Proton MRS of the breast in the clinical setting

Information for determining whether a primary breast lesion is invasive and its receptor status and grade can be obtained before surgery by performing proton MRS on a fine‐needle aspiration biopsy (FNAB) specimen and analyzing the MRS information by a pattern recognition method. Two‐dimensional MRS, on either specimens or cells, allows the unambiguous assignment of most resonances. When correlated with the spectral regions selected by the pattern recognition method, there are strong indications for the biochemical markers responsible for prognostic information of invasive capacity and metastatic spread. Spectral assignments and biological correlations can be made using cell models. In vivo MRS can distinguish invasive from benign lesions. This pathological distinction can be made from the presence of resonances at discrete frequencies. To achieve this level of spectral resolution and signal‐to‐noise ratio, there are stringent requirements when acquiring and processing the data. The challenge now is to implement two‐dimensional MRS in vivo. Until this is realized, the combination of in vivo MR, for diagnosis and spatial location, and MRS, for image‐guided biopsy to provide information on tumor spread, promises to provide a higher level of preoperative diagnosis than previously achieved. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization of breast cancers and therapy response by MRS and quantitative gene expression profiling in the choline pathway

Tumor choline metabolites have potential for use as diagnostic indicators of breast cancer phenotype and can be non‐invasively monitored in vivo by MRS. Extract studies have determined that the principle diagnostic component of these peaks is phosphocholine (PCho), the biosynthetic precursor to the membrane phospholipid, phosphatidylcholine (PtdCho). The ability to resolve and quantify PCho in vivo would improve the accuracy of this putative diagnostic tool. In addition, determining the biochemical mechanisms underlying these metabolic perturbations will improve the understanding of breast cancer and may suggest potential molecular targets for drug development. Reported herein is the in vivo resolution and quantification of PCho and glycerophosphocholine (GPC) in breast cancer xenografts in SCID mice via image‐guided ³¹P MRS, localized to a single voxel. Tumor metabolites are also detected using ex vivo extracts and high‐resolution NMR spectroscopy and are quantified in the metastatic tumor line, MDA‐mb‐231. Also reported is the quantification of cytosolic and lipid metabolites in breast cells of differing cancer phenotype, and the identification of metabolites that differ among these cell lines. In cell extracts, PCho and the PtdCho breakdown products, lysophosphatidylcholine, GPC and glycerol 3‐phosphate, are all raised in breast cancer lines relative to an immortalized non‐malignant line. These metabolic differences are in direct agreement with differences in expression of genes encoding enzymes in the choline metabolic pathway. Results of this study are consistent with previous studies, which have concluded that increased choline uptake, increased choline kinase activity, and increased phosholipase‐mediated turnover of PtdCho contribute to the observed increase in PCho in breast cancer. In addition, this study presents evidence suggesting a specific role for phospholipase A₂‐mediated PtdCho catabolism. Gene expression changes following taxane therapy are also reported and are consistent with previously reported changes in choline metabolites after the same therapy in the same tumor model. Copyright © 2008 John Wiley & Sons, Ltd.     

31P MRSI and 1H MRS at 7 T: initial results in human breast cancer

This study demonstrates the feasibility of the noninvasive determination of important biomarkers of human (breast) tumor metabolism using high‐field (7‐T) MRI and MRS. ³¹P MRSI at this field strength was used to provide a direct method for the in vivo detection and quantification of endogenous biomarkers. These encompass phospholipid metabolism, phosphate energy metabolism and intracellular pH. A double‐tuned, dual‐element transceiver was designed with focused radiofrequency fields for unilateral breast imaging and spectroscopy tuned for optimized sensitivity at 7 T. T₁‐weighted three‐dimensional MRI and ¹H MRS were applied for the localization and quantification of total choline compounds. ³¹P MRSI was obtained within 20 min per subject and mapped in three dimensions over the breast with pixel volumes of 10 mL. The feasibility of monitoring in vivo metabolism was demonstrated in two patients with breast cancer during neoadjuvant chemotherapy, validated by ex vivo high‐resolution magic angle spinning NMR and compared with data from an age‐matched healthy volunteer. Concentrations of total choline down to 0.4 mM could be detected in the human breast in vivo. Levels of adenosine and other nucleoside triphosphates, inorganic phosphate, phosphocholine, phosphoethanolamine and their glycerol diesters detected in glandular tissue, as well as in tumor, were mapped over the entire breast. Altered levels of these compounds were observed in patients compared with an age‐matched healthy volunteer; modulation of these levels occurred in breast tumors during neoadjuvant chemotherapy. To our knowledge, this is the first comprehensive MRI and MRS study in patients with breast cancer, which reveals detailed information on the morphology and phospholipid metabolism from volumes as small as 10 mL. This endogenous metabolic information may provide a new method for the noninvasive assessment of prognostic and predictive biomarkers in breast cancer treatment. Copyright © 2011 John Wiley & Sons, Ltd.     

