Estimating blood oxygenation from photoacoustic images: can a simple linear spectroscopic inversion ever work?
Estimating blood oxygenation from photoacoustic images: can a simple linear spectroscopic inversion ever work?
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DOI：
10.1117/1.jbo.24.12.121914
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发表时间：
2019-12-01
影响因子：
3.5
通讯作者：
Cox, Benjamin T.
中科院分区：
文献类型：
--
作者：
Hochuli, Roman;An, Lu;Cox, Benjamin T.
线性光谱反演，其中光声振幅被认为与吸收系数成正比，被广泛用于光声成像估计血氧饱和度，因为它的简单性。不幸的是，他们没有考虑到组织内光影响的波长依赖性的空间变化，这引入了“光谱着色”，这是一个潜在的重要误差来源。然而，准确地校正光谱着色是具有挑战性的，因此我们研究了是否存在条件，例如，波长集，在这些条件下，可以忽略光谱着色，并且仍然使用线性反演获得准确的氧合测量。当选择波长时，可以获得准确的氧化估计(i)最小化光谱着色，（ii）避免不良调节，以及（iii）保持足够高的信噪比（SNR）以使估计有意义。哪些波长满足这些条件并不明显，而且它们很可能因不同的成像场景而变化，因此很难找到一般规则。通过数值模拟，我们从实验误差的来源中分离出光谱着色的影响。结果表明，使用波长在500 nm和1000 nm之间产生不准确的氧合估计，而仔细选择波长在620- 920 nm范围内可以产生更准确的氧合值。然而，这只有在对真正的氧合进行良好的事先估计时才能实现。即使在这种理想的情况下，也表明，在使用线性光谱反演以获得准确的血氧估计时，必须相当小心地选择波长。这表明，对于特定的成像场景，使用线性光谱反演获得准确可靠的氧合估计需要对该场景进行仔细的建模或实验研究，考虑到仪器、组织解剖、可能的SO2范围和图像形成过程。(C)作者。根据知识共享署名4.0未移植许可协议，由SPIE发布。
Linear spectroscopic inversions, in which photoacoustic amplitudes are assumed to be directly proportional to absorption coefficients, are widely used in photoacoustic imaging to estimate blood oxygen saturation because of their simplicity. Unfortunately, they do not account for the spatially varying wavelength-dependence of the light fluence within the tissue, which introduces "spectral coloring," a potentially significant source of error. However, accurately correcting for spectral coloring is challenging, so we investigated whether there are conditions, e.g., sets of wavelengths, where it is possible to ignore the spectral coloring and still obtain accurate oxygenation measurements using linear inversions. Accurate estimates of oxygenation can be obtained when the wavelengths are chosen to (i) minimize spectral coloring, (ii) avoid ill-conditioning, and (iii) maintain a sufficiently high signal-to-noise ratio (SNR) for the estimates to be meaningful. It is not obvious which wavelengths will satisfy these conditions, and they are very likely to vary for different imaging scenarios, making it difficult to find general rules. Through the use of numerical simulations, we isolated the effect of spectral coloring from sources of experimental error. It was shown that using wavelengths between 500 nm and 1000 nm yields inaccurate estimates of oxygenation and that careful selection of wavelengths in the 620- to 920-nm range can yield more accurate oxygenation values. However, this is only achievable with a good prior estimate of the true oxygenation. Even in this idealized case, it was shown that considerable care must be exercised over the choice of wavelengths when using linear spectroscopic inversions to obtain accurate estimates of blood oxygenation. This suggests that for a particular imaging scenario, obtaining accurate and reliable oxygenation estimates using linear spectroscopic inversions requires careful modeling or experimental studies of that scenario, taking account of the instrumentation, tissue anatomy, likely SO2 range, and image formation process. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.