Highly multimodal structure of high topological charge extreme ultraviolet vortex beams.

Optical beams carrying orbital angular momentum are a very active field of research for their prospective applications, especially at short wavelengths. We consider here such beams produced through high-harmonic generation (HHG) in a rare gas and analyze the characterization of their high-charge vortex structure by an extreme ultraviolet Hartmann wavefront sensor. We show that such HHG beams are generally composed of a set of numerous vortex modes. The sensitivity of the intensity and phase of the HHG beam to the infrared laser aberrations is investigated using a deformable mirror.

Hartmann wavefront sensor characterization of a high charge vortex beam in the extreme ultraviolet spectral range.

We demonstrate for the first time, to the best of our knowledge, the ability of extreme ultraviolet (XUV) Hartmann wavefront sensors to characterize high charge vortex beams produced by high-order harmonic generation up to the order of 25. We also show that phase matched absorption limited high harmonic generation is able to maintain the high charge vortex structure of the XUV beam even in a rather long (1 cm) generation medium.

Gain dynamics in quickly ionized plasma for seeded operated soft x-ray lasers.

Harmonic seeded operation of a neon-like titanium plasma-based soft x-ray laser is described. The plasma amplifier is pumped with a variation of the grazing incidence technique involving a fast and localized ionization step. We discuss its effect on gain dynamics by measuring the amplifying factor as a function of the delay between pump pulse and harmonic seed. Two different regimes are pointed out, following the pumping scheme used. For one of them, a delay in the gain generation compared with the pumping laser pulse is observed.

Low energy prepulse for 10 Hz operation of a soft-x-ray laser.

The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.

Gain lifetime measurement of a Ni-like Ag soft X-ray laser.

Experimental results of a two-stage Ni-like Ag soft X-ray laser operated in a seed-amplifier configuration are presented. Both targets were pumped applying the double-pulse grazing incidence technique with intrinsic travelling wave excitation. The injection of the seed X-ray laser into the amplifier target was realized by a spherical mirror. The results show amplification of the seed X-ray laser and allow for a direct measurement of the gain lifetime. The experimental configuration is suitable for providing valuable input for computational simulations.

Impact of scatter correction on D2 receptor occupancy measurements using 123I-IBZM SPECT: comparison to 11C-Raclopride PET.

Reported values of D(2) receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower when measured with (123)I-IBZM SPECT than with (11)C-Raclopride PET. Image degrading factors such as attenuation, distance-dependent collimator response and scatter could account for this difference. While attenuation correction is routinely applied to SPECT images, the other degradations are not usually accounted for. The aim of this work was to assess the impact of scatter correction on D(2) RO quantification with (123)I-IBZM SPECT, and to compare the results of both corrected and un-corrected SPECT values with (11)C-Raclopride PET measurements. Phantom experiments as well as within-subject human data from a previous study were used for this purpose. SPECT images were reconstructed using filtered back-projection including attenuation correction (FBP(A)), ordered subsets expectation maximization including attenuation and point spread function corrections (OSEM(A+PSF)) and ordered subsets expectation maximization including attenuation, point spread function and scatter corrections (OSEM(A+PSF+SCT)). PET images were reconstructed using the FBP algorithm and corrected for attenuation, scatter, random coincidences and dead time. Quantification of receptor availability was performed using the tissue ratio at pseudoequilibrium for SPECT, and the simplified reference tissue model (SRTM) for PET. Analysis was performed using both occipital cortex (occ) and cerebellum (cer) as reference regions for both modalities. When images were reconstructed using FBP(A), SPECT D(2) RO values were significantly lower as compared with PET leading to a D(2) RO difference of -20% (CI(95%): -13, -27%) (occ) and -23% (CI(95%): -14, -31%) (cer). When images were reconstructed using OSEM(A+PSF), SPECT D(2) RO values were also lower as compared with PET leading to a D(2) RO difference of -21% (CI(95%): -14, -27%) (occ) and -24% (CI(95%): -18, -30%) (cer). When images were reconstructed using OSEM(A+PSF+SCT), the D(2) RO bias was reduced to -6% (CI(95%): 0, -13%) (occ) and -11% (CI(95%): -4, -18%) (cer). These data suggest that the scatter correction plays a major role in explaining the differences between D(2) RO measurements using (123)I-IBZM SPECT and (11)C-Raclopride PET.