In vivo mouse myocardial 31P MRS using three‐dimensional image‐selected in vivo spectroscopy (3D ISIS): technical considerations and biochemical validations

³¹P MRS provides a unique non‐invasive window into myocardial energy homeostasis. Mouse models of cardiac disease are widely used in preclinical studies, but the application of ³¹P MRS in the in vivo mouse heart has been limited. The small‐sized, fast‐beating mouse heart imposes challenges regarding localized signal acquisition devoid of contamination with signal originating from surrounding tissues. Here, we report the implementation and validation of three‐dimensional image‐selected in vivo spectroscopy (3D ISIS) for localized ³¹P MRS of the in vivo mouse heart at 9.4 T. Cardiac ³¹P MR spectra were acquired in vivo in healthy mice (n = 9) and in transverse aortic constricted (TAC) mice (n = 8) using respiratory‐gated, cardiac‐triggered 3D ISIS. Localization and potential signal contamination were assessed with ³¹P MRS experiments in the anterior myocardial wall, liver, skeletal muscle and blood. For healthy hearts, results were validated against ex vivo biochemical assays. Effects of isoflurane anesthesia were assessed by measuring in vivo hemodynamics and blood gases. The myocardial energy status, assessed via the phosphocreatine (PCr) to adenosine 5′‐triphosphate (ATP) ratio, was approximately 25% lower in TAC mice compared with controls (0.76 ± 0.13 versus 1.00 ± 0.15; P < 0.01). Localization with one‐dimensional (1D) ISIS resulted in two‐fold higher PCr/ATP ratios than measured with 3D ISIS, because of the high PCr levels of chest skeletal muscle that contaminate the 1D ISIS measurements. Ex vivo determinations of the myocardial PCr/ATP ratio (0.94 ± 0.24; n = 8) confirmed the in vivo observations in control mice. Heart rate (497 ± 76 beats/min), mean arterial pressure (90 ± 3.3 mmHg) and blood oxygen saturation (96.2 ± 0.6%) during the experimental conditions of in vivo ³¹P MRS were within the normal physiological range. Our results show that respiratory‐gated, cardiac‐triggered 3D ISIS allows for non‐invasive assessments of in vivo mouse myocardial energy homeostasis with ³¹P MRS under physiological conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Assessment of early docetaxel response in an experimental model of human breast cancer using DCE‐MRI,ex vivo HR MAS,and in vivo 1H MRS

The purpose of this study was to evaluate the use of dynamic contrast‐enhanced (DCE) MRI, in vivo ¹H MRS and ex vivo high resolution magic angle spinning (HR MAS) MRS of tissue samples as methods to detect early treatment effects of docetaxel in a breast cancer xenograft model (MCF‐7) in mice. MCF‐7 cells were implanted subcutaneously in athymic mice and treated with docetaxel (20, 30, and 40 mg/kg) or saline six weeks later. DCE‐MRI and in vivo ¹H MRS were performed on a 7 T MR system three days after treatment. The dynamic images were used as input for a two‐compartment model, yielding the vascular parameters K^trans and v_e. HR MAS MRS, histology, and immunohistochemical staining for proliferation (Ki‐67), apoptosis (M30 cytodeath), and vascular/endothelial cells (CD31) were performed on excised tumor tissue. Both in vivo spectra and HR MAS spectra were used as input for multivariate analysis (principal component analysis (PCA) and partial least squares regression analysis (PLS)) to compare controls to treated tumors. Tumor growth was suppressed in docetaxel‐treated mice compared to the controls. The anti‐tumor effect led to an increase in K^trans and v_e values in all the treated groups. Furthermore, in vivo MRS and HR MAS MRS revealed a significant decrease in choline metabolite levels for the treated groups, in accordance with reduced proliferative index as seen on Ki‐67 stained sections. In this study DCE‐MRI, in vivo MRS and ex vivo HR MAS MRS have been used to demonstrate that docetaxel treatment of a human breast cancer xenograft model results in changes in the vascular dynamics and metabolic profile of the tumors. This indicates that these MR methods could be used to monitor intra‐tumoral treatment effects. Copyright © 2009 John Wiley & Sons, Ltd.     

