<p>Over the past 200 years, the Earth's atmospheric carbon dioxide (CO₂) concentration has increased by more than 35%, and climate experts predict that CO₂ levels may double by the end of this century. Understanding the mechanisms of resource management in plants is fundamental for predicting how plants will respond to the increase in atmospheric CO₂. Plant productivity sustains life on Earth and is a principal component of the planet's system that regulates atmospheric CO₂ concentration. As such, one of the central goals of plant science is to understand the regulatory mechanisms of plant growth in a changing environment. Short-lived positron-emitting radiotracer techniques provide time-dependent data that are critical for developing models of metabolite transport and resource distribution in plants and their microenvironments. To better understand the effects of environmental changes on resource transport and allocation in plants, we have developed a system for real-time measurements of metabolite transport in plants using short-lived positron-emitting radiotracers. This thesis project includes the design, construction, and demonstration of the capabilities of this system for performing real-time measurements of metabolite transport in plants.</p><p>The short-lived radiotracer system described in this dissertation takes advantage of the combined capabilities and close proximity of two research facilities at Duke University: the Triangle Universities Nuclear Laboratory (TUNL) and the Duke University Phytotron, which are separated by approximately 100 meters. The short-lived positron-emitting radioisotopes are generated using the 10-MV tandem Van de Graaff accelerator located in the main TUNL building, which provides the capability of producing short-lived positron-emitting isotopes such as carbon-11 (¹¹C; 20 minute half-life), nitrogen-13 (¹³N; 10 minute half-life), fluorine-18 (¹⁸F; 110 minute half-life), and oxygen-15 (¹⁵O; 2 minute half-life). The radioisotopes may be introduced to plants as biologically active molecules such as ¹¹CO₂, ¹³NO₃^-, ¹⁸F^--[H₂O], and H₂<sup>15<\sup>O. Plants for these studies are grown in controlled-environment chambers at the Phytotron. The chambers offer an array of control for temperature, humidity, atmospheric CO₂ concentration, and light intensity. Additionally, the Phytotron houses one large reach-in growth chamber that is dedicated to this project for radioisotope labeling measurements.</p><p>There are several important properties of short-lived positron-emitting radiotracers that make them well suited for use in investigating metabolite transport in plants. First, because the molecular mass of a radioisotope-tagged compound is only minutely different from the corresponding stable compound, radiotracer substances should be metabolized and transported in plants the same as their non-radioactive counterparts. Second, because the relatively high energy gamma rays emitted from electron-positron annihilation are attenuated very little by plant tissue, the real-time distribution of a radiotracer can be measured <em>in vivo</em> in plants. Finally, the short radioactive half-lives of these isotopes allow for repeat measurements on the same plant in a short period of time. For example, in studies of short-term environmental changes on plant metabolite dynamics, a single plant can be labeled multiple times to measure its responses to different environmental conditions. Also, different short-lived radiotracers can be applied to the same plant over a short period of time to investigate the transport and allocation of various metabolites.</p><p>This newly developed system provides the capabilities for production of ¹¹CO₂ at TUNL, transfer of the ¹¹CO₂ gas from the target area at TUNL to a radiation-shielded cryogenic trap at the Phytotron, labeling of photoassimilates with ¹¹C, and <em>in vivo</em> gamma-ray detection for real-time measurements of the radiotracer distribution in small plants. The experimental techniques and instrumentation that enabled the quantitative biological studies reported in this thesis were developed through a series of experiments made at TUNL and the Phytotron. Collimated single detectors and coincidence counting techniques were used to monitor the radiotracer distribution on a coarse spatial scale. Additionally, a prototype Versatile Imager for Positron Emitting Radiotracers (VIPER) was built to provide the capability of measuring radiotracer distributions in plants with high spatial resolution (~2.5 mm). This device enables detailed quantification of real-time metabolite dynamics on fine spatial scales.