An iterative sparse deconvolution method for simultaneous multicolor 19 F-MRI of multiple contrast agents.

PURPOSE: 19 F-MRI is gaining widespread interest for cell tracking and quantification of immune and inflammatory cells in vivo. Different fluorinated compounds can be discriminated based on their characteristic MR spectra, allowing in vivo imaging of multiple 19 F compounds simultaneously, so-called multicolor 19 F-MRI. We introduce a method for multicolor 19 F-MRI using an iterative sparse deconvolution method to separate different 19 F compounds and remove chemical shift artifacts arising from multiple resonances. METHODS: The method employs cycling of the readout gradient direction to alternate the spatial orientation of the off-resonance chemical shift artifacts, which are subsequently removed by iterative sparse deconvolution. Noise robustness and separation was investigated by numerical simulations. Mixtures of fluorinated oils (PFCE and PFOB) were measured on a 7T MR scanner to identify the relation between 19 F signal intensity and compound concentration. The method was validated in a mouse model after intramuscular injection of fluorine probes, as well as after intravascular injection. RESULTS: Numerical simulations show efficient separation of 19 F compounds, even at low signal-to-noise ratio. Reliable chemical shift artifact removal and separation of PFCE and PFOB signals was achieved in phantoms and in vivo. Signal intensities correlated excellently to the relative 19 F compound concentrations (r-2 = 0.966/0.990 for PFOB/PFCE). CONCLUSIONS: The method requires minimal sequence adaptation and is therefore easily implemented on different MRI systems. Simulations, phantom experiments, and in-vivo measurements in mice showed effective separation and removal of chemical shift artifacts below noise level. We foresee applicability for simultaneous in-vivo imaging of 19 F-containing fluorine probes or for detection of 19 F-labeled cell populations.

Improved cellular uptake of perfluorocarbon nanoparticles for in vivo murine cardiac 19F MRS/MRI and temporal tracking of progenitor cells.

Herein, we maximize the labeling efficiency of cardiac progenitor cells (CPCs) using perfluorocarbon nanoparticles (PFCE-NP) and 19F MRI detectability, determine the temporal dynamics of single-cell label uptake, quantify the temporal viability/fluorescence persistence of labeled CPCs in vitro, and implement in vivo, murine cardiac CPC MRI/tracking that could be translatable to humans. FuGENEHD-mediated CPC PFCE-NP uptake is confirmed with flow cytometry/confocal microscopy. Epifluorescence imaging assessed temporal viability/fluorescence (up to 7 days [D]). Nonlocalized murine 19F MRS and cardiac MRI studied label localization in terminal/longitudinal tracking studies at 9.4 T (D1-D8). A 4-8 fold 19F concentration increase is evidenced in CPCs for FuGENE vs. directly labeled cells. Cardiac 19F signals post-CPC injections diminished in vivo to ~31% of their values on D1 by D7/D8. Histology confirmed CPC retention, dispersion, and macrophage-induced infiltration. Intra-cardiac injections of PFCE-NP-labeled CPCs with FuGENE can be visualized/tracked in vivo for the first time with 19F MRI.

Chemical shift encoding (CSE) for sensitive fluorine-19 MRI of perfluorocarbons with complex spectra.

