Percorrer por autor "Oliveira, Joana"
A mostrar 1 - 6 de 6
Resultados por página
Opções de ordenação
- Minimisation of acquisition time in a TOF PET/CT scanner without compromising image qualityPublication . Oliveira, Joana; Parafita, Rui; Branco, SusanaSignificant improvements have been made in Positron Emission Tomography (PET) to enhance the image quality, namely, the development of time-of-flight (TOF) technology. This technique is useful to localize the emission point of the beta plus-emitter (β+) radiopharmaceutical inside the body, allowing better lesion contrast and leading to a short scan time. The main goal of this study is to investigate the shortest acquisition time without compromising the image quality in both a NEMA body phantom and patients, using a TOF PET/Computed Tomography (PET/CT) scanner and the radionuclide Gallium-68 (68Ga). Image quality parameters and quantification in terms of standardized uptake value (SUV) were acquired. A time between 45 and 60 s per bed position is proposed for future clinical practices.
- Minimisation of acquisition time in a TOF PET/CT scanner without compromising image qualityPublication . Oliveira, Joana; Parafita, Rui; Branco, SusanaIntroduction - Significant improvements have been made in Positron Emission Tomography/Computed Tomography (PET/CT) to enhance the image quality, namely, the development of time-of-flight (TOF) technology. This technique is useful to localize the emission point of the beta plus-emitter (β+) radiopharmaceutical inside the body, allowing better lesion contrast, especially for large patients, improving structural details and leading to a short scan time. The main goal of this study is to verify the shortest acquisition time per bed position, in a TOF PET scanner, without compromising the image quality, in both phantom and clinical imaging. Methods - For that purpose, images of a torso NEMA phantom were acquired with different acquisition times per bed position (30, 45, 60, 80 and 120 s) in a TOF PET/CT scanner (GEMINI TF 16, Philips), using Gallium-68 (68Ga) citrate. Clinical images were also acquired of an aleatory patient (male, 64 y) with 68Ga-prostate specific membrane antigen (68Ga-PSMA). Image quality parameters, such as signal-to-noise ratio (SNR), noise, contrast, contrast-to-noise ratio (CNR), contrast recovery coefficient (CRC) and quantification in terms of standardized uptake value (SUV) were acquired. Results - The increased contrast and CRC in larger spheres and with longer acquisition times produces an increase on the noise, leading to a decrease in SNR and CNR. In phantom imaging, SUVmax varied between 1.1 and 1.6 for background (normal uptake) and between 2.1 and 8.0 for spheres (abnormal uptake). A strong correlation was found for both SUVmax and SUVmean between the different acquisition times (R>0.7). Inpatient imaging, spleen showed higher SNR, contrast, noise, and CNR than liver. Median SUVmax was 7.1 for liver, 9.8 for spleen and 1.8 for bone. Conclusions - A time between 45 and 60 s per bed position is proposed for future clinical practices, allowing schedule more scans per day, contributing to an optimization of protocols without compromising the image quality.
- A new insight into the degradation of anthocyanins: reversible versus the irreversible chemical processesPublication . Sousa, Diogo; Basílio, Nuno; Oliveira, Joana; Freitas, Victor De; Pina, FernandoThe kinetics and thermodynamics of the pH-dependent reversible and irreversible processes leading to color fading of pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, and cyanidin-3-O-glucoside dyes in aqueous solutions are reported. Following the addition of base to the flavylium cation, the quinoidal bases disappear by three distinct steps: (i) in an acidic medium by a biexponential process, in which the faster step is controlled by the hydration reaction and the slower one by cistrans isomerization; the degradation process occurs essentially from the anionic quinoidal base; (ii) in a basic medium (pH > 9.5), in which the disappearance of the anionic bases is monoexponential, with the rate proportional to the hydroxyl concentration (hydroxyl attack), leading to anionic chalcones (cis and trans) at equilibrium-the slower degradation step occurs from the di- and trianionic chalcones; and (iii) in the pH region circa 7.7 < pH < 9.5, in which hydration and hydroxyl attacks are much slower than anionic quinoidal base degradation (which is the rate-controlling step) and the equilibrium cannot be attained.