Fourier-limited seeded soft x-ray laser pulse.

We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1+/-0.3 mA, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.

Optimization of soft x-ray amplifier by tailoring plasma hydrodynamics.

Plasma-based seeded soft x-ray lasers have the potential to generate a high-energy, highly coherent, short pulse beam. Owing to their high density, plasmas created by interaction of an intense laser with a solid target should store the highest amount of energy among all plasma amplifiers. However, to date output energy from seeded solid amplifiers remains as low as 60 nJ. We demonstrated that careful tailoring of the plasma shape is crucial for extracting energy stored in the plasma. With 1-mm-wide plasma, energy as high as 20 microJ in sub-ps pulses is achievable. With such tailored plasma, gain and pumping efficiency have been increased by nearly a factor of 10 as compared to the narrower plasma amplifiers studied here.

Neurotransmission SPECT and MR registration combining mutual and gradient information.

PURPOSE: Image registration is important in functional image analysis. In neurotransmission single photon emission tomography (nSPECT), specific uptake sites can be accurately localized by superimposing the SPECT study onto a high-resolution structural image such as a magnetic resonance (MR) of the subject. Mutual-information (MI)-based algorithms are usually employed for this purpose. Nevertheless, nSPECT/MR registration using MI is often limited by the low count rates present in nSPECT. Several works have proposed extensions of the MI measures to include gradient information (GI) from the images but their performance has not been evaluated in SPECT studies. METHODS: In this work, the accuracy of the MI including gradient information (MIG) was compared with the standard MI using data from healthy volunteers and data simulating a specific uptake reduction using three different radioligands: 123I-IBZM, 123I-ADAM, 123I-R91150. RESULTS: The results showed that MIG-based registration yielded better accuracy than MI. The MIG-based similarity measures were less sensitive to sparse sampling and diminished computational time without a substantial decrease in registration accuracy. CONCLUSIONS: Accuracy of nSPECT/MR registration is improved when gradient information is included in the MI-based algorithm, which makes MIG-based registration potentially useful for clinical applications.

Quantitative study of 10 Hz operation of a soft x-ray laser-energy stability and target considerations.

A soft x-ray laser from Ni-like Mo, pumped in grazing incidence (GRIP), is analyzed with regard to high repetition rate operation. Reliable lasing is obtained, but with significant energy fluctuations attributed mainly to beam pointing jitter from the pump laser. Two modes of operation are compared: continuously moving target and stationary target. With a moving target the soft X-ray output is constant on average, whereas the repeated use of the same target position leads to a pulse energy which increases for several tens of shots. This effect might be caused by improved guiding of the pump laser in the formed groove and the removal, through laser ablation, of the oxide layer on the target surface.

Impact of Region-of-Interest Delineation Methods, Reconstruction Algorithms, and Intra- and Inter-Operator Variability on Internal Dosimetry Estimates Using PET.

PURPOSE: Human dosimetry studies play a central role in radioligand development for positron emission tomography (PET). Drawing regions of interest (ROIs) on the PET images is used to measure the dose in each organ. In the study aspects related to ROI delineation methods were evaluated for two radioligands of different biodistribution (intestinal vs urinary). PROCEDURES: PET images were simulated from a human voxel-based phantom. Several ROI delineation methods were tested: antero-posterior projections (AP), 3D sub-samples of the organs (S), and a 3D volume covering the whole-organ (W). Inter- and intra-operator variability ROI drawing was evaluated by using human data. RESULTS: The effective dose estimates using S and W methods were comparable to the true values. AP methods overestimated (49 %) the dose for the radioligand with intestinal biodistribution. Moreover, the AP method showed the highest inter-operator variability: 11 ± 1 %. CONCLUSIONS: The sub-sampled organ method showed the best balance between quantitative accuracy and inter- and intra-operator variability.

