Garra B S, Shawker T H, Nassi M, Russell M A
Ultrason Imaging. 1984 Oct;6(4):396-407. doi: 10.1177/016173468400600402.
Attenuation measurements of various tissue mimicking phantoms and three different groups of patients were obtained using a modified commercial sector scanner. Estimates of attenuation were made using the spectral shift method with mean frequencies at different depths of a region of interest being obtained by both zero crossing and fast Fourier transform techniques. The accuracy and precision of both techniques was compared in phantoms and it was found that the FFT technique yielded less day-to-day variation (SD=3 percent) than the zero crossing technique (5 percent). For larger regions of interest, the range of variation in both techniques was more similar. Day-to-day variation in livers of normal patients was much larger than that seen in phantoms (10 to 15 percent) suggesting that in vivo measurements may be less precise due to actual daily changes in patients' livers. Attenuation estimates of phantoms were high by approximately 0.16 dB/MHz/cm compared to values obtained by transmission techniques. The attenuation values of livers in a group of 31 normal patients ranged from 0.214 dB/cm/MHz to 0.849 dB/cm/MHz with a mean of 0.627 +/- 0.126 dB/cm/MHz for the zero crossing technique while the mean value using the FFT technique was 0.86 +/- 0.168 dB/cm/MHz. A group of 26 Gauchers disease patients also showed wide variation with a mean attenuation value of 0.768 +/- 0.21 dB/cm/MHz using the FFT technique. This was significantly different than that of the normal group (p less than .05). Also, a group of 22 chronic B hepatitis patients was examined, having a mean attenuation value of 0.823 +/- 0.21 dB/cm/MHz, not significantly different from those of normal patients. Highly significant differences were found between the three groups when the power spectrum bandwidths of signals received were compared. These differences may be due to differences in the dependence of attenuation as a function of frequency between the groups and may represent a useful tissue characterization parameter.
使用改良的商用扇形扫描仪获取了各种组织模拟体模和三组不同患者的衰减测量值。通过谱移法进行衰减估计，利用过零技术和快速傅里叶变换技术获取感兴趣区域不同深度处的平均频率。在体模中比较了这两种技术的准确性和精密度，发现快速傅里叶变换技术的日常变化（标准差 = 3%）比过零技术（5%）小。对于较大的感兴趣区域，两种技术的变化范围更相似。正常患者肝脏的日常变化比体模中的大得多（10%至15%），这表明由于患者肝脏的实际日常变化，体内测量可能不太精确。与通过透射技术获得的值相比，体模的衰减估计值大约高0.16 dB/MHz/cm。31名正常患者肝脏的衰减值范围为0.214 dB/cm/MHz至0.849 dB/cm/MHz，过零技术的平均值为0.627±0.126 dB/cm/MHz，而使用快速傅里叶变换技术的平均值为0.86±0.168 dB/cm/MHz。一组26名戈谢病患者使用快速傅里叶变换技术时也显示出较大变化，平均衰减值为0.768±0.21 dB/cm/MHz。这与正常组有显著差异（p小于0.05）。此外，检查了一组22名慢性B型肝炎患者，其平均衰减值为0.823±0.21 dB/cm/MHz，与正常患者无显著差异。比较接收到的信号的功率谱带宽时，发现三组之间存在高度显著差异。这些差异可能是由于各组之间衰减随频率的依赖性不同，可能代表一个有用的组织特征参数。