</p><p>The full capabilities of this radiotracer system were utilized in an investigation of the effects of elevated atmospheric CO₂ concentration and root nutrient availability on the transport and allocation of recently fixed carbon, including that released from the roots via exudation or respiration, in two grass species. The ¹¹CO₂ gas was introduced to a leaf on the plants grown at either ambient or elevated atmospheric CO₂. Two sequential measurements were performed per day on each plant: a control nutrient solution labeling immediately followed by labeling with a 10-fold increase or decrease in nutrient concentration. The real-time distribution of ¹¹C-labeled photoassimilate was measured <em>in vivo</em> throughout the plant and root environment. This measurement resulted in the <em>first</em> observation of a rapid plant response to short-term changes in nutrient availability via correlated changes in the photoassimilate allocation to root exudates. Our data indicated that root exudation was consistently enhanced at lower nutrient concentrations. Also, we found that elevated atmospheric CO₂ increased the velocity of photoassimilate transport throughout the plant, enhanced root exudation in an annual crop grass, and reduced root exudation in a perennial native grass.</p> / Dissertation

Fluorescence-enhanced optical imaging using near-infrared (NIR) light developed for in-vivo molecular targeting and reporting of cancer provides promising opportunities for diagnostic imaging. However, prior to the administration of unproven contrast agents, the benefits of fluorescence-enhanced optical imaging must be assessed in feasibility phantom studies. A novel intensified charge-coupled device (ICCD) imaging system has been developed to perform 3-D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. This study is unique since it (i) employs a large tissue-mimicking phantom (~1087 cc), which is shaped and sized to resemble a female breast and part of the extended chest wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diagnostic 3-D fluorescence-enhanced optical tomography is demonstrated using 0.5-1 cc single and multiple targets contrasted from their surrounding by ??M concentrations of Indocyanine green (ICG) in the breast-shaped phantom (10 cm diameter), under varying conditions of target-to-background absorption contrast ratios (1:0 and 100:1) and target depths (up to 3 cm deep). Boundary surface fluorescence measurements of referenced amplitude and phase shift were used along with the coupled diffusion equation of light propagation in order to perform 3-D image reconstructions using the approximate extended Kalman filter (AEKF) algorithm, and hence differentiate the target from the background based on fluorescent optical contrast. Detection of single and multiple targets is demonstrated under various conditions of target depths (up to 2 cm deep), absorption optical contrast ratio (1:0 and 100:1), target volumes (0.5-1 cc), and multiple targets (up to three 0.5 cc targets). The feasibility of 3-D image reconstructions from simultaneous multiple point excitation sources are presented. Preliminary lifetime imaging studies with 1:2 and 2:1 optical contrast in fluorescence lifetime of the contrast agents is also demonstrated. The specificity of the optical imager is further assessed from homogeneous phantom studies containing no fluorescently contrasted targets. While nuclear imaging currently provides clinical diagnostic opportunities using radioactive tracers, molecular targeting of tumors using non-ionizing NIR contrast agents tomographically imaged using the frequency-domain ICCD imaging system could possibly become a new method of diagnostic imaging.

