Hyperpolarized Magnetic Resonance Research Articles

Dissolution DNP for in vivo preclinical studies

The tremendous polarization enhancement afforded by dissolution dynamic nuclear polarization (DNP) can be taken advantage of to perform preclinical in vivo molecular and metabolic imaging. Following the injection of molecules that are hyperpolarized via dissolution DNP, real-time measurements of their biodistribution and metabolic conversion can be recorded. This technology therefore provides a unique and invaluable tool for probing cellular metabolism in vivo in animal models in a noninvasive manner. It gives the opportunity to follow and evaluate disease progression and treatment response without requiring ex vivo destructive tissue assays. Although its considerable potential has now been widely recognized, hyperpolarized magnetic resonance by dissolution DNP remains a challenging method to implement for routine in vivo preclinical measurements. The aim of this article is to provide an overview of the current state-of-the-art technology for preclinical applications and the challenges that need to be addressed to promote it and allow its wider dissemination in the near future.

Regional Heterogeneity of Chronic Obstructive Pulmonary Disease Phenotypes: Pulmonary 3He Magnetic Resonance Imaging and Computed Tomography

Pulmonary ventilation may be visualized and measured using hyperpolarized 3He magnetic resonance imaging (MRI) while emphysema and its distribution can be quantified using thoracic computed tomography (CT). Our objective was to phenotype ex-smokers with COPD based on the apical-to-basal distribution of ventilation abnormalities and emphysema to better understand how these phenotypes change regionally as COPD progresses. We evaluated 100 COPD ex-smokers who provided written informed consent and underwent spirometry, CT and 3He MRI. 3He MRI ventilation imaging was used to quantify the ventilation defect percent (VDP) for whole-lung and individual lung lobes. Regional VDP was used to generate the apical-lung (AL)-to-basal-lung (BL) difference (ΔVDP); a positive ΔVDP indicated AL-predominant and negative ΔVDP indicated BL-predominant ventilation defects. Emphysema was quantified using the relative-area-of-the-lung ≤−950HU (RA950) of the CT density histogram for whole-lung and individual lung lobes. The AL-to-BL RA950 difference (ΔRA950) was generated with a positive ΔRA950 indicating AL-predominant emphysema and a negative ΔRA950 indicating BL-predominant emphysema. Seventy-two ex-smokers reported BL-predominant MRI ventilation defects and 71 reported AL-predominant CT emphysema. BL-predominant ventilation defects (AL/BL: GOLD I = 18%/82%, GOLD II = 24%/76%) and AL-predominant emphysema (AL/BL: GOLD I = 84%/16%, GOLD II = 72%/28%) were the major phenotypes in mild-moderate COPD. In severe COPD there was a more uniform distribution for ventilation defects (AL/BL: GOLD III = 40%/60%, GOLD IV = 43%/57%) and emphysema (AL/BL: GOLD III = 64%/36%, GOLD IV = 43%/57%). Basal-lung ventilation defects predominated in mild-moderate GOLD grades, and a more homogeneous distribution of ventilation defects was observed in more advanced grade COPD; these differences suggest that over time, regional ventilation abnormalities become more homogenously distributed during disease progression.

Constant-variable flip angles for hyperpolarized media MRI

The longitudinal magnetization of hyperpolarized media, such as hyperpolarized 129Xe, 3He, etc., is nonrenewable. When the MRI data acquisition begins at the k-domain center, a constant flip angle (CFA) results in an image of high signal-to-noise ratio (SNR) but sacrifices the accuracy of spatial information. On the other hand, a variable flip angle (VFA) strategy results in high accuracy but suffers from a low SNR. In this paper, we propose a novel scheme to optimize both the SNR and accuracy, called constant-variable flip angles (CVFA). The proposed scheme suggests that hyperpolarized magnetic resonance signals are firstly acquired through a train of n∗ CFA excitation pulses, followed by a train of N–n∗ VFA excitation pulses. We simulate and optimize the flip angle used in the CFA section, the number of CFA excitation pulses, the number of VFA excitation pulses, and the initial and final variable flip angles adopted in the VFA section. Phantom and in vivo experiments demonstrate the good performance of the CVFA designs and their ability to maintain both high SNR and spatial resolution.