[Scientific evidence on the use of high-intensity focal ultrasound (HIFU) in the treatment of prostatic carcinoma]. / Evidencia científica actual sobre la utilidad del ultrasonido de alta intensidad (HIFU) en el tratamiento del adenocarcinoma prostático.

OBJECTIVES: To evaluate in the literature scientific evidence on the use of High-Intensity Focal Ultrasound (HIFU) in the treatment of prostatic carcinoma (PC). METHOD: Three database are searched: PubMed, Cochrane Library, HTA database. Several articles were selected taking into account number of cases, inclusion criteria, duration of follow-up period. We have evaluated the best evidence available through a systematic review of clinical efficacy and cost-effectiveness of HIFU in the treatment of PC. We analized global survival, disease-free survival, and quality of life, including complications, adversal effects and acceptance of the technique. RESULTS: Publications available are focused on two main indications of the therapy: first step of management of PC and salvage therapy for locally recurrent PC after external beam radiotherapy. It was very difficult to draw conclusions on the relative benefits of the HIFU: lack of high or medium quality evidence and no comparisons between this technique an standard treatments. In relation to results on cost-effectiveness, no relevant studies were identified in order to get conclusions on the quality of the treatment. Most of reports offered disparity in the definition of free survival disease concept. This fact produce some misunderstanding of results and conclusions cannot be drawn correctly. Inclusion criteria were also heterogeneous between authors. CONCLUSIONS: No high-quality clinical evidence can be established currently on the utility of HIFU as treatment of prostatic cancer. An important fact to stress is the capacity of therapy to produce tumour necrosis both as first-step treatment and as salvage therapy. No conclusions can be drawn in the long-term due to the paucity of controlled and randomized trials with adequate follow-up to establish benefits in terms of global survival and quality of life (balance adversal effects/benefits), lack of comparisons with standard options as long as different definitions of free-survival disease.

Validation of semi-quantitative methods for DAT SPECT: influence of anatomical variability and partial volume effect.

The aim of this work was to evaluate the influence of anatomical variability between subjects and of the partial volume effect (PVE) on the standardized Specific Uptake Ratio (SUR) in [(123)I]FP-bib SPECT studies. To this end, magnetic resonance (MR) images of 23 subjects with differences in the striatal volume of up to 44% were segmented and used to generate a database of 138 Monte Carlo simulated SPECT studies. Data included normal uptakes and pathological cases. Studies were reconstructed by filtered back projection (FBP) and the ordered-subset expectation-maximization algorithm. Quantification was carried out by applying a reference method based on regions of interest (ROIs) derived from the MR images and ROIs derived from the Automated Anatomical Labelling map. Our results showed that, regardless of anatomical variability, the relationship between calculated and true SUR values for caudate and putamen could be described by a multiple linear model which took into account the spill-over phenomenon caused by PVE (R² ≥ 0.963 for caudate and ≥0.980 for putamen) and also by a simple linear model (R(2) ≥ 0.952 for caudate and ≥0.973 for putamen). Calculated values were standardized by inverting both linear systems. Differences between standardized and true values showed that, although the multiple linear model was the best approach in terms of variability (X² ≥ 11.79 for caudate and ≤7.36 for putamen), standardization based on a simple linear model was also suitable (X² ≥ 12.44 for caudate and ≤12.57 for putamen).

Monte Carlo simulations versus experimental measurements in a small animal PET system. A comparison in the NEMA NU 4-2008 framework.

