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Aerobic training (AT) is indicated in type 2 diabetes mellitus (T2DM) to control hyperglycaemia and inflammation. AT improves bone microarchitecture and resistance to fracture. The intensity of AT and the mechanisms that lead to the improvement in bone quality are still unknown. Using a mouse model of T2DM, we evaluated the effects of two intensities of forced AT. We divided mice into: sedentary (SED), T2DM-SED, low runners (LOW), T2DM-LOW, high runners (HIGH) and T2DM-HIGH. The AT for low was 8 m/minute (m/min); 5° slope or high 18 m/min; 15° slope for 2 months. We measured metabolic parameters, the serum cytokines concentration, lipocalin-2 (LCN-2) and adiponectin; and the tibial concentrations of LCN-2, tumour necrosis factor alpha (TNF-α) and protein carbonylation (CO). We evaluated femur morphometry and biomechanical properties. We performed multiple correlation analysis. The T2DM-LOW versus T2DM-SED group, shown an increase of interleukin (IL)-10 (417 ± 90 vs 102 ± 25 pg/mL) and improved trabecular bone (BV/TV: 31.8 ± 2.3 vs 19.25 ± 1.4%; Tb.Sp.: 1.62 ± 0.02 vs 2.0 ± 0.07 mm), by a decrease bone CO (3.4 ± 0.1 vs 6.0 ± 0.5 nmol/mg), bone TNF-α (84 ± 4 vs 239 ± 13 pg/mL) and LCN-2 (2887 ± 23 vs 3418 ± 105 pg/mL). The T2DM-HIGH versus T2DM-SED group showed a greater hypoglycaemic effect (228 ± 10 vs 408 ± 5 mg/dL), with improved cortical bone density (0.26 ± 0.012 vs 0.21 ± 0.007 mm) and fracture resistance (102 ± 8 vs 78 ± 5 MPa), by a reduction of bone TNF-α (77 ± 34 vs 239 ± 13 pg/mL); LCN-2 (2768 ± 20 vs 3418 ± 105 pg/mL) and CO (4.8 ± 0.5 vs 6.0 ± 0.5 nmol/mg). In conclusion, AT improves bone morphometry and biomechanical properties by reducing the bone inflammatory microenvironment.

Purpose Gallium-66 is a non-conventional positron emitter that stands out not only for its high potential to label peptides, proteins and antibodies, but also because it can provide spatio-temporal information of relatively slow physiological processes in the body due to its conveniently long half-life of 9.5 h. However, 66Ga emits the most energetic positrons for PET imaging. The lack of information of the positron range effect on spatial resolution for this positron emitter is an issue, particularly in preclinical imaging. Methods The line spread function (LSF) in tissue-equivalent materials with densities between 0.2 and 1.93 g/cm3 was obtained with 66Ga and 18F. A complementary study with the NEMA NU 4-2008 image quality phantom is also included. Results High-energy positrons moving in lower density materials produce far-reaching activity distributions. The LSFs were characterized with Lorentzian-Gaussian fits, with spatial resolution (FWHM) in the 2.14–3.2 mm range, and long tails extending a few tens of mm depending on the material type and density. A narrowing of the LSF was observed for lung-equivalent materials, indicating the lack of enough material for the positron annihilation to take place. The NEMA NU 4-2008 image quality phantom produced blurred images, notoriously observed in the hot and cold cylinders used for evaluation of recovery coefficients (RC) and spill-over ratios (SOR), producing very low RC and very large SOR. Conclusions Quantitative PET imaging with the non-conventional 66Ga is hampered due to the large range of its high-energy positrons affecting both spatial resolution and activity concentration quantification.

Exercise encourages active and healthy aging, maintaining functional and physical capabilities. This study aimed to assess the effects of a long-term moderate aerobic exercise protocol on bone microarchitecture and fragility associated with chronic inflammation and oxidative stress in aging. Male BALB/c mice (n = 10 per group) underwent a moderate exercise protocol from 13 weeks to 27 (adulthood age) or 108 weeks of age (elderly age) and were then sacrificed. Age-match sedentary mice were included as a control group. Serum cortisol concentrations were determined by chemiluminescent immunoassay, C-reactive protein (CRP) by a turbidimetric assay, advanced glycation end-products (AGEs) and malondialdehyde (MDA) by fluorescent spectroscopy, and total glutathione (GSH) by colorimetric method. The right femur was dissected formorphometric and densitometricanalysis bycomputerized microtomography (µCT),and biomechanical properties were assessed usinga three-point bending device. Musclefrom the same extremitywas obtained to determine relative mRNA expression ofpro-inflammatory cytokines (TNF-α and IL-6) by RT-qPCR.Statistical differences were evaluated by two-way ANOVA and Holm-Sidak method post hoc with P 0.05. In elderly mice, moderate exercise increased glutathione levels and microarchitecture complexity but decreased bone fragility and oxidative stress markers, cortisol, and pro-inflammatory cytokines. In conclusion, these results suggest a strong link between a pro-inflammatory state and age-conditioned oxidative stress on bone quality. Thus, on a human scale, moderate aerobic exercise may improve bone quality during aging.