- Numerical modeling of cardiomyocytes using Finite Element MethodPublication . Oliveira, Joana; Rodrigues, José AlbertoIn recent years, the use of mathematical and geometrical models has been enabling the simulation of biological complex systems. Models of cardiac cells provide the possibility to understand the biochemistry and biomechanics of cardiac cells and cardiovascular diseases. The main objective of this work is to simulate the calcium flux and contractile activity of the cardiomyocyte, resorting on the Finite Element Method, and to develop a modelling tool with which we can simulate the key physiological aspects of the cardiac myocytes: Calcium concentration and contraction potential (% of shortening). To test our model's performance several tests were applied varying the local active cellular tension driven by the intracellular calcium concentration (Tu), and the position of T-tubules in the cell, from left to right and up to bottom. Our results show that the behaviour of our model is faithful to what is known to be true with the cell's physiology and pathological conditions.
- Numerical simulation of excitation-contraction in isolated cardiomyocytesPublication . Rodrigues, José Alberto; Oliveira, JoanaWe present and study a mathematical model to simulate the calcium flux and contractile activity of the cardiomyocyte, resorting on the Finite Element Method. This Model of cardiac cells provide the possibility to understand the biochemistry and biomechanics of cardiac cells and cardiovascular diseases. Heart Failure is considered the ultimate cardiac disease, a condition with no effective cure which is highly related with the function of cardiomyocytes and consequently with the concentration of calcium, affecting the contractile activity of the cardiomyocyte. In order to test our model’s performance, several tests were applied varying the local active cellular tension driven by the intracellular calcium concentration and the localization of the main calcium influx. The results are expressed in the graphics of calcium concentration over time, maximum cardiomyocyte contraction and the gradient of calcium diffusion. Our results show that the behaviour of our models is faithful to what is known to be true with cell’s physiology and pathological conditions.
- Valorising food waste using black soldier fly larvae: a One Health assessment of mycotoxin bioaccumulation and mycotoxigenic fungi under industrial-scale conditionsPublication . Oliveira, Joana; Cervantes, Renata; Pena, Pedro; Gomes, Bianca; Kosicki, Robert; Trindade, Alexandre; Murta, Daniel; Viegas, Carla; Twarużek, Magdalena; Assunção, RicardoFood waste is a major challenge for environmental sustainability and food security. Black soldier fly larvae (BSFL, Hermetia illucens) offer a sustainable solution by converting food waste into high-quality protein, aligned with One Health principles. However, concerns over bioaccumulation of contaminants, including fungi and mycotoxins, have limited the use of food waste as insect substrate. This study evaluated whether BSFL bioaccumulate mycotoxins under industrial-scale rearing conditions, using bioaccumulation factors, while also assessing contamination with fungi of mycotoxin-producing potential. To do that, approximately two tonnes of food waste were collected from restaurants in Santarém, Portugal, processed into a test substrate, along with the cereal-based Gainesville diet as a control. Larvae were reared for 14 days, and samples of substrates, larvae, frass, and BSF meal were analysed for fungal contamination and mycotoxin concentration using culture-based methods and liquid chromatography-tandem mass spectrometry, respectively. Mycotoxigenic fungi belonging to Fusarium, Aspergillus, and Penicillium were predominantly below the limit of detection in larvae. Deoxynivalenol (DON), zearalenone (ZEN), and HT-2 toxin were detected in the substrates, but none of these mycotoxins were detected or quantified in larvae, with bioaccumulation factors consistently below one, indicating no significant accumulation. DON and ZEN were also detected in frass, in some cases at higher concentrations than in the corresponding initial substrates. These findings demonstrate that, under the conditions tested, BSFL did not bioaccumulate the mycotoxins detected in the rearing substrates, while their occurrence in frass highlights the importance of considering contaminant distribution across outputs of the bioconversion process. Overall, this study supports the safe use of BSFL for industrial-scale food waste valorisation and highlights their contribution to improving public health.