Department of Radiology, Harvard Medical School and Brigham & Women's Hospital, Boston, Massachusetts 02115, USA.
J Acoust Soc Am. 2011 Oct;130(4):1810-9. doi: 10.1121/1.3625236.
Chirp-encoded excitation has been utilized for increased signal-to-noise ratio (SNR) in both linear and harmonic imaging. In either case, it is necessary to isolate the relevant frequency band to avoid artifacts. In contrast, the present study isolates and then combines the fundamental and the higher harmonics, treating them as a single, extended bandwidth. Pulse-inverted sum and difference signals are first used to isolate even and odd harmonics. Matched filters specific to the source geometry and the transmit signal are then separately applied to each harmonic band. Verification experiments are performed using up to the third harmonic resulting from an underwater chirp excitation. Analysis of signal peaks after scattering from a series of steel and nylon wires indicates increased compression using the extended bandwidth, as compared to well-established methods for fundamental and second harmonic chirp compression. Using third harmonic bands, a mean pulse width of 56% relative to fundamental compression and 48% relative to second harmonic compression was observed. Further optimization of the compression by altering the transmission indicated 17% additional reduction in the pulse width and a 47% increase in peak-to-sidelobe ratio. Overall, results establish the feasibility of extended bandwidth signal compression for simultaneously increasing SNR and signal resolution.
啁啾编码激励已被用于提高线性和谐波成像中的信噪比 (SNR)。在这两种情况下，都有必要隔离相关的频带以避免伪影。相比之下，本研究将基波和各次谐波隔离并组合在一起，将它们视为单个扩展带宽。首先使用脉冲反转和差信号来隔离奇次和偶次谐波。然后将特定于源几何形状和发射信号的匹配滤波器分别应用于每个谐波频段。使用水下啁啾激励产生的第三谐波进行验证实验。对一系列钢线和尼龙线散射后的信号峰值进行分析表明，与基本和二次谐波啁啾压缩的既定方法相比，使用扩展带宽可实现更高的压缩比。使用三次谐波带，与基本压缩相比，相对脉冲宽度为 56%，与二次谐波压缩相比，相对脉冲宽度为 48%。通过改变传输进一步优化压缩，可使脉冲宽度进一步降低 17%，并使峰值与旁瓣比提高 47%。总体而言，结果表明扩展带宽信号压缩同时提高 SNR 和信号分辨率是可行的。
