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香蕉後熟期間醣類變化之磁振化學位移影像分析

Analyses of Sugar Content in Bananas during Ripening Using Chemical Shift Imaging

摘要


本研究利用磁振造影的化學位移影像(chemical shift imaging, CSI)技術,探討香蕉果肉後熟前後之醣類變化,並比較在3T和7T不同磁場所得到之影像與頻譜的品質。經交互選擇成像參數TR(重複時間,repetition time)與空間解析度做為控制組及對照組,並以水的最大SNR(signal-to-noise ratio)與PSNR(peak-signal-to-noise ratio)為依據判斷影像品質,可得到7T的最佳成像參數:TR為1000 ms與空間解析度為64×64。若以0.5M葡萄糖水溶液做為基準,觀察香蕉果肉和果皮後熟後之醣類變化,3T測得之果肉中醣類增加比例約為130%,7T則為158%,而果皮的變化不大。若比較高效液相層析儀(HPLC)的實驗結果,可印證果肉內醣類成分的確有增加趨勢。另解析3T與7T磁振造影儀的影像資料,以比較兩者的影像品質、頻譜解析能力與醣類偵測能力。7T中水的最大SNR為810、PSNR為3371,皆較3T所得之數據高;7T頻譜解析度為0.013ppm、水之峰值線寬為0.214ppm,亦較3T解析度高。代表在較高的磁場之下,影像品質較高而解析不同化學鍵結之能力較強。然而以葡萄糖水溶液之醣-水比例值為基準,觀測香蕉果肉含醣比例時,兩磁場的差異性並不大。所以在磁振頻譜上,有參考物質做為比較基準時-例如水溶液-在量化物質含量時,於不同磁場強度實驗結果是一致的。若從影像品質與頻譜解析度等因子考量,較高磁場可得到較佳的分析結果。

並列摘要


Chemical shift imaging, an extension of MRI (Magnetic resonance imaging) technique, was employed to detect the change of sugar content in bananas during the ripening process in different magnetic fields: 3 tesla and 7 tesla. In order to choose the optimal imaging parameters, the maximum SNR and PSNR in water were chosen as the indexes representing image quality. The optimal imaging parameters of TR=1000 ms and spatial resolution=64×64 were determined by adjusting various TR and various spatial resolutions in imaging experiments using a 7T spectrometer. Comparing the change of sugar content of pulp and peel based on a phantom of 0.5 M glucose solution, the results show that the sugar content in pulp increases 130 % in 3T MRI and 158 % in 7T MRI after ripening process. However, the change of sugar content in peel was not notably different after ripening. These results were confirmed with separate experiments using HPLC. We further compared the image quality, spectroscopic resolution and the capability of sugar content detection using 3T and 7T spectrometers. The results show that SNR=810 and PSNR=3371 in 7T CSI are higher than those in 3T CSI and spectral resolution=0.013 ppm and linewidth of spectra in water=0.214 ppm in 7T CSI are better than those in 3T CSI. The smaller spectral resolution and linewidth led to a higher capability of discerning different chemical bonds in the spectroscopic domain. When analyzing the sugar-to-water ratio and the sugar ratio in a glucose solution with pulp, the results obtained in different magnetic fields were similar. Therefore, when the chemical compounds can be normalized with a reference chemical compound, such as water, the ratio is similar in chemical shift images obtained in different magnetic fields. However, a higher magnetic field will result in better image quality as well as better spectroscopic resolution as shown by the experimental results in this study.

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