Hyperpolarized Metabolic MR Imaging of Acute Myocardial Changes and Recovery after Ischemia-Reperfusion in a Small-Animal Model.

To implement hyperpolarized magnetic resonance (MR) imaging in an animal model of ischemia-reperfusion and to assess in vivo the regional changes in pyruvate metabolism within the 1st hour and at 1 week after a brief episode of coronary occlusion and reperfusion. All animal experiments were performed with adherence to the Swiss Animal Protection law and were approved by the regional veterinary office. A closed-chest rat model was implemented by using an inflatable balloon secured around the left coronary artery. Animals were placed in an MR system 5-7 days after surgery. [1-(13)C]pyruvate was polarized by using a home-built multisample hyperpolarizer. Hyperpolarized pyruvate was injected at five stages: at baseline; at reperfusion after 15 minutes of coronary occlusion; and at 30 minutes, 60 minutes, and 1 week after ischemia reperfusion. The conversion of pyruvate into lactate and bicarbonate was imaged by using dedicated MR sequences alongside wall motion and delayed enhancement imaging. After imaging, the heart was removed and stained to delineate the area at risk (AAR). Differences between AAR and remote myocardium were assessed by using a repeated measures analysis of variance and a post hoc Bonferroni multiple comparison test. Data were collected in 12 animals. Occlusion led to hypokinesia of the anterior or anterolateral segments of the myocardium. At reperfusion, the average lactate-to-bicarbonate ratio increased in the AAR relative to that at baseline (from 1.93 ± 0.48 to 3.01 ± 0.74, P < .001) and was significantly higher when compared with that in the remote area (1.91 ± 0.38, P < .001). In the 60 minutes after occlusion, the lactate-to-bicarbonate ratio in the AAR recovered but was still elevated relative to that in the remote area. One week after ischemia-reperfusion, no difference between AAR and remote area could be detected. Hyperpolarized metabolic MR imaging can be used to successfully detect acute changes in [1-(13)C]pyruvate metabolism after ischemia-reperfusion, thereby enabling in vivo monitoring of the metabolic effects of reperfusion strategies.

Metabolic Imaging as a Biomarker of Early Radiation Response in Tumors.

(13)C-pyruvate hyperpolarized magnetic resonance imaging (HP-MRI) is emerging as a viable quantitative biomarker for solid tumor response and normal tissue toxicity after radiotherapy. This technology effectively predicts response related to metabolic agents or alterations in the tumor microenvironment, but challenges remain to be addressed to ensure successful translational implementation. See related article by Saito et al., p. 5073.

Hyperpolarized nanodiamond with long spin-relaxation times.

The use of hyperpolarized agents in magnetic resonance, such as 13C-labelled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarization technique is the inherently short spin-relaxation times, typically <60 s for 13C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance 13C spins in synthetic nanodiamond can be hyperpolarized at cryogenic and room temperature without the use of free radicals, and, owing to their solid-state environment, exhibit relaxation times exceeding 1 h. Combined with the already established applications of nanodiamonds in the life sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized magnetic resonance.

The Sensitivity of Phosphocholine 13C Chemical Shifts to pH

Phosphocholine is a useful magnetic resonance (MR) biomarker for cancer. 13C hyperpolarized MR is likely to enhance the detection of this compound by orders of magnitude. The ability to differentiate phosphocholine from its precursor, choline, in live tissues, is unique to MR and depends on the 13C chemical shifts. The dependence of phosphocholine 13C chemical shifts on pH was investigated. We found that under viable physiological conditions of pH > 7, the chemical shift of phosphocholine 13C is stable and the chemical shift distance from the choline 13C signals is preserved. Under acidic intracellular conditions of 6.0 < pH < 7, the pH could be sensed by the phosphocholine 13C chemical shifts. Crucial and damaging pH changes to values lower than 6.0 could be sensed at very high sensitivity. The highest precision for pH determination is obtained when considering the chemical shift difference between positions 1 and 2 of phosphocholine. The solution composition of human plasma did not affect the response of phosphocholine 13C chemical shifts to pH.

