Catálogo de publicaciones - revistas

<jats:p>A realistic model of human retinal tissues to simulate thermal performance of optical laser photocoagulation therapy is presented. The key criteria to validate the treatment effectiveness is to ensure the photocoagulation temperature between 60 and 70 °C is reached in the treatment region of interest. The model presented consists of truncated volumes of the retinal pigment epithelium (RPE) and adjacent retinal tissues. Two cases of choroid pigmentation are modelled to signify extreme cases of human eye difference: albino and dark colour choroid pigmentation. Conditions for consistent heating over the irradiated treatment spot is modelled for laser beams with different intensity profiles: ‘top-hat’, Gaussian and ‘donut’ modes. The simulation considers both uniform heating within retinal tissue layers and spatial intensity decay due to absorption along the direction of laser propagation. For a 500 <jats:italic>μ</jats:italic>m spot, pulse length 100 ms and incident power to the cornea of 200 mW, realistic spatial variation in heating results in peak temperatures increasing within the RPE and shifting towards the choroid in the case of choroidal pigmentation. Finite element analysis methodology, where heat transfer theory governs the temperature evolution throughout tissues peripheral to the irradiated RPE is used to determine the zone of therapeutic benefit. While a TEM<jats:sub>01</jats:sub> donut mode beam produces lower peak temperatures in the RPE for a given incident laser power, it reduces the volume of retinal tissue reaching excessive temperatures and maximises the zone of therapeutic benefit. Described are simulation limitations, boundary conditions, grid size and mesh growth factor required for realistic simulation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigated the effects of indirect apoptotic cell death due to vascular damage on tumor response to a single large dose with an improved two-dimensional cellular automata model. The tumor growth was simulated by considering the oxygen and nutrients supplied to the tumor through the blood vessels. The cell damage processes were modeled by taking account of the direct cell death and the indirect death due to the radiation-induced vascular damages. The radiation increased the permeation of oxygen and nutrients through the blood vessel or caused the breakdown of the vasculature. The amount of oxygen in cancer cells affected the response of cancer cells to radiation and the tumor growth rate after irradiation. The lack of oxygen led to the apoptotic death of cancer cells. We calculated the tumor control probability (TCP) at different radiation doses, the probability of apoptotic death, the threshold of the oxygen level for indirect apoptotic death, the average oxygen level in cancer cells and the vessel survival probability after radiation damage. Due to the vessel damage, indirect cell death led to a 4% increase in TCP for the dose ranging from 15 Gy to 20 Gy. TCP increased with increasing the probability of apoptotic death and the threshold of the oxygen level for indirect apoptotic death due to increased apoptotic death. The variation of TCP as a function of the average oxygen level exhibited the minimum at the average oxygen level of 2.7%. The apoptosis increased as the average oxygen level decreased, leading to an increasing TCP. On the other hand, the direct radiation damage increased, and the apoptosis decreased for higher average oxygen level, resulting in a higher TCP. We showed by modeling the radiation damage of blood vessels in a 2D CA simulation that the indirect apoptotic death of cancer cells, caused by the reduction of the oxygen level due to vascular damage after high dose irradiation, increased TCP.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In interior cardiac computed tomography (CT) imaging, the x-ray beam is collimated to a limited field-of-view covering the heart volume, which decreases the radiation exposure to surrounding tissues. Spectral CT enables the creation of virtual monochromatic images (VMIs) through a computational material decomposition process. This study investigates the utility of VMIs for beam hardening (BH) reduction in interior cardiac CT, and further, the suitability of VMIs for coronary artery calcium (CAC) scoring and volume assessment is studied using spectral photon counting detector CT (PCD-CT). <jats:italic>Ex vivo</jats:italic> coronary artery samples (<jats:italic>N =</jats:italic> 18) were inserted in an epoxy rod phantom. The rod was scanned in the conventional CT geometry, and subsequently, the rod was positioned in a torso phantom and re-measured in the interior PCD-CT geometry. The total energy (TE) 10–100 keV reconstructions from PCD-CT were used as a reference. The low energy 10–60 keV and high energy 60–100 keV data were used to perform projection domain material decomposition to polymethyl methacrylate and calcium hydroxylapatite basis. The truncated basis-material sinograms were extended using the adaptive detruncation method. VMIs from 30–180 keV range were computed from the detruncated virtual monochromatic sinograms using filtered back projection. Detrending was applied as a post-processing method prior to CAC scoring. The results showed that BH artefacts from the exterior structures can be suppressed with high (≥100 keV) VMIs. With appropriate selection of the monoenergy (46 keV), the underestimation trend of CAC scores and volumes shown in Bland-Altman (BA) plots for TE interior PCD-CT was mitigated, as the BA slope values were −0.02 for the 46 keV VMI compared to −0.21 the conventional TE image. To conclude, spectral PCD-CT imaging using VMIs could be applied to reduce BH artefacts interior CT geometry, and further, optimal selection of VMI may improve the accuracy of CAC scoring assessment in interior PCD-CT.