Monitoring of gliomas in vivo by diffusion MRI and 1H MRS during gene therapy‐induced apoptosis: interrelationships between water diffusion and mobile lipids

The measurement of water diffusion by diffusion‐weighted MRI (DWI) in vivo offers a non‐invasive method for assessing tissue responses to anti‐cancer therapies. The pathway of cell death after anti‐cancer treatment is often apoptosis, which leads to accumulation of mobile lipids detectable by ¹H MRS in vivo. However, it is not known how these discrete MR markers of cell death relate to each other. In a rodent tumour model [i.e. ganciclovir‐treated herpes simplex thymidine kinase (HSV‐tk) gene‐transfected BT4C gliomas], we studied the interrelationships between water diffusion (Trace{D}) and mobile lipids during apoptosis. Water diffusion and water‐referenced concentrations of mobile lipids showed clearly increasing and interconnected trends during treatment. Of the accumulating ¹H MRS‐visible lipids, the fatty acid ? CH ?CH ? groups and cholesterol compounds showed the strongest associations with water diffusion (r² = 0.30; P < 0.05 and r² = 0.48; P < 0.01, respectively). These results indicate that the tumour histopathology and apoptotic processes during tumour shrinkage can be interrelated in vivo by DWI of tissue water and ¹H MRS of mobile lipids, respectively. However, there is considerable individual variation in the associations, particularly at the end of the treatment period, and in the relative compositions of the accumulating NMR‐visible lipids. The findings suggest that the assessment of individual treatment response in vivo may benefit from combining DWI and ¹H MRS. Absolute and relative changes in mobile lipids may indicate initiation of tumour shrinkage even when changes in tissue water diffusion are still small. Conversely, greatly increased water diffusion probably indicates that substantial cell decomposition has taken place in the tumour tissue when the ¹H MRS resonances of mobile lipids alone can no longer give a reliable estimate of tissue conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Lipid biomarkers of glioma cell growth arrest and cell death detected by 1H magic angle spinning MRS

Biomarkers of early response to treatment have the potential to improve cancer therapy by allowing treatment to be tailored to the individual. Alterations in lipids detected by in vivo MRS have been suggested as noninvasive biomarkers of cell stress and early indicators of cell death. An improved understanding of the relationship between MRS lipids and cell stress in vitro would aid in the translation of this technique into clinical use. Rat BT4C glioma cells were treated with 50 µ m cis‐dichlorodiammineplatinum II (cisplatin), a commonly used chemotherapeutic agent, and harvested at several time points up to 72 h. High‐resolution magic angle spinning ¹H MRS of cells was then performed on a 600‐MHz NMR spectrometer. The metabolites were quantified using a time domain fitting method, TARQUIN. Increases were detected in saturated and polyunsaturated fatty acid resonances early during the exposure to cisplatin. The fatty acid CH₂/CH₃ ratio was unaltered by treatment after allowing for contributions of macromolecules. Polyunsaturated fatty acids increased on treatment, with the group –CH = CH–CH₂–CH = CH– accounting for all the unsaturated fatty acid signals. Transmission electron microscopy, in addition to Nile red and 4',6‐diamino‐2‐phenylindole co‐staining, revealed that the lipid increase was associated with cytoplasmic neutral lipid droplets. Small numbers of apoptotic and necrotic cells were detected by trypan blue, annexin V–fluorescein isothiocyanate‐labelled flow cytometry and DNA laddering after up to 48 h of cisplatin exposure. Propidium iodide flow cytometry revealed that cells accumulated in the G1 stage of the cell growth cycle. In conclusion, an increase in the size of the lipid droplets is detected in morphologically viable cells during cisplatin exposure. ¹H MRS can detect lipid alterations during cell cycle arrest and progression of cell death, and has the potential to provide a noninvasive biomarker of treatment efficacy in vivo. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of hepatic fatty acids in mice with reduced liver fat by ultra‐short echo time 1H‐MRS at 14.1 T in vivo

