Alessandra Flori

Assessment of real-time myocardial uptake and enzymatic conversion of hyperpolarized [1-13C]pyruvate in pigs using slice selective magnetic resonance spectroscopy

Hyperpolarization of ¹³C-labeled energy substrates enables the noninvasive detection and mapping of metabolic activity, in vivo, with magnetic resonance spectroscopy (MRS). Therefore, hyperpolarization and ¹³C MRS can potentially become a powerful tool to study the physiology of organs such as the heart, through the quantification of kinetic patterns under both normal and pathological conditions. In this study we assessed myocardial uptake and metabolism of hyperpolarized [1-¹³C]pyruvate in anesthetized pigs. Pyruvate metabolism was studied at baseline and during dobutamine-induced stimulation. We applied a numerical approach for spectral analysis and kinetic fitting (LSFIT/KIMOfit), making a comparison with a well-known jMRUI/AMARES analysis and γ-variate function, and we estimated the apparent conversion rate of hyperpolarized [1-¹³C]pyruvate into its downstream metabolites [1-¹³C]lactate, [1-¹³C]alanine and [¹³C]bicarbonate in a 3 T MR scanner. We detected an increase in the apparent kinetic constants (k(PX) ) for bicarbonate and lactate of two-fold during dobutamine infusion. These data correlate with the double product (rate-pressure product), an indirect parameter of cardiac oxygen consumption: we observed an increase in value by 46 ± 11% during inotropic stress. The proposed approach might be applied to future studies in models of cardiac disease and/or for the assessment of the pharmacokinetic properties of suitable ¹³C-enriched tracers for MRS.

Real-time cardiac metabolism assessed with hyperpolarized [1-13C]acetate in a large-animal model

Dissolution-dynamic nuclear polarization (dissolution-DNP) for magnetic resonance (MR) spectroscopic imaging has recently emerged as a novel technique for noninvasive studies of the metabolic fate of biomolecules in vivo. Since acetate is the most abundant extra- and intracellular short-chain fatty acid, we focused on [1-(13) C]acetate as a promising candidate for a chemical probe to study the myocardial metabolism of a beating heart. The dissolution-DNP procedure of Na[1-(13) C]acetate for in vivo cardiac applications with a 3 T MR scanner was optimized in pigs during bolus injection of doses of up to 3 mmol. The Na[1-(13) C]acetate formulation was characterized by a liquid-state polarization of 14.2% and a T1Eff in vivo of 17.6 ± 1.7 s. In vivo Na[1-(13) C]acetate kinetics displayed a bimodal shape: [1-(13) C]acetyl carnitine (AcC) was detected in a slice covering the cardiac volume, and the signal of (13) C-acetate and (13) C-AcC was modeled using the total area under the curve (AUC) for kinetic analysis. A good correlation was found between the ratio AUC(AcC)/AUC(acetate) and the apparent kinetic constant of metabolic conversion, from [1-(13) C]acetate to [1-(13) C]AcC (kAcC ), divided by the AcC longitudinal relaxation rate (r1 ). Our study proved the feasibility and the limitations of administration of large doses of hyperpolarized [1-(13) C]acetate to study the myocardial conversion of [1-(13) C]acetate in [1-(13) C]acetyl-carnitine generated by acetyltransferase in healthy pigs.

Dissolution dynamic nuclear polarization of non-self-glassing agents: spectroscopy and relaxation of hyperpolarized [1-13C]acetate.

The intrinsic physicochemical properties of the sample formulation are the key factors for efficient hyperpolarization through dissolution dynamic nuclear polarization (dissolution-DNP). We provide a comprehensive characterization of the DNP process for Na-[1-(13)C]acetate selected as a model for non-self-glassing agents: the solid-state polarization dynamics of different formulations and the effect of the paramagnetic agent (trityl radical) on the pattern of polarization and the relaxation profile were extensively analyzed. We quantified the effects of the glassing agent and Gd(3+)-chelate on DNP performance. The results reported here describe the constraints of the acetate formulation useful for future studies in this field with non-self-glassing enriched molecules.

Detection of 3D Cardiac metabolism after injection of hyperpolarized [1-13C]pyruvate

MRI with hyperpolarised 13C represents a promising modality for in-vivo spectroscopy and provides a unique opportunity for non-invasive assessment of cardiac regional metabolism.

