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The Effect of Flip Angle On Phosphorus-31 MRS Enhancement by the Nuclear Overhauser Effect

J Vasquez*, S Deng , G Clarke , UT Health Sciences Center, San Antonio, TX


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 8

Purpose: To observe the quantitative impact of the nuclear Overhauser effect (nOe) in 31-phosphorus magnetic resonance spectroscopy (31P-MRS) for different concentrations of phosphorus containing substances.

Methods: Three homogenous phantoms containing varying concentrations (25mM, 30mM, 35mM) of H3PO4 were used to assess the nOe enhancement on their respective phosphor spectrum. The phantoms were imaged on a 3T MRI magnet using a 31P/1H dual-tuned surface coil containing a reference compound, MDP, for quantification. Spectra were acquired with a slice selective 31P-MRS DRESS pulse sequence which included adjustable nOe parameters. Signal originated form a slab localized ~4 cm from the coil surface for maximal effect. Scan and nOe parameters were varied to measure signal enhancement. Spectral peaks were fitted using a non-linear-least-squares quantitation algorithm in jMRUI 5.2. Two-way analysis of variance with Enhancement Ratio (ENHANCE) as the dependent variable and concentration (CONC) and flip angle (FLIP) as the two factors. p<0.05 deemed significant.

Results: Spectral analysis indicates that signal enhancement is maximal when the nOe flip angle is maximized. The degree of enhancement varied with TR, increases in signal amplitude > 30% in cases with low TR. The nOe enhancement provided consistent results in concentration quantification within samples of the same concentration.Response :ENHANCE. CONC: F= 0.1785, p=0.6748; FLIP: F=18.9476, p= 8.731e-05; CONCxFLIP: F=0.0485, p=0.8268. [Residuals 41 0.065471 0.0015969].

Conclusion: The results suggest improved signal strength using the nOe in 31P-MRS, which is dependent on the nOe flip angle. Concentration quantification remained uncompromised even as the nOe enhancement varied, which would help measuring low concentrations of phosphorus containing metabolites.


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