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KMID : 0357520090320020177
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Journal of Radiological Science and Technology
2009 Volume.32 No. 2 p.177 ~ p.182
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3T MR Spin Echo T1 Weighted Image at Optimization of Flip Angle
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Bae Sung-Jin
Lim Cheong-Hwan
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Abstract
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Purpose: This study presents the optimization of flip angle (FA) to obtain higher contrast to noise ratio (CNR) and lower specific absorption rate (SAR).
Materials and Methods : T1-weighted images of the cerebrum of brain were obtained from 50 to 130 FA with 10 interval. Signal to noise ratios (SNRs) were calculated for white matter (WM), gray matter (GM), and background noise. The proper FA was analyzed by T-test statistics and Kruskal-wallis analysis using R1 = 1- exp () and Ernst angle cos = exp ().
Results: The SNR of WM at 130 FA is approximately 1.6 times higher than the SNR of WM at 50. The SNR of GM at 130 FA is approximately 1.9 times higher than the SNR of GM at 50. Although the SNRs of WM and GM showed similar trends with the change of FA values, the slowdown point of decrease after linear fitting were different. While the SNR of WM started decreasing at 120 FA, the SNR of GM started decreasing at less than 110. The highest SNRs of WM and GM were obtained at 130 FA. The highest CNRs, however, were obtained at 80 FA.
Conclusion: Although SNR increased with the change of FA values from 50 to 130 at 3T SE T1WI, CNR was higher at 80 FA than at the usually used 90 FA. In addition, the SAR was decreased by using smaller FA. The CNR can be increased by using this optimized FA at 3T MR SE T1WI.
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KEYWORD
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spin echo, T1-weighted image, flip angle, signal to noise ratio, contrast to noise ratio
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