Quantification of the dopamine D2 receptor in the living human caudate nucleus by PET: comparison of in vivo and in vitro kinetic parameters

It is demonstrated that the set of kinetic parameters (including first-order rate constants for the dissociation of N-methylspiperone (NMSP) from, and second-order rate constants for the association of NMSP to, the dopamine D2 and serotonin S2 receptors of the caudate nucleus) which can be derived from previously reported human caudate PET (positron emission tomographic) data is not uniquely determined, but that multiple sets generate approximately equivalent curve fits. In particular, the set consisting of the in vitro values can generate the PET data. Thus, the in vitro rate constants may apply in vivo.     

Quantitation of the human basal ganglia with positron emission tomography: a phantom study of the effect of contrast and axial positioning

The accurate measurement of the concentration of a radioisotope in small structures with positron emission tomography (PET) requires a correction for quantitation loss due to the partial volume effect and the effect of scattered radiation. To evaluate errors associated with measures in the human basal ganglia (BG), a unilateral model of the BG has been inserted in a 20-cm cylinder. The recovery coefficient (RC=measured activity/true activity) for the BG phantom has been measured on a CTI tomograph with different background concentrations (contrast) and at different axial locations in the gantry. The BG was visualized on four or five slices, depending on its position in the gantry and on the contrast used. The RC was 0.75 with no background (contrast equal to 1.0). Increasing the relative radioactivity concentration in the background increased the RC from 0.75 to 2.00 when the contrast was -0.7 (BG相似文献   

Tracer kinetic modeling of 11C-acetate applied in the liver with positron emission tomography

It is well known that 40%-50% of hepatocellular carcinoma (HCC) do not show increased 18F-fluorodeoxyglucose (FDG) uptake. Recent research studies have demonstrated that 11C-acetate may be a complementary tracer to FDG in positron emission tomography (PET) imaging of HCC in the liver. Quantitative dynamic modeling is, therefore, conducted to evaluate the kinetic characteristics of this tracer in HCC and nontumor liver tissue. A three-compartment model consisting of four parameters with dual inputs is proposed and compared with that of five parameters. Twelve regions of dynamic datasets of the liver extracted from six patients are used to test the models. Estimation of the adequacy of these models is based on Akaike Information Criteria (AIC) and Schwarz Criteria (SC) by statistical study. The forward clearance K = K1 * k3/(k2 + k3) is estimated and defined as a new parameter called the local hepatic metabolic rate-constant of acetate (LHMRAct) using both the weighted nonlinear least squares (NLS) and the linear Patlak methods. Preliminary results show that the LHMRAct of the HCC is significantly higher than that of the nontumor liver tissue. These model parameters provide quantitative evidence and understanding on the kinetic basis of C-acetate for its potential role in the imaging of HCC using PET.     

Mapping visual field with positron emission tomography bymathematical modeling of the retinotopic organization in the calcarinecortex

We developed an objective and quantitative method of mapping the human visual field with positron emission tomography (PET) and magnetic resonance imaging (MRI). The regional cerebral blood flow (rCBF) images were acquired with H₂¹⁵O-PET under visual fixation as well as under visual stimulation with flickering diodes arranged along the ring at 0°, 3°, 7°, 14°, 21°, or 29° from the fixation point. After coregistration of PET and MR images, we extracted the surface of the calcarine cortex from the MR images and unfolded it to a two-dimensional (2-D) elliptic plane, on which the activated PET images were superimposed. Then we transformed the unfolded calcarine cortex into the visual field coordinates using the complex logarithmic function proposed by Schwartz. A large individual variation was observed in the retinotopical organization as well as in the morphology of the calcarine cortex. The formula was valid only within 15° from the center of the visual field. The constant parameter in the formula was estimated to be 1.5. The cortical linear magnification factor was 12.1, 2.8, and 1.6 at 0, 5, and 10°, respectively. The areas of the central 10° and 40° in the visual field correspond to 50% and 81% of the calcarine surface, respectively     

