Towards Real-time Metabolic Profiling of Cancer with Hyperpolarized Succinate.

PURPOSE: The energy-yielding mitochondrial Krebs cycle has been shown in many cancers and other diseases to be inhibited or mutated. In most cells, the Krebs cycle with oxidative phosphorylation generates approximately 90% of the adenosine triphosphate in the cell. We designed and hyperpolarized carbon-13 labeled succinate (SUC) and its derivative diethyl succinate (DES) to interrogate the Krebs cycle in real-time in cancer animal models. PROCEDURES: Using Parahydrogen Induced Polarization (PHIP), we generated hyperpolarized SUC and DES by hydrogenating their respective fumarate precursors. DES and SUC metabolism was studied in five cancer allograft animal models: breast (4T1), Renal Cell Carcinoma (RENCA), colon (CT26), lymphoma NSO, and lymphoma A20. RESULTS: The extent of hyperpolarization was 8 ± 2% for SUC and 2.1 ± 0.6% for DES. The metabolism of DES and SUC in the Krebs cycle could be followed in animals 5 s after tail vein injection. The biodistribution of the compounds was observed using 13C FISP imaging. We observed significant differences in uptake and conversion of both compounds in different cell types both in vivo and in vitro. CONCLUSION: With hyperpolarized DES and SUC, we are able to meet many of the requirements for a useable in vivo metabolic imaging compound - high polarization, relatively long T1 values, low toxicity and high water solubility. However, succinate and its derivative DES are metabolized robustly by RENCA but not by the other cancer models. Our results underscore the heterogeneity of cancer cells and the role cellular uptake plays in hyperpolarized metabolic spectroscopy.

Tibiofemoral and patellofemoral mechanics are altered at small knee flexion angles in people with patellofemoral pain.

OBJECTIVES: To test the hypothesis that, at 0° and 20° of knee flexion, patellofemoral contact area would be lower, while tibiofemoral rotation and patellofemoral malalignment would be higher in participants with patellofemoral pain (PFP) compared to pain-free participants. We hypothesized that no differences would be detected at 40° due to increasing patellar stability. DESIGN: Cross-sectional, descriptive study. METHODS: Twenty-seven people with PFP and 29 pain-free people participated. Participants underwent magnetic resonance imaging at 0°, 20°, and 40° knee flexion with the limb in a simulated weight-bearing position. Patellofemoral contact area, tibiofemoral rotation angle, patellofemoral alignment (bisect offset index and patellar tilt angle) were quantified and compared between groups at each angle using Student's t-tests. An a-posteriori comparison was made between the pain-free group and a subgroup of 15 participants with patellofemoral pain who demonstrated a faulty lower limb movement pattern ("medial collapse"). RESULTS: In the patellofemoral pain group, contact area was lower at 0° (203.8±45.5 mm² vs. 224.1±46.6 mm², p=0.05) and 20° (276.8±56.2 mm² vs. 316.7±82.8 mm², p=0.02), bisect offset index (BOS) and patellar tilt angle (PTA) were higher at 0° (bisect offset index: 0.69±0.13 vs. 0.64±0.09, p=0.04; patellar tilt angle: 12.5±7.6° vs. 9.2±5.8°, p=0.04). In the patellofemoral pain subgroup, tibiofemoral rotation was higher at 0° compared to pain-free participants (6.4±5.9° vs. 4.0±4.6°, p=0.07). CONCLUSIONS: While contact area and patellofemoral alignment were altered in people with patellofemoral pain, tibiofemoral rotation was altered in a subgroup of people who demonstrated medial collapse. Subgroup classification may help identify mechanisms of pain and assist in developing targeted interventions.

Fast volumetric spatial-spectral MR imaging of hyperpolarized 13C-labeled compounds using multiple echo 3D bSSFP.

PURPOSE: The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized (13)C-labeled substrates and metabolic products at low concentration. MATERIALS AND METHODS: Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-(13)C]2-hydroxyethylpropionate (HEP) adjacent to a (13)C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set. RESULTS: ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s. CONCLUSION: Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized (13)C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized (13)C-labeled metabolites at lower concentrations as compared to a 2D technique.

