No description available.

No description available.

No description available.

Positron emission tomography (PET) is a nuclear medicine imaging techniquethat uses radiotracers to visualize processes like metabolism and perfusion. Theradiotracer emits positrons, which collide with shell electrons of the atomsthat make up the surrounding tissue. Such a collision produces two gammarayphotons, emitted roughly 180 degrees apart [1]. PET captures thesephotons using a cylindrical arrangement of detectors. When two photons aredetected simultaneously by different detectors, it registers as a line of response(LOR). These LORs are then pre-processed into a sinogram. A mathematicalreconstruction method is used to computationally recover the 3D distribution ofthe radiotracer (activity map) from the sinogram. However, genuine LORs can becorrupted by false LORs that come from scattering, random events, and spuriousevents. Mitigating these in reconstruction algorithms is essential for improvingPET imaging accuracy and reliability.This paper explores the theoretical foundation of the Time of Flight (TOF) SingleScatter Simulation (SSS) model by Watson (2007) [2]. It also includes a Pythonimplementation of the MATLAB code associated with [2]. The model modelsCompton scattering to accurately estimate scattered photons in PET.Incorporating TOF data into the SSS model improves estimation accuracy, albeitat the cost of increased computational time. To expedite computations, thealgorithm was simplified by restricting operations to a subset of rings anddetectors and by pre-processing images through cropping and downscaling.Interpolation fills in missing data, ensuring complete estimation.The outcome of this project is a Python implementation that exhibited a strongcorrelation with the estimates obtained using the MATLAB implementation. Anotable issue arose during the comparison between the main components ofthe SSS algorithm in Python and MATLAB. The Euclidean norm between theresults from these two implementations was significant, indicating that they wereon different scales. Nevertheless, both implementations accurately predictedthe scatter in the same locations and relative magnitudes, despite the scalediscrepancy. Investigation into the discrepancy’s cause is ongoing, but theproject demonstrates the feasibility of implementing the TOF SSS algorithm inPython.

This present thesis comprise two major parts both experimental and numerical study which have been conducted in four distinct steps as following: (1) Design, construction, and evaluation of control and hydrodynamic of a bioreactor system. (2) Visualization of fluid flow perfusion in the hollow fibre membrane bioreactor (HFMB) using a biomedical noninvasive imaging technique, i.e. positron emission tomography (PET). (3) Development of a mathematical model for analyzing a hybrid hollow fibre membrane bioreactor (hHFMB) and (4) Development of a dynamic and two-porous media model for analyzing the HFMB with the aid of computational fluid dynamics (CFD), specifically for bone tissue engineering application. The experimental part includes the steps 1 and 2. In the step 1, the flow perfusion bioreactor system has been designed and constructed. The experimental evaluations of hydrodynamic, and control were performed. In this system, mean pressure, mean flow rate, frequency and waveform of the pulsatile pressure and flow rate can be modulated and controlled over the time to simulate both physiological and non-physiological conditions. The temperature, dissolved oxygen, and pH can be controlled.This bioreactor system can be applied to a variety of scaffold configurations, geometries, and sizes as the cell/tissue culture chamber is adjustable in length.This system is autoclavable, and compatible with noninvasive medical imaging techniques. Designing of the inlet and outlet manifold of the bioreactor were performed according to data obtained from CFD simulation of the flow distribution to achieve high efficiencies in the uniformity of flow perfusion. In the second step, PET was proposed for the very first time and a small animal PET system was used to obtain new information about steady and pulsatile flow patterns in the HFMB for tissue engineering applications. The non-homogeneous tracer distribution, as found with PET imaging, implies the occurrence of non-efficient regions with respect to mass transfer. In steady inlet flow condition, a non-uniform distribution of radioactive tracer was obtained. In contrast, the pulsatile inlet flow generated more uniform perfusion than that of steady flow. Further, it was found that in the case of pulsatile flow, the accumulation of the tracer within the bioreactor was efficiently less than that of steady inlet flow at the same condition. Therefore, in one hand these findings have the potential to improve bioreactor design and in the other hand can explore a very important rout to employ PET in developing bioreactors for tissue engineering applications. The numerical part includes the step 3 and 4 in which the numerical study has