Quantitative Brain PET. Comparison of 2D and 3D Acquisitions on the GE Advance Scanner.
ABSTRACT PURPOSE: Recent developments in the design of positron emission tomography (PET) scanners have made three-dimensional (3D) data acquisition attractive because of significantly higher sensitivity compared to the conventional 2D mode (with lead/tungsten septa extended). However, the increased count rate in 3D mode comes at the cost of increased scatter, randoms, and dead time. Several schemes to correct for these effects have been proposed and validated in phantom studies. In this study, we evaluated the overall improvement afforded by 3D imaging in quantitative human brain PET studies carried out at our institution.METHODS: Subjects were studied using sequential/interleaved 2D and 3D data acquisition with a GE Advance scanner. We calculated regional and global cerebral glucose metabolism with [(18)F]flourodeoxyglucose (FDG) and estimated rate constants for striatal [(18)F]fluorodopa (FDOPA) uptake.RESULTS: FDG: Global mean glucose metabolic rates were in almost complete agreement (within 1%) between the two modes whereas the regional differences ranged from -7.7% to +9% for all cortical structures. However, for small regions (<2 cm(2)) like caudate nuclei, the maximum difference was 14.7%. FDOPA: A significant improvement in image quality was evident in 3D mode and there was complete agreement between the estimated parameters in the two scanning modes for the same noise equivalent counts: Striatal-to-occipital ratio (SOR) and striatal FDOPA uptake (K(i)(FD)) had mean differences of less than 2% and 5%, respectively.CONCLUSIONS: 3D FDG studies can be done with either half the injected dose or half the scan duration to a comparable 2D study. 3D PET imaging has distinct advantages over 2D in the quantitative fluorodopa studies.
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ABSTRACT: AimSome positron emission tomography (PET) cameras offer the possibility of choosing between the 2D and 3D acquisition modes. Due to the lack of comparative and objective data in the litterature between the two modes in clinical routine conditions, we have performed a comparative study based on the assessment of qualitative and quantitative parameters.Materials and methodsA series of 33 FDG PET studies has been prospectively selected in the nuclear medicine department. All studies have been performed with a Discovery ST® camera (GE healthcare) first in the 2D or 3D mode according to the usual criteria of the department. Then a new single step was acquired on a pathological region using the other mode. The same single slice was chosen and analyzed in the two modes (blindly and in random order) by seven nuclear physicians in terms of qualitative and quantitative parameters.ResultsThe 2D mode is significantly better than 3D concerning the overall image quality for patients with a body mass index (BMI) > 27.5 (p = 0.006) and concerning the confidence in lesion reporting for patients with a BMI > 25 (p = 0.01). The mean number of detected lesions is not affected by the acquisition mode but it is significantly correlated with the image quality and the confidence in lesion reporting (p = 0.07 and p = 0.013, respectively).Conclusion With the Discovery ST PET-CT, the 2D mode gives better results than 3D for overweight and obese patients in terms of image quality and confidence in lesion reporting.Medecine Nucleaire 10/2007; 31(10):538–544. DOI:10.1016/j.mednuc.2007.02.006 · 0.16 Impact Factor
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ABSTRACT: This report identifies evidence of partially functional cerebral regions in catastrophically injured brains. To study five patients in a persistent vegetative state (PVS) with different behavioural features, we employed [(18)F]fluorodeoxyglucose-positron emission tomography (FDG-PET), MRI and magnetoencephalographic (MEG) responses to sensory stimulation. Each patient's brain expressed a unique metabolic pattern. In three of the five patients, co-registered PET/MRI correlate islands of relatively preserved brain metabolism with isolated fragments of behaviour. Two patients had suffered anoxic injuries and demonstrated marked decreases in overall cerebral metabolism to 30-40% of normal. Two other patients with non-anoxic, multifocal brain injuries demonstrated several isolated brain regions with relatively higher metabolic rates, that ranged up to 50-80% of normal. Nevertheless, their global metabolic rates remained <50% of normal. MEG recordings from three PVS patients provide clear evidence for the absence, abnormality or reduction of evoked responses. Despite major abnormalities, however, these data also provide evidence for localized residual activity at the cortical level. Each patient partially preserved restricted sensory representations, as evidenced by slow evoked magnetic fields and gamma band activity. In two patients, these activations correlate with isolated behavioural patterns and metabolic activity. Remaining active regions identified in the three PVS patients with behavioural fragments appear to consist of segregated corticothalamic networks that retain connectivity and partial functional integrity. A single patient who suffered severe injury to the tegmental mesencephalon and paramedian thalamus showed widely preserved cortical metabolism, and a global average metabolic rate of 65% of normal. The relatively high preservation of cortical metabolism in this patient defines the first functional correlate of clinical- pathological reports associating permanent unconsciousness with structural damage to these regions. The specific patterns of preserved metabolic activity identified in these patients do not appear to represent random survivals of a few neuronal islands; rather they reflect novel evidence of the modular nature of individual functional networks that underlie conscious brain function. The variations in cerebral metabolism in chronic PVS patients indicate that some cerebral regions can retain partial function in catastrophically injured brains.Brain 07/2002; 125(Pt 6):1210-34. · 10.23 Impact Factor
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ABSTRACT: Measurement of the regional cerebral blood flow (rCBF) is an important parameter in the evaluation of cerebral function. With positron emission tomography (PET) rCBF has predominantly been quantified using the short-lived radiotracer oxygen-15 labelled water (H 2 15 O) and an adaptation of the Kety one-tissue compartment autoradiographic model. The values attained in putative grey matter, however, are systematically underestimated because of the limited scanner resolution. For this reason we applied a dynamic kinetic two-tissue compartment model including a fast and a slow flow component each with a perfusable tissue fraction. In the fast component rCBF was 2-2.5 times greater than grey matter values using traditional autoradiography in both human and monkey. Visual stimulation in human gave a corrected rCBF increase of approximately 40%. Visual stimulation was also used to indirectly validate carbon-10 labelled carbondioxide ( 10 CO 2 ), a new very short-lived rCBF PET tracer with a half-life of only 19.3 seconds. This allowed an increase in the number of independent PET scans per subject from 12-14 using H 2 15 O to 64 using 10 CO 2 . The experiment demonstrated a maximal activation response in the visual cortex at a 10-15 Hz stimulation frequency. The use of the rCBF PET mapping technique is illustrated by studies of the organization of language and the oculomotor system. With respect to the former, we found confirmation of neuropsychological evidence of the involvement of the left supramarginal/angular gyrus in reading in Japanese of a phonologically based script system, Kana, and of the left posterior inferior temporal gyrus in reading of a morphogram based script system, Kanji. Concerning the organization of the oculomotor system we found overlapping areas in fronto-parietal cortex involved in maintaining visual fixation, and performing visually guided and imagined eye movements. These data show that overt eye movements are not a prerequisite of the activation of classical cortical oculomotor regions and underscore the involvement of these areas in other behaviours such as visual attention and saccade inhibition. During eye movements in the dark an increased activation response in the parieto-occipital cortex can be found. This can be interpreted as effects of the gaze-sensitive neurons that are used to objectively localize objects relative to the body, and efferent copies of motor commands, used to predict the visual consequences of eye movements to maintain visual continuity. Defect efferent copies are in some neurobiological models of schizophrenia thought to contribute to passivity phenomena. The clinical perspective of brain mapping techniques is to preoperatively locate eloquent areas, e.g. motor function, language, and memory, allowing the achievement of optimal neurosurgical resection with the preservation of neurological function.Danish medical bulletin 12/2007; 54(4):289-305. · 1.01 Impact Factor