In this work a comparison between experimental and simulated data using GATE and PeneloPET Monte Carlo simulation packages is presented. All simulated setups, as well as the experimental measurements, followed exactly the guidelines of the NEMA NU 4-2008 standards using the microPET R4 scanner. The comparison was focused on spatial resolution, sensitivity, scatter fraction and counting rates performance. Both GATE and PeneloPET showed reasonable agreement for the spatial resolution when compared to experimental measurements, although they lead to slight underestimations for the points close to the edge. High accuracy was obtained between experiments and simulations of the system's sensitivity and scatter fraction for an energy window of 350-650 keV, as well as for the counting rate simulations. The latter was the most complicated test to perform since each code demands different specifications for the characterization of the system's dead time. Although simulated and experimental results were in excellent agreement for both simulation codes, PeneloPET demanded more information about the behavior of the real data acquisition system. To our knowledge, this constitutes the first validation of these Monte Carlo codes for the full NEMA NU 4-2008 standards for small animal PET imaging systems.

Prefrontal and temporal blood flow in schizophrenia: resting and activation technetium-99m-HMPAO SPECT patterns in young neuroleptic-naive patients with acute disease.

UNLABELLED: This study assesses prefrontal and temporal regional cerebral blood flow (rCBF) changes in young, neuroleptic-naive schizophrenic patients with acute disease. METHODS: A selected population of 10 young, never-treated schizophrenic women with acute disease was studied by two hexamethylpropyleneamine oxime (HMPAO) brain SPECT sessions, performed 48 hr apart, both at rest and during a prefrontal activation task using the Wisconsin Card Sort Test (WCST). All patients met Diagnostic and Statistical Manual of Mental Disorders, 3rd edition-revised criteria for schizophrenia or schizophreniform disorder, were neuroleptic-naive and had acute symptoms. RESULTS: Under resting conditions, the schizophrenic group had significantly higher rCBF in the prefrontal regions, mainly in the left side and including the anterior cingulate, than did the controls. In addition, schizophrenic patients showed significant interhemispheric differences in prefrontal and posterior temporal index values at rest (left hyperfrontality and left hypotemporality). During WCST activation, the control group showed significant increases in prefrontal blood flow, whereas the schizophrenic group did not. CONCLUSION: These results support a physiologic dysfunction of the prefrontal cortex in schizophrenia that is present at the onset of the illness prior to neuroleptic treatment. Furthermore, both left hyperfrontality and left hypotemporality may indicate a brain lateralization defect in schizophrenia.

Expression of proadrenomedullin derived peptides in the mammalian pituitary: co-localization of follicle stimulating hormone and proadrenomedullin N-20 terminal peptide-like peptide in the same secretory granules of the gonadotropes.

Expression of proadrenomedullin-derived peptides in the rat, cow and human pituitary was studied by a variety of techniques. Immunocytochemical detection showed a widespread expression of adrenomedullin peptide in the adenohypophysis and the neural lobe, with low expression in the intermediate pituitary. Proadrenomedullin N-20 terminal peptide (PAMP)-immunoreactivity was also present in the anterior pituitary but showed a more marked heterogeneous distribution, with cells going from very strong to negative immunostaining. Lower levels of PAMP were found in the neural lobe. Interestingly, the distribution of adrenomedullin and PAMP immunoreactivity in the anterior pituitary did not completely overlap. In the present study, we concentrated our efforts to determine which cell type of the adenohypophysis expresses PAMP. Paraffin and semithin serial sections immunostained for PAMP and the classical pituitary hormones revealed that a subpopulation of the gonadotropes expresses high levels of PAMP-immunoreactive material. Ultrastructural analysis clearly showed PAMP-immunoreactivity in the follicle stimulating hormone (FSH)-containing large secretory granules of the gonadotropes, suggesting simultaneous secretion of PAMP and FSH by this cell type. Three mouse adenohypophysis-derived cell lines (AtT20, GH3, and alphaT3-1 derived from corticotropes, lacto/somatotropes and gonadotropes, respectively) were also analysed and showed expression of both proadrenomedullin-derived peptides and their mRNA. Functional studies in these three cell lines showed that neither adrenomedullin nor PAMP was able to stimulate cAMP production in our experimental conditions. Taken together, our results support that proadrenomedullin derived peptides are expressed in the pituitary in cell-specific and not overlapping patterns, that could be explained by differences in postranslational processing. Our data showing costorage of PAMP and FSH in the same secretory granules open a way by which PAMP could be involved in the control of reproductive physiology in a coordinated manner with FSH.