PURPOSE: To implement a fluorine-19 (19 F) chemical shift encoding (CSE) approach for the sensitive imaging of molecules with multi-resonance spectra to remove their chemical shift displacement (CSD) artifacts, and to characterize its sensitivity versus established pulse sequences. METHODS: The feasibility of CSE spoiled gradient echo (GRE) and balanced steady-state free precession (bSSFP) was first demonstrated in a phantom study. The dependence of the sensitivity of CSE-bSSFP on several pulse sequence parameters was then established, after which the occurrence of out-of-plane excitation was assessed for 2D and 3D techniques. Next, the sensitivity (in mm-3 s-0.5 ) of both CSE techniques was compared to bSSFP ultrashort echo time (bSSFP-UTE) imaging and multi-chemical-shift-selective turbo spin echo (MCSS-TSE) in a second phantom study. Finally, the sensitivity of the CSE-bSSFP, bSSFP-UTE, and MCSS-TSE pulse sequences was compared in a preliminary in vivo mouse study. RESULTS: Both CSE approaches were successfully implemented and resulted in negligible residual CSD artifacts, while large-volume 3D acquisitions should be considered to reduce problems related to out-of-plane excitation. CSE-bSSFP was shown to have a higher sensitivity than the bSSFP-UTE and MCSS-TSE pulse sequences (15.8 ± 1.3 vs. 11.7 ± 1.0 vs. 13.3 ± 0.9 mm-3 s-0.5 , respectively, P < 0.001), whereas CSE-GRE technique had a lower sensitivity (4.8 ± 1.1 mm-3 s-0.5 ). CONCLUSION: CSE 19 F MR imaging enables the unambiguous visualization of compounds with complex spectra, and provides high sensitivity both in vitro and in vivo. Magn Reson Med 79:2724-2730, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Quantification of vascular damage in acute kidney injury with fluorine magnetic resonance imaging and spectroscopy.

PURPOSE: To design a fluorine MRI/MR spectroscopy approach to quantify renal vascular damage after ischemia-reperfusion injury, and the therapeutic response to antithrombin nanoparticles (NPs) to protect kidney function. METHODS: A total of 53 rats underwent 45 min of bilateral renal artery occlusion and were treated at reperfusion with either plain perfluorocarbon NPs or NPs functionalized with a direct thrombin inhibitor (PPACK:phenyalanine-proline-arginine-chloromethylketone). Three hours after reperfusion, kidneys underwent ex vivo fluorine MRI/MR spectroscopy at 4.7 T to quantify the extent and volume of trapped NPs, as an index of vascular damage and ischemia-reperfusion injury. Microscopic evaluation of structural damage and NP trapping in non-reperfused renal segments was performed. Serum creatinine was quantified serially over 7 days. RESULTS: The damaged renal cortico-medullary junction trapped a significant volume of NPs (P = 0.04), which correlated linearly (r = 0.64) with the severity of kidney injury 3 h after reperfusion. Despite global large vessel reperfusion, non-reperfusion in medullary peritubular capillaries was confirmed by MRI and microscopy, indicative of continuing hypoxia due to vascular compromise. Treatment of animals with PPACK NPs after acute kidney injury did not accelerate kidney functional recovery. CONCLUSIONS: Quantification of ischemia-reperfusion injury after acute kidney injury with fluorine MRI/MR spectroscopy of perfluorocarbon NPs objectively depicts the extent and severity of vascular injury and its linear relationship to renal dysfunction. The lack of kidney function improvement after early posttreatment thrombin inhibition confirms the rapid onset of ischemia-reperfusion injury as a consequence of vascular damage and non-reperfusion. The prolongation of medullary ischemia renders cortico-medullary tubular structures susceptible to continued necrosis despite restoration of large vessel flow, which suggests limitations to acute interventions after acute kidney injury, designed to interdict renal tubular damage. Magn Reson Med 79:3144-3153, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Attenuated Accumulation of Novel Fluorine (19F)-Labeled Bile Acid Analogues in Gallbladders of Fibroblast Growth Factor-15 (FGF15)-Deficient Mice.

Our work has focused on defining the utility of fluorine (19F)-labeled bile acid analogues and magnetic resonance imaging (MRI) to identify altered bile acid transport in vivo. In the current study, we explored the ability of this approach to differentiate fibroblast growth factor-15 (FGF15)-deficient from wild-type (WT) mice, a potential diagnostic test for bile acid diarrhea, a commonly misdiagnosed disorder. FGF15 is the murine homologue of human FGF19, an intestinal hormone whose deficiency is an underappreciated cause of bile acid diarrhea. In a pilot and three subsequent pharmacokinetic studies, we treated mice with two 19F-labeled bile acid analogues, CA-lys-TFA and CA-sar-TFMA. After oral dosing, we quantified 19F-labeled bile acid analogue levels in the gallbladder, liver, small and large intestine, and plasma using liquid chromatography mass spectrometry (LC-MS/MS). Both 19F bile acid analogues concentrated in the gallbladders of FGF15-deficient and WT mice, attaining peak concentrations at approximately 8.5 h after oral dosing. However, analogue levels in gallbladders of FGF15-deficient mice were several-fold less compared to those in WT mice. Live-animal 19F MRI provided agreement with our LC-MS/MS-based measures; we detected robust CA-lys-TFA 19F signals in gallbladders of WT mice but no signals in FGF15-deficient mice. Our finding that 19F MRI differentiates FGF15-deficient from WT mice provides additional proof-of-concept for the development of 19F bile acid analogues and 19F MRI as a clinical test to diagnose bile acid diarrhea due to FGF19 deficiency and other disorders.