In this work we investigate the effects due to photon attenuation and scattering in a Positron Emission Mammography (PEM) study using the GATE (Geant4 Application for Tomographic Emission) Monte Carlo (MC) code. Breast phantoms with different shapes and volumes placed within a scanner geometry similar to IFUNAM’s PEM prototype under development were considered. The results show that attenuation and scatter effects for 511 keV photons depend strongly on the breast phantom volume (and thus, breast thickness). For breast volumes between 200 and 950 ml, scatter contributions vary from 24% to 58%, while the attenuation of primary photons are significant, within 36% and 73%. Our results indicate, overall, that the larger the breast volume, the larger these effects. This implies that for a clinical study to provide precise and quantitative information, complex corrections pre- or post- image reconstruction must necessarily be implemented.

In this work we developed and validated a Monte Carlo simulation framework of the imaging systems of the Varian TrueBeam STx Linac, and studied the scatter contribution in MV and kV cone-beam CT images. The simulations were validated by comparing measured PDD (Percentage Depth Dose) curves, off-axis profiles and transmission curves with those calculated with the DOSXYZnrc code and a dosimetric model of the detector response using the theoretical energy spectra. The transmission curves were obtained by imaging Al and Cu step-wedge phantoms with the MV system. A parallelized code was used to estimate cone-beam CT projections separating the scatter and primary contributions, optimizing the code using variance reduction techniques (VRTs). The models developed in this work show very good agreement with experimental measurements and with previous results reported in the literature. The use of VRTs allowed quick estimation of the scatter contributions with a speed up factor of 20. This MC framework was used to develop an iterative scatter correction method based on fast simulations of low-resolution voxel models and sparse angular sampling. The iterative scatter correction method showed very good results in both kV and MV cone-beam CT images, improving image quality by reducing the cupping artifact and improving the estimation of the CT numbers.

The parallax error introduced by incorrectly assigning the lines-of-response defined by the annihilation photon pairs, limits the attainable spatial resolution in positron emission imaging. Knowledge of the exact position of interaction (x, y, z) inside the scintillation crystal, including the depth of interaction z of the 511 keV photons, reduces this error. In this work, the depth of interaction (DOI) was determined in two different scintillator materials: EJ-232 plastic and LYSO scintillation crystals. These were coupled to an 8×8 silicon photomultiplier (SiPM) array. An analysis of the light distributions produced inside the crystals enabled the determination of the DOI position, allowing the correction for parallax errors. This method is expected to be used in a Positron Emission Mammography (PEM) prototype under development.

In this work the scintillation energy spectra originating from the background radioactivity from polished monolithic lutetium yttrium oxyorthosilicate coupled to position-sensitive silicon photomultipliers (SiPM) was studied using the open source Monte Carlo simulation package ANTS2. Two crystal sizes, fully and partially covering the photosensor area, three surface crystal wrappings (black, specular or diffuse) and the full signal formation process in the photosensor were considered. The simulation results were validated with experimental data acquired under the same geometric and detector operating conditions. In all cases ANTS2 simulated spectra have very good agreement with experimental results, reproducing the expected shape, with correct onset and end at 88 and 1190 keV, respectively, as well as sharp edges at the reference energies of 88, 88 + 202, 88 + 307 and 88 + 202 + 307 keV. The normalized root-mean square error between simulated and measured spectra varied between 4.3% and 10.4%.

We describe a cell culture irradiation model based on the use of a 6 MV linear accelerator. The determination of dose delivered to the cell culture relied upon a carefully validated Monte Carlo simulation of the linear accelerator head, followed by radiation transport calculations of relative dose on a model of the clonogenic assay, which included the cell culture flask and supporting media. Absolute dose was determined by cross calibration of the Monte Carlo model with ionization chamber measurements along the central axis of a water phantom. An experimental setup based on the irradiation model was used to obtain survival curves of a human cell line of glioblastoma multiforme (U-373 MG). Our measurements show excellent agreement with data previously reported in the literature.

In this work an experimental investigation was carried out to study the effect that positron range has over positron emission tomography (PET) scans through measurements of the line spread function (LSF) in tissue-equivalent materials. Line-sources consisted of thin capillary tubes filled with (18)F, (13)N or (68)Ga water-solution inserted along the axis of symmetry of cylindrical phantoms constructed with the tissue-equivalent materials: lung (inhale and exhale), adipose tissue, solid water, trabecular and cortical bone. PET scans were performed with a commercial small-animal PET scanner and image reconstruction was carried out with filtered-backprojection. Line-source distributions were analyzed using radial profiles taken on axial slices from which the spatial resolution was determined through the full-width at half-maximum, tenth-maximum, twentieth-maximum and fiftieth-maximum. A double-Gaussian model of the LSFs was used to fit experimental data which can be incorporated into iterative reconstruction methods. In addition, the maximum activity concentration in the line-sources was determined from reconstructed images and compared to the known values for each case. The experimental data indicates that positron range in different materials has a strong effect on both spatial resolution and activity concentration quantification in PET scans. Consequently, extra care should be taken when computing standard-uptake values in PET scans, in particular when the radiopharmaceutical is taken up by different tissues in the body, and more even so with high-energy positron emitters.