(13)C-labeled biochemical probes for the study of cancer metabolism with dynamic nuclear polarization-enhanced magnetic resonance imaging.

In recent years, advances in metabolic imaging have become dependable tools for the diagnosis and treatment assessment in cancer. Dynamic nuclear polarization (DNP) has recently emerged as a promising technology in hyperpolarized (HP) magnetic resonance imaging (MRI) and has reached clinical relevance with the successful visualization of [1-13C] pyruvate as a molecular imaging probe in human prostate cancer. This review focuses on introducing representative compounds relevant to metabolism that are characteristic of cancer tissue: aerobic glycolysis and pyruvate metabolism, glutamine addiction and glutamine/glutamate metabolism, and the redox state and ascorbate/dehydroascorbate metabolism. In addition, a brief introduction of probes that can be used to trace necrosis, pH changes, and other pathways relevant to cancer is presented to demonstrate the potential that HP MRI has to revolutionize the use of molecular imaging for diagnosis and assessment of treatments in cancer.

Abstract 210: In vivo metabolic imaging to differentiate aggressive versus indolent prostate cancer

Abstract Purpose: Many prostate cancers (PCa) detected by screening are indolent (will not leave the prostate) however, 90% of patients will receive immediate treatment such as surgery or radiation therapy. There is a pressing need in the clinic for determining the aggressiveness of PCa that allows the whole prostate to be examined and is directly correlated to the metastatic behavior of the tumor. We are using a multi-prong approach to understand the metabolic changes that occur in the progression of PCa. (1) We are metabolic profiling tumor and normal prostate tissue. (2) We are metabolic profiling both the intracellular and secretion/consumption of metabolites of four human prostate cancer cell lines with different aggressiveness profiles: RWPE-1 (non-tumorigenic, considered benign), RWPE-2 (non-metastatic), PC3 (aggressive, castration resistant), most aggressive cell line PC3M (castration resistant). (3) We are following the progression of PCa with hyperpolarized magnetic resonance (MR) agents in PCa animal models. Hyperpolarization allows for over &amp;gt;10,000 fold sensitivity enhancement using conventional MRI and MRS. The polarization (signal enhancement) can be retained on the metabolites of the hyperpolarized molecule. Hyperpolarization allows for in vivo real time metabolic profiling. Results: Based on our metabolic profiling of PCa tissue and cell culture, we observe significant differences in uptake of glutamine and the amount of intracellular glutamine, differences in phosphocholine and glycerophosphocholine, and differences in intracellular succinate levels between aggressive versus non-aggressive cell lines and in PCa tissue versus normal prostate tissue. In addition, in our hands we see no significant difference in the glycolytic rate (production of lactate) between the indolent and aggressive PCa cell lines in culture. Using dynamic nuclear polarization, we are designing new in vivo methods for interrogating metabolic pathways. Using our chemical reaction-induced multi-molecular polarization (CRIMP) technique, we can fully transfer the high polarization levels of pyruvate in an irreversible reaction to 1-13C acetate and 13C-carbon dioxide without substantial signal loses. Because hyperpolarized carbon dioxide nearly instantly equilibrates with bicarbonate in the aqueous environment, the pH of the media can be simply calculated from the signal intensity ratio of the two compounds using the Henderson Hasselbalch equation. Discussion: As an alternative to hyperpolarized pyruvate for analysis of the aggressiveness of prostate cancer, compounds that more comprehensively interrogate glutaminolysis, choline metabolism, and the Krebs cycle in combination may provide better metabolic imaging information. Using the CRIMP technique and single component hyperpolarization of 15N-choline, we are currently using MR to metabolically image PCa animal models. Citation Format: Niki Zacharias Millward, Christopher McCullough, Youngbok Lee, Jingzhe Hu, Prasanta Dutta, David Piwnica-Worms, Pratip Bhattacharya. In vivo metabolic imaging to differentiate aggressive versus indolent prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 210. doi:10.1158/1538-7445.AM2015-210

Metabolic response of prostate cancer to nicotinamide phophoribosyltransferase inhibition in a hyperpolarized MR/PET compatible bioreactor.