been performed for 3-D bone tissue growth in HFMB as a case study for large-scale tissue culture. In the step 3, the feasibility of utilizing newly proposed hHFMB for the growth of mesenchymal stem cells (MSCs) to form bone tissue was investigated using numerical simulations. To this aim, a mathematical model using a CFD code was developed to optimize the design and operation parameters of hHFMB for the growth of MSCs. The volume averaging method was used to formulate mass balance for the nutrients and the cells in the porous extracapillary space (ECS) of the hHFMB. The cell-scaffold construct in the ECS of the hollow fibres and membrane wall were treated as porous medium. Cell volume fraction dependent porosity, permeability, and diffusivity of mass were used in the model. The simulations allowed the simultaneous prediction of nutrient distribution and nutrient-dependent cell volume fraction. In addition, this model was used to study the effects of the operating and design parameters on the nutrient distribution and cell growth within the bioreactor. The modeling results demonstrated that the fluid dynamics within the ECS and transport properties and uptake rates in hHFMB were sufficient to support MSCs required for clinical-scale bone tissue growth in vitro and enabled to solve nutrition difficulties because of high cell density and scaffold size. In the step 4, the new dynamic and two-porous media model has been used for analyzing the nutrient-dependent MSCs growth in order to form the bone tissue in the HFMB. In the present model, hollow fibre scaffold within the bioreactor was treated as a porous domain. The domain consists of the porous lumen region available for fluid flow and the porous ECS region, filled with collagen gel containing cells, for growing tissue mass. Furthermore, the contributions of several design and process parameters, which enhance the performance of the bioreactor, were studied. In addition, the dynamic evaluation of cell growth, oxygen and glucose distributions were quantitatively analyzed. The obtained information can be used for better designing of the bioreactor, determining of suitable operational conditions and scale up of the bioreactor for engineering of clinical-scale bone tissue.--Résumé abrégé par UMI.

Résumé : La résistance à l’insuline est un facteur de risque important pour le développement du diabète de type 2. Un désordre au niveau du métabolisme postprandial, qui se manifeste par une diminution relative du stockage des acides gras (AG) dans les tissus adipeux, mène à un débordement plasmatique des AG et à leur canalisation dans les tissus maigres tels que le cœur, le foie et les muscles squelettiques sous forme de dépôts ectopiques. Ce phénomène, connu sous le nom de lipotoxicité, se développe dans un contexte de balance énergétique positive chronique favorisée par la consommation alimentaire excessive ainsi que la sédentarité et peut varier entre les hommes et les femmes. Plusieurs études démontrent que le changement des habitudes de vie peut corriger ces désordres métaboliques. Notre laboratoire a développé une méthode unique pour étudier le métabolisme des AG de façon non invasive à l’aide d’un traceur radioactif, l’acide 14(R,S)-fluoro-6-thia-heptadécanoïque ([indice supérieur 18]F-FTHA), un analogue des acides gras à longue chaines utilisé en tomographie par émission de positrons. Nos études antérieures ont démontré que chez les sujets intolérants au glucose (IG+) on observe des niveaux de captage des AG dans le myocarde plus élevés associés à une fraction d’éjection du ventricule gauche ainsi qu’un volume d'éjection systolique diminués. À la suite d’une intervention d’un an axée sur les habitudes de vie des sujets IG+, on note une diminution du captage des AG dans le myocarde ainsi qu’une amélioration des paramètres de la fonction cardiaque. Cependant, chez des sujets IG+ ayant suivi une restriction calorique d’une semaine sans modifications de leur niveau d’activité physique, nous avons observé une augmentation du captage des AG dans le myocarde en parallèle avec une diminution de la fraction d’éjection du ventricule gauche. La restriction calorique, l’activité physique et la perte de poids influencent le métabolisme des substrats énergétiques et la fonction cardiaque chez les IG+, mais le sexe biologique est aussi un facteur important qui agit sur ces derniers. Le captage élevé des AG par le cœur chez les hommes est expliqué par des niveaux de chylomicrons plus élevés alors que chez les femmes il est associé à l’obésité. Bien que nos études ne nous ont pas permis de faire un lien entre les habitudes de vie des sujets IG+ et les anomalies métaboliques observées en période postprandiale chez ces sujets ni d’identifier quels changements dans leurs habitudes de vie ont contribué aux améliorations métaboliques dans le myocarde, elles nous ont amenées à redéfinir nos outils méthodologiques pour mieux étudier les habitudes de vie et de prendre en considération les différences entre les hommes et les femmes dans nos études futures. / Abstract : Insulin resistance is a major risk factor for the development of type 2 diabetes. Abnormalities in postprandial metabolism, which are characterized by a relative decrease in fatty acid storage capacity in adipose tissue leading to fatty acid spillover into the systemic circulation, give rise to ectopic fat deposition in non adipose tissues such as the heart, the liver and skeletal muscles. This phenomenon, commonly referred to as lipotoxicity, arises within the context of a chronic positive energy balance which is the direct result of excessive food consumption together with decreased energy expenditure and may be different in men and women. Many studies have shown, however, that metabolic abnormalities are reversible with changes in lifestyle habits. Our laboratory has developed a unique non-invasive method to study dietary fatty acid (DFA) metabolism using a radioactive tracer, 14(R,S)-[[superscript 18]F]-fluoro-6-thia-heptadecanoic acid ([superscript 18]F-FTHA), a long-chain fatty acid analogue, in combination with positron emission tomography. Our previous work demonstrated that patients with impaired glucose tolerance (IGT+) display an increase in myocardial DFA partitioning associated with a decreased left ventricular ejection fraction and stroke volume. Following a one-year lifestyle intervention regimen in IGT+ subjects, a reduction in myocardial DFA uptake as well as an improvement in cardiac function parameters was observed. However, IGT+ subjects who participated in a short-term caloric restriction while maintaining their usual level of physical activity, experienced an increase in myocardial DFA partitioning in parralel with a decreased left ventricular ejection fraction. Caloric restriction, physical activity and weight loss all have an impact on energy substrate metabolism and cardiac function in IGT+ patients, but gender is a major determinant as well. Increased myocardial DFA uptake in men is driven largely by elevated circulating chylomicron-TG levels whereas in women it appears to be associated with obesity. Although it was not possible for us to establish a link between IGT+ patients’ lifestyle habits and the postprandial metabolic abnormalities that they display nor to identify which lifestyle changes contributed to the metabolic improvements in the heart observed after the intervention, our studies helped redefine our methodological tools for assessing lifestyle parameters and underlined the importance of considering gender differences in our future studies.

The dopamine D2 receptor exists in vitro in two states of agonist affinity: a high-affinity state mediating dopamine’s physiological effects, and a physiologically-inert low-affinity state. Our primary goal was to determine the in vivo relevance of this two-affinity-state model for the agonist PET radiotracer [11C]-(+)-PHNO, developed for measurement of the D2 high-affinity state. Our second goal was to characterize the regional D2 versus D3 pharmacology of [3H]-(+)-PHNO binding and assess its utility for measuring drug occupancy at both receptor subtypes. Using ex vivo dual-radiotracer experiments in conscious rats, we showed that, contrary to the two-affinity-state model, the binding of [11C]-(+)-PHNO and the antagonist [3H]-raclopride were indistinguishably inhibited by D2 partial agonist (aripiprazole), indirect agonist (amphetamine) and full agonist ((-)-NPA) pretreatment. Furthermore, ex vivo [11C]-(+)-PHNO binding was unaffected by treatments that increase in vitro high-affinity state density (chronic amphetamine, ethanol-withdrawal), whereas unilateral 6-OHDA lesion, which increases total D2 receptor expression, similarly increased the ex vivo binding of [11C]-(+)-PHNO and [3H]-raclopride. These results do not support the in vivo validity of the two-affinity-state model, suggesting instead a single receptor state for [11C]-(+)-PHNO and [3H]-raclopride in conscious rat. Importantly, we also demonstrated that the increased amphetamine-sensitivity of the agonist radiotracers [11C]-(+)-PHNO and [11C]-(-)-NPA, commonly seen in isoflurane-anaesthetized animals and cited as evidence for the two-affinity-state model, is due to the confounding effects of anaesthesia. Using in vitro and ex vivo autoradiography in rat and the D3 receptor-selective drug SB277011, we found that [3H]-(+)-PHNO binding in striatum and cerebellum lobes 9 and 10 was due exclusively to D2 and D3 receptor binding, respectively, but in other extra-striatal regions to a mix of the two receptor subtypes. Surprisingly, the D3 contribution to [3H]-(+)-PHNO binding was greater ex vivo than in vitro. Also surprising, several antipsychotic drugs, at doses producing 80% D2 occupancy, produced insignificant (olanzapine, risperidone, haloperidol) or small (clozapine, ~35%) D3 occupancy, despite similarly occupying both receptor subtypes in vitro. These data reveal a significant discrepancy between in vitro and ex vivo measures of dopamine receptor binding and suggest that the D3 occupancy is not necessary for the therapeutic effect of antispychotic drugs.