Radiochromic films are dosimeters with more favorable characteristics than other two-dimensional (2D) radiation detectors. Transmission film scanners using a linear charge-coupled device (CCD) array have a drawback of variation in response along the detector array, which may result in a nonuniform transmission of signal over the scanned image. This study uses 2D gamma index analysis to compare two methods for correcting the nonuniform response of EBT2: the first method was based on the new red:blue method proposed by the manufacturer (to compensate for small nonuniformities in the film coating) and the second method, proposed by Menegotti et al. (2008), was based on dose-dependent matrix correction factors. The gamma index analysis shows that both the methods are comparably accurate for all the criteria values used for evaluation (1 mm/1%, 2 mm/2%, 3 mm/3%). Centers around the world use both the methods to correct EBT2 local heterogeneities, but it is important to note that the former method has several advantages such as less time consumption and easy implementation.

A standard protocol for performance evaluation of positron emission mammography (PEM) systems has not yet been established. In this work we propose a methodology based on the design of specific phantoms for this imaging modality with component dimensions in accordance with typical breast lesion sizes together with the adaptation of current international protocols designed for clinical and preclinical positron emission tomographs (PET) systems. This methodology was used to evaluate the performance of the Flex Solo II PEM scanner in terms of spatial resolution, uniformity and contrast lesion detectability, recovery coefficients and spill-over ratios. Positron range effects were studied with 18F and 68Ga, which have very different energy spectra. Our results indicate that in-plane spatial resolution of the system is around 3.0 mm and 4.4 mm for 18F and 68Ga, respectively. Lesion detectability tests with sphere diameters between 4 and 10 mm confirmed that the PEM system can resolve all the spheres (hot or cold). Percent contrast values for 18F lie between 6%–38% and 34%–51% for hot- and cold- spheres, respectively; the corresponding intervals for 68Ga are lower, 4%–25% and 32%–44%. Regarding uniformity quantification, the system shows percentage standard deviations within 4.9%–5.7%, while the percent background variability measurements ranged between 6.7% and 10.9% for both radionuclides. Recovery coefficients measured with hot rod diameters between 1.5 and 9 mm, have values between 0.2–1.05 and 0.17–0.69 for 18F and 68Ga, respectively. Spill-over ratios have large values (0.22 in average) for both radionuclides. Our results indicate that the phantoms and the methodology developed in this work can serve as the basis for establishing an image quality protocol for the systematic evaluation of PEM systems, with a potential extension for performance evaluation of dedicated breastPET scanners.

Lutetium oxyorthosilicate (LSO) or lutetium yttrium oxyorthosilicate (LYSO) are the scintillator materials most widely used today in PET detectors due to their convenient physical properties for the detection of 511 keV annihilation photons. Natural lutetium contains 2.6% of 176Lu which decays beta to excited states of 176Hf producing a constant background signal. Although previous works have studied the background activity from LSO/LYSO, the shape of the spectrum, resulting from β-particle and γ radiation self-detection, has not been fully explained. The present work examines the contribution of the different β-particle and γ-ray interactions to provide a fuller comprehension of this background spectrum and to explain the differences observed when using crystals of different sizes. To this purpose we have shifted the continuous β-particle energy spectrum of 176Lu from zero to the corresponding energy value for all combinations of the isomeric transitions of 176Hf (γ-rays/internal conversion). The area of each shifted β-spectrum was normalized to reflect the probability of occurrence. To account for the probability of the γ-rays escaping from the crystal, Monte Carlo simulations using PENELOPE were performed in which point-like sources of monoenergetic photons were generated, inside LYSO square base prisms (all 1 cm thick) of different sizes: 1.0 cm to 5.74 cm. The analytic distributions were convolved using a varying Gaussian function to account for the measured energy resolution. The calculated spectra were compared to those obtained experimentally using monolithic crystals of the same dimensions coupled to SiPM arrays. Our results are in very good agreement with the experiment, and even explain the differences observed due to crystal size. This work may prove useful to calibrate and assess detector performance, and to measure energy resolution at different energy values.

We present the performance evaluation of a large-area detector module based on the ArrayC-60035-64P, an 8 × 8 array of tileable, 7.2 mm pitch, silicon photomultipliers (SiPM) by SensL, covering a total area of 57.4 mm × 57.4 mm. We characterized the ArrayC-60035-64P, operating at room temperature, using LYSO pixelated crystal arrays of different pitch sizes (1.075, 1.430, 1.683, 2.080 and 2.280 mm) to determine the resolvable crystal size. After an optimization process, a 7 mm thick coupling light guide was used for all crystal pitches. To identify the interaction position a 16-channel (8 columns, 8 rows) symmetric charge division (SCD) readout board together with a center-of-gravity algorithm was used. Based on this, we assembled the detector modules using a 40 × 40 LYSO, 1.43 mm pitch array, covering the total detector area. Calibration was performed using a 137 Cs source resulting in excellent crystal maps with minor geometric distortion, a mean 4.1 peak-to-valley ratio and 9.6% mean energy resolution for 662 keV photons in the central region. The resolvability index was calculated in the x and y directions with values under 0.42 in all cases. We show that these large area SiPM arrays, combined with a 16-channel SCD readout board, can offer high spatial resolution, without processing a big number of signals, attaining excellent energy resolution and detector uniformity.

