Amplitude modulated chirp excitation to reduce grating lobes and maintain ultrasound intensity at the focus of an array.
Amplitude modulated chirp excitation to reduce grating lobes and maintain ultrasound intensity at the focus of an array.
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DOI：
10.1016/j.ultras.2013.03.014
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发表时间：
2013-09
期刊：
影响因子：
4.2
通讯作者：
Oelze, Michael L.
中科院分区：
文献类型：
--
作者：
Karunakaran, Chandra P.;Oelze, Michael L.
在高强度聚焦超声（HIFU）与治疗阵列的应用过程中，栅瓣的存在会导致非预期组织区域的加热。因此，减少治疗阵列中的栅瓣是一个重要的目标。减少治疗阵列中的栅瓣的一种方式是用宽带信号（这里定义为>10%的分数带宽）激励阵列。为了实现超声阵列中栅瓣水平的降低，可以利用编码波形，其降低栅瓣水平，同时保持空间峰值时间平均强度。在这项研究中，一个5 MHz，9元，1.25 mm的元素间的间距线阵激励的正弦波形，传统的线性啁啾，和修改后的线性啁啾。两个啁啾都跨越换能器的−3 dB带宽。传统的线性调频脉冲是一种宽带信号，线性扫描频率在2.5至7.5 MHz之间，所有频率分量以相等的幅度激励。修改的线性调频信号也扫描2.5和7.5 MHz之间的频率，但幅度被加权，使得边缘（频带的低频和高频）被比频带中心更多的能量激发。在模拟中，使用Field II从阵列产生正弦、常规啁啾和修改的啁啾激励的场图案并进行比较。对于实验，从5 MHz的单元件换能器的波束图案映射使用水听器的正弦，传统的啁啾和修改啁啾激励。来自换能器的每个场被重复并求和以产生来自9个元件的阵列的场。针对每个激励估计主瓣和栅瓣中的时间平均强度（dB）的差异并进行比较。结果表明，与主瓣相比，啁啾信号导致光栅瓣水平的降低，即，聚焦下降10 dB，聚焦和转向下降6 dB。与传统的啁啾激励相比，对于修改的啁啾激励，观察到栅瓣水平进一步降低1dB，这对应于栅瓣位置处的能量沉积降低约21%。
During application of high intensity focused ultrasound (HIFU) with therapy arrays, the existence of grating lobes can cause heating at unintended tissue regions. Therefore, the reduction of grating lobes in therapeutic arrays is an important goal. One way to reduce the grating lobes in therapy arrays is to excite the arrays with broadband signals (defined here as >10% fractional bandwidth). To achieve a reduction in grating lobe levels in an ultrasonic array, coded waveforms can be utilized that reduce the grating lobe levels while maintaining the spatial peak temporal average intensity. In this study, a 5-MHz, 9-element, 1.25 mm inter-elemental spacing linear array was excited by a sinusoidal waveform, a conventional linear chirp, and a modified linear chirp. Both chirps spanned the −3-dB bandwidth of the transducer. The conventional chirp was a broadband signal with a linear sweep of frequencies between 2.5 and 7.5 MHz, with all frequency components excited with equal amplitude. The modified chirp signal also swept the frequencies between 2.5 and 7.5 MHz, but the amplitude was weighted such that the edges (low and high frequencies of the band) were excited with more energy than the center of the band. In simulations, the field patterns for the sinusoidal, conventional chirp and modified chirp excitations were produced from the array using Field II and compared. For experiments, the beam pattern from a 5-MHz single-element transducer was mapped using a hydrophone for the sinusoidal, conventional chirp and modified chirp excitation. Each field from the transducer was repeated and summed to produce a field from an array of 9 elements. The difference in the time averaged intensity (in dB) in the main lobe and grating lobes were estimated for each excitation and compared. The results demonstrated that the chirp signals resulted in decreases in grating lobe levels compared to the main lobe, i.e. 10 dB down for focusing and 6 dB down for focusing and steering. A further 1 dB decrease in grating lobe levels was observed for the modified chirp excitation compared to the conventional chirp excitation, which corresponds to ~21% reduction in energy deposition at the grating lobe location.
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DOI：
10.1109/58.139123
发表时间：
1992-03-01
影响因子：
3.6
作者：
JENSEN, JA;SVENDSEN, NB
通讯作者：
SVENDSEN, NB
DOI：
10.1109/58.655626
发表时间：
1997-09-01
影响因子：
3.6
作者：
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作者：
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影响因子：
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作者：
Hutchinson, EB;Hynynen, K
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2.3
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