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Deep learning algorithms for radiation therapy treatment planning automation require large patient datasets and complex architectures that often take hundreds of hours to train. Some of these algorithms require constant dose updating (such as with reinforcement learning) and may take days. When these algorithms rely on commerical treatment planning systems to perform dose calculations, the data pipeline becomes the bottleneck of the entire algorithm’s efficiency. Further, uniformly accurate distributions are not always needed for the training and approximations can be introduced to speed up the process without affecting the outcome. These approximations not only speed up the calculation process, but allow for custom algorithms to be written specifically for the purposes of use in AI/ML applications where the dose and fluence must be calculated a multitude of times for a multitude of different situations. Here we present and investigate the effect of introducing matrix sparsity through kernel truncation on the dose calculation for the purposes of fluence optimzation within these AI/ML algorithms. The basis for this algorithm relies on voxel discrimination in which numerous voxels are pruned from the computationally expensive part of the calculation. This results in a significant reduction in computation time and storage. Comparing our dose calculation against calculations in both a water phantom and patient anatomy in Eclipse without heterogenity corrections produced gamma index passing rates around 99% for individual and composite beams with uniform fluence and around 98% for beams with a modulated fluence. The resulting sparsity introduces a reduction in computational time and space proportional to the square of the sparsity tolerance with a potential decrease in cost greater than 10 times that of a dense calculation allowing not only for faster caluclations but for calculations that a dense algorithm could not perform on the same system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Commercially available fully spectroscopic pixelated cadmium telluride (CdTe) detector systems have been adopted lately for benchtop x-ray fluorescence (XRF) imaging/computed tomography (XFCT) of objects containing metal nanoprobes such as gold nanoparticles (GNPs). To date, however, some important characteristics of such detector systems under typical operating conditions of benchtop XRF/XFCT imaging systems are not well known. One important but poorly studied characteristic is the effect of detector bias-voltage on photon counting efficiency, energy resolution, and the resulting material detection limit. In this work, therefore, we investigated these characteristics for a commercial pixelated detector system adopting a 1-mm-thick CdTe sensor (0.25-mm pixel-pitch), known as HEXITEC, incorporated into an experimental benchtop cone-beam XFCT system with parallel-hole detector collimation. The detector system, operated at different bias-voltages, was used to acquire the gold XRF/Compton spectra from 1.0 wt% GNP-loaded phantom irradiated with 125 kVp x-rays filtered by 1.8-mm Tin. At each bias-voltage, the gold XRF signal, and the full-width-at-half-maximum at gold K<jats:italic>α</jats:italic> <jats:sub>2</jats:sub> XRF peak (∼67 keV) provided photon counting efficiency and energy resolution, respectively. Under the current experimental conditions, the detector photon counting efficiency and energy resolution improved with increasing bias-voltage by ∼41 and ∼29% at −300V; ∼54 and ∼35% at −500V, respectively, when compared to those at −100V. Consequently, the GNP detection limit improved by ∼26% at −300V and ∼30% at −500V. Furthermore, the homogeneity of per-pixel energy resolution within the collimated detector area improved by ∼34% at −300V and ∼54% at −500V. These results suggested the gradual improvements in the detector performance with increasing bias-voltage up to −500V. However, at and beyond −550V, there were no discernible improvements in photon counting efficiency and energy resolution. Thus, the bias-voltage range of −500 to −550V was found optimal under the current experimental conditions that are considered typical of benchtop XRF/XFCT imaging tasks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> <jats:bold>Introduction:</jats:bold> Internal organ motion and deformations may cause dose degradations in proton therapy (PT) that are challenging to resolve using conventional image-guidance strategies. This study aimed to investigate the potential of <jats:italic>range guidance</jats:italic> using water-equivalent path length (WEPL) calculations to detect dose degradations occurring in PT. <jats:bold>Materials and methods:</jats:bold> Proton ranges were estimated using WEPL calculations. Field-specific isodose surfaces in the planning CT (pCT), from robustly optimised five-field proton plans (opposing lateral and three posterior/posterior oblique beams) for locally advanced prostate cancer patients, were used as starting points. WEPLs to each point on the field-specific isodoses in the pCT were calculated. The corresponding range for each point was found in the repeat CTs (rCTs). The spatial agreement between the resulting surfaces in the rCTs (hereafter referred to as iso-WEPLs) and the isodoses re-calculated in rCTs was evaluated for different dose levels and Hausdorff thresholds (2-5 mm). Finally, the sensitivity and specificity of detecting target dose degradation (V95%&lt;95%) using spatial agreement measures between the iso-WEPLs and isodoses in the pCT was evaluated. <jats:bold>Results:</jats:bold> The spatial agreement between the iso-WEPLs and isodoses in the rCTs depended on the Hausdorff threshold. The agreement was 65-88% for a 2 mm threshold, 83-96% for 3 mm, 90-99% for 4 mm, and 94-99% for 5 mm, across all fields and isodose levels. Minor differences were observed between the different isodose levels investigated. Target dose degradations were detected with 82-100% sensitivity and 75-80% specificity using a 2 mm Hausdorff threshold for the lateral fields. <jats:bold>Conclusion:</jats:bold> Iso-WEPLs were comparable to isodoses re-calculated in the rCTs. The proposed strategy could detect target dose degradations occurring in the rCTs and could be an alternative to a fully-fledged dose re-calculation to detect anatomical variations severely influencing the proton range.