Nano-sized particles are widely regarded as a tool to study biological events at cellular and molecular levels. However, there are only a few imaging modalities that can visualize interactions between nanoparticles and living cells. A new technique -- pulsed magneto-motive ultrasound imaging, capable of in-vivo imaging of magnetic nanoparticles at improved depth and in real-time is introduced in this study. In pulsed magneto-motive ultrasound imaging, an external high-strength pulsed magnetic field is applied to induce motion within magnetically labeled tissue and ultrasound is used to detect the induced internal tissue motion. A laboratory prototype of a pulsed magneto- motive ultrasound imaging system was built, tested and optimized through modeling and experimental studies using tissue-mimicking phantoms, ex-vivo tissue samples and in- vivo mouse tumor model. The results demonstrated a sufficient contrast between normal and iron-laden tissue labeled with ultra-small magnetic nanoparticles. Finally, further modifications and research directions are discussed which can eventually lead to development of a clinically applicable pulsed magneto-motive ultrasound imaging system. / text

Accurate detection of the spread of cancer is critical for planning the best treatment strategy for a patient. Currently, an invasive sentinel lymph node biopsy is commonly used to detect metastases after a primary tumor is detected. This procedure results in patient morbidity, requires weeks of waiting, and is prone to sampling error. This dissertation presents new developments in an emerging biomedical imaging modality – photoacoustic imaging – and their application to improving the detection of metastases in the lymphatic system in a metastatic mouse model of squamous cell carcinoma of the oral cavity. Label-free spectroscopic photoacoustic imaging is demonstrated to detect hypoxia that results from the development of sub-millimeter cancer foci in the lymph node. In order to improve the sensitivity to micrometastases, molecularly-activated plasmonic nanosensers which are targeted to the epidermal growth factor receptor are introduced. The nanosensors are demonstrated to detect metastases consisting of only a few tens of cells. Improvements to spectroscopic photoacoustic imaging are then demonstrated by selecting imaging wavelengths based on the spectral properties of the optical absorbers. Finally, a new contrast agent – silica-coated gold nanoplates – are used to map the sentinel lymph node with high contrast. The final result is a set of tools that can be used to noninvasively detect micrometastases and improve molecular photoacoustic imaging. / text

Gold nanoparticles attain an intense focus in biomedical imaging applications due to their unique optical properties, facile conjugation with biomolecules, and biocompatibility. Although a considerable amount of work towards the development of gold nanoparticles has been completed, these promising contrast agents have not yet reached the clinic due to several challenges including efficient accumulation at the diseased site, sensitivity of detection in vivo, potential adverse effects, and clearance from the body. High signal-to-background ratio is required to enhance sensitivity of detection. Because near infrared (near-IR) light has the best tissue penetration, contrast agents designed to work in this range can significantly increase imaging sensitivity. Moreover, efficient targeting of the molecular biomarkers on diseased cells can decrease the required dosage, increase the site-specific accumulation, and enhance the imaging sensitivity. Molecular-specific contrast agents developed in this project use directional attachment of antibody molecules to the nanoparticle surface, enhancing the targeting efficacy. Additionally, cell-based delivery of diagnostic and therapeutic agents is gaining much interest due to the immune cells’ special access to the avascular, diseased regions. The contrast agents developed in this project enable detection of just a few cells per unit of imaging volume, enable multiplex imaging, and open up a possibility for tracking different cell populations with noninvasive photoacoustic and ultrasound imaging. Finally, the clearance of nanoparticles from the body dictates their clinical translation. The in vivo pharmacokinetics study along with the proposed in vitro model explored in this project will enable fast, reliable, and cost-efficient screening of promising agents and facilitate quick optimization of nanoparticles for their potential use in the clinic. / text

As new therapeutic targets and drugs are discovered for B-cell lymphoma and other cancers, companion diagnostics are also needed to determine target engagement, therapeutic efficacy, and patient segmentation for clinical trials. We first employed synthetic chemistry to build a platform for modifying small molecule drugs into imaging probes, using the poly(ADP-ribose) polymerase 1 (PARP1) inhibitor AZD2281 (Olaparib) as a model for technology development. Our results showed that small-molecule companion imaging drugs can be used for fluorescence imaging in cells, as well as for pharmacokinetic studies and positron emission tomography (PET) imaging in vivo, without significantly perturbing their target binding properties or cellular uptake. To apply this approach to B-cell lymphoma drugs currently in clinical trials, we modified an irreversible inhibitor of Bruton's Tyrosine Kinase (BTK), PCI-32765 (Ibrutinib), with the fluorophore Bodipy FL (BFL), and used it for imaging in cells and in a mouse window-chamber xenograft model. The excellent co-localization of our probe (Ibrutinib-BFL) with BTK demonstrated its utility for studying additional BTK inhibitors and as a companion imaging probe. In parallel, we hypothesized that central nervous system (CNS) lymphoma diagnosis from paucicellular cerebrospinal fluid (CSF) samples could be improved with molecular profiling of putative lymphoma cells trapped in a customized microfluidic chip. Following fabrication and characterization of a polydimethylsiloxane (PDMS) diagnostic device containing an array of affinity-free single-cell capture sites, we were able to efficiently recover >90% of lymphocytes, perform immunostaining on chip, and apply an image-processing algorithm to group cells based on their molecular marker expression, such as kappa/lambda light chain restriction. Additionally, in combination with Ibrutinib-BFL or other imaging drugs, we demonstrated the potential for on-chip drug imaging for use in conjunction with drug development. Finally, we applied bioorthogonal conjugation chemistries on cellulose paper for potential applications in lowering the cost of drug screening. We anticipate that these approaches will enable direct, molecular information for personalized treatment decisions in B-cell lymphomas, as well as provide a roadmap for the development of companion diagnostic probes and devices for additional indications.