Dual Photoacoustic/Ultrasound Multi-Parametric Imaging from Passion Fruit-like Nano-Architectures

Ultrasound (US) imaging is a well-established diagnostic technique to image soft tissues in real time, while photoacoustic (PA) is an emerging imaging technique employed to collect molecular information. Integration of PA and US imaging provides complementary information enhancing diagnostic accuracy without employing ionizing radiations. The development of contrast agents able to combine PA and US features is pivotal to improve the significance of PAUS imaging and for PAUS-guided treatment of neoplasms. Here, we demonstrate in relevant ex-vivo models that disassembling passion fruit-like nano-architectures (pfNAs) can be employed in PAUS imaging. pfNAs are composed by silica nanocapsules comprising aggregates of commercial NIR-dyes-modified polymers and ultrasmall gold nanoparticles. The intrinsic US and PA features of pfNAs have been fully characterized and validated in tissue-mimicking materials and in ex vivo preparations. Moreover, the application of a multi-parametric approach has allowed the increase of information extrapolated from collected images for a fine texture analysis.

3D cardiac Chemical Shift Imaging of [1-13C] hyperpolarized acetate and pyruvate in pigs

Background 13C Dynamic Nuclear Polarization (DNP) with rapid dissolution together with Magnetic Resonance Chemical Shift Imaging (CSI) have been used for non-invasive real-time metabolic assessment in cardiac experimental models on a clinical 3T scanner. Here, we report an in vivo comparison of hyperpolarized [1-13C] pyruvate and [1-13C] acetate perfusion and metabolism: a method based on a 3D Spiral CSI sequence is presented for obtaining spatially and spectrally-resolved information on whole heart cardiac metabolism.

A radiofrequency system for in vivo hyperpolarized (13) C MRS experiments in mice with a 3T MRI clinical scanner.

Hyperpolarized carbon-13 magnetic resonance spectroscopy (MRS) is a powerful tool to explore tissue metabolic state, by permitting the study of intermediary metabolism of biomolecules in vivo. However, a number of technological problems still limit this technology and need innovative solutions. In particular, the low molar concentration of derivate metabolites give rise to low signal-to-noise ratio (SNR), which makes the design and development of dedicated radiofrequency (RF) coils a fundamental task. In this article, the authors describe the simulation and the design of a RF coils configuration for MR experiments in mice, constituted by a 1 H whole body volume RF coil for imaging and a 13 C single circular loop surface RF coil for performing 13 C acquisitions. After the building, the RF system was employed in an in vivo experiment in a mouse injected with hyperpolarized [1-13 C]pyruvate by using a 3 T clinical MR scanner. SCANNING 38:710-719, 2016.

Segmental analysis of cardiac metabolism by hyperpolarized [1-13C] pyruvate: an in-vivo 3D MRI study in pigs

Summary An image analysis method was developed to obtain a 3D map of the pyruvate metabolites distribution in the LV in hyperpolarised 13C MRI. The obtained polar maps follow the standardized LV AHA segmentation, allowing reproducible and standardized LV segmental analysis. Background

Characterization of iron oxide-gold core-shell multifunctional nanoparticles in biomedical imaging

Core-shell iron oxide-gold nanoparticles (Fe3O4@Au) can be considered a smart platform for polyvalent presentation on account of their globular shape, tunable size, facile surface chemistry, and biocompatibility. We reported the synthesis and the characterization of Fe3O4@Au nanoparticles with transmission electron microscopy (TEM), dynamic light scattering (DLS), ultraviolet visible spectroscopy (UV-Vis), and we investigated their applicability as contrast agents for Magnetic Resonance Imaging (MRI). The measurement of longitudinal and transverse relaxation times of water protons in homogeneous aqueous dispersions of Fe3O4@Au nanoparticles with biocompatible coating at different concentrations allowed the assessment of longitudinal (r1) and transverse (r2) relaxivities at 1.5 and 3 T. The use of conjugated Fe3O4@Au nanoparticles as negative contrast agents could open up new perspectives for the development of novel tools for nanomedicine and for targeted delivery-MRI contrast enhancement systems and photo-optical applications in biomedicine.

Spectroscopic and photoacoustic characterization of encapsulated iron oxide super-paramagnetic nanoparticles as a new multiplatform contrast agent

Recently, a number of photoacoustic (PA) agents with increased tissue penetration and fine spatial resolution have been developed for molecular imaging and mapping of pathophysiological features at the molecular level. Here, we present bio-conjugated near-infrared light-absorbing magnetic nanoparticles as a new agent for PA imaging. These nanoparticles exhibit suitable absorption in the near-infrared region, with good photoacoustic signal generation efficiency and high photo-stability. Furthermore, these encapsulated iron oxide nanoparticles exhibit strong super-paramagnetic behavior and nuclear relaxivities that make them useful as magnetic resonance imaging (MRI) contrast media as well. Their simple bio-conjugation strategy, optical and chemical stability, and straightforward manipulation could enable the development of a PA probe with magnetic and spectroscopic properties suitable for in vitro and in vivo real-time imaging of relevant biological targets.