The relationship between glycogen synthesis, biofilm formation and virulence in salmonella enteritidis.

Salmonella enteritidis accumulated large quantities of intracellular polysaccharide when grown in unrestricted nutrient conditions. Dense, abundant cytoplasmic granules were observed by electron microscopy in sections stained by the periodic acid-chlorite technique, indicating that the polysaccharide was of the glycogen type. When biofilm-producing S. enteritidis was pre-incubated in media containing increasing levels of glucose concentration, the levels of both cytoplasmic glycogen and biofilm rose correlatively to a point where a ceiling effect was observed. Studies carried out with activators and inhibitors of glycogen biosynthesis confirmed that biofilm was formed from glycogen cell stores. On the other hand, the virulence of the biofilm-producing strain in infected chickens increased proportionally to the amount of stored glycogen, suggesting a possible role of the glycogen depot in the virulence of S. enteritidis.

Dynamic model of the left ventricle for use in simulation of myocardial perfusion SPECT and gated SPECT.

Simulation is a useful tool in cardiac SPECT to assess quantification algorithms. However, simple equation-based models are limited in their ability to simulate realistic heart motion and perfusion. We present a numerical dynamic model of the left ventricle, which allows us to simulate normal and anomalous cardiac cycles, as well as perfusion defects. Bicubic splines were fitted to a number of control points to represent endocardial and epicardial surfaces of the left ventricle. A transformation from each point on the surface to a template of activity was made to represent the myocardial perfusion. Geometry-based and patient-based simulations were performed to illustrate this model. Geometry-based simulations modeled (1) a normal patient, (2) a well-perfused patient with abnormal regional function, (3) an ischaemic patient with abnormal regional function, and (4) a patient study including tracer kinetics. Patient-based simulation consisted of a left ventricle including a realistic shape and motion obtained from a magnetic resonance study. We conclude that this model has the potential to study the influence of several physical parameters and the left ventricle contraction in myocardial perfusion SPECT and gated-SPECT studies.

Optimal filtering values in renogram deconvolution.

The evaluation of the isotopic renogram by means of the renal retention function (RRF) is a technique that supplies valuable information about renal function. It is not unusual to perform a smoothing of the data because of the sensitivity of the deconvolution algorithms with respect to noise. The purpose of this work is to confirm the existence of an optimal smoothing which minimises the error between the calculated RRF and the theoretical value for two filters (linear and non-linear). In order to test the effectiveness of these optimal smoothing values, some parameters of the calculated RRF were considered using this optimal smoothing. The comparison of these parameters with the theoretical ones revealed a better result in the case of the linear filter than in the non-linear case. The study was carried out simulating the input and output curves which would be obtained when using hippuran and DTPA as tracers.

The influence of a relaxation parameter on SPECT iterative reconstruction algorithms.

Algebraic reconstruction techniques (ARTs) have been intensively studied in image reconstruction. However, reconstructed images often exhibit a characteristic noise when applied to emission tomography. In this work, we study the influence of the ART relaxation parameter and identify values of that parameter which yield smooth images and good convergence. The study includes both simulated and real single photon emission computed tomographic (SPECT) data. In the simulated studies, scattering, attenuation, noise and detector response were included. Relaxation factors ranging between 0.01 and 0.35 were considered. Total counts in projections were between 2.5 x 10(5) and 10(6) in one slice. The goodness of the reconstructions was assessed by using the correlation coefficient between the pattern and the actual reconstruction (CC), the background coefficient of variation (CV), the contrast (CON) and the signal-to-noise ratio (SNR). The results show that values for the relaxation factor and number of interations close to 0.1 and 8, respectively, yield reconstructed images in which CC, CV, CON and SNR have well balanced values and CC, CV and SNR are very close to the extremal. An increase in either the number of iterations or in the relaxation factor results in a rise of CON but the other three FOMs deteriorate. The results from the real phantom, which are in agreement with those of the simulated studies, validate the simulation method and demonstrate the influence of the relaxation parameter.