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Purpose MRI can be utilized for quantitative characterization of tissue. To assess e.g. water fractions or diffusion coefficients for compartments in the brain, a decomposition of the signal is necessary. Imposing standard models carries the risk of estimating biased parameters if model assumptions are violated. This work introduces a data-driven multicomponent analysis, the monotonous slope non-negative matrix factorization (msNMF), tailored to extract data features expected in MR signals. Methods The msNMF was implemented by extending the standard NMF with monotonicity constraints on the signal profiles and their first derivatives. The method was validated using simulated data, and subsequently applied to both ex vivo DWI data and in vivo relaxometry data. Reproducibility of the method was tested using the latter. Results The msNMF recovered the multi-exponential signals in the simulated data and showed superiority to standard NMF (based on the explained variance, area under the ROC curve, and coefficient of variation). Diffusion components extracted from the DWI data reflected the cell density of the underlying tissue. The relaxometry analysis resulted in estimates of edema water fractions (EWF) highly correlated with published results, and demonstrated acceptable reproducibility. Conclusion The msNMF can robustly separate MR signals into components with relation to the underlying tissue composition, and may potentially be useful for e.g. tumor tissue characterization.

13C Magnetic Resonance Spectroscopy (MRS) using hyperpolarized 13C-labeled pyruvate as a substrate offers a measure of pyruvate-lactate interconversion and is thereby a marker of the elevated aerobic glycolysis (Warburg effect) generally exhibited by cancer cells. Here, we aim to compare hyperpolarized [1-13C]pyruvate MRS with simultaneous 18F-2-fluoro-2-deoxy-D-glucose (FDG) PET in a cross-sectional study of canine cancer patients. Methods: Canine cancer patients underwent integrated PET/MRI using a clinical whole-body system. Hyperpolarized [1-13C]pyruvate was obtained using dissolution-DNP. 18F-FDG PET, dynamic 13C MRS, 13C MRS Imaging (MRSI) and anatomical 1 H MRI was acquired from 17 patients. Apparent pyruvate-to-lactate rate constants were estimated from dynamic 13C MRS. 18F-FDG Standard Uptake Values and maximum [1-13C]lactate-to-total-13C ratios were obtained from tumor regions of interest. Following inspection of data, patients were grouped according to main cancer type and linear regression between measures of lactate generation and 18FFDG uptake were tested within groups. Between groups, the same measures were tested for group differences. Results: The main cancer types of the 17 patients were sarcoma (n = 11), carcinoma (n = 5) and mastocytoma (n = 1). Significant correlations between pyruvate-to-lactate rate constants and 18F-FDG uptake were found for sarcoma patients, whereas no significant correlations appeared for carcinoma patients. The sarcoma patients showed a non-significant trend towards lower 18F-FDG uptake and higher lactate generation than carcinoma patients. However, the ratio of lactate generation to 18F-FDG uptake was found to be significantly higher in sarcoma as compared to carcinoma. The results were found both when lactate generation was estimated as an apparent pyruvate-to-lactate rate constant from dynamic 13C MRS and as an [1-13C]lactate to total 13C ratio from 13C MRSI. Conclusions: A comparison of hyperpolarized [1-13C]pyruvate MRS with simultaneous 18F-FDG PET indicate that lactate generation and 18F-FDG uptake in cancers can be related and that their relation depend on cancer type. This finding could be important for the interpretation and eventual clinical implementation of hyperpolarized 13C. In addition, the differences between the two modalities may allow for better metabolic phenotyping performing hybrid imaging in the form of hyperPET

AIM: Hyperpolarized 13C-pyruvate magnetic resonance spectroscopic imaging (MRSI) is a real-time metabolic imaging technique, which can be combined with positron emission tomography (PET). In this pilot study, we explore the potential of combined hyperpolarized 13C-MRSI and FDG-PET for imaging of infection. METHODS: Three pigs were inoculated with S. aureusbacteria in the right tibia and saline in the left tibial bone. FDG-PET, 1H-MRI and 13C-MRSI was performed using a clinical whole-body PET/MR system (Siemens Biograph mMR, Erlangen, Germany). Hyperpolarized13C-pyruvate was prepared using a SpinLab System (GE Healthcare, Pittsburgh, PA, USA). 13C-lactate to 13C-pyruvate ratio and FDG SUV was reported in anatomical regions of interest covering bone and regions of inflammation and abscess defined on 1H-MRI. Histopathological examination was performed of both legs. RESULTS: An abscess was observed outside the right (infected bone) on 1H-MRI and confirmed by histopathology. In the abscess the 13C-lactate to 13C-pyruvate ratio was increased as compared to the inflammatory region of the control leg. 18F-FDG uptake showed no clear trend when comparing abscess versus inflammation, but showed an increase considering the infected bone versus the control. In the abscess, the FDG-PET signal distribution had highest intensity in the abscess membrane, whereas the maximum of the13C lactate ratio appears in the abscess cavity. DISCUSSION: The apparent different spatial enhancement pattern of FDG uptake and 13C lactate ratio in abscess suggests that they are independent biomarkers and that hyperpolarized 13C-MRSI is a method with potential for clinical imaging of infection and treatment response.