Alterations in the hepatic lipid content (HLC) and fatty acid composition are associated with disruptions in whole body metabolism, both in humans and in rodent models, and can be non‐invasively assessed by ¹H‐MRS in vivo. We used ¹H‐MRS to characterize the hepatic fatty‐acyl chains of healthy mice and to follow changes caused by streptozotocin (STZ) injection. Using STEAM at 14.1 T with an ultra‐short T_E of 2.8 ms, confounding effects from T₂ relaxation and J‐coupling were avoided, allowing for accurate estimations of the contribution of unsaturated (UFA), saturated (SFA), mono‐unsaturated (MUFA) and poly‐unsaturated (PUFA) fatty‐acyl chains, number of double bonds, PU bonds and mean chain length. Compared with in vivo ¹H‐MRS, high resolution NMR performed in vitro in hepatic lipid extracts reported longer fatty‐acyl chains (18 versus 15 carbons) with a lower contribution from UFA (61 ± 1% versus 80 ± 5%) but a higher number of PU bonds per UFA (1.39 ± 0.03 versus 0.58 ± 0.08), driven by the presence of membrane species in the extracts. STZ injection caused a decrease of HLC (from 1.7 ± 0.3% to 0.7 ± 0.1%), an increase in the contribution of SFA (from 21 ± 2% to 45 ± 6%) and a reduction of the mean length (from 15 to 13 carbons) of cytosolic fatty‐acyl chains. In addition, SFAs were also likely to have increased in membrane lipids of STZ‐induced diabetic mice, along with a decrease of the mean chain length. These studies show the applicability of ¹H‐MRS in vivo to monitor changes in the composition of the hepatic fatty‐acyl chains in mice even when they exhibit reduced HLC, pointing to the value of this methodology to evaluate lipid‐lowering interventions in the scope of metabolic disorders. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantification of skeletal muscle mitochondrial function by 31P magnetic resonance spectroscopy techniques: a quantitative review

Magnetic resonance spectroscopy (MRS) can give information about cellular metabolism in vivo which is difficult to obtain in other ways. In skeletal muscle, non‐invasive ³¹P MRS measurements of the post‐exercise recovery kinetics of pH, [PCr], [Pi] and [ADP] contain valuable information about muscle mitochondrial function and cellular pH homeostasis in vivo, but quantitative interpretation depends on understanding the underlying physiology. Here, by giving examples of the analysis of ³¹P MRS recovery data, by some simple computational simulation, and by extensively comparing data from published studies using both ³¹P MRS and invasive direct measurements of muscle O₂ consumption in a common analytical framework, we consider what can be learnt quantitatively about mitochondrial metabolism in skeletal muscle using MRS‐based methodology. We explore some technical and conceptual limitations of current methods, and point out some aspects of the physiology which are still incompletely understood.     

MRS characterization of central neurocytomas using glycine

This study reports in vivo MRS findings in 11 patients with histologically diagnosed central neurocytomas, which are rare intraventricular tumors of neuronal origin. Single‐voxel ¹H MRS was carried out prior to surgery using a point‐resolved spectroscopy sequence with TR = 6 s, TE = 135 ms and 128 scans. In vitro high‐resolution ¹H spectroscopy was also carried out on two surgically excised samples. The striking features of the spectra from the central neurocytomas were the presence of high glycine, decreased N‐acetylaspartate, increased choline and alanine. Retrospective, blind analysis of the spectra by two independent observers correctly identified all but one central neurocytoma based on the presence of glycine. The presence of glycine and prominent choline in the ¹H MR spectrum is a characteristic feature of the central neurocytomas, and could be used to characterize and differentiate them from other brain tumors. Copyright © 2011 John Wiley & Sons, Ltd.     

