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We present an ab-initio study of GaP bulk as a test case to show the importance of going beyond the single particle Density Functional Theory (DFT) scheme in the calculation of excited state properties. The inclusion of many-body effects within the GW approach for the determination of electronic gaps, and of excitonic effects in the calculations of the dielectric function, is discussed. Comparison with one-particle DFT results and with experimental data are presented.

We summarize the theoretical framework and some of the computational methods currently used for the calculation of the optical properties of surfaces within the “ab initio” scheme. Applications and examples are given for calculations including self-energy, excitonic, and local-field effects, with an emphasis on convergence problems and on the approximations related to the pseudopotential approach.

Abstract. The differential diagnosis among various types of non-functioning sellar and parasellar tumours is sometimes difficult using currently available methods of morphological imaging. The aim of this study was to define whether assessment of the uptake of [¹⁸F]fluoro-ethyl-spiperone (FESP) with positron emission tomography (PET) could be helpful for the differential diagnosis of pituitary adenomas and other parasellar lesions, and for establishing the appropriate therapeutic approach. The population examined comprised 16 patients with the diagnosis of primary tumour of the sellar/parasellar region who were waiting to undergo surgical treatment. The results demonstrated that PET with [¹⁸F]FESP is a very specific method for differentiating adenomas from craniopharyngiomas and meningiomas. The visual interpretation of images allows such differentiation at approximately 70 min after tracer injection. Semiquantitative analysis of the dynamic PET data confirmed the results of visual interpretation, demonstrating that the uptake of [¹⁸F]FESP was consistently (i.e. throughout the series) at least two- to threefold higher in non-functioning adenomas than in other parasellar tumours as early as 70 min after tracer injection, and that it increased still further thereafter. It is concluded that PET with [¹⁸F]FESP might be of clinical value in those cases in which the differential diagnosis among various histological types of sellar tumour is uncertain with conventional methods.

The relationship between severity of coronary artery stenosis (CAS) and myocardial 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) uptake in the fasting state, assessed with positron emission tomography (PET), was examined in a series of 48 patients with CAS undergoing both studies for diagnostic purposes. The data analysis was based on the subdivision of the left ventricular myocardium into four segments defined in relation to ventricular vascularization: the anterior and septal segments, perfused by the left anterior descending artery; the lateral segment, perfused by the left circumflex; and the inferior segment, perfused by the right coronary artery. The 192 segments were grouped according to degree of CAS: 10–50, II 51–75; III 76–90; IV 91–99; V and VI occluded coronary artery with good or poor collaterals, respectively. An 18F-FDG index was determined as the tissue/blood pool radioactivity ratio in each segment. The statistical analysis was performed by one-way ANOVA, multiple comparison tests and the chi-squared test. The proportion of segments with 18F-FDG uptake was also analysed for a linear trend across the ordered levels of CAS. The 18F-FDG index in groups I to V was significantly higher than in controls, but it was not different among the groups with CAS, except for group V versus I. However, the proportion of segments with enhanced 18F-FDG uptake was correlated to the degree of CAS. In cases of complete occlusion of a major afferent coronary artery, the proportion of segments with 18F-FDG uptake varied in relation to the presence of collaterals. Although the 18F-FDG index is inadequate for estimating the severity of CAS, it provides useful information on the metabolism of segments perfused by collateral circulation.