Metabolic shifts in disease are of great interest for the development of novel therapeutics. In cancer treatment, these therapies exploit the metabolic phenotype associated with oncogenesis and cancer progression. One recent strategy involves the depletion of the cofactors needed to maintain the high rate of glycolysis seen with the Warburg effect. Specifically, blocking nicotinamide adenine dinucleotide (NAD) biosynthesis via nicotinamide phosphoribosyltransferase (NAMPT) inhibition depletes cancer cells of the NAD needed for glycolysis. To characterize this metabolic phenotype in vivo and describe changes in flux with treatment, non-invasive biomarkers are necessary. One such biomarker is hyperpolarized (HP) [1-(13) C] pyruvate, a clinically translatable probe that allows real-time assessment of metabolism. We therefore developed a cell perfusion system compatible with HP magnetic resonance (MR) and positron emission tomography (PET) to develop translatable biomarkers of response to NAMPT inhibition in reduced volume cell cultures. Using this platform, we observed a reduction in pyruvate flux through lactate dehydrogenase with NAMPT inhibition in prostate cancer cells, and showed that both HP lactate and 2-[(18) F] fluoro-2-deoxy-D-glucose (FDG) can be used as biomarkers for treatment response of such targeted agents. Moreover, we observed dynamic flux changes whereby HP pyruvate was re-routed to alanine, providing both positive and negative indicators of treatment response. This study demonstrated the feasibility of a MR/PET compatible bioreactor approach to efficiently explore cell and tissue metabolism, the understanding of which is critical for developing clinically translatable biomarkers of disease states and responses to therapeutics.

Novel Approaches to Imaging Tumor Metabolism

The field of metabolism research has made a dramatic resurgence in recent years, fueled by a newfound appreciation of the interactions between metabolites and phenotype. Metabolic substrates and their products can be biomarkers of a wide range of pathologies, including cancer, but our understanding of their in vivo interactions and pathways has been hindered by the robustness of noninvasive imaging approaches. The past 3 decades have been flushed with the development of new techniques for the study of metabolism in vivo. These methods include nuclear-based, predominantly positron emission tomography and magnetic resonance imaging, many of which have been translated to the clinic. The purpose of this review was to introduce both long-standing imaging strategies as well as novel approaches to the study of perturbed metabolic pathways in the setting of carcinogenesis. This will involve descriptions of nuclear probes labeled with C and F as well C for study using hyperpolarized magnetic resonance imaging. Highlighting both advantages and disadvantages of each approach, the aim of this summary was to provide the reader with a framework for interrogation of metabolic aberrations in their system of interest.

Hyperpolarized magnetic resonance as a sensitive detector of metabolic function.

Hyperpolarized magnetic resonance allows for noninvasive measurements of biochemical reactions in vivo. Although this technique provides a unique tool for assaying enzymatic activities in intact organs, the scope of its application is still elusive for the wider scientific community. The purpose of this review is to provide key principles and parameters to guide the researcher interested in adopting this technology to address a biochemical, biomedical, or medical issue. It is presented in the form of a compendium containing the underlying essential physical concepts as well as suggestions to help assess the potential of the technique within the framework of specific research environments. Explicit examples are used to illustrate the power as well as the limitations of hyperpolarized magnetic resonance.

