Absolute Quantitation for MR Molecular Imaging of Angiogenesis

Medical imaging is undergoing a transition from an art that is used to make static images of human physiology into a scientific tool that employs advanced techniques to measure clinically relevant data. Recently, the role of magnetic resonance imaging in cardiovascular and oncological research has grown, largely due to the implementation of new quantitative techniques in the clinic. Magnetic resonance imaging (MRI) and spectroscopy (MRS) are particularly rich in their capability to quantify both physiology and disease via biomarker detection. While this is true for many applications of MRI in cardiovascular and oncological research, 19F MR molecular imaging is particularly useful when coupled to the use of emerging site-targeted molecular imaging agents for diagnosis and therapy, such as αvβ3 integrin-targeted perfluorocarbon (PFC) nanoparticle (NP) emulsions. Unfortunately, the radiological world is realizing that although image quality may be consistently high, the absolute quantitative values being calculated vary widely across time, techniques, laboratories, and imaging platforms. The overall objective of this work is to advance the state of the art for 19F MR molecular imaging of perfluorocarbon nanoparticle emulsion contrast agents. To reach this objective, three specific aims have been identified: (1) to create new tools and techniques for 19F MR molecular imaging of PFC nanoparticles, (2) to develop translatable procedures for absolute quantification of 19F nuclei with MR molecular imaging, and (3) to evaluate the potential for clinical translation with ex vivo and in vivo preclinical experiments. Robust, standardized techniques are developed in this work to improve the accuracy of in vivo quantitative 19F MR molecular imaging, validate system performance, calibrate measurements to ensure repeatability of these quantitative metrics, and evaluate the potential for clinical translation. As these quantitative metrics become routine in medical imaging procedures, these standardized calibrations and techniques are expected to be critical for accurate interpretation of underlying pathophysiology. This will also impact the development of new therapies and diagnostic techniques/agents by reducing the variability of image-based measurements, thereby increasing the impact of the studies and reducing the overall time and cost to translate new technologies into the clinic

Eight-channel transceiver RF coil array tailored for (1)H/(19)F MR of the human knee and fluorinated drugs at 7.0 T

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1) H/(19) F MR of the human knee at 7.0 T following application of (19) F-containing drugs. The (1) H/(19) F RF coil array includes a posterior module with two (1) H loop elements and two anterior modules, each consisting of one (1) H and two (19) F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19) F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) - a (19) F-containing non-steroidal anti-inflammatory drug - to determine T1 and T2 and to study the (19) F signal-to-dose relationship. The suitability of the proposed approach for (1) H/(19) F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. QL /QU was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1) H/(19) F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19) F-containing medicinal compounds in vivo

New MRI Techniques for Nanoparticle Based Functional and Molecular Imaging

Although in clinical use for several decades, magnetic resonance imaging: MRI) is undergoing a transition from a qualitative anatomical imaging tool to a quantitative technique for evaluating myriad diseases. Furthermore, MRI has made great strides as a potential tool for molecular imaging of cellular and tissue biomarkers. Of the candidate contrast agents for molecular MRI, the excellent bio-compatibility and adaptability of perfluorocarbon nanoparticles: PFC NP) has established these agents as a potent targeted imaging agent and as a functional platform for non-invasive oxygen tension sensing. Direct readout and quantification of PFC NP can be achieved with fluorine: 19F) MRI because of the unique 19F signal emanating from the core PFC molecules. However, the signal is usually limited by the modest accumulated concentrations as well as several special NMR considerations for PFC NP, which renders 19F MRI technically challenging in terms of detection sensitivity, scan time, and image reconstruction. In the present dissertation, some of the pertinent NMR properties of PFC NP are investigated and new 19F MRI techniques developed to enhance their performance and expand the biomedical applications of 19F MRI with PFC NP. With the use of both theoretical and experimental methods, we evaluated J-coupling modulation, chemical shift and paramagnetic relaxation enhancement of PFC molecules in PFC NP. Our unique contribution to the technical improvement of 19F MRI of small animal involves:: 1) development of general strategies for RF 1H/19F coil design;: 2) design of novel MR pulse sequences for 19F T1 quantification; and: 3) optimization of imaging protocols for distinguishing and visualizing multiple PFC components: multi-chromatic 19F MRI). The first pre-clinical application of our novel 19F MRI techniques is blood vessel imaging and rapid blood oxygen tension measurement in vivo. Blood vessel anatomy and blood oxygen tension provide pivotal physiological information for routine diagnosis of cardiovascular disease. Using our novel Blood: flow)-Enhanced-Saturation-Recovery: BESR) sequence, we successfully visualized reduced flow caused by thrombosis in carotid arteries and jugular veins, and we quantified the oxygen tension in the cardiac ventricles of the mouse. The BESR sequence depicted the expected oxygenation difference between arterial and venous blood and accurately registered the response of blood oxygen tension to high oxygen concentration in 100% oxygen gas. This study demonstrated the potential application of PFC NP as a blood oxygen tension sensor and blood pool MR contrast agent for angiography. Another pre-clinical application investigated was functional kidney imaging with 19F MRI of circulating PFC NP. Conventional functional kidney imaging typically calls for the injection of small molecule contrast agents that may be nephrotoxic, which raises concerns for their clinical applications in patients with renal insufficiency. We demonstrated that our 19F MRI technique offers a promising alternative functional renal imaging approach that generates quantitative measurement of renal blood volume and intrarenal oxygenation. We successfully mapped the expected heterogeneous distribution of renal blood volume and confirmed the presence of an oxygenation gradient in healthy kidneys. We validated the diagnostic capability of 19F MRI in a mouse model of acute ischemia/reperfusion kidney injury. We also employed 19F MRI as a tool to test the therapeutic efficacy of a new nanoparticle-based drug, i. e. PPACK: D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone) PFC NP, which was postulated to inhibit microvascular coagulation during acute kidney injury. Based on our preliminary 19F MRI findings, we observed that PPACK PFC NP effectively reduced coagulation in our animal model, as evidenced by lesser accumulation of particles trapped by the clotting process. This finding suggests the potential for 19F MRI to be used as a drug monitoring tool as well in common medical emergencies such as acute kidney failure