Study of the resolution performance of an array of discrete detectors with independent readouts for positron emission tomography

The intrinsic resolution characteristics of an original detection system for very high resolution positron emission tomography (PET) based on arrays of small discrete crystals individually coupled to solid state photodetectors are evaluated. The results obtained demonstrate the excellent three-dimensional (3-D) resolving capability of a detection system based on the EG&G/RCA C30994 detector module. The analysis of the various components contributing to the resolution has shown that the geometry of the detector and the intercrystal scattering both contribute to limit the achievable intrinsic resolution. The geometrical component is dominant off the central region of the camera field as a result of intercrystal penetration when the array is irradiated at an angle. Intercrystal scattering must be properly rejected to achieve the intrinsic resolution determined by the detector geometry.     

Multimodality Bayesian algorithm for image reconstruction inpositron emission tomography: a tissue composition model

The use of anatomical information to improve the quality of reconstructed images in positron emission tomography (PET) has been extensively studied. A common strategy has been to include spatial smoothing within boundaries defined from the anatomical data. The authors present an alternative method for the incorporation of anatomical information into PET image reconstruction, in which they use segmented magnetic resonance (MR) images to assign tissue composition to PET image pixels. The authors model the image as a sum of activities for each tissue type, weighted by the assigned tissue composition. The reconstruction is performed as a maximum a posteriori (MAP) estimation of the activities of each tissue type. Two prior functions, defined for tissue-type activities, are considered. The algorithm is tested in realistic simulations employing a full physical model of the PET scanner     

Positron emission tomography with a large axial acceptance angle: signal-to-noise considerations

A volume imaging positron emission tomography (PET) scanner with a large acceptance angle, such as the PENN-PET, offers fine spatial sampling and resolution in three dimensions, and a high sensitivity because of the inclusion of all cross-plane rays. The signal-to-noise ratio (SNR) is used to evaluate image quality for different scanning conditions of the PENN-PET using an activated cylindrical phantom with cold spheres of various sizes. Raising the energy threshold to 400 keV improves the SNR by lowering the scatter fraction, though it also reduces the sensitivity. Increasing the axial acceptance angle from +/-1.3 degrees to +/-6.5 degrees improves the SNR by increasing the sensitivity, even with a two-dimensional reconstruction algorithm, which compromises spatial resolution in the axial direction for points at the edge of the radial field of view. Initial results show that a three-dimensional reconstruction offers an improved SNR over a two-dimensional reconstruction that does not use all cross-plane rays.     

Noninvasive measurement of regional cerebral blood flow change with H(2)(15)O and positron emission tomography using a mechanical injector and a standard arterial input function

To estimate changes in regional cerebral blood flow (rCBF) without arterial sampling in the study of functional-anatomical correlations in the human brain, using (15)O-labeled water and PET, a standard arterial input function was generated from the input function in 10 normal volunteers with dose calibration and peak time normalization. The speed and volume of injection were precisely controlled with a mechanical injector. After global normalization of each tissue activity image, the standard arterial input function was applied to obtain estimated CBF images. Relative changes in estimated rCBF to whole brain mean CBF(DeltaFest) and those in regional tissue activity (DeltaC) were compared with true relative rCBF changes (DeltaF) in 40 pairs of images obtained from 6 normal volunteers. DeltaFest correlated well with DeltaF, whereas DeltaC consistently underestimated DeltaF. This noninvasive method simplifies the activation studies and provides the accurate estimation of relative flow changes.     

An evaluation of the algorithms for determining local cerebral metabolic rates of glucose using positron emission tomography dynamic data

Measurement of the local cerebral metabolic rate of glucose (LCMRGlc) and the individual rate constant parameters of the [(18 )F]2-fluoro-2-deoxy-D-glucose (FDG) model can provide a clearer understanding and insight to the physiological processes in the human brain, and a quicker and more accurate means of diagnosis in clinical applications. A systematic study using simulated and clinical tissue time activity data is presented to evaluate several existing and newly developed major algorithms used for determining LCMRGlc and the individual rate constants from positron emission tomography dynamic data. The computational and statistical properties of the autoradiographic approach, weighted and unweighted nonlinear least squares methods, Patlak graphic approach, weighted integration method, linear least squares and generalized linear least squares methods are investigated and discussed in this paper.     