Integration of MRI and MRS approaches to monitor molecular imaging and metabolomic effects of trabectedin on a preclinical ovarian cancer model

Although several drugs are available to treat recurrences of human epithelial ovarian cancer (EOC), clinical responses often remain short lived and lead to only marginal improvements in patients' survival. One of the new drugs proposed for recurrent platinum‐resistant EOC patients is trabectedin (Trab), a marine‐derived antitumor agent initially isolated from the tunicate Ecteinascidia turbinata and currently produced synthetically. Predictive biomarkers of therapy response to this drug and the potential use of non‐invasive functional MRI and MRS approaches for an early assessment of Trab efficacy have not yet been evaluated, although they might be relevant for improving the clinical management of EOC patients. In the present work we combined functional and spectroscopic magnetic resonance technologies, such as in vivo diffusion‐weighted MRI and ¹H MRS, with ex vivo high resolution MRS (HR‐MRS) metabolomic analyses, with the aim of identifying new pharmacodynamic markers of Trab effectiveness on well characterized, highly aggressive human SKOV3.ip (a HER2‐enriched cell variant derived from SKOV3 cells) EOC xenografts. In vivo treatment with Trab (three consecutive weekly 0.2 mg/kg i.v. injections) resulted in the following: (1) a significant reduction of in vivo tumor growth, along with the formation in cancer lesions of diffuse hyper‐intense areas detected by T₂‐weighted MRI and attributed to necrosis, in agreement with histopathology findings; (2) significant increases in the apparent diffusion coefficient mean and median values versus saline‐treated control tumors; and (3) a significant reduction in the choline‐containing metabolites' signal detected by quantitative in vivo MRS. Multivariate and quantitative HR‐MRS analyses on ex vivo tissue samples revealed Trab‐induced alterations in phospholipid and glucose metabolism identified as a decrease in phosphocholine and an increase in lactate. Collectively, these data identify Trab‐induced functional MRI and MRS alterations in EOC models as a possible basis for further developments of these non‐invasive imaging methods to improve the clinical management of EOC patients.     

Brain temperature and pH measured by 1H chemical shift imaging of a thulium agent

Temperature and pH are two of the most important physiological parameters and are believed to be tightly regulated because they are intricately related to energy metabolism in living organisms. Temperature and/or pH data in mammalian brain are scarce, however, mainly because of lack of precise and non‐invasive methods. At 11.7 T, we demonstrate that a thulium‐based macrocyclic complex infused through the bloodstream can be used to obtain temperature and pH maps of rat brain in vivo by ¹H chemical shift imaging (CSI) of the sensor itself in conjunction with a multi‐parametric model that depends on several proton resonances of the sensor. Accuracies of temperature and pH determination with the thulium sensor – which has a predominantly extracellular presence – depend on stable signals during the course of the CSI experiment as well as redundancy for temperature and pH sensitivities contained within the observed signals. The thulium‐based method compared well with other methods for temperature (¹H MRS of N‐acetylaspartate and water; copper–constantan thermocouple wire) and pH (³¹P MRS of inorganic phosphate and phosphocreatine) assessment, as established by in vitro and in vivo studies. In vitro studies in phantoms with two compartments of different pH value observed under different ambient temperature conditions generated precise temperature and pH distribution maps. In vivo studies in α‐chloralose‐anesthetized and renal‐ligated rats revealed temperature (33–34°C) and pH (7.3–7.4) distributions in the cerebral cortex that are in agreement with observations by other methods. These results show that the thulium sensor can be used to measure temperature and pH distributions in rat brain in vivo simultaneously and accurately with using biosensor imaging of redundant. Copyright © 2008 John Wiley & Sons, Ltd.     