Rupture of atherosclerotic plaque is closely related to plaque composition. Currently, plaque composition cannot be clinically characterized by any imaging modality. The objective of this dissertation is to use a recently developed imaging modality – ultrasound-guided intravascular photoacoustic (IVPA) imaging – to detect the distribution of two critical components in atherosclerotic plaques: lipid and phagocytically active macrophages. Under the guidance of intravascular ultrasound imaging, spectroscopic IVPA imaging is capable of detecting the spatially resolving optical absorption property inside a vessel wall. In this study, contrast in spectroscopic IVPA imaging was provided by either the endogenous optical property of lipid or optically absorbing contrast agent such as gold nanoparticles (Au NPs). Using a rabbit model of atherosclerosis, this dissertation demonstrated that ultrasound guided spectroscopic IVPA imaging could simultaneously image lipid deposits as well as macrophages labeled in vivo with Au NPs. Information of macrophage activity around lipid rich plaques may help to identify rupture-prone or vulnerable plaques. The results show that ultrasound guided IVPA imaging is promising for detecting plaque composition in vivo. Clinical use of ultrasound guided IVPA imaging may significantly improve the accuracy of diagnosis and lead to more effective treatments of atherosclerosis. / text

In the current thesis, spatio-temporal evaluation of the endogenous angiogenic response to ischemia was perfomed. After vascular occlusion, ischemic angiogenesis is an important reparative mechanism and can ameliorate the outcome of ischemic disease. Diabetic foot ulcers affect almost 15% of diabetic patients and are the leading cause of amputations worldwide (Yoon et al., 2005). Diminished blood flow because of atherosclerotic occlusive disease of the peripheral arteries of diabetic patients, in conjunction with anatomic and functional microcirculatory impairments contribute to development of trophic ulcerations, infections and gangrene of the lower extremities, frequently requiring amputation of the leg (Sasso et al., 2005). Numerous studies have confirmed the impaired post-ischemic angiogenesis in diabetes (Yoon et al., 2005; Sasso et al., 2005). Consequently, wound healing patterns are disturbed in diabetes mainly due to decreased ischemia-driven angiogenesis (Yoon et al., 2005). Integrin ανβ3 is a promising imaging target of angiogenic activity which is up-regulated on activated endothelial cells (ECs) but not on quiescent ones. Molecular imaging (MI) of ανβ3 integrin expression with the aid of a dedicated high resolution gamma camera, is a very sensitive imaging approach for the evaluation of angiogenesis in the rabbit hindlimb ischemia model. Furthermore, diabetes mellitus (DM) was induced, to study the effects of this pathology on the spatio-temporal