Characterization of perfluorocarbon relaxation times and their influence on the optimization of fluorine-19 MRI at 3 tesla.

PURPOSE: To characterize and optimize 19 F MRI for different perfluorocarbons (PFCs) at 3T and quantify the loss of acquisition efficiency as a function of different temperature and cellular conditions. METHODS: The T1 and T2 relaxation times of the commonly used PFCs perfluoropolyether (PFPE), perfluoro-15-crown-5-ether (PFCE), and perfluorooctyl bromide (PFOB) were measured in phantoms and in several different conditions (cell types, presence of fixation agent, and temperatures). These relaxation times were used to optimize pulse sequences through numerical simulations. The acquisition efficiency in each cellular condition was then determined as the ratio of the signal after optimization with the reference relaxation times and after optimization with its proper relaxation times. Finally, PFC detection limits were determined. RESULTS: The loss of acquisition efficiency due to parameter settings optimized for the wrong temperature and cellular condition was limited to 13%. The detection limits of all PFCs were lower at 24 °C than at 37 °C and varied from 11.8 ± 3.0 mM for PFCE at 24 °C to 379.9 ± 51.8 mM for PFOB at 37 °C. CONCLUSION: Optimizing 19 F pulse sequences with a known phantom only leads to moderate loss in acquisition efficiency in cellular conditions that might be encountered in in vivo and in vitro experiments. Magn Reson Med 77:2263-2271, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Very low field 19F MRI of perfluoro-octylbromide: Minimizing chemical shift effects and signal loss due to scalar coupling.

19F images have been obtained from perflurooctylbromide (PFOB) at very low magnetic field (50 mT). The small spectral dispersion (in Hz) means that all fluorine nuclei contribute to the signal without chemical shift artifacts or the need for specialized imaging sequences. Turbo spin echo trains with short interpulse intervals and full 180° refocussing pulses suppress scalar coupling, leading to long apparent T2 values and highly efficient data collection. Overall, the detection efficiency of PFOB is very similar that of water in tissue.

Biomedical 19F MRI Using Perfluorocarbons.

Background-free fluorine (19F) MR imaging exhibits an excellent degree of specificity, and facilitates among others the in vivo visualization of inflammatory processes. Merging19F MR images with morphologically matching1H MR images enables the exact anatomic localization of the observed19F signal. Biochemically inert nanoemulsions of perfluorocarbons, which are known to be taken up by the macrophage/monocyte system, are widely used as contrast agents for preclinical applications. Herein, the most common protocols are described to obtain high-resolution and artifact-free19F MR images even for compounds with complex19F MR spectra. In addition, we report on the utilization of perfluorocarbons with individual spectral identities and targeting approaches to specifically visualize thrombi by19F MRI.

Anti-angiogenic Nanotherapy Inhibits Airway Remodeling and Hyper-responsiveness of Dust Mite Triggered Asthma in the Brown Norway Rat.