Review of magnetic resonance spectroscopy in the liver and the pancreas.

Proton magnetic resonance spectroscopy is a powerful tool for in vivo biochemical characterization of normal and abnormal tissues. The initial application in the abdomen was the measurement of fat concentration in the liver using chemical shift imaging. The success of chemical shift imaging in providing a semiquantitative measure of liver fat concentration led to the application of the more quantitative single-voxel volume-selective spectroscopy of the liver. This single-voxel volume-selective spectroscopic technique is able to characterize the different lipids and metabolites present in the liver and the pancreas, providing information about the ratio of unsaturated and saturated lipids. The purposes of this article were to review the spectroscopic techniques and to discuss some of the clinical applications of these techniques in the abdomen.

Magnetic resonance measurement of diffusion in the abdomen.

Diffusion-weighted (DW) magnetic resonance imaging is an emerging noninvasive technique increasing its spectrum of use in the abdomen. Diffusion-weighted imaging has been used as add-on to routine abdominal protocol because it may potentially substitute contrast-enhanced imaging in cases under risk of nephrogenic systemic fibrosis. The apparent diffusion coefficient (ADC) images calculated from DW images enable qualitative and quantitative evaluations of tissue water mobility and functional environment because of changes in intracellular, extracellular, and intravascular tissue compartments. This article presents the basic physics of the ADC measurement, the techniques for performing ADC measurements of the liver and the pancreas, and the clinical applications of DW imaging.

Diffusion-weighted magnetic resonance imaging of the pancreas.

Diffusion-weighted imaging (DWI) assesses the random motion of the water protons. The technique is more frequently used in body imaging, and recent investigations showed its use in pancreatic imaging. Diffusion-weighted imaging can be helpful as a complementary imaging method in the differentiation between mass-forming focal pancreatitis and pancreatic adenocarcinoma. The apparent diffusion coefficient (ADC) values derived from DWI can distinguish between simple pancreatic cyst, inflammatory cysts, and cystic neoplasms of the pancreas. Presence of parenchymal fibrosis in chronic pancreatitis causes diffusion restriction and results in lower ADC values on baseline DWI. The ADC values reveal either delayed peak after secretin stimulation or lower peak values in patients with early chronic pancreatitis, which may be helpful to depict chronic pancreatitis in its earliest stage. In this paper, we reviewed the technical aspects of DWI and its use in pancreatic imaging.

Pancreatic diffusion-weighted imaging (DWI): comparison between mass-forming focal pancreatitis (FP), pancreatic cancer (PC), and normal pancreas.

PURPOSE: To compare diffusion-weighted imaging (DWI) findings and the apparent diffusion coefficient (ADC) values of pancreatic cancer (PC), mass-forming focal pancreatitis (FP), and the normal pancreas. MATERIALS AND METHODS: DWI (b = 0 and 600 seconds/mm(2)) findings of 14 patients with mass-forming FP proven by histopathology and or clinical follow-up, 10 patients with histopathologically-proven PC, and 14 subjects with normal pancreatic exocrine function and normal imaging findings were retrospectively evaluated. ADC values of the masses, the remaining pancreas, and the normal pancreas were measured. RESULTS: On b = 600 seconds/mm(2) DWI, mass-forming FP was visually indistinguishable from the remaining pancreas whereas PC was hyperintense relative to the remaining pancreas. The mean ADC value of PC (1.46 +/- 0.18 mm(2)/second) was significantly lower than the remaining pancreas (2.11 +/- 0.32 x 10(-3) mm(2)/second; P < 0.0001), mass-forming FP (2.09 +/- 0.18 x 10(-3) mm(2)/second; P < 0.0001), and pancreatic gland in the control group (1.78 +/- 0.07 x 10(-3) mm(2)/second; P < 0.0005). There was no significant difference of ADC values between the mass-forming focal pancreatitis and the remaining pancreas (2.03 +/- 0.2 x 10(-3) mm(2)/second; P > 0.05). CONCLUSION: Differences on DWI may help to differentiate PC, mass-forming FP, and normal pancreas from each other.