The case of the missing glutamine

A theoretical study was performed to determine the accuracy and repeatability of multiple one‐dimensional pulse sequences in the quantification of glutamine concentration at 3 T. Variable repeatability (12% to > 50%) and significant absolute error (?50% to +70%) were noted for the eight pulse sequences considered. Data acquired in vivo using three of the pulse sequences used for simulation matched the predicted repeatability well; among the pulse sequences considered, point‐resolved spectroscopy (TE = 80 ms) offered minimal error and acceptable repeatability (12%) for brain glutamine measurements. Following correction for the expected bias of each pulse sequence, consistent glutamine measurements, in the 1‐mM range, were reported with the three sequences. An explanation for the mismatch between in vivo ¹H MRS and in vitro ¹³C/¹H MRS at high field was attempted. Copyright © 2011 John Wiley & Sons, Ltd.     

MRI accurately identifies early murine mammary cancers and reliably differentiates between in situ and invasive cancer: correlation of MRI with histology

MRI methods that accurately identify various stages of mouse mammary cancer could provide new knowledge that may have a direct impact on the management of breast cancer in patients. This research investigates whether we can accurately follow the progression from in situ to invasive cancer by the evaluation of in vivo and ex vivo MRI, and in comparison with histology as the gold standard for the diagnosis and staging of cancer. Six C3(1)SV40Tag virgin female mice, aged 12–16 weeks, were studied. At this age, these mice develop in situ cancer that resembles human ductal carcinoma in situ (DCIS). Fast spin‐echo images of inguinal mammary glands were acquired at 9.4 T. After in vivo MRI, mice were sacrificed; inguinal mammary glands were excised and fixed in formalin for ex vivo MRI. Three‐dimensional, volume‐rendered, in vivo and ex vivo MR images were then correlated with histology. High‐resolution ex vivo scans facilitated the comparison of in vivo scans with histology. The sizes of mammary cancers classified as in situ on the basis of histology ranged from 150 to 400 µm in largest diameter, and the average signal intensity relative to muscle was 1.40 ± 0.18 on T₂‐weighted images. Cancers classified as invasive on the basis of histology were >400 µm in largest diameter, and the average intensity relative to muscle on T₂‐weighted images was 2.34 ± 0.26. Using a cut‐off of 400 µm in largest diameter to distinguish between in situ and invasive cancers, a T₂‐weighted signal intensity of at least 1.4 times that of muscle for in situ cancer, and at least 2.3 times that of muscle for invasive cancer, 96% of in situ and 100% of invasive cancers were correctly identified on in vivo MRI, using histology as the gold standard. Precise MRI–histology correlation demonstrates that MRI reliably detects early in situ cancer and differentiates in situ from invasive cancers in the SV40Tag mouse model of human breast cancer. Copyright © 2015 John Wiley & Sons, Ltd.     

Combined MR,fluorescence and histology imaging strategy in a human breast tumor xenograft model

Applications of molecular imaging in cancer and other diseases frequently require the combination of in vivo imaging modalities, such as MR and optical imaging, with ex vivo optical, fluorescence, histology and immunohistochemical imaging to investigate and relate molecular and biological processes to imaging parameters within the same region of interest. We have developed a multimodal image reconstruction and fusion framework that accurately combines in vivo MRI and MRSI, ex vivo brightfield and fluorescence microscopic imaging and ex vivo histology imaging. Ex vivo brightfield microscopic imaging was used as an intermediate modality to facilitate the ultimate link between ex vivo histology and in vivo MRI/MRSI. Tissue sectioning necessary for optical and histology imaging required the generation of a three‐dimensional reconstruction module for two‐dimensional ex vivo optical and histology imaging data. We developed an external fiducial marker‐based three‐dimensional reconstruction method, which was able to fuse optical brightfield and fluorescence with histology imaging data. The registration of the three‐dimensional tumor shape was pursued to combine in vivo MRI/MRSI and ex vivo optical brightfield and fluorescence imaging data. This registration strategy was applied to in vivo MRI/MRSI, ex vivo optical brightfield/fluorescence and histology imaging datasets obtained from human breast tumor models. Three‐dimensional human breast tumor datasets were successfully reconstructed and fused with this platform. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous in vivo assessment of cardiac and hepatic metabolism in the diabetic rat using hyperpolarized MRS