Abstract : Normal aging is accompanied by several metabolic and structural changes in the brain and a heightened risk of cognitive decline. These brain changes may increase the chances of later developing Alzheimer’s disease. The first major objective of the present work was to quantify, through positron emission tomography (PET) and volumetric magnetic resonance (MR) imaging techniques, the effects of normal aging on brain metabolism and structure. Our results indicate that brain glucose hypometabolism can be present in older individuals who remain cognitively normal. Cognitive status was assessed using age-normalised neuropsychological tests. Brain glucose hypometabolism was quite specific and affected primarily the prefrontal cortex and the caudate nucleus. Due to the high variation in plasma ketones, brain ketone hypometabolism per se was not present in older persons (≥65 years old). However, a lower rate constant for brain ketone uptake was fairly widespread in our healthy older group. Lower regional brain volume during normal aging was widespread throughout the cortex and was more apparent than cortical thickness loss. The second major objective was to characterize brain ketone and glucose metabolism in the context of mild Alzheimer’s disease. Glucose hypometabolism in Alzheimer’s disease was present in the temporoparietal cortex when compared with cognitively normal older adults. However, no significant differences in brain ketone metabolism or rate constant were found between the two groups. Alternative energy sources to glucose may therefore be beneficial to the Alzheimer’s disease brain, at least early in the disease process, in order to maintain neuronal capacity and limit synaptic loss and decline in memory and cognition. // Résumé : Au cours du vieillissement normal, le cerveau va subir plusieurs changements métaboliques et structuraux qui vont accroitre le risque de déclin cognitif et du fait même augmenter le risque de développer la maladie d’Alzheimer. Les objectifs du présent travail étaient de : 1) quantifier l’effet du vieillissement normal sur la structure et le métabolisme du cerveau, grâce aux techniquesd’imagerie tomographie par émission de positons et l’imagerie par résonance magnétique ; 2) caractériser le métabolisme cérébral des deux substrats énergétiques du cerveau, le glucose et les cétones, dans un contexte de la maladie d’Alzheimer. Nos résultats indiquent qu’un hypométabolisme du glucose est présent chez des personnes âgées (65 ans et plus) qui démontrent pourtant une cognition normale. Cette diminution du métabolisme cérébral du glucose est observée spécifiquement au niveau des régions du cortex préfrontal et du noyau caudé. Du fait d’une grande variabilité au niveau des concentrations plasmatiques en cétones, aucune diminution du métabolisme des cétones n’a été constatée chez les personnes âgées. En revanche, la constante de transfert des cétones au cerveau était globalement diminuée. En ce qui concerne l’atrophie cérébrale au cours du vieillissement normal, nous avons observé qu’elle était globale, qu’elle concerne l’ensemble du cerveau et qu’elle était plus marquée que la diminution de l’épaisseur corticale. En comparant des personnes âgées en bonne santé à des personnes ayant la maladie d’Alzheimer, nous avons également confirmé que chez ces dernières, le métabolisme du glucose est diminué spécifiquement au niveau du cortex temporopariétal. Cependant, aucune différence entre les deux groupes de personnes n’a été observée en ce qui concerne le métabolisme cérébral des cétones. Ainsi en fournissant des substrats énergétiques autres que le glucose, il serait donc possible de maintenir les capacités neuronales, limiter la perte synaptique et ralentir le déclin cognitif. Ceci pourrait constituer une stratégie prometteuse dans la prévention et le traitement complémentaire au début de la maladie d’Alzheimer.

