In vivo ultrasound thermography in presence of temperature heterogeneity and natural motions.
In vivo ultrasound thermography in presence of temperature heterogeneity and natural motions.
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DOI：
10.1109/tbme.2014.2358075
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发表时间：
2015-02
期刊：
影响因子：
--
通讯作者：
Ebbini ES
中科院分区：
文献类型：
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作者：
Bayat M;Ballard JR;Ebbini ES
实时超声热成像最近已经在商业上可用的诊断成像探头上得到证明。体外实验结果表明，对亚治疗聚焦超声引起的小的局部温度变化具有高灵敏度。然而，大多数已发表的结果都是基于热致回波应变模型，该模型假设成像帧之间的温度变化极小。在此假设下，回波应变计算使用低通轴向微分器，这是由有限脉冲响应（FIR）数字滤波器实现。在本文中，我们介绍了一种新的模型，温度估计采用递归轴向滤波器，作为一个空间微分积分器的回波位移。该滤波器是从第一性原理推导出来的，它在计算两帧之间的空间温度变化时考虑了不均匀的温度基线。这是与先前提出的无限小回波应变滤波器（δ-ESF）方法的主要区别。我们表明，新的方法可以实现一阶无限脉冲响应（IIR）数字滤波器与深度相关的空间频率响应。体外实验结果表明，与δ-ESF方法相比，该方法在抑制估计温度的空间变化方面具有优势，而无需对回波应变进行专门的低通滤波。新的递归回波应变滤波器（RESF）的性能也说明了使用亚治疗局部加热在哥本哈根大鼠在体内的后肢期间获得的回波数据。除了RESF，我们还使用了自适应空间滤波器来去除实时数据收集过程中的运动和变形伪影。自适应滤波算法的描述和比较与未经补偿的估计时空温度分布。结果表明，在体内超声热成像具有高灵敏度和特异性的可行性。
Real-time ultrasound thermography has been recently demonstrated on commercially-available diagnostic imaging probes. In vitro experimental results demonstrate high sensitivity to small, localized temperature changes induced by subtherapeutic focused ultrasound. Most of the published results, however, are based on a thermally-induced echo strain model that assumes infinitesimal change in temperature between imaging frames. Under this assumption, the echo strain is computed using a lowpass axial differentiator which is implemented by a finite impulse response (FIR) digital filter. In this paper, we introduce a new model for temperature estimation which employs a recursive axial filter that acts as a spatial differentiator-integrator of echo shifts. The filter is derived from first principles and it accounts for a nonuniform temperature baseline when computing the spatial temperature change between two frames. This is a major difference from the previously proposed infinitesimal echo strain filter (δ-ESF) approach. We show that the new approach can be implemented by a first-order infinite impulse response (IIR) digital filter with depth-dependent spatial frequency response. Experimental results in vitro demonstrate the advantages over the δ-ESF approach in terms of suppressing the spatial variations in the estimated temperature without resorting to ad hoc lowpass filtering of echo strains. The performance of the new recursive echo strain filter (RESF) is also illustrated using echo data obtained during sub-therapeutic localized heating in the hind limb of Copenhagen rat in vivo. In addition to the RESF, we have used an adaptive spatial filter to remove motion and deformation artifacts during real-time data collection. The adaptive filtering algorithm is described and comparisons with uncompensated estimated spatio-temporal temperature profiles are given. The results demonstrate the feasibility of in vivo ultrasound thermography with high sensitivity and specificity.