) and single-photon emission tomography (SPET) of 99mTc-hexamethyl-propylene amine oxime (HMPAO) were performed under identical resting conditions within 3 h in 20 patients with probable Alzheimers disease (AD), 12 patients with vascular dementia (VD) and 13 normal persons. In the temporoparietal association cortex similar impairment of relative regional cerebral glucose metabolism (rCMRGI) and relative HMPAO uptake (rCBF) was found. In addition PET showed hypometabolism in the occipital association cortex. The functional pattern was condensed to a ratio of regional values of association areas divided by regional values of structures that are typically less affected by AD. In normals this ratio was significantly related to age for PET metabolic data (r = −0.66, P = 0.01). The ratio was significantly lower in AD than in VD and controls for both rCMRGI and rCBF. In AD only, the metabolic ratio was related to severity of dementia (r = 0.54, P = 0.003) and age (r = 0.64, P = 0.003). Metabolic differences between normals and AD patients were less obvious in old age. In contrast, there were no significant correlations between the perfusion ratio and severity of dementia or age. Comparing the metabolic and perfusion ratio by receiver operating characteristic curves, PET differentiated AD from normals only marginally better than SPET. Differentiation between AD and VD was much better achieved by PET. Our results suggest that both PET and SPET can distinguish AD patients from controls, whereas for differentiation between AD and VD SPET is of little value.

2[18F]-fluoro-2-deoxy-D-glucose positron emission tomography is a sensitive tool for the detection of occult primary cancer (carcinoma of unknown primary syndrome) with head and neck lymph node manifestation

Abstract The x and Q 2 dependence of the single photon exchange cross section d 2 σ /d Q 2 d x and the proton structure functions F 2 ( x , Q 2 ) and R ( x , Q 2 ) have been measured in deep inelastic muon proton scattering in the region 0.02 x Q 2 2 . By comparing data at different incident muon energies R was found to have little kinematic dependence and an average value of −0.010 ± 0.037 (stat.) ± 0.102 (stat.). The observed deviations from scaling gave the value of Λ MS , the QCD mass scale parameter, to be 105 −45 +55 (stat.) −45 +85 (syst.) MeV. The fraction of the momentum of the nucleon carried by gluons was found to be ∼56% at Q 2 ∼22.5 GeV 2 . It is shown that to obtain a description of the data for F 2 ( x , Q 2 ) together with that measured in deep inelastic electron-proton scattering at lower Q 2 it is necessary to include additional higher twist contributions. The value of Λ MS remains unchanged with the inclusion of these contributions which were found to have an x -dependence of the form x 3 /(1 − x ).