<p>Kolorektalni karcinom je treća po redu maligna bolest po broju novoobolelih u svetskoj populaciji, posle karcinoma pluća i dojke. Petogodi&scaron;nje preživljavanje od kolorektalnog karcinoma u SAD-u je 59-66%, u zemljama Zapadne Evrope oko 60% a u Autonomnoj Pokrajuni Vojvodini 27%. U razvijenim zemljama se sprovode skrining programi koji omogućavaju rano otkrivanje malignih bolesti, međutim, u Srbiji takav program ne postoji. Stoga je potrebno iznaći nove načine u inicijalnom menadžmentu obolelih od ove bolesti, koji će indirektno povećati njihovo preživljavanje. Jedan od načina je primena &scaron;to savremenijih dijagnostičkih metoda koji će precizno definisati stadijum. PET-CT je imidžing metoda koja poslednjih godina zauzima značajno mesto u određivanju stadijuma malignih bolesti i dijagnostikovanju recidiva. Fuzionisanjem skenova PET-a i CT-a dobija se PET-CT slika koja prikazuje funkcionalno stanje pojedinih tkiva i organa (PET) sa anatomskim detaljima (CT). Cilj istraživanja je bio da se utvrdi vrednost PET-CT pregleda u određivanju stadijuma KRK kao i u planiranju radioterapije. Nakon pregleda, pacijenti su ili operisani ili podvrgnuti planiranju radioterapije. Kod operisanih pacijenata poredilo se određivanje stadijuma PET-CT pregledom i PH metodom.Utvrđeno je da kod određivanja T stadijuma ne postoji statistički značajna razlika u<br />određivanju stadijuma KRK između navedene dve metode odnosno da je senzitivnost za ovaj parameter 90,7%. PET-CT pregled ima nisku senzitivnost za procenjivanje proboja mezorektalne fascije koja iznosi 77,3%. U određivanju N stadijuma, PET-CT pregled se pokazao kao visokosenzitivan (85,8%). Od 4 pacijenta kod kojih su dijagnostikovane metastatske lezije jetre, kod svih su one i patohistolo&scaron;ki verifikovane &scaron;to predstavlja 100% tačnost. Kod poređenja planiranja radioterapije na osnovu PET-CT pregleda i samo CT simulatora, za GTV meru, ova vrednost je u grupi pacijenata kod kojih je planiranje vr&scaron;eno nakon fuzije CT i PET-CT slike bila za 65,5% manja u odnosu na retrospektivnu grupu kod koje je planiranje vr&scaron;eno samo na osnovu CT pregleda. Za CTV volumene, dobijena je statistički značajna razlika u poređenju prospektivne i retrospektivne grupe u smislu manjih volumena u prvoj grupi. Kod poređenja PTV volumena, nije dobijena statistički značajna razlika. Takođe, kada se poredila doza zračenja koju su primili organi od rizika (m.be&scaron;ika i glave femura), dobijeno je da su statistički značajno manje doze primili navedeni organi u prospektivnoj grupi, kada se planirnaje vr&scaron;ilo pomoću PET-CT slajsova. Na&scaron;i rezultati pokazuju da bi kod dve trećine pacijenata do&scaron;lo do promene u terapijskom modalitetu kada bi svaki pacijent inicijalno, pre bilo kakve terapije bio podvrgnut PET-CT pregledu. Istraživanjem je potvrđena hipoteza da primena PET-CT pregleda ima značaja u inicijalnom određivanju stadijuma KRK kod većine pacijenata (96,3% pacijenata). Takođe je potvrđeno da ova metoda ima veliku vrednost u planiranju radioterapije smanjujući ozračivanje zdravih tkiva i pobolj&scaron;avajući kvalitet terapije tumora.</p> / <p>Colorectal carcinoma is third malignant disease by the frequency of appearance worldwide, following lung and breast cancer. Five-year survival from colorectal cancer is 59-66% in the USA, 60% in Western Europe and 27% in Region of Vojvodina. In developed countries, screening programs that provide early detection of the malignancies are in use, but in Serbia such program doesn&rsquo;t exsist.Therefore, upgrading of the initial colorectal cancer management is necessary in order of survival benefit. Accurate preoperative staging is essential in determining the optimal therapeutic procedures and planning for individual patients. Advances in imaging technology have raised interest in the potential role of PET-CT examination for staging of colorectal cancer. By PET and CT scan fusion, functional and anatomical informations are both provided. Aim of this study was to evaluate PET-CT examination in colorectal cancer staging and radiotherapy planning. After examination, patients underwent surgery or radiotherapy. In operated group, histopathological examination was the reference standard. Analysing the use of PET-CT in T stage evaluation our results showed high