Photoacoustic tomography (PAT) combines optical and acoustic imaging to generate high-resolution images of microvasculature. Inherent sensitivity to hemoglobin permits PAT to image blood vessels but precludes discriminating neovascular from maturing microvasculature. α(v)β(3)-Gold nanobeacons (α(v)β(3)-GNBs) for neovascular molecular PAT were developed, characterized, and demonstrated in vivo using a mouse Matrigel-plug model of angiogenesis. PAT results were microscopically corroborated with fluorescent α(v)β(3)-GNB localization and supporting immunohistology in Rag1(tm1Mom) Tg(Tie-2-lacZ)182-Sato mice. α(v)β(3)-GNBs (154 nm) had 10-fold greater contrast than blood on an equivolume basis when imaged at 740 nm to 810 nm in blood. The lowest detectable concentration in buffer was 290 nM at 780 nm. Noninvasive PAT of angiogenesis using a 10-MHz ultrasound receiver with α(v)β(3)-GNBs produced a 600% increase in signal in a Matrigel-plug mouse model relative to the inherent hemoglobin contrast pretreatment. In addition to increasing the contrast of neovessels detected at baseline, α(v)β(3)-GNBs allowed visualization of numerous angiogenic sprouts and bridges that were undetectable before contrast injection. Competitive inhibition of α(v)β(3)-GNBs with α(v)β(3)-NBs (no gold particles) almost completely blocked contrast enhancement to pretreatment levels, similar to the signal from animals receiving saline only. Consistent with other studies, nontargeted GNBs passively accumulated in the tortuous neovascular but provided less than half of the contrast enhancement of the targeted agent. Microscopic studies revealed that the vascular constrained, rhodamine-labeled α(v)β(3)-GNBs homed specifically to immature neovasculature (PECAM(+), Tie-2(-)) along the immediate tumor periphery, but not to nearby mature microvasculature (PECAM(+), Tie-2(+)). The combination of PAT and α(v)β(3)-GNBs offered sensitive and specific discrimination and quantification of angiogenesis in vivo, which may be clinically applicable to a variety of highly prevalent diseases, including cancer and cardiovascular disease.

Detection of sentinel lymph node (SLN) using photoacoustic imaging is an emerging technique for noninvasive axillary staging of breast cancer. Due to the absence of intrinsic contrast inside the lymph nodes, exogenous contrast agents are used for photoacoustic detection. In this work, we have demonstrated near infrared detection of SLN with gold nanobeacons (GNB) providing the photoacoustic contrast in a rodent model. We found that size dictates the in vivo characteristics of these nanoparticles in SLN imaging. Larger nanobeacons with high pay loads of gold were not as efficient as smaller size nanobeacons with lower pay loads for this purpose. Colloidal GNBs were designed as a nanomedicine platform with "soft" nature that is amenable to bio-elimination, an essential feature for in vivo efficacy and safety. The GNBs were synthesized as lipid-or polymerencapsulated colloidal particles incorporating tiny gold nanoparticles (2-4 nm) in three tunable sizes (90 nm, 150 nm and 290 nm). Smaller GNBs were noted trafficking through the lymphatic system and accumulating more efficiently in the lymph nodes in comparison to the bigger nanoagents. At 20 min, the GNBs reached the SLN and were no longer observed within the draining lymphatic vessel. Within one hour post injection, the contrast ratio of the lymphnodes with the surrounding blood vessels was 9:1. These findings were also supported by analytical measurements of the ex vivo tissue samples. Results indicate that cumulative nanoparticle deposition in lymph nodes is size dependent and that high payloads of gold, although offering greater contrast in vitro, may yield nanoagents with poor intradermal migration and lymphatic transport characteristics.

Non-invasive cellular and molecular imaging techniques are emerging as a multidisciplinary field that offers promise in understanding the components, processes, dynamics and therapies of disease at a molecular level. Magnetic resonance imaging (MRI) is an attractive technique due to the absence of radiation and high spatial resolution which makes it advantageous over techniques involving radioisotopes. Typically paramagnetic and superparamagnetic metals are used as contrast materials for MR based techniques. Gadolinium has been the predominant paramagnetic contrast metal until the discovery and association of the metal with nephrogenic systemic fibrosis (NSF) in some patients with severe renal or kidney disease. Manganese was one of the earliest reported examples of paramagnetic contrast material for MRI because of its efficient positive contrast enhancement. In this review manganese based contrast agent approaches will be presented with a particular emphasis on nanoparticulate agents. We have discussed both classically used small molecule based blood pool contrast agents and recently developed innovative nanoparticle-based strategies highlighting a number of successful molecular imaging examples.