distribution of angiogenesis. In order to evaluate the whole spectrum of endogenous process of collateralization after occlusion of an artery, Digital Subtraction Angiography (DSA) was also used for the visualization of larger collaterals. During the first part of the study DM experimental protocol was investigated in order to find the appropriate protocol for the induction of long-term diabetic animal model, as it is a methodology that has not yet been standardized. At the same time a cohort of animals underwent endovascular embolization for the establishment of hindlimb ischemia and were imaged with the aid of a MI radiotracer technique in order to deal with unresolved issues and establish the imaging protocol. The study included seven New Zealand White (NZW) rabbits that underwent unilateral percutaneous endovascular embolization of the femoral artery, for the establishment of hindlimb ischemia that triggers the endogenous process of collateralization. The contralateral limb was not embolized and served as a control. The employed radiotracer for angiogenesis imaging, was a 99mTc labeled cyclic RGD peptide [c RGDfk-His]-99mTc that binds specifically to ανβ3 integrin via the three amino acid sequence Arginine-Glycine-Aspartic acid or RGD. Image acquisition was performed with a high resolution gamma camera and all animals underwent molecular imaging on the 3rd and the 9th day post-embolization. In all animals DSA was performed on the 9th day post-embolization. The acquired images demonstrated that retention of the radiotracer at the ischemic tissue is remarkably increased compared to the non-ischemic hindlimb (normal limb) (16020 ± 2309 vs. 13139 ± 2493 on day 3; p=0.0014 and 21616 ± 2528 vs. 13362 ± 2529 on day 9; p<0.0001, respectively). In addition, radiotracer retention in normal limbs seems to be increased at day 9 in normal limbs compared to day 3 (p=0.0112). DSA at day 9, demonstrated that the mean vessel length detected was significantly superior in the normal compared to the ischemic limb (mean value 3680 ± 369.8 vs.2772 ± 267.7; p< 0.0001, respectively). Angiogenesis was successfully detected using a 99mTc labeled cyclic RGD peptide MI technique and was significantly more pronounced in the ischemic compared to normal limbs, both at day 3 and day 9 after embolization. The peak of the phenomenon was detected at day 9. Increased mean vessel length in the normal compared to the ischemic limb demonstrates that although angiogenesis is pronounced in day 9, arteriogenesis is not sufficiently pronounced and that the phenomenon of arteriogenesis has just initiated. The study of the angiogenic response to ischemia, has not yet been completed as MI of diabetic animals with hindlimb ischemia is underway and not completed due to many difficulties and delay in different phases of the experiment. With the conclusion of the MI of diabetic animals