In this work microPET scans and Monte Carlo simulations of line sources containing 18F, 13N and 68Ga were performed to study the effect that positron range has over the spatial resolution of PET images. The experimental studies were carried out using a microPET Focus 120 scanner with a reported axial spatial resolution of 1.44 mm. Line sources consisted of thin capillary tubes filled with a water solution containing a known activity concentration of the radionuclides and placed inside six different tissue equivalent cylindrical phantoms. Image reconstruction was performed using filtered backprojection and from the axial images, radial profiles were extracted to compute the spatial resolution for all radionuclide-material combinations. One dimensional line sources inside cylinders were simulated using PENELOPE to obtain the line spread functions (LSFs) of all the radionuclide-material combinations. Our results indicate that spatial resolution depends strongly on the radionuclide (positron energy) and the d...

In this work, a Monte Carlo simulation of a positron emission mammography (PEM) prototype under development at the Institute of Physics, UNAM, is presented. The simulated geometry included two parallel detector modules with a 73 mm separation. Each module consisted of 3 detector blocks, each one formed by an array of 38×38 lutetium yttrium orthosilicate crystal elements of 1.96×1.96×10 mm3 at 2 mm pitch. An energy resolution of 26% for 511 keV photons, a 350-650 keV energy window and a 6 ns coincidence window were assumed. Image reconstruction was performed using focal plane tomography. Spatial resolution was assessed through the point spread function at different positions within the field of view (FOV). In addition, image quality was evaluated following the NEMA NU 4-2008 protocol. Different depth-of-interaction (DOI) assumptions were considered. The best spatial resolution (0.75 mm FWHM) was obtained when depth-of-interaction information was used, deteriorating drastically to 2.21 mm when DOI is unknow...

Monte Carlo (MC) dose calculations in radiotherapy typically use Computed Tomography (CT) images of the patient since they can provide electron density (ρe) and effective atomic number (Zeff) information of tissues. An accurate calculation of absorbed dose and appropriate correction for inhomogeneities is partially determined by the Hounsfield Units (HU) dependence on these parameters. In this work HU calibration results are presented in terms of Zeff and ρe by using tissue-equivalent materials and a dual-energy CT method. We compared calculated values of Zeff and ρe with the ones provided by the manufacturer. Mean percentage differences (MPD) of 3.2% were observed for Zeff, while for ρe the average difference was 4.1%. When beam hardening correction was applied, the MPD on Zeff and ρe extraction were 2.4% and 3.2%, respectively.

Small animal microcomputed tomography (microCT) studies with iodine-based contrast media are commonly used in preclinical research. While the use of contrast media improves the quality of the images, it can also result in an increase in the absorbed dose to organs with high concentration of the contrast agent, which might cause radiation damage to the animal. In this work we present the results of a Monte Carlo investigation of a microCT dosimetry study using mouse-sized cylindrical water phantoms with iodine contrast insets for different X-ray spectra (Mo and W targets, 30−80 kVp), iodine concentrations (0, 5, 10 and 15 mg mL −1 ) and contrast object sizes (3 and 10 mm diameter). Our results indicate an absorbed dose increase in the contrast-inset regions with respect to the absorbed dose distribution within a reference uniform water phantom. The calculated spatial absorbed dose distributions show large gradients due to beam hardening effects, and large absorbed dose enhancement as the mean energy of the beam and iodine concentration increase. We have found that absorbed doses in iodine contrast objects can increase by a factor of up to 12 for a realistic 80 kVp X-ray spectra and an iodine concentration of 15 mg mL −1 .

This work is aimed at studying the possible dependence of the thermoluminescent response of LiF:Mg,Ti (TLD-100) on the X-ray beam spectrum. TLD-100 chips were irradiated with 20 keV effective energy filtered tungsten X-ray spectra, generated by a tube operated at 30, 40, 50, 60, 70 and 80 kV, and the response was measured relative to the response to 60Co gammas. TLDs were exposed in air at air kerma values between 50 and 300 mGy. Glow curve deconvolution into 8 peaks (3, 4, 5, 6a, 6b, 7, 8 and 9) was performed in order to evaluate the response of individual peaks and regions of interest in the glow curve. Results show that all peaks display a linear response, at least up to 200 mGy, for all X-ray beam qualities. The relative response of the total glow curve area, the dosimetric region (peaks 3 + 4 + 5) and peaks 5 to 9 is statistically constant for beams generated by voltages from 30 to 70 kV; for 80 kV, the values are lower by about 20% for peaks 8 and 9 and 9% for the rest. The relative efficiency for the glow curve area, the dosimetric region and peaks 5 (1.15, 1.10 and 1.13), peaks 8 and 9 (2.05 and 1.55) do not depend on the beam spectrum between 30 and 70 kV, while for 80 kV the efficiency is lower. For peaks 6a, 6b and 7, relative efficiencies (1.91, 2.94 and 2.60) are voltage independent.

