Parahydrogen-Polarized [1-13 C]Pyruvate for Reliable and Fast Preclinical Metabolic Magnetic Resonance Imaging.

Hyperpolarization techniques increase nuclear spin polarization by more than four orders of magnitude, enabling metabolic MRI. Even though hyperpolarization has shown clear value in clinical studies, the complexity, cost and slowness of current equipment limits its widespread use. Here, a polarization procedure of [1-13 C]pyruvate based on parahydrogen-induced polarization by side-arm hydrogenation (PHIP-SAH) in an automated polarizer is demonstrated. It is benchmarked in a study with 48 animals against a commercial dissolution dynamic nuclear polarization (d-DNP) device. Purified, concentrated (≈70-160 mM) and highly hyperpolarized (≈18%) solutions of pyruvate are obtained at physiological pH for volumes up to 2 mL within 85 s in an automated process. The safety profile, image quality, as well as the quantitative perfusion and lactate-to-pyruvate ratios, are equivalent for PHIP and d-DNP, rendering PHIP a viable alternative to established hyperpolarization techniques.

Metabolic Tumor Imaging with Rapidly Signal-Enhanced 1-13 C-Pyruvate-d3.

The metabolism of malignant cells differs significantly from that of healthy cells and thus, it is possible to perform metabolic imaging to reveal not only the exact location of a tumor, but also intratumoral areas of high metabolic activity. Herein, we demonstrate the feasibility of metabolic tumor imaging using signal-enhanced 1-13 C-pyruvate-d3 , which is rapidly enhanced via para-hydrogen, and thus, the signal is amplified by several orders of magnitudes in less than a minute. Using as a model, human melanoma xenografts injected with signal-enhanced 1-13 C-pyruvate-d3, we show that the conversion of pyruvate into lactate can be monitored along with its kinetics, which could pave the way for rapidly detecting and monitoring changes in tumor metabolism.

A reproducible dynamic phantom for sequence testing in hyperpolarised 13C-magnetic resonance.

OBJECTIVE: To develop a phantom system which can be integrated with an automated injection system, eliminating the experimental variability that arises with manual injection; for the purposes of pulse sequence testing and metric derivation in hyperpolarised 13C-MR. METHODS: The custom dynamic phantom was machined from Ultem and filled with a nicotinamide adenine dinucleotide and lactate dehydrogenase mixture dissolved in phosphate buffered saline. Hyperpolarised [1-13C]-pyruvate was then injected into the phantom (n = 8) via an automated syringe pump and the conversion of pyruvate to lactate monitored through a 13C imaging sequence. RESULTS: The phantom showed low coefficient of variation for the lactate to pyruvate peak signal heights (11.6%) and dynamic area-under curve ratios (11.0%). The variance for the lactate dehydrogenase enzyme rate constant (kP) was also seen to be low at 15.6%. CONCLUSION: The dynamic phantom demonstrates high reproducibility for quantification of 13C-hyperpolarised MR-derived metrics. Establishing such a phantom is needed to facilitate development of hyperpolarsed 13C-MR pulse sequenced; and moreover, to enable multisite hyperpolarised 13C-MR clinical trials where assessment of metric variability across sites is critical. ADVANCES IN KNOWLEDGE: The dynamic phantom developed during the course of this study will be a useful tool in testing new pulse sequences and standardisation in future hyperpolarised work.

Quasi-continuous production of highly hyperpolarized carbon-13 contrast agents every 15 seconds within an MRI system.

Hyperpolarized contrast agents (HyCAs) have enabled unprecedented magnetic resonance imaging (MRI) of metabolism and pH in vivo. Producing HyCAs with currently available methods, however, is typically time and cost intensive. Here, we show virtually-continuous production of HyCAs using parahydrogen-induced polarization (PHIP), without stand-alone polarizer, but using a system integrated in an MRI instead. Polarization of ≈2% for [1-13C]succinate-d2 or ≈19% for hydroxyethyl-[1-13C]propionate-d3 was created every 15 s, for which fast, effective, and well-synchronized cycling of chemicals and reactions in conjunction with efficient spin-order transfer was key. We addressed these challenges using a dedicated, high-pressure, high-temperature reactor with integrated water-based heating and a setup operated via the MRI pulse program. As PHIP of several biologically relevant HyCAs has recently been described, this Rapid-PHIP technique promises fast preclinical studies, repeated administration or continuous infusion within a single lifetime of the agent, as well as a prolonged window for observation with signal averaging and dynamic monitoring of metabolic alterations.

Inherited salt-losing tubulopathies are associated with immunodeficiency due to impaired IL-17 responses.