with hindlimb ischemia, the study will be completed and we expect to demonstrate the effect of DM on the spatio-temporal pattern of angiogenesis, providing a valuable tool in clinical practice for the precise and early diagnosis and therapy assessment of the ‘diabetic foot’. / Σκοπός της παρούσας μελέτης ήταν η χωρο-χρονική εκτίμηση της ενδογενούς αγγειογενετικής διαδικασίας ως απόκριση στο ερέθισμα της προκλητής ισχαιμίας. Μετά από απόφραξη αρτηρίας, η επαγόμενη αγγειογένεση είναι ένα σημαντικός μηχανισμός αποκατάστασης που μπορεί να περιορίσει το αποτέλεσμα της ισχαιμίας. Το έλκος του ‘διαβητικού ποδιού’ εμφανίζεται στο 15% περίπου των ασθενών που πάσχουν από διαβήτη και αποτελεί την κύρια αιτία ακρωτηριασμού του κάτω άκρου, μετά τα ατυχήματα (Yoon et al., 2005). Η μειωμένη αιματική ροή λόγω της αποφρακτικής αρτηριοπάθειας που οφείλεται στην αθηροσκληρωτική προσβολή των περιφερικών αρτηριών των διαβητικών, σε συνδυασμό με ανατομική και λειτουργική φθορά του αγγειακού δικτύου της μικροκυκλοφορίας, οδηγούν στην ανάπτυξη ελκών, μολύνσεων και γάγγραινας των κάτω άκρων που πολύ συχνά οδηγεί στον ακρωτηριασμό του ποδιού (Sasso et al., 2005). Πολυάριθμες μελέτες όμως έχουν δείξει ότι η αγγειογένεση που επάγεται από κρίσιμη ισχαιμία, στην παθολογία του διαβήτη δεν είναι φυσιολογική (Yoon et al., 2005; Sasso et al., 2005). Συνεπώς στον διαβήτη και ο μηχανισμός επούλωσης πληγών δεν συμβαίνει φυσιολογικά κυρίως λόγω ελαττωματικής ενδογενούς αγγειογένεσης ως απόκριση στην ισχαιμία (Yoon et al., 2005). Το μόριο της ιντεγκρίνης ανβ3 υπερεκφράζεται στα ενεργοποιημένα ενδοθηλιακά κύτταρα που συμμετέχουν στην αγγειογενετική διαδικασία αλλά όχι στο ανενεργό ή αλλιώς «σιωπηλό» ενδοθήλιο. Συνεπώς αποτελεί έναν πολύ καλό μοριακό στόχο για απεικόνιση και δείκτη της αγγειογενετικής δραστηριότητας. Η Μοριακή Απεικόνιση (ΜΑ) του επιπέδου έκφρασης του μορίου ιντεγκρίνης ανβ3 με τη χρήση ραδιοϊσοτοπικών τεχνικών έχει το πλεονέκτημα υψηλής ευαισθησίας ανίχνευσης πολύ χαμηλών συγκεντρώσεων του ραδιοϊχνηθέτη σε σχέση με τις συμβατικές τεχνικές (x-ray computed tomography (CT) angiography, contrast-enhanced ultrasound και high-resolution magnetic resonance angiography). Ο σκοπός της μελέτης μας ήταν να ερευνήσουμε τις δυνατότητες της ΜΑ με την βοήθεια γ-κάμερας υψηλής διακριτικής ικανότητας και πειραματικού μοντέλου κονίκλου με ίσχαιμο οπίσθιο άκρο. Επιπλέον ένα σημαντικό μέρος της μελέτης αφορούσε την εφαρμογή του πρωτοκόλλου για τη πρόκληση διαβήτη ώστε να γίνει μελέτη της επίδρασης της συγκεκριμένης παθολογίας στην χωρο-χρονική κατανομή της αγγειογένεσης. Προκειμένου να αποδοθεί μία συνολική εκτίμηση του ενδογενούς μηχανισμού αποκατάστασης του αγγειακού δικτύου, εφαρμόστηκε Ψηφιακή Αφαιρετική Αγγειογραφία για την εκτίμηση της δημιουργίας παράπλευρου δικτύου. Στη πρώτη φάση της μελέτης, έγινε διερεύνηση του πρωτοκόλλου πρόκλησης διαβήτη δεδομένου ότι η μεθοδολογία παρουσιάζει