Abstract
The feasibility of conducting in vivo non-localized 31P Magnetic Resonance Spectroscopy (MRS) with a 1.0T extremity scanner and the potential to increase accessibility of this important diagnostic tool for low cost applications is revisited. This work presents a custom transmit-only quadrature birdcage, four-element receive coil array, and spectrometer interfaced to a commercial ONI 1.0T magnet for enabling multi-channel, non-1H frequency capabilities. A custom, magnetic resonance compatible plantar flexion-extension exercise device was also developed to enable exercise protocols. The coils were assessed with bench measurements and 31P phantom studies before an in vivo demonstration. In pulse and acquire spectroscopy of a phantom, the array was found to improve the signal-to-noise ratio (SNR) by a factor of 1.31 and reduce the linewidth by 13.9% when compared to a large loop coil of the same overall size. In vivo testing results show that two averages and a four second repetition time for a temporal resolution of eight seconds was sufficient to obtain phosphocreatine recovery values and baseline pH levels aligned with expected literature values. Initial in vivo human skeletal muscle 31P MRS allowed successful monitoring of metabolic changes during an 18-minute exercise protocol. Adding an array coil and multinuclear capability to a commercial low-cost 1.0T extremity scanner enabled the observation of characteristic 31P metabolic information, such as the phosphocreatinerecovery rate and underlying baseline pH.
Highlights
31P magnetic resonance spectroscopy (MRS) offers a unique noninvasive method to investigate in vivo metabolism and further improve our understanding of many disease processes
Through the quantification of phosphocreatine (PCr), inorganic phosphate (Pi), and adenosine triphosphate (ATP) compounds, metabolism can be observed from 31P spectra
The feasibility of using a 1T extremity scanner for in vivo dynamic 31P spectroscopy has been demonstrated through the acquisition of 31P spectra from a healthy volunteer using a custom four-element array and associated hardware
Summary
31P magnetic resonance spectroscopy (MRS) offers a unique noninvasive method to investigate in vivo metabolism and further improve our understanding of many disease processes. Understanding in vivo human 31P spectra includes interests in skeletal muscle energetics, neuromuscular disorder, cerebral phosphorylated metabolites, coronary heart disease and metabolic characteristics in tumors [1]-[6]. In many of these studies, observing 31P spectra over time is required to monitor energetics. The relatively low concentrations of phosphorus in the body paired with the need for a highly homogeneous magnet make 31P spectroscopy challenging. Despite some efforts and success at performing 31P spectroscopy at 1.5T [3], [6]-[8], most current 31P spectroscopy is performed on high field 3.0T and ultra-high field 7.0T systems [9]-[13]
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