Although angiogenesis is a hallmark feature of asthmatic inflammatory responses, therapeutic anti-angiogenesis interventions have received little attention. Objective: Assess the effectiveness of anti-angiogenic Sn2 lipase-labile prodrugs delivered via αvß3-micellar nanotherapy to suppress microvascular expansion, bronchial remodeling, and airway hyper-responsiveness in Brown Norway rats exposed to serial house dust mite (HDM) inhalation challenges. Results: Anti-neovascular effectiveness of αvß3-mixed micelles incorporating docetaxel-prodrug (Dxtl-PD) or fumagillin-prodrug (Fum-PD) were shown to robustly suppress neovascular expansion (p<0.01) in the upper airways/bronchi of HDM rats using simultaneous 19F/1H MR neovascular imaging, which was corroborated by adjunctive fluorescent microscopy. Micelles without a drug payload (αvß3-No-Drug) served as a carrier-only control. Morphometric measurements of HDM rat airway size (perimeter) and vessel number at 21d revealed classic vascular expansion in control rats but less vascularity (p<0.001) after the anti-angiogenic nanotherapies. CD31 RNA expression independently corroborated the decrease in airway microvasculature. Methacholine (MCh) induced respiratory system resistance (Rrs) was high in the HDM rats receiving αvß3-No-Drug micelles while αvß3-Dxtl-PD or αvß3-Fum-PD micelles markedly and equivalently attenuated airway hyper-responsiveness and improved airway compliance. Total inflammatory BAL cells among HDM challenged rats did not differ with treatment, but αvß3+ macrophages/monocytes were significantly reduced by both nanotherapies (p<0.001), most notably by the αvß3-Dxtl-PD micelles. Additionally, αvß3-Dxtl-PD decreased BAL eosinophil and αvß3+ CD45+ leukocytes relative to αvß3-No-Drug micelles, whereas αvß3-Fum-PD micelles did not. Conclusion: These results demonstrate the potential of targeted anti-angiogenesis nanotherapy to ameliorate the inflammatory hallmarks of asthma in a clinically relevant rodent model.

In vivo MR detection of fluorine-labeled human MSC using the bSSFP sequence.

Mesenchymal stem cells (MSC) are used to restore deteriorated cell environments. There is a need to specifically track these cells following transplantation in order to evaluate different methods of implantation, to follow their migration within the body, and to quantify their accumulation at the target. Cellular magnetic resonance imaging (MRI) using fluorine-based nanoemulsions is a great means to detect these transplanted cells in vivo because of the high specificity for fluorine detection and the capability for precise quantification. This technique, however, has low sensitivity, necessitating improvement in MR sequences. To counteract this issue, the balanced steady-state free precession (bSSFP) imaging sequence can be of great interest due to the high signal-to-noise ratio (SNR). Furthermore, it can be applied to obtain 3D images within short acquisition times. In this paper, bSSFP provided accurate quantification of samples of the perfluorocarbon Cell Sense-labeled cells in vitro. Cell Sense was internalized by human MSC (hMSC) without adverse alterations in cell viability or differentiation into adipocytes/osteocytes. The bSSFP sequence was applied in vivo to track and quantify the signals from both Cell Sense-labeled and iron-labeled hMSC after intramuscular implantation. The fluorine signal was observed to decrease faster and more significantly than the volume of iron-associated voids, which points to the advantage of quantifying the fluorine signal and the complexity of quantifying signal loss due to iron.

Design and evaluation of a novel trifluorinated imaging agent for assessment of bile acid transport using fluorine magnetic resonance imaging.

Previously, we developed a trifluorinated bile acid, CA-lys-TFA, with the objective of noninvasively assessing bile acid transport in vivo using (19) F magnetic resonance imaging (MRI). CA-lys-TFA was successfully imaged in the mouse gallbladder, but was susceptible to deconjugation in vitro by choloylglycine hydrolase (CGH), a bacterial bile acid deconjugating enzyme found in the terminal ileum and colon. The objective of the present study was to develop a novel trifluorinated bile acid resistant to deconjugation by CGH. CA-sar-TFMA was designed, synthesized, and tested for in vitro transport properties, stability, imaging properties, and its ability to differentially accumulate in the gallbladders of normal mice, compared with mice with known impaired bile acid transport (deficient in the apical sodium-dependent bile acid transporter, ASBT). CA-sar-TFMA was a potent inhibitor and substrate of ASBT and the Na(+) /taurocholate cotransporting polypeptide. Stability was favorable in all conditions tested, including the presence of CGH. CA-sar-TFMA was successfully imaged and accumulated at 16.1-fold higher concentrations in gallbladders from wild-type mice compared with those from Asbt-deficient mice. Our results support the potential of using MRI with CA-sar-TFMA as a noninvasive method to assess bile acid transport in vivo.