The design and evaluation of a large-area detector module for positron emission imaging applications, is presented. The module features a SensL ArrayC-60035-64P-PCB solid state detector (8×8 array of tileable silicon photomultipliers by SensL, 7.2 mm pitch) covering a total area of 57.4×57.4 mm2. The detector module was formed using a pixelated array of 40×40 lutetium-yttrium oxyorthosilicate (LYSO) scintillator crystal elements with 1.43 mm pitch. A 7 mm thick coupling light guide was used to allow light sharing between adjacent SiPM. A 16-channel symmetric charge division (SCD) readout board was designed to multiplex the number of signals from 64 to 16 (8 columns and 8 rows) and a center-of-gravity algorithm to identify the position. Data acquisition and digitization was accomplished using a custom-made system based on FPGAs boards. Crystal maps were obtained using 18F-positron sources and Voronoi diagrams were used to correct for geometric distortions and to generate a non-uniformity correction matrix. All measurements were taken at a controlled room temperature of 22oC. The crystal maps showed minor distortion, 90% of the 1600 total crystal elements could be identified, a mean peak-to-valley ratio of 4.3 was obtained and a 10.8% mean energy resolution for 511 keV annihilation photons was determined. The performance of the detector using our own readout board was compared to that using two different commercially readout boards using the same detector module arrangement. We show that these large-area SiPM arrays, combined with a 16-channel SCD readout board, can offer high spatial resolution, excellent energy resolution and detector uniformity and thus, can be used for positron emission imaging applications.

A positron emission tomography system for small animals has been designed for research purposes, and developed at Instituto de Fi?sica, UNAM, Mexico. Its detection modules are based on pixelated scintillator LYSO crystal arrays coupled to Hamamatsu H8500 position-sensitive photomultiplier tubes. The front-end electronics are based on nuclear instrumentation modules (NIM) and in-house built readout circuits. Peak signal digitization is performed with a commercial analogue-to-digital acquisition (DAQ) board. The system has been characterized for spatial, timing and energy resolution, system dead time, absolute sensitivity, scatter fraction and noise equivalent count rate (NEC). The results indicate that the detection modules are able to identify individual crystals (out of 400) with up to 8-to-1 peak-to-valley ratios with individual crystal energy resolution ranging from 7 to 15% at 511 keV. The timing resolution is 1.9 ns and the system dead time was found to be 16.8 ?s and 42.1 ?s for 0.5 ml and 10 ml volume sources, respectively. The measured absolute system sensitivity is 0.11% and the scatter fraction from a glass capillary inside a 2.5 cm diameter mouse phantom is 21.5%. A true NEC maximum value was not achieved with the system due to saturation of the PS-PMT output signals for activities above 0.27 mCi. Results from a Na18 F PET bone scan of a 30 g mouse are shown.

Non-filtered X-ray spectra from three tubes (Oxford Instruments Ultrabright microfocus W anode, Apogee Series 5000 with W and Mo anodes) appropriate for microCT scanners have been measured using a CdTe solid-state detector. The normalized and efficiency-corrected spectra have been parameterized using Boone et al. [10] third-order polynomial expression, obtaining good agreement with the data (typical mean ratio between parameterization and measurement equals 1.02, with standard deviation 0.10). Attenuation of the computed spectra by external filters was analytically simulated, obtaining results that agree well with direct measurements. The air kerma angular distribution of the X-ray beams was measured and the magnitude of the heel effect was evaluated. Tungsten collimators provided by the detector manufacturer had to be used to reduce dead time and it was found that their apertures do not necessarily agree with the nominal values.

A microPET system for small animal studies is currently being developed at Instituto de Fisica, UNAM. The main goal of this project is to build a cost-effective benchtop system that could be suitable for research purposes. The basic design uses off-the-shelf components and is being assembled using nuclear instrumentation modules and in-house built readout circuits. The detection modules are based on pixelated scintillator LYSO crystal arrays coupled to Hamamatsu H8500 position-sensitive photomultiplier tubes with a resistive chain readout system. Pulse digitization is performed with a commercial fast analogue-to-digital data acquisition board. The uniformity, cross-talk and aperture function of the photomultipliers have been measured. The modules are able to identify individual crystals (out of 400) with a 4-to-1 peak-to-valley ratio. The measured energy resolution of 22 Na spectra in individual crystals ranges from 7% to 15%; the dead time of the system is between 17 and 42 μs depending on the source volume, and the resolving time is 1.16±0.01 ns. The design and characterization of the system includes Monte Carlo simulations of the detectors.