Understanding and assessing diabetic metabolism is vital for monitoring disease progression and improving treatment of patients. In vivo assessments, using MRI and MRS, provide non‐invasive and accurate measurements, and the development of hyperpolarized ¹³C spectroscopy in particular has been demonstrated to provide valuable metabolic data in real time. Until now, studies have focussed on individual organs. However, diabetes is a systemic disease affecting multiple tissues in the body. Therefore, we have developed a technique to simultaneously measure metabolism in both the heart and liver during a single acquisition. A hyperpolarized ¹³C MRS protocol was developed to allow acquisition of metabolic data from the heart and liver during a single scan. This protocol was subsequently used to assess metabolism in the heart and liver of seven control male Wistar rats and seven diabetic rats (diabetes was induced by three weeks of high‐fat feeding and a 30 mg/kg injection of streptozotocin). Using our new acquisition, we observed decreased cardiac and hepatic pyruvate dehydrogenase flux in our diabetic rat model. These diabetic rats also had increased blood glucose levels, decreased insulin, and increased hepatic triglycerides. Decreased production of hepatic [1‐¹³C]alanine was observed in the diabetic group, but this change was not present in the hearts of the same diabetic animals. We have demonstrated the ability to measure cardiac and hepatic metabolism simultaneously, with sufficient sensitivity to detect metabolic alterations in both organs. Further, we have non‐invasively observed the different reactions of the heart and liver to the metabolic challenge of diabetes.     

In vivo T2 relaxation time measurement with echo‐time averaging

The accuracy of metabolite concentrations measured using in vivo proton (¹H) MRS is enhanced following correction for spin–spin (T₂) relaxation effects. In addition, metabolite proton T₂ relaxation times provide unique information regarding cellular environment and molecular mobility. Echo‐time (TE) averaging ¹H MRS involves the collection and averaging of multiple TE steps, which greatly simplifies resulting spectra due to the attenuation of spin‐coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T₂ relaxation information, the aim of the present proof‐of‐concept study was to develop a novel data processing scheme to estimate metabolite T₂ relaxation times from TE‐averaged ¹H MRS data. Spectral simulations are used to validate the proposed TE‐averaging methods for estimating methyl proton T₂ relaxation times for N‐acetyl aspartate, total creatine, and choline‐containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior‐occipital cortex of 10 healthy control subjects. Compared with standard methods, distinct advantages of this approach include built‐in macromolecule resonance attenuation, in vivo T₂ estimates closer to reported values when maximum TE ≈ T₂, and the potential for T₂ calculation of metabolite resonances otherwise inseparable in standard ¹H MRS spectra recorded in vivo. Copyright © 2014 John Wiley & Sons, Ltd.     

Covariance J‐resolved spectroscopy: Theory and application in vivo

Magnetic resonance spectroscopy (MRS) is a powerful tool capable of investigating the metabolic status of several tissues in vivo. In particular, single‐voxel‐based ¹H spectroscopy provides invaluable biochemical information from a volume of interest (VOI) and has therefore been used in a variety of studies. Unfortunately, typical one‐dimensional MRS data suffer from severe signal overlap and thus important metabolites are difficult to distinguish. One method that is used to disentangle overlapping resonances is the two‐dimensional J‐resolved spectroscopy (JPRESS) experiment. Due to the long acquisition duration of the JPRESS experiment, a limited number of points are acquired in the indirect dimension, leading to poor spectral resolution along this dimension. Poor spectral resolution is problematic because proper peak assignment may be hindered, which is why the zero‐filling method is often used to improve resolution as a post‐processing step. However, zero‐filling leads to spectral artifacts, which may affect visualization and quantitation of spectra. A novel method utilizing a covariance transformation, called covariance J‐resolved spectroscopy (CovJ), was developed in order to improve spectral resolution along the indirect dimension (F₁). Comparison of simulated data demonstrates that peak structures remain qualitatively similar between JPRESS and the novel method along the diagonal region (F₁ = 0 Hz), whereas differences arise in the cross‐peak (F₁≠0 Hz) regions. In addition, quantitative results of in vivo JPRESS data acquired on a 3T scanner show significant correlations (r²>0.86, p<0.001) when comparing the metabolite concentrations between the two methods. Finally, a quantitation algorithm, ‘COVariance Spectral Evaluation of ¹H Acquisitions using Representative prior knowledge’ (Cov‐SEHAR), was developed in order to quantify γ‐aminobutyric acid and glutamate from the CovJ spectra. These preliminary findings indicate that the CovJ method may be used to improve spectral resolution without hindering metabolite quantitation for J‐resolved spectra.     

