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首页> 外文期刊>IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control >Quantitative real-time blood flow estimation with intravascular ultrasound in the presence of in-plane flow
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Quantitative real-time blood flow estimation with intravascular ultrasound in the presence of in-plane flow

机译：在存在面内血流的情况下利用血管内超声进行实时定量血流估计

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摘要

Previously, we showed a source of error in blood flow estimation introduced by in-plane flow using a slow-time finite-impulse response (FIR) filter-bank method measuring blood flow through the image plane of an intravascular ultrasound (IVUS) catheter array. There is a monotonic relationship between flow velocity and the normalized second moment of the slow-time spectrum when flow is orthogonal to the image plane of a side-looking catheter array. However, this relationship changes in the presence of in-plane flow, as slow-time spectra shift and spread with varying in-plane and out-of-plane components. These two effects increase the normalized spectral second moment, resulting in flow overestimates. However, by resampling the received signal with variable time delay from pulse to pulse (i.e., tilting the slow-time signals), the slow-time spectrum shifts back to direct current (DC), and the orthogonal estimation method can be used. We present a method to correct this overestimation and accurately estimate blood flow through the image plane in real time. Initially, the tilt delay needed to shift the slow-time spectrum back to DC at each point within the flow field is calculated. Knowing this tilt delay, a tilted slow-time signal is obtained for the velocity component normal to the image plane, and its spectrum is estimated using a filter-bank. That spectrum then is used to estimate the flow speed using a mapping function closely related to the monotonic relationship between the slow-time spectrum and flow speed observed for orthogonal flow. To accurately estimate flow angles, we modified the filter-bank algorithm, applying slow-time filter coefficients in a tilted arrangement and studying the slow-time spectral energy as a function of tilt. The slow-time spectral estimate is constructed with the tilted output of eight narrow, band-pass filters from a filter-bank. Independent simulations show that, for blood slowing at angles between /spl plusmn/6/spl deg/ and /spl plusmn/15/spl deg/ at a speed of 300 mm/s, flow velocity would be overestimated by as much as 38.79% and 249%, respectively, using the direct filter-bank approach. However, this error can be corrected using the modified method presented here, reducing the maximum overestimation error by a factor of 2.6-9 and 10.88 for those angles, respectively. Although the remaining error is riot negligible, the volume flow rate, calculated by integrating the flow velocity over the entire vessel lumen, differs by only 3% or less from the true value over the angular range considered here. This represents an improvement of a factor of 40 over uncompensated estimates at maximum flow angles. Consequently, the modified real-time method can quantitatively measure flow in most IVUS applications in which the catheter's image plane is not precisely orthogonal to the flow direction.
机译：以前，我们展示了使用慢时有限冲激响应（FIR）滤波器组方法通过平面内流动引入的血流估计误差来源，该方法通过流过血管内超声（IVUS）导管阵列的图像平面来测量血流。当流量正交于侧视导管阵列的像平面时，流速和慢速频谱的归一化第二矩之间存在单调关系。但是，这种关系在存在平面内流动时会发生变化，因为慢速光谱会随着平面内和平面外分量的变化而移动和扩展。这两个影响会增加归一化频谱的第二矩，从而导致流量过高。然而，通过以可变的时间延迟从脉冲到脉冲对接收信号进行重采样（即，倾斜慢时间信号），慢时间频谱移回到直流（DC），并且可以使用正交估计方法。我们提出一种方法来纠正这种高估并实时准确地估计通过图像平面的血流量。最初，计算在流场内每个点处将慢速频谱移回DC所需的倾斜延迟。知道了这种倾斜延迟，就获得了垂直于像平面的速度分量的倾斜慢时间信号，并使用滤波器组估计了其频谱。然后，使用与慢速频谱和正交流观测到的流速之间的单调关系密切相关的映射函数，将该光谱用于估算流速。为了准确地估计流角，我们修改了滤波器组算法，以倾斜的方式应用慢时间滤波器系数，并研究了慢时间谱能量随倾斜度的变化。利用来自滤波器组的八个窄带通滤波器的倾斜输出来构建慢时间频谱估计。独立模拟显示，如果血液以300 mm / s的速度在/ spl plusmn / 6 / spl deg /和/ spl plusmn / 15 / spl deg /之间的角度减速，流速将被高估38.79％和249％，分别使用直接滤波器组方法。但是，可以使用此处介绍的修改方法纠正此误差，对于这些角度，最大过高估计误差分别减少2.6-9和10.88倍。尽管剩余误差可以忽略不计，但通过对整个血管腔内的流速进行积分所计算出的体积流量与此处考虑的角度范围内的真实值相差仅3％或更小。与最大流量角下的未补偿估算值相比，该系数提高了40倍。因此，改进的实时方法可以定量测量大多数IVUS应用中的流量，在大多数IVUS应用中，导管的图像平面不精确地垂直于流向。

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