471 research outputs found
PET/CT Imaging in Mouse Models of Myocardial Ischemia
Different species have been used to reproduce myocardial infarction models but in the last years mice became the animals of choice for the analysis of several diseases, due to their short life cycle and the possibility of genetic manipulation. Many techniques are currently used for cardiovascular imaging in mice, including X-ray computed tomography (CT), high-resolution ultrasound, magnetic resonance imaging, and nuclear medicine procedures. Cardiac positron emission tomography (PET) allows to examine noninvasively, on a molecular level and with high sensitivity, regional changes in myocardial perfusion, metabolism, apoptosis, inflammation, and gene expression or to measure changes in anatomical and functional parameters in heart diseases. Currently hybrid PET/CT scanners for small laboratory animals are available, where CT adds high-resolution anatomical information. This paper reviews mouse models of myocardial infarction and discusses the applications of dedicated PET/CT systems technology, including animal preparation, anesthesia, radiotracers, and images postprocessing
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Improved quantification in small animal PET/MR
In translational medicine, complementary functional and morphological imaging techniques are used extensively to observe physiological processes in vivo and to assess structural changes as a result of disease progression. The combination of magnetic resonance imaging (MRI) and positron emission tomography (PET) provides excellent soft tissue contrast from MRI with exceptional sensitivity and specificity from PET. This thesis explores the use of sequentially acquired PET and MR images to
improve the quantification of small animal PET data.
The primary focus was to improve image-based estimates of the arterial input function (AIF), which defines the amount of PET tracer within blood plasma over time. The AIF is required to produce physiological parameters quantifying key processes such as metabolism or perfusion from dynamic PET images. The gold standard for AIF measurement, however, requires serial blood sampling over the course of a PET scan, which is invasive in rat studies but prohibitive in mice due to small total blood volumes.
To address this issue, the geometric transfer matrix (GTM) and recovery coefficient (RC) techniques were applied using anatomical MR images to enable the extraction of partial volume corrected image based AIFs from mouse PET images.
A non-invasive AIF extraction method was also developed for rats, beginning with the optimization of an automated voxel selection algorithm to assist in extracting MR contrast agent signal time courses from dynamic susceptibility contrast (DSC) MRI data. This procedure was then combined with dynamic contrast enhanced (DCE) MRI to track a combined injection of Gadolinium-based contrast agent and PET tracer through the rat brain. By comparison with gold standard tracer blood sample data, it was
found that normalized MRI-based AIFs could be successfully converted into PET tracer AIFs in the first pass phase when fitted with gamma variate functions.
Finally, a MR image segmentation method used to provide PET attenuation correction in mice was validated using the Cambridge split magnet PET/MR scannerâs transmission scanning capabilities. This work recommends that contributions from MR hardware in the PET field of view must be accounted forto gain accurate estimates of tracer uptake and standard uptake values (SUVs).