PASADENA hyperpolarization of 13C biomolecules: equipment design and installation.

OBJECT: The PASADENA method has achieved hyperpolarization of 16-20% (exceeding 40,000-fold signal enhancement at 4.7 T), in liquid samples of biological molecules relevant to in vivo MRI and MRS. However, there exists no commercial apparatus to perform this experiment conveniently and reproducibly on the routine basis necessary for translation of PASADENA to questions of biomedical importance. The present paper describes equipment designed for rapid production of six to eight liquid samples per hour with high reproducibility of hyperpolarization. MATERIALS AND METHODS: Drawing on an earlier, but unpublished, prototype, we provide diagrams of a delivery circuit, a laminar-flow reaction chamber within a low field NMR contained in a compact, movable housing. Assembly instructions are provided from which a computer driven, semi-automated PASADENA polarizer can be constructed. RESULTS: Together with an available parahydrogen generator, the polarizer, which can be operated by a single investigator, completes one cycle of hyperpolarization each 52 s. Evidence of efficacy is presented. In contrast to competing, commercially available devices for dynamic nuclear polarization which characteristically require 90 min per cycle, PASADENA provides a low-cost alternative for high throughput. CONCLUSIONS: This equipment is suited to investigators who have an established small animal NMR and wish to explore the potential of heteronuclear ((13)C and (15)N) MRI, MRS, which harnesses the enormous sensitivity gain offered by hyperpolarization.

Quality assurance of PASADENA hyperpolarization for 13C biomolecules.

OBJECT: Define MR quality assurance procedures for maximal PASADENA hyperpolarization of a biological (13)C molecular imaging reagent. MATERIALS AND METHODS: An automated PASADENA polarizer and a parahydrogen generator were installed. (13)C enriched hydroxyethyl acrylate, 1-(13)C, 2,3,3-d(3) (HEA), was converted to hyperpolarized hydroxyethyl propionate, 1-(13)C, 2,3,3-d(3) (HEP) and fumaric acid, 1-(13)C, 2,3-d(2) (FUM) to hyperpolarized succinic acid, 1-(13)C, 2,3-d(2) (SUC), by reaction with parahydrogen and norbornadiene rhodium catalyst. Incremental optimization of successive steps in PASADENA was implemented. MR spectra and in vivo images of hyperpolarized (13)C imaging agents were acquired at 1.5 and 4.7 T. RESULTS: Application of quality assurance (QA) criteria resulted in incremental optimization of the individual steps in PASADENA implementation. Optimal hyperpolarization of HEP of P = 20% was achieved by calibration of the NMR unit of the polarizer (B (0) field strength +/- 0.002 mT). Mean hyperpolarization of SUC, P = [15.3 +/- 1.9]% (N = 16) in D (2)O, and P = [12.8 +/- 3.1]% (N = 12) in H (2)O, was achieved every 5-8 min (range 13-20%). An in vivo (13)C succinate image of a rat was produced. CONCLUSION: PASADENA spin hyperpolarization of SUC to 15.3% in average was demonstrated (37,400 fold signal enhancement at 4.7 T). The biological fate of (13)C succinate, a normally occurring cellular intermediate, might be monitored with enhanced sensitivity.

Patellofemoral joint contact area is influenced by tibiofemoral rotation alignment in individuals who have patellofemoral pain.

