The Phillips Curve, the Persistence of Inflation, and the Lucas Critique:Evidence from Exchange-Rate Regimes: Comment

The purpose of this comment is to demonstrate that their theoretical result concerning the first order derivative of relative inflation persistence with respect to the degree of accommodation is incorrect. As a consequence, the sign of the first derivative becomes ambiguous. We provide an economic explanation of this result, elaborating on the three distinct transmission mechanisms in the AS (relative) model. Moreover, we propose an economically meaningful modification of the original AS model that restores a strictly positive relation between exchange rate accommodation and relative inflation persistence.international economics and trade ;

2,2,6,6-Tetra­kis(biphenyl-2-yl)-4,4,8,8-tetra­methyl­cyclo­tetra­siloxane

The title compound, [–Si(C12H9)2OSi(CH3)2O–]2, was obtained unintentionally as the product of an attempted crystallization of caesium bis­(biphenyl-2,2′-di­yl)fluoro­silicate from dimethyl­formamide. In the crystal, the mol­ecule is located on an inversion center and the siloxane ring adopts a twist-chair conformation with the two dimethyl-substituted Si atoms lying 0.7081 (5) Å out of the plane defined by the two bis­(biphenyl-2-yl)-substituted Si atoms and the four O atoms. In each Si(C12H9)2 unit, the orientation of one terminal phenyl ring relative to the phenyl­ene ring of the other biphenyl moiety suggests a parallel displaced π–π stacking inter­action [centroid distance = 4.2377 (11) Å and dihedral angle = 15.40 (9)°]

Image Derived Input Functions: Effects of Motion on Tracer Kinetic Analyses

Purpose: To quantify the effects of motion affected image-derived input functions (IDIF) on the outcome of tracer kinetic analyses. Procedures: Two simulation studies, one based on high and the other on low cortical uptake, were performed. Different degrees of rotational and axial translational motion were added to the final frames of simulated dynamic positron emission tomography scans. Extracted IDIFs from motion affected simulated scans were compared to original IDIFs and to outcome of tracer kinetic analysis (volume of distribution, V T). Results: Differences in IDIF values of up to 239 % were found for the last frames. Patient motion of more than 6 ° or 5 mm resulted in at least 10 % higher or lower VT values for the high cortical tracer. Conclusion: The degrees of motion studied are commonly observed in clinical studies and hamper the extraction of accurate IDIFs. Therefore, it is essential to ensure that patient motion is minimal and corrected for

Reproducible Analysis of Rat Brain PET Studies Using an Additional [(18)F]NaF Scan and an MR-Based ROI Template

Background. An important step in the analysis of positron emission tomography (PET) studies of the brain is the definition of regions of interest (ROI). Image coregistration, ROI analysis, and quantification of brain PET data in small animals can be observer dependent. The purpose of this study was to investigate the feasibility of ROI analysis based on a standard MR template and an additional [(18)F]NaF scan. Methods. [(18)F]NaF scans of 10 Wistar rats were coregistered with a standard MR template by 3 observers and derived transformation matrices were applied to corresponding [(11)C]AF150(S) images. Uptake measures were derived for several brain regions delineated using the MR template. Overall agreement between the 3 observers was assessed by interclass correlation coefficients (ICC) of uptake data. In addition, [(11)C]AF150(S) ROI data were compared with ex vivo biodistribution data. Results. For all brain regions, ICC analysis showed excellent agreement between observers. Reproducibility, estimated by calculation of standard deviation of the between-observer differences, was demonstrated by an average of 17% expressed as coefficient of variation. Uptake of [(11)C]AF150(S) derived from ROI analysis closely matched ex vivo biodistribution data. Conclusions. The proposed method provides a reproducible and tracer-independent method for ROI analysis of rat brain PET data

Automatic generation of absolute myocardial blood flow images using [15O]H2O and a clinical PET/CT scanner

PURPOSE: Parametric imaging of absolute myocardial blood flow (MBF) using [(15)O]H(2)O enables determination of MBF with high spatial resolution. The aim of this study was to develop a method for generating reproducible, high-quality and quantitative parametric MBF images with minimal user intervention. METHODS: Nineteen patients referred for evaluation of MBF underwent rest and adenosine stress [(15)O]H(2)O positron emission tomography (PET) scans. Ascending aorta and right ventricular (RV) cavity volumes of interest (VOIs) were used as input functions. Implementation of a basis function method (BFM) of the single-tissue model with an additional correction for RV spillover was used to generate parametric images. The average segmental MBF derived from parametric images was compared with MBF obtained using nonlinear least-squares regression (NLR) of VOI data. Four segmentation algorithms were evaluated for automatic extraction of input functions. Segmental MBF obtained using these input functions was compared with MBF obtained using manually defined input functions. RESULTS: The average parametric MBF showed a high agreement with NLR-derived MBF [intraclass correlation coefficient (ICC) = 0.984]. For each segmentation algorithm there was at least one implementation that yielded high agreement (ICC > 0.9) with manually obtained input functions, although MBF calculated using each algorithm was at least 10% higher. Cluster analysis with six clusters yielded the highest agreement (ICC = 0.977), together with good segmentation reproducibility (coefficient of variation of MBF <5%). CONCLUSION: Parametric MBF images of diagnostic quality can be generated automatically using cluster analysis and a implementation of a BFM of the single-tissue model with additional RV spillover correction. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00259-011-1730-3) contains supplementary material, which is available to authorized users