έλλειψη προτυποποίησης. Παράλληλα εφαρμόστηκε το πρωτόκολλο ισχαιμίας σε μια ομάδα λευκών κονίκλων Νέας Ζηλανδίας για την διερεύνηση του πρωτοκόλλου ΜΑ. Στην μελέτη, χρησιμοποιήθηκαν συνολικά επτά κόνικλοι Νέας Ζηλανδίας οι οποίοι υπεβλήθησαν σε εμβολισμό της μηριαίας αρτηρίας ενός από τα δύο οπίσθια άκρα για την πρόκληση οξείας ισχαιμίας. Στους κόνικλους έγινε ενδοφλέβια έγχυση του κυκλικού επισημασμένου πεπτιδίου [c RGDfk-His]-99mTc που περιέχει την αλληλουχία τριών αμινοξέων Αργινίνης-Γλυκίνης-Ασπαρτικού οξέος (Arginine-Glycine-Aspartic acid or RGD), μέσω της οποίας δεσμεύεται το πεπτίδιο στο μόριο της ιντεγκρίνης ανβ3. Η απεικόνιση του επιπέδου έκφρασης του μορίου ιντεγκρίνης ανβ3 πραγματοποιήθηκε με γ-κάμερα υψηλής διακριτικής ικανότητας την 3η και την 9η ημέρα μετά την απόφραξη της μηριαίας αρτηρίας. Ψηφιακή Αφαιρετική Αγγειογραφία πραγματοποιήθηκε την 9η ημέρα μετά την απόφραξη της μηριαίας αρτηρίας. Τα δεδομένα από την ποσοτικοποίηση των απεικονιστικών δεδομένων, έδειξαν ότι υπάρχει αυξημένη πρόσληψη του ραδιοϊχνηθέτη στη περιοχή ισχαιμίας σε σχέση με τη περιοχή φυσιολογικής αιμάτωσης του ετερόπλευρου άκρου (16020 ± 2309 έναντι 13139 ± 2493 την 3η ημέρα, p=0.0014 και 21616 ± 2528 έναντι 13362 ± 2529 την 9η ημέρα, p<0.0001, αντίστοιχα). Επιπλέον η πρόσληψη του ραδιοϊχνηθέτη στα φυσιολογικά άκρα φαίνεται να είναι αυξημένη την 9η ημέρα σε σχέση με την 3η ημέρα (p=0.0112), γεγονός που μπορεί να αποδοθεί στην σταδιακή συγκέντρωση ενεργοποιημένου ενδοθηλίου και στους φυσιολογικούς ιστούς. Η Ψηφιακή Αφαιρετική Αγγειογραφία έδειξε ότι την 9η ημέρα που έγινε η λήψη δεδομένων, το μέσο μήκος αγγείων στα φυσιολογικά άκρα ήταν αρκετά μεγαλύτερο σε σχέση με τα ίσχαιμα άκρα (μέση τιμή 3680 ± 369.8 έναντι 2772 ± 267.7, p< 0.0001, αντίστοιχα). Η ραδιοϊσοτοπική τεχνική που εφαρμόστηκε για την απεικόνιση του επιπέδου έκφρασης του μορίου ιντεγκρίνης ανβ3 στη παρούσα μελέτη, έδειξε ότι υπάρχει αυξημένη πρόσληψη του ραδιοϊχνηθέτη στη περιοχή ισχαιμίας σε σχέση με τη περιοχή φυσιολογικής αιμάτωσης του ετερόπλευρου άκρου, την 3η ημέρα και την 9η ημέρα μετά την απόφραξη της μηριαίας αρτηρίας. Τα πειραματικά δεδομένα δείχνουν επίσης ότι το φαινόμενο της αγγειογένεσης κορυφώνεται την 9η ημέρα μετά την πρόκληση ισχαιμίας. Επιπλέον τα δεδομένα από τη Ψηφιακή Αφαιρετική Αγγειογραφία την 9η ημέρα, δείχνουν ότι ο ενδογενής μηχανισμός σχηματισμού παράπλευρου δικτύου αν και έχει πυροδοτηθεί δεν έχουν σχηματιστεί ακόμα μεγαλύτερα αγγεία και γι αυτό το λόγο η αρτηριογένεση υπολείπεται της αγγειογένεσης σε αυτή τη φάση. Για την ολοκλήρωση της μελέτης, εκκρεμεί η απεικόνιση των διαβητικών κονίκλων με ίσχαιμο οπίσθιο άκρο η οποία καθυστέρησε λόγω επιμέρους δυσκολιών στη διαδικασία των πειραμάτων. Η ΜΑ δεικτών της αγγειογένεσης σε άκρο που πάσχει από ισχαιμία παρουσία διαβήτη, δύναται να έχει τεράστια εφαρμογή στην κλινική πράξη για την ιατρική παρακολούθηση του ‘διαβητικού ποδιού’.

