New methods for evaluating atherosclerotic disease with ultrasound have been developed that go beyond simple anatomic characterization and instead yieldinformation on plaque or vascular phenotype. This talk will focus on new developments in ultrasound molecular imaging techniques. Contrast-enhanced ultrasound relies on the acoustic detection of encapsulated microbubble or gas-containing nano-scale contrast agents. Ultrasound signal from these agents is produced by stable or inertial cavitation that occurs in the fluctuating pressures of the acoustic field. It is possible to target ultrasound microbubble contrast agents to disease-related cellular and molecular processes. Targeting has been possible by either changing the chemical constituents on the bubble shell, or by conjugating specific ligands to the surface of the microbubbles. This talk will focus on some of the recentadvances in molecular imaging with targeted ultrasound contrast agents that include:

1. angiogenesis imaging in ischemic tissues including evaluating the effects of stem cell therapy;
2. imaging inflammation by targeting immune cells or endothelial adhesion molecules in atherosclerosis and tissue ischemia/injury; and
3. thrombus targeting for diagnostic and therapeutic aims.

Recent interdisciplinary research at the interface of optical molecular imaging science and nanotechnology has generated novel imaging probes with unique design strategies. However, most in vivo applications are hampered by insufficient resolution at the target site. This limitation is a product of low fluorescent signal amplification and specificity of the probe for the event of interest. Various recently developed imaging probes described by the term "fluorescent signal activation methods", which are also known as activatable probes, have shown promising results. However, many of these probes are thus far limited in usefulness in vivo, mainly because of low target-to-background ratios or lack of stability in physiological conditions after intravenous injection. Therefore, the development of more sophisticated and reliable activatable probes capable of boosting the intensity of fluorescent signals at the region of interest (ROI) with specific target recognition properties isurgently needed. This talk will use matrix metalloproteinases (MMPs) as exemplary proteases and apply several nanoparticle platforms such as self-assembled chitosan nanoparticle (CNP), ferritin nanocage, gold nanoparticles, and gold-iron oxide nanoflowers for in vivo imaging of MMP activity with goal of achieving ultrafast activation and minimal background.

PET has demonstrated its utility as a powerful tool for studying neurotransmitter-protein interactions in the brain. For specific neurotransmitter systems, there are often options in the selection of PET radioligands. For PET studies with small sample sizes, it is critical to consider the sensitivity of a PET radiotracer for measuring potential disruptions in neuroreceptor binding. This presentation will discuss the characterization of several PET radioligands for the dopamine (D2/D3), serotonin (5-HT1A) and nicotinic (a4b2 nAChRs) systems and their applications to disease specific models in neurodevelopment with the goal of choosing the most sensitive marker for the application.

Nuclear imaging techniques like PET and SPECT as well as optical imaging approaches have a much higher intrinsic sensitivity than Magnetic Resonance (MR), which explains why these techniques are traditionally preferred for molecular and cellular imaging applications. MR is remarkably versatile as it provides anatomical, micro-structural and functional as well as metabolic information of intact tissues in vivo, in a non-invasive manner. For these reasons, the technique is widely used in biomedical research in the preclinical setting and finds extensive use in the clinic. A number of years ago our laboratory has begun to explore the challenges and opportunities in making MR imaging (MRI) suitable for molecular and cellular imaging applications. This lecture will deal with:

1. the design of powerful contrast materials (often based on nano-particles when sparse molecular markers are to be detected);
2. the development of optimized MRI detection sequences that are aimed to explore the capabilities of MRI for absolute contrast agent quantification;
3. the utility of multi-modal imaging approaches for exploiting the sensitivity of 1H-MRI to contrast agent compartmentalization effects.

Examples of molecular and cellular imaging applications will be taken from our studies in mouse models of cancer and cardiovascular diseases, including atherosclerosis, abdominal aorta aneurysms and myocardial infarction.

