9:-9:15. 3D Data Acquisition for Whole Body Images on the ECAT HR+

Purpose: Evaluation of 3D clinical whole-body FDG PET imaging using recent improvements in data correction and reconstruction methods.Methods: Phantom studies following the NEMA NU 2-2000 draft were performed to evaluate count loss and accuracy of attenuation and scatter correction algorithms. Phantom results were used to estimate 3D vs. 2D efficiency. For patient studies, an established 2D imaging protocol (9 min emission, 3 min transmission acquisition per bed position, commencing 60 min after injection of 15 mCi FDG) was used. This was followed by a 3D acquisition of the same duration, commencing approximately 110 min later, so that 3D acquisition was performed with approximately 50% lower patient activity than 2D. Images were compared in terms of anatomic structural definition and visible artifacts.The count loss study showed that in a dose range of 10-15 mCi, 3D produced an approximately two-fold increase in effective NEC compared to 2D. The phantom imaging study showed slightly improved target to background ratios for both hot and the cold "lesions" when using 3D imaging. In 5 patients studied so far, comparison of 2D and 3D studies demonstrated no systematic differences in image quality between the two methods.Conclusion: 3D whole-body imaging with improved image reconstruction may permit a two-fold reduction in emission acquisition time or injected dose, without decrease in image quality compared to standard 2D imaging techniques.

Spatial transformation during 3D reconstruction in positron emission tomography.

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.

Cerebral representation of one's own past: neural networks involved in autobiographical memory.

We studied the functional anatomy of affect-laden autobiographical memory in normal volunteers. Using H2 15O positron emission tomography (PET), we measured changes in relative regional cerebral blood flow (rCBF). Four rCBF measurements were obtained during three conditions: REST, i.e.,, subjects lay at rest (for control); IMPERSONAL, i.e., subjects listened to sentences containing episodic information taken from an autobiography of a person they did not know, but which had been presented to them before PET scanning (nonautobiographical episodic memory ecphory); and PERSONAL, i.e., subjects listened to sentences containing information taken from their own past (autobiographical episodic memory ecphory). Comparing IMPERSONAL with REST (nonautobiographical episodic memory ecphory) resulted in relative rCBF increases symmetrically in both temporal lobes including the temporal poles and medial and superior temporal gyri. The same loci, however, with a stronger lateralization to the right hemisphere were activated in the comparison PERSONAL to REST (autobiographical episodic memory ecphory). In addition, the right temporomesial, right dorsal prefrontal, right posterior cingulate areas, and the left cerebellum were activated. A comparison of PERSONAL and IMPERSONAL (autobiographical vs nonautobiographical episodic memory ecphory) demonstrated a preponderantly right hemispheric activation including primarily right temporomesial and temporolateral cortex, right posterior cingulate areas, right insula, and right prefrontal areas. The right temporomesial activation included hippocampus, parahippocampus, and amygdala. These results suggest that a right hemispheric network of temporal, together with posterior, cingulate, and prefrontal, areas is engaged in the ecphory of affect-laden autobiographical information.

Individual functional anatomy of verb generation.

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.

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/microCi/ml in two-dimensional (2D) mode and increases to 1.46 Mcps/microCi/ml in 3D mode. Count rate performance was investigated for different low energy discriminator thresholds. Smaller detector blocks improve noise equivalent counts by approximately 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-maximal (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.