This thesis concludes that small animal MR data taken in the same imaging session can provide non-invasive methods to improve PET image quantification, giving added value to combined PET/MR studies over those conducted using PET alone.This PhD project was supported by a Medical Research Council (MRC) studentship, with grant code SRAG/038
Perspectives on Nuclear Medicine for Molecular Diagnosis and Integrated Therapy
nuclear medicine; diagnostic radiolog
Extraction de la courbe d'entrée à partir des images TEP du coeur chez le petit animal pour la modélisation pharmacocinétique
Dans cette thĂšse, nous prĂ©sentons l'ensemble de nos contributions relatives Ă la mise en oeuvre et Ă la validation de techniques d'extraction d'une courbe de l'activitĂ© d'un traceur radioactif, dite courbe d'entrĂ©e (CE), Ă partir des images enregistrĂ©es par tomographie d'Ă©mission par positrons (TEP). Cette courbe est primordiale pour la quantification de paramĂštres physiologiques et mĂ©taboliques comme le mĂ©tabolisme du glucose au niveau du myocarde chez le petit animal. La modalitĂ© d'imagerie TEP sert Ă dĂ©celer, Ă des phases souvent prĂ©coces, le dysfonctionnement d'un organe par un examen mĂ©dical. L'examen consiste en une injection d'un Ă©lĂ©ment radioactif, Ă©metteur de positrons attachĂ©s Ă une molĂ©cule caractĂ©risĂ©e par les mĂȘmes propriĂ©tĂ©s chimiques et biologiques qu'une molĂ©cule naturelle, et de suivre son activitĂ© temporelle. La quantitĂ© du traceur mesurĂ©e dans le plasma sanguin en fonction du temps constitue la CE, tandis que la radioactivitĂ© mesurĂ©e dans les tissus par la TEP constitue la rĂ©ponse des tissus. La CE et la rĂ©ponse des tissus sont les fonctions fondamentales d'un modĂšle mathĂ©matique appelĂ© "le modĂšle pharmacocinĂ©tique" qui estime les paramĂštres physiologiques et mĂ©taboliques. Habituellement la CE est obtenue d'une maniĂšre invasive par un prĂ©lĂšvement sanguin qui se fait parallĂšlement Ă l'acquisition des donnĂ©es. En plus, elle nĂ©cessite une chaĂźne de prĂ©paration pour enregistrer la concentration du traceur radioactif dans le plasma et une frĂ©quence d'Ă©chantillonnage corrĂ©lĂ©e avec le dĂ©coupage de la sĂ©quence d'images. Dans le cadre de nos recherches, nous avons dĂ©veloppĂ© des techniques d'extraction de la CE directement Ă partir d'une sĂ©quence d'images TEP. Cette approche prĂ©sente l'avantage d'ĂȘtre non-invasive et permet un contrĂŽle sur la frĂ©quence d'Ă©chantillonnage temporel. NĂ©anmoins, la rĂ©solution spatiale, les limites physiques, les limites physiologiques et les limites mĂ©thodologiques reliĂ©es Ă la reconstruction d'images sont des facteurs qui dĂ©tĂ©riorent la qualitĂ© de la courbe. Dans un premier temps, nous avons appliquĂ© un concept probabiliste Ă l'intĂ©rieur de deux rĂ©gions d'intĂ©rĂȘts (Ris) tracĂ©es sur la sĂ©quence d'images dĂ©limitant le ventricule gauche et le myocarde. La mĂ©thode estime la fraction du sang dans les deux rĂ©gions pour dĂ©terminer une CE non dĂ©gradĂ©e par les effets mentionnĂ©s prĂ©cĂ©demment. Cette approche a permis de corriger la courbe en tenant compte des effets causĂ©s par la contamination spatiale. Dans un deuxiĂšme temps, nous avons travaillĂ© sur la rĂ©duction de l'effet du mouvement du coeur et des poumons sur la qualitĂ© de la CE. Pour cela, nous avons utilisĂ© une acquisition de donnĂ©es synchronisĂ©e par rapport Ă l'Ă©lectrocardiogramme (ECG). Cette acquisition nĂ©cessite un suivi automatique des RIs sur les diffĂ©rents cadres synchronisĂ©s. Pour remĂ©dier aux effets de la faible rĂ©solution spatiale des images, nous avons dĂ©veloppĂ© un modĂšle particulier d'un contour dĂ©formable qui rĂ©pond aux faiblesses des images TEP. Notre modĂšle est capable de dĂ©limiter