sensitivity of 90,7%. PET-CT examination has low sensitivity in analyzing mesorectal fascia involvement (77,3%). It was showed that PET-CT is very sensitive in N staging (85,8%). Four of the patients had liver metastases on PET-CT, and all of them were histopathologicaly confirmed, so the accuracy of M staging was 100%. In radiotherapy planning comparison, for GTV measure, we concluded that PET-CT planning provide 65,5% less tumor irradiated volume compared with CT planning. For CTV volumes, our results show that there is statistically significant difference between prospective and retrospective group with smaller volumes in the first group. In PTV volume comparison, the difference wasn&rsquo;t statistically significant. Also, when we compared doses that received organs of risk (bladder, femoral heads), we got statistically significant differences which means that less doses patients received in prospective group where planning was performed with PET-CT scans. Our results show that after initial PET-CT examination therapy modality changes in two thirds of the patients. This study confirmed the hypothesis that PET-CT has an impact on initial colorectal cancer staging in most of the patients (96,3% of the patients). Also, this examination has a great value in radiotherapy planning because it decriases radiation of the healty tissue and provides better quality of tumor therapy.</p>

Alzheimer’s disease (AD) is the leading cause of dementia and is alone responsible for 60-70% of all cases of dementia. Though sharing clinical symptoms with other types of dementia, the hallmarks of AD are the abundance of extracellular depositions of β-amyloid (Aβ) plaques, intracellular neurofibrillary tangles of hyper phosphorylated tau proteins and synaptic depletion. The onset of the physiological hallmarks may precede clinical symptoms with a decade or more, and once clinical symptoms occur it may be difficult to separate AD from other types of dementia based on clinical symptoms alone. Since the introduction of radiolabeled Aβ tracer substances for positron emission tomography (PET) imaging it is possible to image the Aβ depositions in-vivo, strengthening the confidence in the diagnosis. Because the accumulation of Aβ may occur years before the first clinical symptoms are shown and even reach a plateau, Aβ PET imaging may not be feasible for disease progress monitoring. However, a negative scan may be used to rule out AD as the underlying cause to the clinical symptoms. It may also be used as a predictor to evaluate the risk of developing AD in patients with mild cognitive impairment (MCI) as well as monitoring potential effects of anti-amyloid drugs.Though currently validated for dichotomous visual assessment only, there is evidence to suggest that quantification of Aβ PET images may reduce inter-reader variability and aid in the monitoring of treatment effects from anti-amyloid drugs.The aim of this thesis was to refine existing methods and develop new ones for processing, quantification and visualization of Aβ PET images to aid in the diagnosis and monitoring of potential treatment of AD in clinical routine. Specifically, the focus for this thesis has been to find a way to fully automatically quantify and visualize a patient’s Aβ PET image in such way that it is presented in a uniform way and show how it relates to what is considered normal. To achieve the aim of the thesis registration algorithms, providing the means to register a patient’s Aβ PET image to a common stereotactic space avoiding the bias of different uptake patterns for Aβ- and Aβ+ images, a suitable region atlas and a 3-dimensional stereotactic surface projections (3D SSP) method, capable of projecting cortical activity onto the surface of a 3D model of the brain without sampling white matter, were developed and evaluated.The material for development and testing comprised 724 individual amyloid PET brain images from six distinct cohorts, ranging from healthy volunteers to definite AD. The new methods could be implemented in a fully automated workflow and were found to be highly accurate, when tested by comparisons to Standards of Truth, such as defining regional uptake from PET images co-registered to magnetic resonance images, post-mortem histopathology and the visual consensus diagnosis of imaging experts.