Fusion of positron emission tomography (PET) and gene array data: a new approach for the correlative analysis of molecular biological and clinical data

The combined assessment of data obtained by positron emission tomography (PET) and gene array techniques provide new capabilities for the interpretation of kinetic tracer studies. The correlative analysis of the data helps to detect dependencies of the kinetics of radiotracer on gene expression. Furthermore, gene expression may be predicted using regression functions if a significant correlation exists, which raises new aspects regarding the interpretation of dynamic PET examinations. The development of new radiopharmaceuticals requires the knowledge of the enhanced expression of genes, especially genes controlling receptors and cell surface proteins. The GenePET program facilitates an interactive approach together with the use of key words to identify possible targets for new radiopharmaceuticals.     

Count rate performances of TTVO3: the CEA-LETI time-of-flight positron emission tomograph

The authors present the count rate performance of the CEA-LETI TTVO3 time-of-flight positron emission tomography (PET) system using both physical measurements and H(2)(15)O bolus human myocardial studies. They also present a comparison between the counting statistics of H(2)(15)O brain studies performed on this machine and on the latest available high-resolution brain bismuth germanate (BGO) tomograph, the ECAT 953B/31. During the 80 mCi cerebral blood flow study, the count rate reached 100 K events/s, and the same experiment performed on a high-resolution BGO brain machine gave only a 30% increase in signal. These results demonstrate that TTVO3 is particularly suitable for H(2)(15)O flow studies.     

Automatic generation of noise-free time-activity curve with gated blood-pool emission tomography using deformation of a reference curve

This paper describes a new method for assessing clinical parameters from a noisy regional time-activity curve (TAC) in tomographic gated blood-pool ventriculography. This method is based on a priori knowledge on the shape of a TAC, and shape approximation. The rejection method was used to generate different random Poisson deviates, covering standard count levels, of six representative TACs in order to test and compare the proposed method with harmonic and multiharmonic reconstruction methods. These methods were compared by evaluating four clinical parameters: time of end systole, amplitude, peak ejection and filling rates. Overall, the accuracy of assessment of these parameters was found to be better with the method described in this paper than with standard multiharmonic fits.     

Verification of the algorithm for emission tomography of plasma inhomogeneities in a plasma-chemical reactor using the Langmuir multiprobe

The few-view emission tomography (ET) of plasma, which introduces physical properties of objects into a reconstruction algorithm, requires a reliable experimental verification using independent methods for validating an adopted model of plasma inhomogeneities. The chosen test object—low-temperature argon plasma in a reactor with a remote plasma source—allows one to study the two-dimensional spatial distribution of a concentration of Ar⁺ ions, which is calculated using the two-view ET, and to verify results using direct measurements by a Langmuir multiprobe located in the plane of tomographic scanning. Studies are carried out for the chamber pressure 2–12 mTorr; the sensitivity of the ion-field homogeneity to the external magnetic field is estimated. A close agreement between concentration fields of Ar⁺, which are measured and reconstructed by tomography, is obtained. The divergence between the probe method and the ET data reconstruction with respect to two views is not above 10%.     

Transcranial direct current stimulation: estimation of the electric field and of the current density in an anatomical human head model

This paper investigates the spatial distribution of the electric field and of the current density in the brain tissues induced by transcranial direct current stimulation of the primary motor cortex. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain structures, such as the cortex, the white matter, the cerebellum, the hippocampus, the medulla oblongata, the pons, the midbrain, and the thalamus. The influence of varying the anode area, the cathode area, and the injected current was also investigated. An electrode area as the one typically used in clinical practice (i.e., both electrodes equal to 35 cm(2)) resulted into complex and diffuse amplitude distributions over all the examined brain structures, with the region of maximum induced field being below or close to the anode. Variations in either the anode or cathode area corresponded to changes in the field amplitude distribution in all the brain tissues, with the former variation producing more diffuse effects. Variations in the injected current resulted, as could be expected, in linearly correlated changes in the field amplitudes.     