le ventricule gauche et le myocarde sur les images d'une façon quasi-automatique. Finalement, nous avons gĂ©nĂ©ralisĂ© l'idĂ©e de l'extraction de la CE pour diffĂ©rents traceurs tels que le glucose marquĂ© au fluor ([indice supĂ©rieur 18]F-FDG), l'ammoniaque marquĂ© Ă l'azote ([indice supĂ©rieur 13]N-ammoniaque), le [indice supĂ©rieur 82] rubidium ([indice supĂ©rieur 82]Rb) et l'acĂ©tate marquĂ© au carbone ([indice supĂ©rieur 11]C-acĂ©tate). Le modĂšle que nous avons dĂ©veloppĂ© est basĂ© sur l'estimation de la CE par l'analyse en composante indĂ©pendante (ACI) et la distribution gaussienne gĂ©nĂ©ralisĂ©e (DGG). Tous nos rĂ©sultats pour le traceur [indice supĂ©rieur 18]F-FDG sont comparĂ©s Ă la mĂ©thode de rĂ©fĂ©rence classique, Ă savoir le prĂ©lĂšvement sanguin. Les rĂ©sultats de l'extraction de la CE par l'ACI ont Ă©tĂ© comparĂ©s Ă ceux extraits par la mĂ©thode de rĂ©fĂ©rence et par la moyenne de l'activitĂ© d'une RI segmentĂ©e manuellement sur les images. Les rĂ©sultats montrent l'apport de la mĂ©thode sur l'amĂ©lioration de la courbe lorsque celle-ci est dĂ©gradĂ©e par la contamination croisĂ©e. Le travail accompli dans cette thĂšse montre la possibilitĂ© de contourner les limites de l'imagerie TEP par l'utilisation d'approches statistiques dans le but d'extraire une CE fiable. Les mĂ©thodes dĂ©veloppĂ©es reprĂ©sentent une alternative Ă la mĂ©thode invasive d'Ă©chantillonnage sanguin
DĂ©veloppement dâoutils quantitatifs pour le suivi par imagerie TEP/TDM de la rĂ©ponse Ă la chimiothĂ©rapie et de sa toxicitĂ©
Lâobjectif de ce projet de doctorat est de dĂ©velopper des outils quantitatifs pour le suivi des traitements de chimiothĂ©rapie pour le cancer du sein et de leurs effets cardiotoxiques Ă lâaide de lâimagerie TEP dynamique. Lâanalyse cinĂ©tique en TEP dynamique permet lâĂ©valuation de paramĂštres biologiques in vivo. Cette analyse peut ĂȘtre utilisĂ© pour caractĂ©riser la rĂ©ponse tumorale Ă la chimiothĂ©rapie et les effets secondaires nĂ©fastes qui peuvent en rĂ©sulter.
Le premier article de cette thĂšse dĂ©crit la mise au point des techniques dâanalyse cinĂ©tique qui utilisent la fonction dâentrĂ©e dâun radiotraceur dĂ©rivĂ© de lâimage dynamique. Des corrections de contamination radioactive externe (Ă©panchement) et de lâeffet de volume partiel ont Ă©tĂ© nĂ©cessaires pour standardiser lâanalyse cinĂ©tique et la rendre quantitative.
Le deuxiĂšme article porte sur lâĂ©valuation dâun nouveau radiotraceur myocardique. Le [indice supĂ©rieur 11]C-acĂ©toacĂ©tate, un nouveau radiotraceur basĂ© sur un corps cĂ©tonique, a Ă©tĂ© comparĂ© au [indice supĂ©rieur 11]C-acĂ©tate, couramment utilisĂ© en imagerie cardiaque TEP. Lâutilisation de [indice supĂ©rieur 3]H-acĂ©tate et [indice supĂ©rieur 14]C-acĂ©toacĂ©tate ont permis dâĂ©lucider la cinĂ©tique de ces traceurs depuis la fonction dâentrĂ©e et la captation par les mitochondries cardiaques qui reflĂšte la consommation en oxygĂšne, jusquâĂ la libĂ©ration de leurs principaux mĂ©tabolites rĂ©ciproques ([indice supĂ©rieur 3]H[indice infĂ©rieur 2]O et [indice supĂ©rieur 14]CO[indice infĂ©rieur 2]).
Le troisiĂšme et dernier article de cette thĂšse prĂ©sente lâintĂ©gration dâun modĂšle qui Ă©value la rĂ©serve cardiaque de perfusion et de consommation en oxygĂšne. Un modĂšle de cardiomyopathie a Ă©tĂ© Ă©tabli Ă lâaide dâun agent chimiothĂ©rapeutique contre le cancer du sein, la doxorubicine, reconnu comme Ă©tant cardiotoxique. Un protocole de repos/effort a permis dâĂ©valuer la capacitĂ© dâaugmentation de perfusion et de consommation en oxygĂšne par le coeur. La dĂ©monstration dâune rĂ©serve cardiaque rĂ©duite caractĂ©rise la cardiotoxicitĂ©.