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cell encapsulation within the microspheres using a semi-permeable polymer allows the two-way transfer of molecules such as oxygen, nutrients, and growth factors. The main advantages of cell encapsulation technology include controlling the problems involved in transplanting rejection in tissue engineering applications and reducing the long-term need for immunosuppressive drugs following organ transplantation to eliminate the side effects. Cell-laden microgels can also be used in 3D cell cultures, wound healing, and cancerous clusters for drug testing. Since cell encapsulation is used for different purposes, several techniques have been developed to encapsulate cells. Droplet-based microfluidics is one of the most valuable techniques in cell encapsulating. This study aimed to review the geometries and the mechanisms proposed in microfluidic systems to precisely control cell-laden microgels production with different biopolymers. We also focused on alginate gelation techniques due to their essential role in cell encapsulation applications. Finally, some applications of these microgels and researches will be explored.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The COVID-19 crisis has alerted the research community to re-purpose scientific tools that can effectively manage emergency pandemic situations. Researchers were never so desperate to discover a ‘magic bullet’ that has significant clinical benefits with minimal or no side effects. At the beginning of the pandemic, due to restricted access to traditional laboratory techniques, many research groups delved into computational screening of thousands of lead molecules that could inhibit SARS-CoV-2 at one or more stages of its infectious cycle. Several <jats:italic>in silico</jats:italic> studies on natural derivatives point out their potency against SARS-CoV-2 proteins. However, theoretical predictions and existing knowledge on related molecules reflect their poor oral bioavailability due to biotransformation in the gut and liver. Nanotechnology has evolved into a key field for precise and controlled delivery of various drugs that lack aqueous solubility, have low oral bioavailability and possess pronounced toxicity in their native form. In this review, we discuss various nanoformulations of natural products with favorable ADME properties, and also briefly explore nano-drug delivery to lungs, the primary site of SARS-CoV-2 infection. Natural products are also envisioned to augment nanotechnology-based (1) personnel protective equipment for <jats:italic>ex vivo</jats:italic> viral inactivation and (2) wearable sensors that perform rapid and non-invasive analysis of volatile organic compounds in exhaled breath of the infected person after therapeutic food consumption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Diabetic peripheral neuropathy (DPN) is associated with loss of motor units (MUs), which can cause changes in the activation pattern of muscle fibres. This study investigated the pattern of muscle activation using high-density surface electromyography (HD-sEMG) signals from subjects with type 2 diabetes mellitus (T2DM) and DPN. Thirty-five adults participated in the study: 12 healthy subjects (HV), 12 patients with T2DM without DPN (No-DPN) and 11 patients with T2DM with DPN (DPN). HD-sEMG signals were recorded in the tibialis anterior muscle during an isometric contraction of ankle dorsiflexion at 50% of the maximum voluntary isometric contraction (MVIC) during 30-s. The calculated HD-sEMG signals parameters were the normalised root mean square (RMS), normalised median frequency (MDF), coefficient of variation (CoV) and modified entropy (ME). The RMS increased significantly (<jats:italic>p</jats:italic> = 0.001) with time only for the DPN group, while the MDF decreased significantly (<jats:italic>p</jats:italic> &lt; 0.01) with time for the three groups. Moreover, the ME was significantly lower (<jats:italic>p</jats:italic> = 0.005), and CoV was significantly higher (<jats:italic>p</jats:italic> = 0.003) for the DPN group than the HV group. Using HD-sEMG, we have demonstrated a reduction in the number of MU recruited by individuals with DPN. This study provides proof of concept for the clinical utility of this technique for identifying neuromuscular impairment caused by DPN.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The attenuation coefficients are important input values in estimating not only the dose and exposure in radiotherapy and medical imaging, but also in the proper design of photon shields. While studies are widely available above 1 keV, the attenuation coefficients of human tissues for photon energies less than 1 keV have not been studied yet. In this study, the attenuation coefficients of water and some human tissues were estimated for low energy photons using the MCNP6.1 code in the energy region 0.1 keV–1 keV. Mass attenuation coefficients were estimated at photon energies of 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000 eV for water and ten human tissues (Soft, Breast, Lung, Bone, Brain, Eye lens, Ovary, Skin, Thyroid and Prostate). Results were compared with those available in literature and a fairly good agreement has been obtained. These data were then used to calculate the mean free path, half value layer, tenth value layer, effective atomic number and specific gamma-ray constant (useful for calculation of dose rate) as well. Moreover, for comparison the effective atomic number of the water has been obtained using the results of this work and using the data available in NIST database from 0.1 to 1 keV. In addition, the human tissues were compared with some tissue equivalent materials in terms of effective atomic number and specific gamma-ray constant to study the tissue equivalency from the results, the muscle-equivalent liquid with sucrose has been found to be the best tissue equivalent material for soft tissue, eye lens and brain with relative difference below 4.1%.</jats:p>