Summary: Accuracy in in vivo quantitation of brain func tion with positron emission tomography (PET) has often been limited by partial volume effects. This limitation be comes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with dif ferent degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocam pus, irrespective of the GM volume. GM PET was apPositron emission tomography (PET) permits in vestigation of physiological and biochemical pro cesses in human brain in vivo, and has yielded new insights into both normal physiology and diseases (Kuhl et aI. , 1982;Foster, 1983; Wagner et aI. , 1983; Frost et aI., 1985;Phelps and Mazziotta, 1985;Frost, 1986; Yamaguchi et aI. , 1986; Yoshii et aI., Abbreviations used: AU, arbitrary units; FWHM, full width at half-maximum; OM, gray matter; MRI, magnetic resonance im aging; PET, positron emission tomography; RMSE, relative mean-squared error; ROI, region of interest; SPOR, spoiled grass; WM, white matter. 571plied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetec ted in the PET image before correction for partial volume effects. In computer simulations, errors in the segmenta tion of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate de termination of the actual radiotracer concentration in hu man brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration re flects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM. Key Words: Brain gray matter-Positron emission tomography-Magnetic resonance imaging-Partial vol ume effects-Aging-Dementia-Brain atrophy.1988; Fowler, 1990; Frost and Wagner, 1990; Leen ders et aI., 1990;Martin et al., 1991; Mayberg et aI. , 1991). Nevertheless, a limitation of PET remains: its relatively poor spatial resolution. As a result, PET quantification, especially in structures smaller than two times the full width at half-maximum (FWHM) of the tomograph, is affected by partial volume effects (Hoffmann et aI. , 1979). Given that the in-plane FWHM of current PET instruments ranges from 2.6 mm (Valk et aI. , 1990) to about 14 mm, tracer activity in many brain structures, in cluding the neocortex, is often underestimated. In neocortex, gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) spaces are convo luted, and cannot be resolved using PET instrumen tation; a cortical PET signal thus reflects the aver age tracer concentr...

In postmortem studies of patients with schizophrenia, D2 dopamine receptors in the basal ganglia have been observed to be more numerous than in patients with no history of neurological or psychiatric disease. Because most patients with schizophrenia are treated with neuroleptic drugs that block D2 dopamine receptors in the caudate nucleus, it has been suggested that this increase in the number of receptors is a result of adaptation to these drugs rather than a biochemical abnormality intrinsic to schizophrenia. With positron emission tomography (PET), the D2 dopamine receptor density in the caudate nucleus of living human beings was measured in normal volunteers and in two groups of patients with schizophrenia--one group that had never been treated with neuroleptics and another group that had been treated with these drugs. D2 dopamine receptor densities in the caudate nucleus were higher in both groups of patients than in the normal volunteers. Thus, schizophrenia itself is associated with an increase in brain D2 dopamine receptor density.

In all, 19 research subjects, with current histories of frequent cocaine use, were exposed to cocaine-related cues to elicit drug craving. We measured the change of occupancy of dopamine at D2-like receptors with positron emission tomography (PET) and inferred a change of intrasynaptic dopamine (endogenous dopamine release), based on the displacement of radiotracer [11 C]raclopride. Receptor occupancy by dopamine increased significantly in putamen of participants who reported cue-elicited craving compared to those who did not. Further, the intensity of craving was positively correlated with the increase in dopamine receptor occupancy in the putamen. These results provide direct evidence that occupancy of dopamine receptors in human dorsal striatum increased in proportion to subjective craving, presumably because of increased release of intrasynaptic dopamine.

BackgroundLocal public health agencies play a central role in response to an influenza pandemic, and understanding the willingness of their employees to report to work is therefore a critically relevant concern for pandemic influenza planning efforts. Witte's Extended Parallel Process Model (EPPM) has been found useful for understanding adaptive behavior in the face of unknown risk, and thus offers a framework for examining scenario-specific willingness to respond among local public health workers. We thus aim to use the EPPM as a lens for examining the influences of perceived threat and efficacy on local public health workers' response willingness to pandemic influenza.Methodology/Principal FindingsWe administered an online, EPPM-based survey about attitudes/beliefs toward emergency response (Johns Hopkins∼Public Health Infrastructure Response Survey Tool), to local public health employees in three states between November 2006 – December 2007. A total of 1835 responses were collected for an overall response rate of 83%. With some regional variation, overall 16% of the workers in 2006-7 were not willing to “respond to a pandemic flu emergency regardless of its severity”. Local health department employees with a perception of high threat and high efficacy – i.e., those fitting a ‘concerned and confident’ profile in the EPPM analysis – had the highest declared rates of willingness to respond to an influenza pandemic if required by their agency, which was 31.7 times higher than those fitting a ‘low threat/low efficacy’ EPPM profile.Conclusions/SignificanceIn the context of pandemic influenza planning, the EPPM provides a useful framework to inform nuanced understanding of baseline levels of – and gaps in – local public health workers' response willingness. Within local health departments, ‘concerned and confident’ employees are most likely to be willing to respond. This finding may allow public health agencies to design, implement, and evaluate training programs focused on emergency response attitudes in health departments.