RF Coil Design, Imaging Methods and Measurement of Ventilation with 19F C3F8 MRI

This thesis attempts to address the challenge of low signal in fluorinated gas ventilation imaging and optimize imaging methods considering the particular MR parameters of C3F8 by the following approaches: (i) Exploration of coil designs capable of imaging both proton (1H – 63.8 MHz at 1.5T) and fluorine (19F – 60.1 MHz at 1.5T) nuclei involved: 1. The novel use of microelectromechanical systems to switch a single transceive vest coil between the two nuclei was compared to hard-wired or PIN diode switching. 2. The design of an 8 element transceive array with an additional 6 receive only coils for 19F imaging. MEMs was utilized for broadband transmit-receive switching. 3. The amalgamation of a ladder resonator coil with a 6-element transceive array to reduce SAR and improve transmit homogeneity when compared to standard vest coil designs. (ii) Development of imaging methods involved: 1. The optimization and comparison of steady-state free precession and spoiled gradient 19F imaging with C3F8 at 1.5T and 3T. Simulation of the optimal SNR was verified through comprehensive phantom and in-vivo imaging experiments. 2. The investigation of compressed sensing via incoherent sparse k-space sampling to maximize the resolution in 19F ventilation imaging under the constraint of low SNR. Retrospective simulation with hyperpolarized gas images were corroborated by prospective 19F imaging of a 3D printed lung phantom and in-vivo measurements of the lungs. (iii) In-vivo ventilation metrics obtained by 19F ventilation imaging were explored by: 1. The in-vivo mapping of T1 at 1.5T and 3T and mapping of FV and T2* at 3 T. The apparent diffusion coefficient (1.5T) and the evaluation of ventilated volume (1.5T and 3T) was also compared to imaging performed with 129Xe (1.5T). 2. The optimization of imaging for the evaluation of percent ventilated volume with 19F at 3T with a commercial birdcage coil

Molecular Imaging of Inflammation - current and emerging technologies for diagnosis and treatment

Inflammation is a key factor in multiple diseases including primary immune-mediated inflammatory diseases e.g. rheumatoid arthritis but also, less obviously, in many other common conditions, e.g. cardiovascular disease and diabetes. Together, chronic inflammatory diseases contribute to the majority of global morbidity and mortality. However, our understanding of the underlying processes by which the immune response is activated and sustained is limited by a lack of cellular and molecular information obtained in situ. Molecular imaging is the visualization, detection and quantification of molecules in the body. The ability to reveal information on inflammatory biomarkers, pathways and cells can improve disease diagnosis, guide and monitor therapeutic intervention and identify new targets for research. The optimum molecular imaging modality will possess high sensitivity and high resolution and be capable of non-invasive quantitative imaging of multiple disease biomarkers while maintaining an acceptable safety profile. The mainstays of current clinical imaging are computed tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and nuclear imaging such as positron emission tomography (PET). However, none of these have yet progressed to routine clinical use in the molecular imaging of inflammation, therefore new approaches are required to meet this goal. This review sets out the respective merits and limitations of both established and emerging imaging modalities as clinically useful molecular imaging tools in addition to potential theranostic applications