Abstract B37: Patient-derived tissue culture model systems of renal cell carcinoma for development of clinically translatable metabolic biomarkers

Abstract Aim: Renal cell carcinomas (RCCs) is a diverse group of tumors of varying aggressiveness. The development of noninvasive biomarkers of RCC aggressiveness is hindered by a lack of relevant model systems that recapitulate the human situation. In this study, we report the development of patient- derived tumor tissue slice ex vivo and in vivo models in conjunction with clinically translatable non-invasive hyperpolarized (HP) 13C magnetic resonance (MR) imaging technique for the metabolic evaluation of RCC. HP MR is a powerful tool that allows dynamic measurement of specific enzymatic processes implicated in tumorigenesis, and has recently been applied to prostate cancer patients. Methods: Tissue slice cultures (TSCs): RCC tissues were obtained from 8mm cores of nephrectomy cases, precision cut into 300 μm thick disks to allow for maximal oxygen and nutrient diffusion. Long-term tissue viability was assessed by biochemical assays (ATP luciferase, LIVE/DEAD) and phosphorous (31P) MR. Immunohistohcemical staining was also performed to characterize the RCC. Ex vivo evaluation of TSCs in a bioreactor: 4 tissue slices were kept alive in a micro-engineered MR compatible perfusion system. MR data were acquired on a narrow-bore 11.67T Varian INOVA equipped with a 5mm broadband probe. HP 13C MR was acquired dynamically following injection of HP pyruvate and DHA (dehydroascorbate) to assess metabolism in the RCC tissue slices. Animal model: The RCC tissue slices were implanted under the renal capsule of immune-compromised mice. Mice underwent multipramateric proton imaging in addition to dynamic HP 13C MR at 14T (Agilent microimaging system). For the HP MR, a 2D echo-planar based spectral spatial selective pulse sequence was used to obtain dynamic lactate images, post injection of 80mM of HP [1-13C]pyruvate. HP [1-13C] pyruvate has been used to study glycolysis in tumors. Results and Discussion: Ex vivo model: TSCs were viable in the bioreactor for up to 48 hours as confirmed by βNTP levels in 31P spectrum. The 31P spectra displayed characteristic metabolite peaks in the TSCs as seen in RCC patients, with dominant phosphor-ester peaks. Following injection of HP [1-13C] pyruvate into the bioreactor, a dynamic flux to lactate of 0.05 nmols/s/mg tissue was observed in the RCC tissue slices. Additionally we observed the conversion of DHA to Vitamin C in the tumor tissue slices. RCCs are known to have high level of reactive oxygen species, and the combination of this tumor model with HP DHA offers the possibility to interrogate redox potential which is implicated in tumor aggressiveness and treatment response. In vivo model: TSCs were grafted successfully in the sub-renal capsule for even low-grade tumors. Mean tumor ADC measurement of 1.23e-3 mm2/sec in the implanted tumor is similar to that reported in renal cancers clinically. Contrast enhancement of the tumor also confirmed engraftment and perfusion. Elevated HP lactate conversion was observed in the tumor graft, demonstrating the potential of the in vivo model for in-depth metabolic evaluation of tumors that more closely emulate the human situation. IHC of tumor grafts showed the persistence of human vasculature and oncogenic markers. Conclusion: The patient-derive tumor models described above may further enhance our understanding of RCC metabolism and development of clinically relevant biomarkers of tumor aggressiveness and therapy response. Citation Format: Renuka Sriram, Kayvan R. Keshari, Mark Van Criekinge, John Kurhanewicz, David M. Wilson, Donna M. Peehl, Robert Bok, Wang J. Zhen. Patient-derived tissue culture model systems of renal cell carcinoma for development of clinically translatable metabolic biomarkers. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B37.

Toward hyperpolarized molecular imaging of HIV: synthesis and longitudinal relaxation properties of (15) N-Azidothymidine.