Most small-animal positron emission tomography imaging systems nowadays use scintillator crystal arrays coupled to position-sensitive photomultiplier tubes (PS-PMT) as their detector modules. Individual crystal region identification to set tight energy thresholds has been introduced to reduce scatter and pileup events. In this work, we have used Voronoi diagrams to implement both tasks in a fast and efficient way for data analysis from a 20×20 LYSO crystal array coupled to Hamamatsu H8500 PS-PMT. This module forms part of a benchtop microPET system currently being developed at UNAM, Mexico. The results show that the use of individual crystal energy windows does not reduce image distortions, caused by pulse pileup, in 2-D data acquisition projections obtained with our system.

Optical and ageing properties of hydrophobic silica aerogel have been measured. The optical observations include the determination of the index of refraction of individual aerogel samples, and transmittance measurements. Concerning ageing, we investigate possible explanations for an appreciable decrease on the light yield observed in the aerogel tiles used in the AMS-01 Cherenkov detector, flown on board of the NASA Discovery Shuttle. Measurements were carried out simulating the vacuum and thermal cycle to which the aerogel was subject. These tests indicate that this material is very sensitive to residual contaminants that might be present during the vacuum pumping and/or gas admission process.

A model is proposed to understand the non-linear response of Si detectors to high Z particles, which are responsible for the pulse height defect (PHD). In this phenomenon, inefficient charge collection due to charge carrier recombination is related to high energy density regions in the vicinity of the particle track, while contributions from non-ionizing atomic collisions are also estimated from the radial distribution of scattered lattice ions. These model calculations successfully reproduce published PHD data, while predicting unexpected effects in silicon-based semiconductor detection of high (relativistic) energy heavy ions. This is used to explain what seemed as intriguing features of silicon-tracker data from the Alpha Magnetic Spectrometer space project. The present model is proposed to obtain reliable ion energy measurements using silicon detectors.

The remarkable non-linear response of a Si p–i–n detector to relatively low- Z ( Z , to just three overall quantities, which have a simple physical interpretation.

We have modified an analytical model of induced light production by energetic ions interacting in scintillating materials. The original model is based on the distribution of energy deposited by secondary electrons produced along the ion's track. The range of scattered electrons, and thus the energy distribution, depends on a classical impact parameter between the electron and the ion's track. The only adjustable parameter of the model is the quenching density ρq. The modification here presented, consists in proposing a quantum impact parameter that leads to a better fit of the model to the experimental data at low incident ion energies. The light output response of CsI(Tl) detectors to low energy ions (

Two species of fossil polydesmidan millipedes (Diplopoda: Polydesmida) embedded in amber are described from Miocene strata near Simojovel, in the Chiapas Highlands, Mexico. Maatidesmus paachtun gen. et sp. nov., placed into Chelodesmidae Cook, 1895, and Anbarrhacus adamantis gen. et sp. nov., assigned in the family Platyrhacidae Pocock, 1895. Morphological data from fossil specimens have been recovered using 3D X-ray micro-computed tomography and regular to infrared-reflected microscopy. Both fossil species are recognizable as new primarily but not exclusively, by collum margin modification and remarkable paranotal and metatergite dorsal sculpture.

X-ray luminescence optical tomography (XLOT) is an emerging hybrid imaging modality in which X-ray excitable particles (phosphor particles) emit optical photons when stimulated with a collimated X-ray beam. XLOT can potentially combine the high sensitivity of optical imaging with the high spatial resolution of X-ray imaging. For reconstruction of XLOT data, we compared two reconstruction algorithms, conventional filtered backprojection (FBP) and a new algorithm, X-ray luminescence optical tomography with excitation priors (XLOT-EP), in which photon propagation is modeled with the diffusion equation and the X-ray beam positions are used as reconstruction priors. Numerical simulations based on dose calculations were used to validate the proposed XLOT imaging system and the reconstruction algorithms. Simulation results showed nanoparticle concentrations reconstructed with XLOT-EP are much less dependent on scan depth than those obtained with FBP. Measurements at just two orthogonal projections are sufficient for XLOT-EP to reconstruct an XLOT image for simple source distributions. The heterogeneity of X-ray energy deposition is included in the XLOT-EP reconstruction and improves the reconstruction accuracy, suggesting that there is a need to calculate the X-ray energy distribution for experimental XLOT imaging. © 2014 Society of Photo-Optical Instrumentation Engineers.

In this work we report the calculation of the deposited energy distribution produced by an x-ray luminescence optical tomography (XLOT) system in a phantom containing different concentrations of Gd2O2S:Eu nanoparticles. The calculations were performed via Monte Carlo simulation considering spectra from a W target x-ray tube operating between 30 and 90 kVp, with 1.0 mm Al added filtration. CT and XLOT tomographic images were reconstructed from the same data. The results show that XLOT has better detectability than CT alone, that the dose scales linearly with kVp for a fixed concentration of Gd2O2S:Eu and air-kerma rate, the scattered radiation contribution to the total dose and signal is about 20% and that the dose ratio for a 3 mm diameter insert containing 10 mg/ml Gd2O2S embedded in a 30 mm diameter water phantom is 6:1. This ratio drops to less than 2:1 for a 1 mg/ml concentration. Finally we show that the method of conjugate images can be used to correct for artifacts due to attenuation effects in XLO...