The first part of the discussion will provide an overview of a number of optical imaging methods and relevant animal models that can be used to study of the angiogenic process on various levels ranging from intravital microscopy to whole body optical imaging. The cost effective and non-invasive character of optical imaging makes it an ideal approach for repeated measurement and follow up of treatment over time. The second part of the discussion will be about how new imaging system that combines fluorescent intravital video microscopy (FIVM) and dynamic light scattering imaging (DLSI) makes possible to study simultaneously various parameters related to vascular physiology. The final part of the discussion addressed to the new challenges and possible clinical applications of multimodal optical imaging.

Cardiovascular molecular imaging has grown explosively over the last fifteen years, but translation into clinically available imaging agents and techniques has lagged. NHLBI recently convened a working group of experts in the field to assess the current state of cardiovascular molecular imaging, to identify areas where cardiovascular molecular imaging was likely to have an impact, to explore barriers to the translation of molecular imaging toward clinical application, and to inform the NHLBI on national priorities for the promotion of translation of cardiovascular molecular imaging. This talk will focus on areas of clinical need and imaging agents that are in clinical or preclinical testing; on roadblocks to the broader translation of these agents; and on ways to overcome these roadblocks.

Advances in cancer biology have rapidly produced many exploitable targets (e.g. acidic tumor pH, cell surface receptors) and corresponding target-specific ligands (e.g. peptides/peptoids, mAbs) for personalized diagnosis and therapy of cancer. Nanomedicine has received considerable attention as a highly integrated diagnostic and therapeutic platform for cancer. Achieving high biological specificity has been the main challenge for the successful development of these nanoplatforms. In this presentation, I will discuss the recent advances on the development of tunable, ultra-pH sensitive (UPS)micelles for cancer imaging applications. Dye-labeled UPS nanoprobes have a fast fluorescence response (<10 ms), up to 130-fold increase of emission intensity between OFF and ON states, and only require <0.25 pH unit for activation (vs. 2 pH unit for small molecular dyes). Nanoprobes with different transition pH can be selectively activated in acidic tumor microenvironment or angiogenic vasculature in solid tumors. This capability allows for the development of pH-activatable imaging probes or nanocarriers that can target tumor acidic pHe and specific subcellular organelles for cancer-specific imaging and therapy.

This presentation will focus on methods to validate non-invasive PET radiotracers for the quantification of loco-regional hypoxia. MicroPET images will be shown of different hypoxia tracers and their uptake kinetics discussed. The use of compartmental analysis to define parametric images will be compared against single late time point imaging. Digital autoradiography will be used to determine the intra-tumoral distributions of different hypoxia tracers, compared against exogenous and endogenous hypoxia-related proteins, exogenous hypoxia markers and hypoxia reporter-gene expression. Experiments to validate PET imaging of tumor hypoxia using image guided partial oxygen probes will be discussed. The lecture will conclude with efforts to quantify the hypoxia distribution in clinical studies with head and neck patients.

Due to thousands iron atom content providing large T2* effect, iron oxide nanoparticles are suitable MR-contrastophores for molecular and cellular imaging. The synthesis of Ultra Small superParamagnetic Iron Oxide nanoparticles (USPIO) is a complex process and coating such as polymeric or monomeric hydrophilic molecules is required to prevent destabilization and agglomeration of the colloidal suspension. Nanoparticles are usually taken up by macrophages in the liver, spleen and bone marrow, which are easily accessible macrophage-rich tissues. Coating optimization, to limit phagocytosis in liver and spleen, results in longer blood half-lives allowing USPIO to reach other targets in deep territories. Pharmacophores such as peptides or small organic ligands grafting, which is performed by chemical functionalization on the nanoparticule surface, open up a wide range of targeting applications. Several MR sequences based on r1, r2 and magnetic susceptibility of USPIO can be used in combination for nanoparticle detection and quantification. Biodistribution, affinity, biocompatibility and biodegradability are important challenges to overcome for clinical applications.