Clinical characteristics and biomarkers of breast cancer associated with choline concentration measured by 1H MRS

This study investigated the association between the total choline (tCho) concentration and the clinical characteristics and biomarker status of breast cancer. Sixty‐two patients with breast cancer, 1.5 cm or larger in size on MR images, were studied. The tCho concentration was correlated with the MRI features, contrast enhancement kinetics, clinical variables and biomarkers. Pairwise two‐tailed Spearman's nonparametric test was used for statistical analysis. The tCho concentration was higher in high‐grade than moderate‐/low‐grade tumors (p = 0.04) and in tumors with higher K_trans and k_ep (p < 0.001 for both). The association of tCho concentration with age (p = 0.05) and triple negative biomarker (p = 0.09) approached significance. tCho was not detected in 17 patients, including 15 with invasive ductal cancer and two with infiltrating lobular cancer. Fifteen of the 17 patients had moderate‐ to low‐grade cancers, and 11 had human epidermal growth factor‐2‐negative cancer, suggesting that these two factors might lead to false‐negative choline. Higher tCho concentration in high‐grade tumors and tumors with higher K_trans and k_ep indicates that choline is associated with cell proliferation and tumor angiogenesis. The higher choline level in younger women may be caused by their more aggressive tumor type. The results presented here may aid in the better interpretation of ¹H MRS for the diagnosis of breast lesions. Copyright © 2010 John Wiley & Sons, Ltd.     

Non‐invasive detection of glycine as a biomarker of malignancy in childhood brain tumours using in‐vivo 1H MRS at 1.5 Tesla confirmed by ex‐vivo high‐resolution magic‐angle spinning NMR

Management of brain tumours in children would benefit from improved non‐invasive diagnosis, characterisation and prognostic biomarkers. Metabolite profiles derived from in‐vivo MRS have been shown to provide such information. Studies indicate that using optimum a priori information on metabolite contents in the construction of linear combination (LC) models of MR spectra leads to improved metabolite profile estimation. Glycine (Gly) is usually neglected in such models due to strong overlap with myo‐inositol (mI) and a low concentration in normal brain. However, biological studies indicate that Gly is abundant in high‐grade brain tumours. This study aimed to investigate the quantitation of Gly in paediatric brain tumours using MRS analysed by LCModel?, and its potential as a non‐invasive biomarker of malignancy. Single‐voxel MRS was performed using PRESS (TR 1500 ms, TE 30 ms/135 ms) on a 1.5 T scanner. Forty‐seven cases (18 high grade (HG), 17 low grade (LG), 12 ungraded) were retrospectively selected if both short‐TE and long‐TE MRS (n = 33) or short‐TE MRS and high‐resolution magic‐angle spinning (HRMAS) of matched surgical samples (n = 15) were available. The inclusion of Gly in LCModel? analyses led to significantly reduced fit residues for both short‐TE and long‐TE MRS (p < 0.05). The Gly concentrations estimated from short‐TE MRS were significantly correlated with the long‐TE values (R = 0.91, p < 0.001). The Gly concentration estimated by LCModel? was significantly higher in HG versus LG tumours for both short‐TE (p < 1e‐6) and long‐TE (p = 0.003) MRS. This was consistent with the HRMAS results, which showed a significantly higher normalised Gly concentration in HG tumours (p < 0.05) and a significant correlation with the normalised Gly concentration measured from short‐TE in‐vivo MRS (p < 0.05). This study suggests that glycine can be reliably detected in paediatric brain tumours using in‐vivo MRS on standard clinical scanners and that it is a promising biomarker of tumour aggressiveness. Copyright © 2009 John Wiley & Sons, Ltd.