The images in positron emission tomography (PET) represent three dimensional dynamic distributions of biologically interesting molecules labelled with positron emitting radionuclides (radiotracers). Spatial localisation of the radio-tracers is achieved by detecting in coincidence two collinear photons which are emitted when the positron annihilates with an ordinary electron. In order to obtain quantitatively accurate images in PET, it is necessary to correct for the effects of photon attenuation within the subject being imaged. These corrections can be obtained using singles-mode photon transmission scanning. Although suitable for small animal PET, these scans are subject to high amounts of contamination from scattered photons. Currently, no accurate correction exists to account for scatter in these data. The primary purpose of this work was to implement and validate an analytical scatter correction for PET transmission scanning. In order to isolate the effects of scatter, we developed a simulation tool which was validated using experimental transmission data. We then presented an analytical scatter correction for singles-mode transmission data in PET. We compared our scatter correction data with the previously validated simulation data for uniform and non-uniform phantoms and for two different transmission source radionuclides. Our scatter calculation correctly predicted the contribution from scattered photons to the simulated data for all phantoms and both transmission sources. We then applied our scatter correction as part of an iterative reconstruction algorithm for simulated and experimental PET transmission data for uniform and non-uniform phantoms. We also tested our reconstruction and scatter correction procedure using transmission data for several animal studies (mice, rats and primates). For all studies considered, we found that the average reconstructed linear attenuation coefficients for water or soft-tissue regions of interest agreed with expected values to within 4%. Using a 2.2 GHz processor, the scatter correction required between 6 to 27 minutes of CPU time (without any code optimisation) depending on the phantom size and source used. This extra calculation time does not seem unreasonable considering that, without scatter corrections, errors in the reconstructed attenuation coefficients were between 18 to 45% depending on the phantom size and transmission source used.

This thesis focuses on the evaluation of biomarkers for radio-immunodiagnostics and radio-immunotherapy and on radiosensitization strategies after HSP90 inhibition, as a step towards more personalized cancer medicine. There is a need to develop new tracers that target cancer-specific biomarkers to improve diagnostic imaging, as well as to combine treatment strategies to potentiate synergistic effects. Special focus has been on the cell surface molecule CD44 and its oncogenic variants, which were found to exhibit unique expression patterns in head and neck squamous cell carcinoma (HNSCC). The variant CD44v6 seems to be a promising target, because it is overexpressed in this cancer type and is associated with radioresistance. Two new radioconjugates that target CD44v6, namely, the Fab fragment AbD15179 and the bivalent fragment AbD19384, were investigated with regard to specificity, biodistribution and imaging performance. Both conjugates were able to efficiently target CD44v6-positive tumors in vitro and in vivo. PET imaging of CD44v6 with 124I-AbD19384 revealed many advantages compared with the clinical standard 18F-FDG. Furthermore, the efficacy of the novel HSP90 inhibitor AT13387 and its potential use in combination with radiation treatment were evaluated. AT13387 proved to be a potent new cancer drug with favorable pharmacokinetics. Synergistic combination effects at clinically relevant drug and radiation doses are promising for both radiation dose reduction and minimization of side effects, or for an improved therapeutic response. The AT13387 investigation indicated that CD44v6 is not dependent on the molecular chaperone HSP90, and therefore, radio-immunotargeting of CD44v6 in combination with the HSP90 inhibitor AT13387 might potentiate treatment outcomes. However, EGFR expression levels did correlate with HSP90 inhibition, and therefore, molecular imaging of EGFR-positive tumors may be used to assess the treatment response to HSP90 inhibitors. In conclusion, these results demonstrate how tumor targeting with radiolabeled vectors and chemotherapeutic compounds can provide more specific and sensitive diagnostic tools and treatment options, which can lead to customized treatment decisions and a functional diagnosis that provides more precise and safer drug prescribing, as well as a more effective treatment for each patient.