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超声背散射法已逐渐应用于骨质的评价与诊断. 相比于人体软组织, 致密多孔的骨组织中超声衰减大, 导致接收到的超声信号微弱, 频散失真严重. 骨组织的超声频散衰减通常由超声透射法测量. 然而, 透射法测量的超声衰减为传播路径上组织介质衰减的平均值, 无法区分软组织、皮质骨及松质骨的衰减效应, 无法测量感兴趣区域内松质骨组织的超声衰减. 本文旨在研究松质骨超声频散衰减的背散射测量方法, 分析补偿超声背散射信号频散失真的可行性. 离体测量16块松质骨样本的超声背散射与透射信号(中心频率1 MHz). 采用四种背散射方法(谱移法、谱差法、谱对数差法和混合法)测量松质骨超声频散衰减系数, 与超声透射法测量的频散衰减标准值进行对比. 结果表明, 骨样本超声频散衰减范围为2.3—6.2 dB/mm/MHz, 透射法测量的超声频散衰减(均值 ± 方差)为(4.14 ± 1.14) dB/mm/MHz; 谱移法、谱差法、谱对数差法和混合法测量的频散衰减(均值 ± 方差)分别为(3.88 ± 1.15) dB/mm/MHz, (4.00 ± 0.98) dB/mm/MHz, (3.77 ± 0.84) dB/mm/MHz, (4.05 ± 0.85) dB/mm/MHz. 背散射法测量的频散衰减系数与标准值有较高的相关性( R= 0.78—0.92, p< 0.01), 其中, 谱差法( R= 0.91, p< 0.01)和混合法( R= 0.92, p< 0.01)测量结果更准确(相对误差小于20%). 以上结果说明背散射法测量松质骨超声频散衰减具有可行性, 基于傅里叶变换-逆变换原理可以补偿背散射信号频散衰减失真, 显著提高信号强度, 有利于后续超声背散射骨质评价及成像研究.Ultrasonic backscatter has been gradually applied to the assessment and diagnosis of bone disease. The heavy frequency-dependent attenuation of ultrasound results in weak ultrasonic signals with poor signal-to-noise ratio and serious wave distortions during propagation in cancellous bone. Ultrasonic attenuation measured with the through-transmission method is an averaged result of ultrasonically interrogated tissues (including the soft tissue, cortical bone and cancellous bone). Therefore, the through-transmission measurements can not accurately provide ultrasonic attenuation of cancellous bone of interest. The purpose of this study is to estimate ultrasonic frequency-dependent attenuation with ultrasonic backscatter measurements and to compensate for the frequency-dependent attenuation in an ultrasonic backscatter signal from cancellous bone. In-vitroultrasonic backscatter and through-transmission measurements are performed on 16 cancellous bone specimens by using 1.0-MHz transducers. Spatial scans are performed in a 10 mm × 10 mm scanned region with a spatial interval of 0.5 mm for each bone specimen. The frequency slope of ultrasonic attenuation is measured with the ultrasonic through-transmission signals serving as a standard value. Four different algorithms (the spectral shift method, the spectral difference method, the spectral log difference method, and the hybrid method) are used to estimate the frequency slope of ultrasonic attenuation coefficient from ultrasonic backscatter signal. The results show that the frequency-dependent attenuation coefficient ranges from 2.3 dB/mm/MHz to 6.2 dB/mm/MHz for the bovine bone specimens. The through-transmission measured frequency slope of ultrasonic attenuation coefficient is (4.14 ± 1.14) dB/mm/MHz (mean ± standard deviation), and frequency slopes of ultrasonic attenuation coefficient are estimated by four backscattering methods to be (3.88 ± 1.15) dB/mm/MHz, (4.00 ± 0.98) dB/mm/MHz, (3.77 ± 0.84) dB/mm/MHz, and (4.05 ± 0.85) dB/mm/MHz, respectively. The estimated frequency-dependent attenuation is significantly correlated with the standard attenuation value ( R= 0.78－0.92, p< 0.01), in which the spectral difference method ( R= 0.91, p< 0.01) and the hybrid method ( R= 0.92, p< 0.01) are more accurate with an estimated error less than 20%. The results prove that it is feasible to measure the frequency-dependent attenuation from ultrasonic backscatter signal of cancellous bone. Based on Fourier transform-inverse Fourier transform, the frequency-dependent attenuation can be compensated.The compensated ultrasonic signals are with significantly improved signal intensity and improved signal-to-noise ratio. This study is conducive to the subsequent ultrasonic backscatter measurement and ultrasonic imaging of cancellous bone.
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Keywords:
- ultrasonic backscatter/
- bone evaluation/
- frequency-dependent attenuation/
- attenuation compensation
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] -
样本编号 透射标准值/dB·mm–1·MHz–1 背散射法测量值(相对误差)/dB·mm–1·MHz–1(%) 谱移法 谱差法 谱对数差法 混合法 1 2.30 2.74 (19.1) 2.82 (22.4) 2.77 (20.3) 2.67 (16.2) 2 2.63 2.49 (–5.3) 2.85(8.3) 3.13 (19.3) 2.97 (13.1) 3 2.82 2.39 (–15.3) 2.97 (5.2) 2.78 (–1.4) 3.29 (16.6) 4 3.06 3.04 (–0.6) 2.77 (–9.4) 3.02 (–1.4) 3.02 (–1.3) 5 3.10 2.95 (–4.6) 2.84 (–8.3) 3.39 (9.5) 3.12 (0.8) 6 3.30 2.96 (–10.3) 3.38 (2.3) 2.99 (-9.4) 3.35 (1.7) 7 4.14 2.93 (–29.2) 3.94 (–4.9) 4.21 (1.5) 4.32 (4.3) 8 4.30 3.06 (–28.9) 4.75 (10.5) 3.58 (–16.7) 3.61 (–16.0) 9 4.37 4.80 (9.8) 3.89 (–11.0) 3.66 (–16.2) 4.75 (8.7) 10 4.37 5.10 (–16.9) 4.19 (–4.2) 3.36 (–23.1) 4.25 (–2.7) 11 4.52 3.89 (–13.9) 4.35 (–3.7) 3.87 (–14.3) 4.79 (6.0) 12 4.83 5.35 (10.9) 4.19 (–13.2) 4.53 (–6.1) 4.69 (–2.7) 13 5.29 4.42 (–16.5) 5.68 (7.3) 6.08 (14.9) 5.18 (–2.0) 14 5.50 5.18 (–5.8) 4.38 (–20.0) 4.19 (–23.8) 5.00 (–9.0) 15 5.64 4.73 (–16.2) 5.75 (1.9) 3.96 (–29.9) 5.08 (–9.9) 16 6.19 6.02 (–2.8) 5.25 (–15.3) 4.79 (–22.6) 4.76 (–23.1) 平均值 (标准差) 4.14 (1.14) 3.88 (1.15) 4.00 (0.98) 3.77 (0.84) 4.05 (0.85) 
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