Linearized method: A new approach for kinetic analysis of central dopamine D(2) receptor specific binding

We proposed a new method (;linearized method') to analyze neuroleptic ligand-receptor specific binding in a human brain using positron emission tomography (PET). We derived the linear equation to solve four rate constants, k(3), k(4), k(5), k(6) from PET data. This method does not demand a radioactivity curve in plasma as an input function to the brain, and can perform fast calculations in order to determine rate constants. We also tested the nonlinearized method including nonlinear equations which is a conventional analysis using plasma radioactivity corrected for ligand metabolites as an input function. We applied these methods to evaluate dopamine D(2) receptor specific binding of [(11)C] YM-09151-2. The value of B(max)/K(d)=k(3)/k (4) obtained by the linearized method was 5.72+/-3.1 which was consistent with the value of 5.78+/-3.4 obtained by the nonlinearized method.     

Simulation of human respiration in fMRI with a mechanical model

Obtaining functional magnetic resonance images of the brain is a challenging measurement process having a low characteristic signal-to-noise ratio. Images contain various forms of noise, including those induced by physiologic processes. One of the prevalent disturbances is hypothesized to result from susceptibility fluctuations caused by abdominal volume changes during respiration. To test this hypothesis and characterize the contribution of respiration noise to both magnitude and phase images, a mechanical model of a respiring human was constructed. The model was tested by comparing data from the model with that of a resting human. Power spectrum analyses show that the model induces both phase and magnitude disturbances similar to those in the human. The disturbances are directly related to the frequency of the respiration, with the noise most prevalent in the phase images. Though magnitude image noise is hard to identify in the human, the manikin demonstrates the presence of this disturbance. The construction of the manikin rules out motion as the primary source of the observed fluctuations and variation of the electrical properties of the manikin also indicates that signal fluctuations are not primarily due to eddy currents. Therefore, the changes are most probably induced by bulk susceptibility changes correlating with respiration.     

Securing a wireless sensor network for human tracking: a review of solutions

Currently, wireless sensor networks (WSNs) are formed by devices with limited resources and limited power energy availability. Thanks to their cost effectiveness, flexibility, and ease of deployment, wireless sensor networks have been applied to many scenarios such as industrial, civil, and military applications. For many applications, security is a primary issue, but this produces an extra energy cost. Thus, in real applications, a trade‐off is required between the security level and energy consumption. This paper evaluates different security schemes applied to human tracking applications, based on a real‐case scenario. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrogen model for radiation-induced interface states in SiO2-on-Si Structures: A review of the evidence

A brief review is given of the evidence supporting the “hydrogen model” of interface trap generation in silicon-based MOS structures. Emphasis is placed on the importance of electron spin resonance (ESR) in identifying and quantifying certain crucial defect species, including atomic hydrogen, self-trapped holes, and the interface trap itself — theP _b center. Three types of experiments are considered: (1) low-temperature irradiation and isochronal anneals, (2) pulse radiolysis at room temperature, and (3) exposure of previously-irradiated devices to hydrogen gas. These disparate types of data are all reasonably accounted for by a unified model involving the production of H⁺ and/or H⁰ species in the oxide which subsequently drift to the interface where they react with hydrogen-passivated dangling bonds to formP _b centers.     

The influence of equilibrium self-fields on the spontaneous emission and stimulated emission of fel with a linearly polarized wiggler

The orbits of an electron in a linear wiggler and axial field under the influence of self-fields are calculated. Then the spontaneous emission coefficient and the growth rate of the stimulated scattering are obtained. The numerical results show under some condition the self-fields can enhance the radiation.