STUDY DESIGN: Observational, cohort study. OBJECTIVES: To test the hypothesis that patellar alignment and tibiofemoral rotation alignment explain unique portions of variance in patellofemoral joint contact area in individuals with patellofemoral pain (PFP) and in pain-free control subjects. BACKGROUND: PFP has been proposed to result from increased patellofemoral joint stress due to decreased contact area. Patellar malalignment (lateral displacement and tilt) is believed to be the main contributor to decreased contact area. Recent studies suggest that transverse plane rotation of the femur and/or tibia may also contribute to decreased contact area. METHODS AND MEASURES: Twenty-one subjects with PFP (16 female, 5 male) and 21 pain-free subjects (14 female, 7 male) participated. Subjects underwent magnetic resonance imaging with the knee in full extension and the quadriceps contracted. Measures of patellofemoral joint contact area, lateral patellar displacement, patellar tilt angle, tibiofemoral rotation angle, and patellar width were obtained. Hierarchical multiple regression analyses were performed for each group using contact area as the dependent variable. The order of independent variables was patellar width, patellar tilt angle, and tibiofemoral rotation angle. To avoid multicolinearity, lateral patellar displacement was not included. RESULTS: In the PFP group, patellar width and tibiofemoral rotation angle explained 46% of the variance in contact area. In pain-free subjects, patellar width was the only predictor of contact area, explaining 31% of its variance. Patellar tilt angle did not predict contact area in either group. CONCLUSION: Addressing factors that control tibiofemoral rotation may be indicated to increase contact area and reduce pain in individuals with PFP. Future studies should investigate the contributions of patellar alignment and tibiofemoral rotation to patellofemoral joint contact area at a variety of knee flexion angles.

Towards hyperpolarized (13)C-succinate imaging of brain cancer.

We describe a novel (13)C enriched precursor molecule, sodium 1-(13)C acetylenedicarboxylate, which after hydrogenation by PASADENA (Parahydrogen and Synthesis Allows Dramatically Enhanced Nuclear Alignment) under controlled experimental conditions, becomes hyperpolarized (13)C sodium succinate. Fast in vivo 3D FIESTA MR imaging demonstrated that, following carotid arterial injection, the hyperpolarized (13)C-succinate appeared in the head and cerebral circulation of normal and tumor-bearing rats. At this time, no in vivo hyperpolarized signal has been localized to normal brain or brain tumor. On the other hand, ex vivo samples of brain harvested from rats bearing a 9L brain tumor, 1 h or more following in vivo carotid injection of hyperpolarized (13)C sodium succinate, contained significant concentrations of the injected substrate, (13)C sodium succinate, together with (13)C maleate and succinate metabolites 1-(13)C-glutamate, 5-(13)C-glutamate, 1-(13)C-glutamine and 5-(13)C-glutamine. The (13)C substrates and products were below the limits of NMR detection in ex vivo samples of normal brain consistent with an intact blood-brain barrier. These ex vivo results indicate that hyperpolarized (13)C sodium succinate may become a useful tool for rapid in vivo identification of brain tumors, providing novel biomarkers in (13)C MR spectral-spatial images.

Identification of regenerative tissue cables using in vivo MRI after spinal cord hemisection and schwann cell bridging transplantation.

The purpose of this study was to examine the feasibility of a non-invasive in vivo magnetic resonance imaging (MRI) procedure, performed at 1.5 T, to detect regenerative tissue cables in a rat spinal cord hemisection and Schwann cell (SC) bridging transplantation paradigm. Two months after implantation of a SC-seeded guidance channel (1.25 mm in diameter and 3.0 mm in length) into a T8 spinal cord hemisection-gap lesion, axial fast-spin echo (FSE) T2-weighted MR imaging (T2WI) was performed. Axial T2WI through the graft identified a circular area of low intensity surrounded by high-intensity signal within the guidance channel lumen. Correlative histological assessments of Toluidine blue-stained sections confirmed that the low-intensity signal represented a tissue cable, which, in most cases, contained a substantial number of myelinated axons oriented along the rostro-caudal axis of the spinal cord. The percentage of guidance channel cross-sectional area occupied by the tissue cable, expressed as the tissue cable index (TCI), was also determined from histological sections. Linear regression analysis of the TCI plotted relative to the number of myelinated axons revealed a strong positive correlation (r(2) = 0.85) between these two outcome measures. In addition, the sensitivity of MRI to detect regenerative tissue cables within guidance channels was 86%. These results demonstrate that (1). 1.5 T MR imaging performed 2 months after spinal cord hemisection and SC bridging transplantation is sensitive in detecting low-intensity regenerative tissue cables, and (2). the TCI strongly correlates with the extent of axonal regeneration into implanted SC-seeded guidance channels.