Increased extracellular sodium activates Th17 cells, which provide protection from bacterial and fungal infections. Whilst high salt diets have been shown to worsen autoimmune disease, the immunological consequences of clinical salt depletion are unknown. Here, we investigate immunity in patients with inherited salt-losing tubulopathies (SLT). Forty-seven genotyped SLT patients (with Bartter, Gitelman or EAST Syndromes) are recruited. Clinical features of dysregulated immunity are recorded with a standardised questionnaire and immunological investigations of IL-17 responsiveness undertaken. The effects of altering extracellular ionic concentrations on immune responses are then assessed. Patients are hypokalaemic and hypomagnesaemic, with reduced interstitial sodium stores determined by 23Na-magnetic resonance imaging. SLT patients report increased mucosal infections and allergic disease compared to age-matched controls. Aligned with their clinical phenotype, SLT patients have an increased ratio of Th2:Th17 cells. SLT Th17 and Tc17 polarisation is reduced in vitro, yet STAT1 and STAT3 phosphorylation and calcium flux following T cell activation are unaffected. In control cells, the addition of extracellular sodium (+40 mM), potassium (+2 mM), or magnesium (+1 mM) reduces Th2:Th17 ratio and augments Th17 polarisation. Our results thus show that the ionic environment typical in SLT impairs IL-17 immunity, but the intracellular pathways that mediate salt-driven Th17 polarisation are intact and in vitro IL-17 responses can be reinvigorated by increasing extracellular sodium concentration. Whether better correction of extracellular ions can rescue the immunophenotype in vivo in SLT patients remains unknown.

Dynamic 2D and 3D mapping of hyperpolarized pyruvate to lactate conversion in vivo with efficient multi-echo balanced steady-state free precession at 3 T.

The aim of this study was to acquire the transient MRI signal of hyperpolarized tracers and their metabolites efficiently, for which specialized imaging sequences are required. In this work, a multi-echo balanced steady-state free precession (me-bSSFP) sequence with Iterative Decomposition with Echo Asymmetry and Least squares estimation (IDEAL) reconstruction was implemented on a clinical 3 T positron-emission tomography/MRI system for fast 2D and 3D metabolic imaging. Simulations were conducted to obtain signal-efficient sequence protocols for the metabolic imaging of hyperpolarized biomolecules. The sequence was applied in vitro and in vivo for probing the enzymatic exchange of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate. Chemical shift resolution was achieved using a least-square, iterative chemical species separation algorithm in the reconstruction. In vitro, metabolic conversion rate measurements from me-bSSFP were compared with NMR spectroscopy and free induction decay-chemical shift imaging (FID-CSI). In vivo, a rat MAT-B-III tumor model was imaged with me-bSSFP and FID-CSI. 2D metabolite maps of [1-13 C]pyruvate and [1-13 C]lactate acquired with me-bSSFP showed the same spatial distributions as FID-CSI. The pyruvate-lactate conversion kinetics measured with me-bSSFP and NMR corresponded well. Dynamic 2D metabolite mapping with me-bSSFP enabled the acquisition of up to 420 time frames (scan time: 180-350 ms/frame) before the hyperpolarized [1-13 C]pyruvate was relaxed below noise level. 3D metabolite mapping with a large field of view (180 × 180 × 48 mm3 ) and high spatial resolution (5.6 × 5.6 × 2 mm3 ) was conducted with me-bSSFP in a scan time of 8.2 seconds. It was concluded that Me-bSSFP improves the spatial and temporal resolution for metabolic imaging of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate compared with either of the FID-CSI or EPSI methods reported at 3 T, providing new possibilities for clinical and preclinical applications.

Simultaneous characterization of tumor cellularity and the Warburg effect with PET, MRI and hyperpolarized 13C-MRSI.