Noninvasive magnetic resonance (MR) molecular imaging and targeted drug delivery systems, often referred to as theranostic agents, are being developed to enable improved detection, patient risk stratification, site-specific treatment, and longitudinal monitoring. 1 One example of these agents, a gadolinium-based perfluoro-carbon nanoparticle, has been used to detect, characterize, treat, and follow angiogenesis in preclinical models of cancer and atherosclerosis. Despite the preclinical success of this and related nanotechnology platforms, the recent discovery of nephrogenic systemic fibrosis (NSF), a serious and unexpected side effect of gadolinium blood pool agents observed in some patients with renal disease or following liver transplant, has cast a shadow on currently approved MR contrast agents. 2 Patients with NSF develop thickening of the skin and connective tissues that can inhibit arm and leg movements and even lead to bone fractures. Approximately 5% of patients experience a rapidly progressive course, which may result in death due to widespread fibrosis. The cause of NSF is unknown and there is no effective treatment of this condition. Although gadolinium has been the dominant paramagnetic metal for MR contrast agents, the issue of NSF has induced consideration of alternative approaches.Manganese was one of the first reported examples 3,4 of paramagnetic contrast material studied in cardiac and hepatic MRI because of its efficient R 1 enhancement. Similar to Ca 2+ and unlike the lanthanides, manganese is a natural cellular constituent, and often a cofactor for enzymes and receptors. Manganese blood pool agents, such as mangafodipir trisodium, have been approved as a hepatocyte-specific contrast agent with transient side-effects due to dechelation of manganese from the linear chelate. Nontargeted liposomal agents have included MnSO 4 3c or Mn-DTPA. 3d Release of Mn caused by disruption of the vesicles allowed MR detection of sites where the vesicles were non-specifically entrapped.Manganese(III)-labeled nanobialys (1) are a potential targeted MR theranostic nanoparticle produced by molecular self-assembly of amphiphilic branched polyethylenimine, which has a toroidal shape, tunable particle size, and low polydispersity. The "bialy" shape affords increased stability and presents kinetically stable, porphyrin coupled Mn(III) complexes directly to the surrounding water. In a typical synthesis, commercially available branched polyethylenimines (MW = 10 kDa) are hydrophobically modified (nominal 55% conjugation of the 1° amine) with linoleic acid by activating the carboxylic acid groups with 1-(3′-dimethylaminopropyl)-3-ethylcarbodiimide methiodide (1.2 equiv) and allowing the reaction overnight at ambient temperature. Supramolecular self-assembly of the amphiphilic polymer in anhydrous chloroform, assumes inverted micellar 5 structures (2) that are able to transfer a water soluble new candidate contrast agent Mn(III)-protoporphyrin chloride (Mn-PPC, 4) into chloroform. Synergistic self-assembly of the ag...

Multicolored imaging: A new class of molecular imaging agent has been developed based on low‐molecular‐weight organically soluble bismuth to detect and quantify intraluminal fibrin presented by ruptured plaque in the context of computed tomography angiograms without calcium interference.

We report a novel molecular imaging agent based on Ytterbium (Yb) designed for use with Spectral “multi-color” Computed Tomogrphy (CT). Spectral CT or multi-ycolored CT provides all of the benefits of traditional CT, i.e., rapid tomographic X-ray imaging, but in addition, it simultaneously discriminates metal-rich contrast agents based on the elements unique x-ray K-edge energy signature. Our synthetic approach involved the use of organically soluble Yb(III)-complex to produce nanocolloids of Yb of noncrystalline nature incorporating high density of Yb (>500K/nanoparticle) into a stable metal particle. The resultant particles are constrained to vasculature (~200nm) and are highly selective for binding fibrin in the ruptured atherosclerotic plaque. Nanoparticles exhibited excellent signal sensitivity and the spectral CT technique uniquely discriminates the k-edge signal (60keV) of Yb from calcium (bones). Bio-elimination and preliminary bio-distribution studied reflected the overall safety and defined clearance of these particles in a rodent model.

Photoacoustic tomography (PAT) is emerging as a novel, hybrid, and non ionizing imaging modality, because of its satisfactory spatial resolution and high soft tissue contrast. PAT combines the advantages of both optical and ultrasonic imaging methods. It opens up the possibilities for non-invasive staging of breast cancer and may replace sentinel lymph node (SLN) biopsy in clinic in the near future. In this work, we demonstrate for the first time that Copper can be used as a contrast metal for near infrared detection of SLN using PAT. A unique strategy is adopted to encapsulate multiple copies of Cu as organically soluble small molecule complexes within a phospholipids-entrapped nanoparticle. The nanoparticles assumed a size of 80–90nm, which is the optimum hydrodynamic diameter for its distribution throughout the lymphatic systems. These particles provided at least six times higher signal sensitivity in comparison to blood, which is a natural absorber of light. We also demonstrated that high SLN detection sensitivity with PAT can be achieved in rodent model. This work clearly demonstrates for the first time, the potential use of copper as an optical contrast agent.

This new nanoparticle-based thrombolytic agent provides specific and rapid fibrinolysis in vitro and may have a clinical role in early reperfusion during acute ischemic stroke.