Previously unreported (15) N labeled Azidothymidine (AZT) was prepared as an equimolar mixture of two isotopomers: 1-(15) N-AZT and 3-(15) N-AZT. Polarization decay of (15) N NMR signal was studied in high (9.4 T) and low (~50 mT) magnetic fields. (15) N T1 values were 45 ± 5 s (1-(15) N-AZT) and 37 ± 2 s (3-(15) N-AZT) at 9.4 T, and 140 ± 16 s (3-(15) N-AZT) at 50 mT. (15) N-AZT can be potentially (15) N hyperpolarized by several methods. These sufficiently long (15) N-AZT T1 values potentially enable hyperpolarized in vivo imaging of (15) N-AZT, because of the known favorable efficient (i.e., of the time scale shorter than the longest reported here (15) N T1 ) kinetics of uptake of injected AZT. Therefore, 3-(15) N-AZT can be potentially used for HIV molecular imaging using hyperpolarized magnetic resonance imaging.

Dephosphorylation and biodistribution of 1-¹³C-phospholactate in vivo.

Here, we present a new approach for the delivery of a metabolic contrast agent for in vivo molecular imaging. The use of a phosphate-protecting group that facilitates parahydrogen-induced polarization of 1-(13)C-phospholactate potentially enables the in vivo administration of a hydrogenated hyperpolarized adduct. When injected, nonhyperpolarized 1-(13)C-phospholactate is retained in the vasculature during its metabolic conversion to 1-(13)C-lactate by blood phosphatases as demonstrated here using a mucin 1 mouse model of breast cancer and ex vivo high-resolution (13)C NMR. This multisecond process is a suitable mechanism for the delivery of relatively short-lived (13)C and potentially (15)N hyperpolarized contrast agents using -OH phosphorylated small molecules, which is demonstrated here for the first time as an example of 1-(13)C-phospholactate. Through this approach, DL-1-(13)C-lactate is taken up by tissues and organs including the liver, kidneys, brain, heart, and tumors according to a timescale amenable to hyperpolarized magnetic resonance imaging.

Hyperpolarized Metabolic MR in the Study of Cardiac Function and Disease.

Several diseases of the heart have been linked to an insufficient ability to generate enough energy (ATP) to sustain proper heart function. Hyperpolarized magnetic resonance (MR) is a novel technique that can visualize and quantify myocardial energy metabolism. Hyperpolarization enhances the MR signal from a biological molecule of interest by more than 10,000 times, making it possible to measure its cellular uptake and conversion in specific enzymatic pathways in real time. We review the role of hyperpolarized MR in identifying changes in cardiac metabolism in vivo, and present the extensive literature on hyperpolarized pyruvate that has been used to characterize cardiac disease in various in vivo models, such as myocardial ischemia, hypertension, diabetes, hyperthyroidism and heart failure. The technical aspects of the technique are presented as well as the challenges of translating the technique into clinical practice. Hyperpolarized MR has the prospect of transforming diagnostic cardiology by offering new insights into cardiac disease and potentially even to contribute to personalized therapy based on a thorough understanding of the individual intracellular metabolism.

Evaluation of Hyperpolarized [1-13C]-Pyruvate by Magnetic Resonance to Detect Ionizing Radiation Effects in Real Time

Ionizing radiation (IR) cytotoxicity is primarily mediated through reactive oxygen species (ROS). Since tumor cells neutralize ROS by utilizing reducing equivalents, we hypothesized that measurements of reducing potential using real-time hyperpolarized (HP) magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) can serve as a surrogate marker of IR induced ROS. This hypothesis was tested in a pre-clinical model of anaplastic thyroid carcinoma (ATC), an aggressive head and neck malignancy. Human ATC cell lines were utilized to test IR effects on ROS and reducing potential in vitro and [1-13C] pyruvate HP-MRS/MRSI imaging of ATC orthotopic xenografts was used to study in vivo effects of IR. IR increased ATC intra-cellular ROS levels resulting in a corresponding decrease in reducing equivalent levels. Exogenous manipulation of cellular ROS and reducing equivalent levels altered ATC radiosensitivity in a predictable manner. Irradiation of ATC xenografts resulted in an acute drop in reducing potential measured using HP-MRS, reflecting the shunting of reducing equivalents towards ROS neutralization. Residual tumor tissue post irradiation demonstrated heterogeneous viability. We have adapted HP-MRS/MRSI to non-invasively measure IR mediated changes in tumor reducing potential in real time. Continued development of this technology could facilitate the development of an adaptive clinical algorithm based on real-time adjustments in IR dose and dose mapping.