Modern oncology aims at patient-specific therapy approaches, which triggered the development of biomedical imaging techniques to synergistically address tumor biology at the cellular and molecular level. PET/MR is a new hybrid modality that allows acquisition of high-resolution anatomic images and quantification of functional and metabolic information at the same time. Key steps of the Warburg effect-one of the hallmarks of tumors-can be measured non-invasively with this emerging technique. The aim of this study was to quantify and compare simultaneously imaged augmented glucose uptake and LDH activity in a subcutaneous breast cancer model in rats (MAT-B-III) and to study the effect of varying tumor cellularity on image-derived metabolic information. Methods: For this purpose, we established and validated a multimodal imaging workflow for a clinical PET/MR system including proton magnetic resonance (MR) imaging to acquire accurate morphologic information and diffusion-weighted imaging (DWI) to address tumor cellularity. Metabolic data were measured with dynamic [18F]FDG-PET and hyperpolarized (HP) 13C-pyruvate MR spectroscopic imaging (MRSI). We applied our workflow in a longitudinal study and analyzed the effect of growth dependent variations of cellular density on glycolytic parameters. Results: Tumors of similar cellularity with similar apparent diffusion coefficients (ADC) showed a significant positive correlation of FDG uptake and pyruvate-to-lactate exchange. Longitudinal DWI data indicated a decreasing tumor cellularity with tumor growth, while ADCs exhibited a significant inverse correlation with PET standard uptake values (SUV). Similar but not significant trends were observed with HP-13C-MRSI, but we found that partial volume effects and point spread function artifacts are major confounders for the quantification of 13C-data when the spatial resolution is limited and major blood vessels are close to the tumor. Nevertheless, analysis of longitudinal data with varying tumor cellularity further detected a positive correlation between quantitative PET and 13C-data. Conclusions: Our workflow allows the quantification of simultaneously acquired PET, MRSI and DWI data in rodents on a clinical PET/MR scanner. The correlations and findings suggest that a major portion of consumed glucose is metabolized by aerobic glycolysis in the investigated tumor model. Furthermore, we conclude that variations in cell density affect PET and 13C-data in a similar manner and correlations of longitudinal metabolic data appear to reflect both biochemical processes and tumor cellularity.

Incidence and management of biliary pancreatitis in cholecystectomized patients. Results of a 7-year study.

Data are lacking concerning the frequency of biliary acute pancreatitis in the postcholecystectomy patient. The aim of this study was to identify patients at risk for biliary pancreatitis after cholecystectomy and to describe the therapeutic management of these patients, based on an analysis of 278 unselected patients with acute pancreatitis during a 7-year period. A biliary etiology was presumed in the presence of laboratory findings of cholestasis that could not be explained by another disease, together with the absence of any other known etiology of acute pancreatitis. A biliary cause of disease was found in 132 (47%) of 278 patients. Seventeen (13%) of 132 patients had a history of cholecystectomy. Endoscopic retrograde cholangiopancreatography was performed in all patients with a suspected biliary cause of acute pancreatitis. It showed bile duct stones, microlithiasis, or sludge in 14 patients, and was consistent with typical findings at the papilla of Vater after stone passage in another three patients. No surgical bile duct exploration was necessary. One patient with severe disease and infected pancreatic necrosis died of septic multiorgan failure.

Surgical management of severe pancreatitis including sterile necrosis.

BACKGROUND/PURPOSE: Severe pancreatitis develops in 15% to 20% of patients with acute pancreatitis, morphologically characterized by extra- and intrapancreatic necrosis and associated with single or multiple organ failure. It is well accepted that surgery is indicated in patients with infected pancreatic necrosis. However, management of sterile necrosis is still controversial. In a prospective study, we evaluated the effect of maximal intensive care unit (ICU) treatment combined with prophylactic antibiotics in patients with necrotizing pancreatitis. METHODS: A total of 306 consecutive patients with acute pancreatitis were hospitalized between November 1993 and August 2001. All patients with necrotizing pancreatitis diagnosed by computed tomography received ICU treatment, including antibiotics (imipenem/cilastin). Fine-needle aspiration of pancreatic necrosis was performed in patients with clinical signs of sepsis, and necrosectomy combined with continuous postoperative lavage was indicated when bacterial testing demonstrated infection. In the presence of sterile necrosis, surgery was only performed when there was no clinical improvement despite maximal ICU treatment. RESULTS: Necrotizing pancreatitis was found in 121 patients. Infected necrosis was verified in 41 patients (34%) at a mean of 26 days. Four percent of patients with sterile necrosis and 95% of patients with infected necrosis were operated on. The surgical procedure was successful in 83% of patients as a single intervention; relaparotomy had to be performed in only 7 patients (17%). Pancreatic abscesses were found in 7 patients; four of these were drained interventionally. The overall mortality of the patients with necrotizing pancreatitis was 9.9%. The mortality of patients with sterile and infected necrosis was 2.5% and 24%, respectively (sterile vs infected; P < 0.01). CONCLUSIONS: Due to improved intensive care treatment, including prophylactic antibiotics, surgical intervention is usually not indicated in the early course of severe acute pancreatitis. Surgery is clearly indicated in patients with proven infected necrosis. Patients with sterile necrosis should undergo surgery when there is no clinical improvement within 4 weeks of intensive care treatment. In the majority of patients a single intervention is sufficient. Reinterventions are rare and even in patients with abscess formation are not needed, because these can easily be drained interventionally.