La derniĂšre contribution de cette thĂšse porte sur la mise au point de mĂ©thodes peu invasives pour mesurer la fonction dâentrĂ©e en modĂšle animal avec lâutilisation de lâartĂšre caudale et un compteur microvolumĂ©trique, la bi-modalitĂ© TEP/IRM dynamique avec le Gd-DTPA et lâĂ©tablissement dâun modĂšle dâĂ©valuation simultanĂ© de cardiotoxicitĂ© et rĂ©ponse tumorale chez la souris.
Le dĂ©veloppement dâoutils dâanalyse TEP dans lâĂ©valuation de la cardiotoxicitĂ© lors de traitements du cancer du sein permet de mieux comprendre la relation entre les dommages mitochondriaux et la diminution de la fraction dâĂ©jection
Procedural recommendations of cardiac PET/CT imaging:standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM
With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [18F]FDG, but 4Is PET radiopharmaceuticals beyond [18F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications.</p
Procedural recommendations of cardiac PET/CT imaging: standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM
With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [18F]FDG, but 4Is PET radiopharmaceuticals beyond [18F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications
Non-Invasive Imaging for the Assessment of Cardiac Dose and Function Following Focused External Beam Irradiation
Technological advances in imaging and radiotherapy have led to significant improvement in the survival rate of breast cancer patients. However, a larger proportion of patients are now exhibiting the less understood, latent effects of incidental cardiac irradiation that occurs during left-sided breast radiotherapy. Here, we examine the utility of four-dimensional computed tomography (4D-CT) for the accurate assessment of cardiac dose; and a hybrid positron emission tomography (PET) magnetic resonance imaging (MRI) system to longitudinally study radiation-induced cardiac effects in a canine model.
Using 4D-CT and deformable dose accumulation, we assessed the variation caused by breathing motion in the estimated dose to the heart, left-ventricle, and left anterior descending artery (LAD) of left-sided breast cancer patients. The LAD showed substantial variation in dose due to breathing. In light of this, we suggest the use of 4D-CT and dose accumulation for future clinical studies looking at the relationship between LAD dose and cardiac toxicity.
Although symptoms of cardiac dysfunction may not manifest clinically for 10-15 years post radiation, PET-MRI can potentially identify earlier changes in cardiac inflammation and perfusion that are typically asymptomatic. Using PET-MRI, the progression of radiation-induced cardiac toxicity was assessed in a large animal model. Five canines were imaged using 13N-ammonia and 18F-fluorodeoxyglucose (FDG) PET-MRI to assess changes in myocardial perfusion and inflammation, respectively. All subjects were imaged at baseline, 1 week, 4 weeks, 3 months, 6 months, and 12 months after focused cardiac irradiation. To the best of our knowledge PET has not been previously used to assess cardiac perfusion following irradiation.
The delivered dose to the heart, left ventricle, LAD, and left circumflex artery were comparable to what has been observed during breast radiotherapy. Relative to baseline, a transient increase in myocardial perfusion was observed followed by a gradual return to baseline. However, a persistent increase in FDG uptake was observed throughout the entire left ventricle, including both irradiated and less-irradiated portions of the heart.
In light of these findings, we suggest the use of this imaging approach for future human studies to assess mitigation strategies aimed at minimizing cardiac exposure and long-term toxicity subsequent to left-sided breast irradiation
Advanced imaging techniques for cardiovascular research
According to the World Health Organization, cardiovascular diseases (CVDs) are the first cause of death globally. CVDs are a cluster of disorders that involve heart and blood vessels. Among them, coronary artery disease (CAD) is the most important disease in terms of mortality, causing more than 50% of the annual deaths. Over the last decades, many recognized international organisms, such as the World Health Organization and the American College of Cardiology have done great efforts to reduce the mortality and morbidity of CAD. In this line, accurate diagnosis and cost-effective management of CAD have revealed to be of utmost importance. Several imaging techniques are currently used in the clinical practice to provide a diagnosis and clinical assessment of the disease. Among them, Positron Emission Tomography (PET) is considered to be the âgold standardâ for non invasive assessment of myocardial perfusion and viability, the two most relevant physiological parameters used to diagnose and manage patients with known or suspected CAD..
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