Purpose
To obtain high‐resolution Cr and PCr maps of mouse skeletal muscle using a polynomial and Lorentzian line‐shape fitting (PLOF) CEST method.
Methods
Wild‐type mice and guanidinoacetate ...N‐methyltransferase–deficient (GAMT‐/‐) mice that have low Cr and PCr concentrations in muscle were used to assign the Cr and PCr peaks in the Z‐spectrum at 11.7 T. A PLOF method was proposed to simultaneously extract and quantify the Cr and PCr by assuming a polynomial function for the background and 2 Lorentzian functions for the CEST peaks at 1.95 ppm and 2.5 ppm.
Results
The Z‐spectra of phantoms revealed that PCr has 2 CEST peaks (2 ppm and 2.5 ppm), whereas Cr only showed 1 peak at 2 ppm. Comparison of the Z‐spectra of wild‐type and GAMT‐/‐ mice indicated that, contrary to brain, there was no visible protein guanidinium peak in the skeletal‐muscle Z‐spectrum, which allowed us to extract clean PCr and Cr CEST signals. High‐resolution PCr and Cr concentration maps of mouse skeletal muscle were obtained by the PLOF CEST method after calibration with in vivo MRS.
Conclusions
The PLOF method provides an efficient way to map Cr and PCr concentrations simultaneously in the skeletal muscle at high MRI field.
Magnetic resonance spectroscopy (MRS) and the related technique of magnetic resonance spectroscopic imaging (MRSI) are widely used in both clinical and preclinical research for the non-invasive ...evaluation of brain metabolism. They are also used in medical practice, although their ultimate clinical value continues to be a source of discussion. This chapter reviews the general information content of brain spectra and commonly used protocols for both MRS and MRSI and also touches on data analysis methods and quantitation. The main focus is on proton MRS for application in humans, but many of the methods are also applicable to other nuclei and studies of animal models as well.
Magnetic resonance spectroscopic imaging (MRSI) offers considerable promise for monitoring metabolic alterations associated with disease or injury; however, to date, these methods have not had a ...significant impact on clinical care, and their use remains largely confined to the research community and a limited number of clinical sites. The MRSI methods currently implemented on clinical MRI instruments have remained essentially unchanged for two decades, with only incremental improvements in sequence implementation. During this time, a number of technological developments have taken place that have already greatly benefited the quality of MRSI measurements within the research community and which promise to bring advanced MRSI studies to the point where the technique becomes a true imaging modality, while making the traditional review of individual spectra a secondary requirement. Furthermore, the increasing use of biomedical MR spectroscopy studies has indicated clinical areas where advanced MRSI methods can provide valuable information for clinical care. In light of this rapidly changing technological environment and growing understanding of the value of MRSI studies for biomedical studies, this article presents a consensus from a group of experts in the field that reviews the state‐of‐the‐art for clinical proton MRSI studies of the human brain, recommends minimal standards for further development of vendor‐provided MRSI implementations, and identifies areas which need further technical development.
MR spectroscopic imaging enables noninvasive mapping of metabolites within the body and offers considerable potential for clinical and biomedical research studies. Recent technological advances, in high‐field MRI instrumentation, spatial‐spectral sampling and image reconstruction methods, and data analysis, have greatly improved spatial resolution and the extent of the brain over which metabolites can be mapped. This consensus statement summarizes the state‐of‐the‐art for clinical MRSI studies of the brain and provides a set of implementation standards matched to different clinical applications.
To investigate the feasibility of downfield MR spectroscopic imaging (DF-MRSI) in the human brain at 7T.
A 7T DF-MRSI pulse sequence was implemented based on the previously described methodology at ...3T, with 3D phase-encoding,
spectral-spatial excitation, and frequency selective refocusing. Data were pre-processed followed by analysis using the "LCModel" software package, and metabolite maps created from the LCModel results. Total scan time, including brain MRI and a water-reference MRSI, was 24 min. The sequence was tested in 10 normal volunteers. Estimated metabolite levels and uncertainty values (Cramer Rao lower bounds, CRLBs) for nine downfield peaks were compared between seven different brain regions, anterior cingulate cortex (ACC), centrum semiovale (CSO), corpus callosum (CC), cerebellar vermis (CV), dorsolateral prefrontal cortex (DLPFC), posterior cingulate cortex (PCC), and thalamus (Thal).
DF peaks were relatively uniformly distributed throughout the brain, with only a small number of peaks showing any significant regional variations. Most DF peaks had average CRLB<25% in most brain regions. Average SNR values were higher for the brain regions ACC and DLPFC (˜7 ± 0.95, mean ± SD) while in a range of 3.4-6.0 for other brain regions. Average linewidth (FWHM) values were greater than 35 Hz in the ACC, CV, and Thal, and 22 Hz in CC, CSO, DLPFC, and PCC.
High-field DF-MRSI is able to spatially map exchangeable protons in the human brain at high resolution and with near whole-brain coverage in acceptable scan times, and in the future may be used to study metabolism of brain tumors or other neuropathological disorders.
The utility of magnetic resonance spectroscopy (MRS) in diagnosis and evaluation of treatment response to human brain tumors has been widely documented. The role of MRS in tumor classification, ...tumors versus nonneoplastic lesions, prediction of survival, treatment planning, monitoring of therapy, and post-therapy evaluation is discussed. This article delineates the need for standardization and further study in order for MRS to become widely used as a routine clinical tool.
In this review article we have consolidated the imaging literature of patients with schizophrenia across the full spectrum of modalities in radiology including computed tomography (CT), morphologic ...magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET), and magnetoencephalography (MEG). We look at the impact of various subtypes of schizophrenia on imaging findings and the changes that occur with medical and transcranial magnetic stimulation (TMS) therapy. Our goal was a comprehensive multimodality summary of the findings of state-of-the-art imaging in untreated and treated patients with schizophrenia. Clinical imaging in schizophrenia is used to exclude structural lesions which may produce symptoms that may mimic those of patients with schizophrenia. Nonetheless one finds global volume loss in the brains of patients with schizophrenia with associated increased cerebrospinal fluid (CSF) volume and decreased gray matter volume. These features may be influenced by the duration of disease and or medication use. For functional studies, be they fluorodeoxyglucose positron emission tomography (FDG PET), rs-fMRI, task-based fMRI, diffusion tensor imaging (DTI) or MEG there generally is hypoactivation and disconnection between brain regions. However, these findings may vary depending upon the negative or positive symptomatology manifested in the patients. MR spectroscopy generally shows low
N
-acetylaspartate from neuronal loss and low glutamine (a neuroexcitatory marker) but glutathione may be elevated, particularly in non-treatment responders. The literature in schizophrenia is difficult to evaluate because age, gender, symptomatology, comorbidities, therapy use, disease duration, substance abuse, and coexisting other psychiatric disorders have not been adequately controlled for, even in large studies and meta-analyses.
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