Coalescence and fragmentation of equal and unequal liquid-drop pairs are studied using a new experimental technique in which mercury drops collide while sliding on a horizontal glass surface. The limits for coalescence measured as a function of the incident relative velocity and impact parameter are found to be similar to what has been reported for free-moving drops of other liquids, while new correlations are found to occur among the number, size, speed and angular distribution of fragmentation residues. The predictions of various models, including a dynamic theory originally developed for nuclear reactions, and specifically modified by us for macroscopic applications, are compared with the observations.

X-ray luminescence optical tomography (XLOT) is an emerging hybrid imaging modality in which x-ray excitable particles (phosphor particles) emit optical photons when stimulated with a collimated x-ray beam. XLOT combines the high sensitivity of optical imaging with the high spatial resolution of x-ray imaging. For XLOT reconstruction, we compared two reconstruction algorithms, conventional filtered backprojection (FBP) and a new algorithm, x-ray luminescence optical tomography with excitation priors (XLOT-EP), in which photon propagation is modeled with the diffusion equation and the x-ray beam positions are used as reconstruction priors. Numerical simulations based on dose calculations are used to validate the proposed XLOT imaging system and the reconstruction algorithms. Simulation results show that XLOT can better detect inclusions of particles than x-ray computed tomography (CT) alone. Nanoparticle concentrations reconstructed with XLOT-EP are much less dependent on target depths than those obtained with FBP. Measurements at just two orthogonal projections are sufficient for the XLOT-EP to reconstruct an XLOT image for simple source distributions. The heterogeneity of x-ray dose distribution is included in the XLOT-EP reconstruction and improves the reconstruction accuracy, suggesting that there is a need to calculate the x-ray dose distribution for experimental XLOT imaging. We have built a prototype XLOT imaging system, in which a collimated x-ray bean is used to scan the samples and an electron multiplying charge couple device (EMCCD) is used to collect the optical photons emitted by the x-ray excitable particles. Phantom experiments have been performed to validate the XLOT system and the proposed reconstruction algorithms.

In this work the new data acquisition system (DAQ) for the microPET of the SIBI project is presented. To increase the microPET sensitivity, the inclusion of more detection modules is required, which in turn needs a more sophisticated and compact signal processing system. The new DAQ is based on programmable integrated circuits (FPGAs) and is composed of (i) an 8‐input triggering board with individual channel adjusting capabilities, which can process signals from 8 detector modules working in coincidence mode and (ii) two 10‐channel digitising boards with 12‐bit resolution. The digitised signals are transmitted to a PC through two Ethernet ports in each board. With the new boards the maximum singles counting rate is of the order of 350 kHz, with a dead time of 2.8 μs. Individual crystal maps of two detectors for image corrections have been obtained, with peak‐to‐valley ratios of 5:1. The new FPGA boards will allow the introduction of more detection modules with relatively simple electronics arrangement.

A microCT scanner prototype that uses a micro‐focus x‐ray source and flat panel detector has been developed in our laboratory. In this work the main system characteristics are described and some results of the initial performance evaluation are presented.

Two separate microtomography systems recently developed at Instituto de Fisica, UNAM, produce anatomical (microCT) and physiological images (microPET) of small animals. In this work, the development and initial tests of an image fusion method based on fiducial markers for image registration between the two modalities are presented. A modular Helix/Line‐Sources phantom was designed and constructed; this phantom contains fiducial markers that can be visualized in both imaging systems. The registration was carried out by solving the rigid body alignment problem of Procrustes to obtain rotation and translation matrices required to align the two sets of images. The microCT/microPET image fusion of the Helix/Line‐Sources phantom shows excellent visual coincidence between different structures, showing a calculated target‐registration‐error of 0.32 mm.

The muon intensity attenuation method to detect heterogeneities in large matter volumes is analyzed. Approximate analytical expressions to estimate the collection time and the signal to noise ratio, are proposed and validated by Monte Carlo simulations. Important parameters, including point spread function and coordinate reconstruction uncertainty are also estimated using Monte Carlo simulations., 8 pages, 11 figures, submetted to NIMA

Micro-multileaf collimator systems coupled to linear accelerators for radioneurosurgery treatments require a rigorous dosimetric characterization in order to be used in 3D conformal and intensity modulated stereotactic radiosurgery and radiotherapy applications. This characterization involves high precision measurements of leaf transmission, leakage and beam penumbra through the collimation system and requires the use of detectors with high spatial resolution, high sensitivity and practically no energy dependence. In this work the use of GafChromic EBT radiochromic film to measure the basic dosimetric properties of the m3-mMLC (BrainLAB, Germany) micro-multileaf collimator system integrated to a 6 MV linear accelerator is reported. Results show that average values of transmission and leakage radiation are 0.89 ± 0.07% and 1.08 ± 0.18%, respectively. The 80-20% beam penumbra were found to be 2.83 ± 0.14, 2.62 ± 0.12, 2.77 ± 0.17, 2.88 ± 0.12 and 2.88 ± 0.09 using 9.8, 8.0, 6.0, 4.0 and 2.0 mm square field sizes, respectively, with an average value of 2.80 ± 0.13 mm. These measurements are below the reference values reported by the manufacturer and similar to those reported in the literature for the same type of mMLC using different radiation detectors