[¹⁸F]fluorination of biorelevant arylboronic acid pinacol ester scaffolds synthesized by convergence techniques

Aim: The development of small molecules through convergent multicomponent reactions (MCR) has been boosted during the last decade due to the ability to synthesize, virtually without any side-products, numerous small drug-like molecules with several degrees of structural diversity.(1) The association of positron emission tomography (PET) labeling techniques in line with the “one-pot” development of biologically active compounds has the potential to become relevant not only for the evaluation and characterization of those MCR products through molecular imaging, but also to increase the library of radiotracers available. Therefore, since the [18F]fluorination of arylboronic acid pinacol ester derivatives tolerates electron-poor and electro-rich arenes and various functional groups,(2) the main goal of this research work was to achieve the 18F-radiolabeling of several different molecules synthesized through MCR. Materials and Methods: [18F]Fluorination of boronic acid pinacol esters was first extensively optimized using a benzaldehyde derivative in relation to the ideal amount of Cu(II) catalyst and precursor to be used, as well as the reaction solvent. Radiochemical conversion (RCC) yields were assessed by TLC-SG. The optimized radiolabeling conditions were subsequently applied to several structurally different MCR scaffolds comprising biologically relevant pharmacophores (e.g. β-lactam, morpholine, tetrazole, oxazole) that were synthesized to specifically contain a boronic acid pinacol ester group. Results: Radiolabeling with fluorine-18 was achieved with volumes (800 μl) and activities (≤ 2 GBq) compatible with most radiochemistry techniques and modules. In summary, an increase in the quantities of precursor or Cu(II) catalyst lead to higher conversion yields. An optimal amount of precursor (0.06 mmol) and Cu(OTf)2(py)4 (0.04 mmol) was defined for further reactions, with DMA being a preferential solvent over DMF. RCC yields from 15% to 76%, depending on the scaffold, were reproducibly achieved. Interestingly, it was noticed that the structure of the scaffolds, beyond the arylboronic acid, exerts some influence in the final RCC, with electron-withdrawing groups in the para position apparently enhancing the radiolabeling yield. Conclusion: The developed method with high RCC and reproducibility has the potential to be applied in line with MCR and also has a possibility to be incorporated in a later stage of this convergent “one-pot” synthesis strategy. Further studies are currently ongoing to apply this radiolabeling concept to fluorine-containing approved drugs whose boronic acid pinacol ester precursors can be synthesized through MCR (e.g. atorvastatin)

Smoking and Second Hand Smoking in Adolescents with Chronic Kidney Disease: A Report from the Chronic Kidney Disease in Children (CKiD) Cohort Study

The goal of this study was to determine the prevalence of smoking and second hand smoking [SHS] in adolescents with CKD and their relationship to baseline parameters at enrollment in the CKiD, observational cohort study of 600 children (aged 1-16 yrs) with Schwartz estimated GFR of 30-90 ml/min/1.73m2. 239 adolescents had self-report survey data on smoking and SHS exposure: 21 [9%] subjects had “ever” smoked a cigarette. Among them, 4 were current and 17 were former smokers. Hypertension was more prevalent in those that had “ever” smoked a cigarette (42%) compared to non-smokers (9%), p\u3c0.01. Among 218 non-smokers, 130 (59%) were male, 142 (65%) were Caucasian; 60 (28%) reported SHS exposure compared to 158 (72%) with no exposure. Non-smoker adolescents with SHS exposure were compared to those without SHS exposure. There was no racial, age, or gender differences between both groups. Baseline creatinine, diastolic hypertension, C reactive protein, lipid profile, GFR and hemoglobin were not statistically different. Significantly higher protein to creatinine ratio (0.90 vs. 0.53, p\u3c0.01) was observed in those exposed to SHS compared to those not exposed. Exposed adolescents were heavier than non-exposed adolescents (85th percentile vs. 55th percentile for BMI, p\u3c 0.01). Uncontrolled casual systolic hypertension was twice as prevalent among those exposed to SHS (16%) compared to those not exposed to SHS (7%), though the difference was not statistically significant (p= 0.07). Adjusted multivariate regression analysis [OR (95% CI)] showed that increased protein to creatinine ratio [1.34 (1.03, 1.75)] and higher BMI [1.14 (1.02, 1.29)] were independently associated with exposure to SHS among non-smoker adolescents. These results reveal that among adolescents with CKD, cigarette use is low and SHS is highly prevalent. The association of smoking with hypertension and SHS with increased proteinuria suggests a possible role of these factors in CKD progression and cardiovascular outcomes