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磁共振射频能量吸收率的概念、计算方法与实际运用 被引量:6
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作者 张奇 刘曼芳 黄煌镜 《中国医学影像技术》 CSCD 北大核心 2000年第3期240-240,共1页
随着磁共振扫描技术的不断发展,其主磁场场强与射频激发脉冲的功率也不断提高。现今的高场强磁共振中都引入了一种全新的防护概念:射频能量吸收率(specificabsorptionrate;SAR)。1 SAR的概念人体在行磁共... 随着磁共振扫描技术的不断发展,其主磁场场强与射频激发脉冲的功率也不断提高。现今的高场强磁共振中都引入了一种全新的防护概念:射频能量吸收率(specificabsorptionrate;SAR)。1 SAR的概念人体在行磁共振检查时,将接收射频脉冲的激励。高?.. 展开更多
关键词 磁共振检查 射频激发脉冲 SAR 计算方法
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Optimization of ultrasonic elastography by coded excitation and transmit-side multi-frequency compounding
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作者 张志宏 刘昊霖 +1 位作者 何颖妮 刘东权 《Journal of Central South University》 SCIE EI CAS 2014年第3期1003-1010,共8页
To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography (TFCCE) was propose... To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography (TFCCE) was proposed. TFCCE adopts the chirp signal excitation scheme and strikes a balance in the selection of sub-signal bandwidth, the bandwidth overlap and the number of sub-strain image based on theoretical derivation, so as to further improve the quality of elastic image. Experiments have proved that, compared with the other optimizing methods, the elastographyic signal-to-noise ratio(Re-SN) and contrast-to-noise ratio(Re-CN) are improved significantly with different echo signal-to-noise ratios (ReSN) and attenuation coefficients. When ReSN is 50 dB, compared with short pulse, Rc-SN and Re-CN obtained by TFCCE increase by 53% and 143%, respectively. Moreover, in a deeper investigation (85-95 mm), the image has lower strain noise and clear details. When the attenuation coefficient is in the range of 0-1 dB/(cm.MHz), Re-SN and Re-CN obtained by TFCCE can be kept in moderate ranges of 5〈Re-SN〈6.8 and 11.4〈Re-CN〈15.2, respectively. In particular, for higher tissue attenuation, the basic image quality cannot be ensured with short pulse excitation, while mediocre quality strain figure can be obtained by TFCCE. Therefore, the TFCCE technology can effectively improve the elastography quality and can be applied to ultrasonic clinical trials. 展开更多
关键词 ultrasonic elastography coded excitation transmit-side multi-frequency compounding elastographyic signal-to-noise ratio echo signal-to-noise ratio contrast-to-noise ratio
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