The sizes, temperatures and free neutron to proton ratios of the initial interaction zones produced in the collisions of 40 MeV/nucleon $^{40}$Ar + $^{112}$Sn and 55 MeV/nucleon$^{27}$Al + $^{124}$Sn are derived using total detected neutron plus charged particle multiplicity as a measure of the impact parameter range and number of participant nucleons. The size of the initial interaction zone, determined from a coalescence model analysis, increases significantly with decreasing impact parameter. The temperatures and free neutron to proton ratios in the interaction zones are relatively similar for different impact parameter ranges and evolve in a similar fashion., 7 pages, 8 figures

Modern small-animal PET scanners typically consist of a large number of detectors along with complex electronics to provide tomographic images for research in the preclinical sciences that use animal models. These systems can be expensive, especially for resource-limited educational and academic institutions in developing countries. In this work we show that a small-animal PET scanner can be built with a relatively reduced budget while, at the same time, achieving relatively high performance. The prototype consists of four detector modules each composed of LYSO pixelated crystal arrays (individual crystal elements of dimensions 1 × 1 × 10 mm3) coupled to position-sensitive photomultiplier tubes. Tomographic images are obtained by rotating the subject to complete enough projections for image reconstruction. Image quality was evaluated for different reconstruction algorithms including filtered back-projection and iterative reconstruction with maximum likelihood-expectation maximization and maximum a posteriori methods. The system matrix was computed both with geometric considerations and by Monte Carlo simulations. Prior to image reconstruction, Fourier data rebinning was used to increase the number of lines of response used. The system was evaluated for energy resolution at 511 keV (best 18.2%), system sensitivity (0.24%), spatial resolution (best 0.87 mm), scatter fraction (4.8%) and noise equivalent count-rate. The system can be scaled-up to include up to 8 detector modules, increasing detection efficiency, and its price may be reduced as newer solid state detectors become available replacing the traditional photomultiplier tubes. Prototypes like this may prove to be very valuable for educational, training, preclinical and other biological research purposes.

A procedure for the measurement of spatial dose rate distribution of beta particles emitted by 186Re-liposomes in tumoral tissue, using HS GafChromic films, is presented.HNSCC xenografts were intratumorally injected with 3.7 or 11.1 MBq of 186Re-liposomes, and planar gamma camera images were acquired to determine the liposome retention in the tumor. After imaging, rats were sacrificed and tumors were excised and processed in slices; HS film sections were placed between slices and the tumor lobe was reassembled. Tumors and films were kept in the dark at 4 degrees C for 18 h. After irradiation, films were removed and response was read using a transmission scanner. Films were analyzed to determine two-dimensional spatial dose rate distributions and cumulative dose volume histograms. Dose rate distributions were quantified using a 60Co calibration curve, the 186Re physical half-life, and a perturbation factor that takes into account the effect of the film protective layer.Dose rate distributions are highly heterogeneous with maximal dose rates about 0.4 Gy h(-1) in tumors injected with 3.7 MBq and 1.3 Gy h(-1) in tumors injected with 11.1 MBq. Dose volume histograms showed dose distributed in more than 95% and 80% of the tumor when injected with the lower and the higher activity, respectively.The described procedures and techniques have shown the potential and utility of HS GafChromic film for determination of dose rate distributions in solid tumors injected intratumorally with 186Re-liposomes. The film's structure and the liposomes' biodistribution must be taken into account to obtain quantitative dose measurements.

Positron emission tomography (PET) detection modules consist of pixelated scintillator crystals optically coupled to position sensitive photomultiplier tubes (PS‐PMT). This type of modules should be able to provide sufficient spatial resolution for animal PET applications. We have characterised a Hamamatsu H6568 multianode PS‐PMT. Anode uniformity was obtained by illuminating, via an optical fiber, individual anodes with light pulses from an LED. Using a 4×4 pixelated LYSO crystal, each of 2×2×15 mm3, and a 137Cs radioactive source, the light spread function was obtained. This work forms part of the construction of a microPET system at the Institute of Physics, UNAM.

Preliminary measurements for microCT dosimetry are reported in this work, using TLD‐100 crystals (1×1×1 mm3) within a solid water phantom specially designed with approximate dimensions of a mouse. A dose dependence as a function of radial distance and position along the axis of the phantom was found. Because of the smaller doses used in this work we can say that it is feasible to perform dosimetry measurements with high accuracy using TLD‐100 microcubes.

In this work we study the influence of the purity of the materials used in experimental transmission measurements to obtain data to reconstruct the photon energy spectrum of a 6 MV Linac. We also evaluate the contribution to PDDs due to electron contamination in the reconstructed spectrum.