Validation of Noninvasive Morphological and Diffusion Imaging in Mouse Emphysema by Micro–Computed Tomography and Hyperpolarized 129Xe Magnetic Resonance Imaging

Animal disease models are pivotal in investigating the pathogenesis of emphysema and developing novel drugs, but the modalities to evaluate murine emphysema models have been of limited validity and sensitivity. In this study, we evaluated hyperpolarized (129)Xe magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) compared with traditional methods, such as plethysmography and histology. Elastase-treated mice and adiponectin knockout mice were used as murine emphysema models to evaluate these modalities. Three weeks after elastase administration, significant and heterogeneous emphysema was evaluated according to the mean linear intercept and plethysmography parameters. Notably, the distribution of low-density areas, as examined by micro-CT, correlated with the mean linear intercept and plethysmography parameters in whole lungs. These correlations were also observed in regional areas. Furthermore, we introduced hyperpolarized (129)Xe MRI, which can evaluate gas exchange between the alveoli and blood during spontaneous breathing. Parameters of gas exchange (fD) and alveolar size (Vs/Va) were significantly decreased in elastase-treated mice, and moderately correlated with the plethysmography parameters. Of importance, we could detect a decrease of the fD value in low-density areas with micro-CT, suggesting that gas exchange decreased in emphysematous lesions. Likewise, these parameters (fD and Vs/Va) were also decreased in adiponectin knockout mice, which exhibit emphysema with a homogeneous distribution. We demonstrated the feasibility of (129)Xe MRI and micro-CT in combination with traditional modalities. These noninvasive modalities provide complementary data that can be used for repeated estimations of regional gas exchange and lung morphology.

A platform for designing hyperpolarized magnetic resonance chemical probes

Hyperpolarization is a highly promising technique for improving the sensitivity of magnetic resonance chemical probes. Here we report [15N, D9]trimethylphenylammonium as a platform for designing a variety of hyperpolarized magnetic resonance chemical probes. The platform structure shows a remarkably long 15N spin–lattice relaxation value (816 s, 14.1 T) for retaining its hyperpolarized spin state. The extended lifetime enables the detection of the hyperpolarized 15N signal of the platform for several tens of minutes and thus overcomes the intrinsic short analysis time of hyperpolarized probes. Versatility of the platform is demonstrated by applying it to three types of hyperpolarized chemical probes: one each for sensing calcium ions, reactive oxygen species (hydrogen peroxide) and enzyme activity (carboxyl esterase). All of the designed probes achieve high sensitivity with rapid reactions and chemical shift changes, which are sufficient to allow sensitive and real-time monitoring of target molecules by 15N magnetic resonance.

Cardiovascular Molecular Imaging: New Methodological Strategies

Significant technical advances in small animal molecular imaging techniques and in imaging probes with high specificity for various molecular targets have been produced in the last ten years. Notwithstanding, the clinical applicability of molecular imaging proceeds slowly. In animal experiments, multimodality molecular imaging techniques based on hybrid scanners are increasing, providing more insight into path physiologic phenomena associated with cardiovascular disease. In parallel, we assisted in the development of a new generation of multi-imaging probes, such as PET/MRI probes, particularly effective in hybrid scanners. More recently, in order to gain in inherently low sensitivity of MRI, hyperpolarized magnetic resonance spectroscopy using hyperpolarized (13)C was proposed. Preliminary results obtained in experimental animal studies seem to confirm the potentialities of hyperpolarized (13)C magnetic resonance to monitor myocardial energetics. In this review the preclinical cardiovascular applications and the potential for clinical translation are discussed.