A photoacoustic tomography image reconstruction method based on forward imaging model
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摘要:
在光声层析成像（photoacoustic tomography，PAT）时，不均匀光通量分布、组织复杂的光学和声学特性以及超声探测器的非理想特性等因素会导致重建图像质量下降。本文考虑不均匀光通量、非定常声速、超声探测器的空间脉冲响应和电脉冲响应、有限角度扫描和稀疏采样等因素的影响，建立了前向成像模型。通过交替优化求解成像模型的逆问题，实现光吸收能量分布图和声速分布图的同时重建。仿真、仿体和在体实验结果表明，与反投影法、时间反演法和短滞后空间相干法相比，该方法重建图像的结构相似度和峰值信噪比可分别提高约83%、56%、22%和80%、68%、58%。由上述结果可知，对非理想成像场景采用该方法重建的图像质量有显著提高。
Abstract:Aiming at the issue of degraded image quality in photoacoustic tomography (PAT) caused by the inhomogeneous light fluence distribution, complex optical and acoustic properties of biological tissues, and non-ideal properties of ultrasonic detectors, we propose a comprehensive forward imaging model. The model takes into account variables such as the inhomogeneous light fluence, unsteady speed of sound, spatial and electrical impulse responses of ultrasonic transducers, limited-view scanning, and sparse sampling. The inverse problem of the imaging model is solved by alternate optimization, and images representing optical absorption and speed of sound (SoS) distributions are reconstructed simultaneously. The results indicate that the structural similarity of the reconstructed images of the proposed method can be enhanced by about 83%, 56%, and 22%, in comparison with back projection, time-reversal, and short-lag spatial coherence techniques, respectively. Additionally, the peak signal-to-noise ratio can be improved by approximately 80%, 68% and 58%, respectively. This method considerably enhances the image quality of non-ideal imaging scenarios when compared to traditional techniques.
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图 3 活体小鼠光声层析成像实验系统示意图
Figure 3. Schematic diagram of PAT experimental setup for in vivo mice
图 4 根据全角度密集采样的仿真光声信号重建的图像及其评价指标。(a)光吸收能量分布图；(b)声速分布图；(c)评价指标
Figure 4. Reconstructed distribution maps and their evaluation metrics based on simulated photoacoustic signals that are densely-sampled and collected at a full-angle. (a) AOED distribution maps; (b) SoS distribution; (c) evaluation metrics
图 5 根据有限角度稀疏采样仿真光声信号重建的光吸收能量分布图及其评价指标。(a) 重建图像；(b) 评价指标
Figure 5. Results of images reconstructed from limited-view sparse sampling simulated data and their evaluation metrics. (a) Reconstructed images; (b) evaluation metrics
图 6 仿体图像重建结果及评价指标。(a) 光吸收能量分布图；(b) 声速分布图；(c) 评价指标
Figure 6. Reconstructed distribution maps and their evaluation metrics of phantoms. (a) AOED distribution map; (b) SoS distribution map; (c) evaluation metrics
图 7 小鼠胸腹切片图像重建结果及评价指标。(a) 光吸收能量分布图；(b) 声速分布图；(c) 光吸收能量分布图评价指标
Figure 7. Reconstructed thoracic and abdominal slice images of in vivo mice and evaluation metrics. (a) AOED distribution map; (b) SoS distribution map; (c) evaluation metrics of distribution map
图 8 采用不同迭代初始值时的重建图像和迭代次数。 (a) 重建图像；(b) 重建模型1中不同位置处的AOED所需的迭代次数
Figure 8. Reconstructed distribution maps and the number of iterations with different iterative initial values. (a) Reconstructed images; (b) number of iterations required for AOED at different locations in the reconstructed model 1
图 9 采用不同优化算法重建的AOED分布图及其评价指标。(a) 重建图像；(b) 评价指标
Figure 9. AOED images reconstructed using different optimization algorithms and their evaluation metrics. (a) Reconstructed images; (b) evaluation metrics
图 10 不同固定声速条件下，根据仿真光声信号重建的AOED分布图和评价指标。(a) 重建图像；(b) 评价指标
Figure 10. Reconstructed AOED images and evaluation metrics from simulated data using different fixed speed of sound. (a) Reconstructed images; (b) evaluation metrics
图 11 优化光通量对重建图像质量的影响。 (a) 重建的AOED图像；(b) 评价指标
Figure 11. Effect of optimized luminous flux on reconstructed image quality. (a) Reconstructed AOED image; (b) evaluation metrics
图 12 采用不同的考虑超声探测器响应的方法重建的光吸收能量分布图和评价指标。(a) 重建图像；(b) 评价指标
Figure 12. Images reconstructed by different methods that considering the response of ultrasonic detectors and their evaluation metrics. (a) Reconstructed images; (b) evaluation metrics.
表 1 数值仿真模型的组织特性参数
Table 1. Tissue property parameters of numerical phantoms
组织
名称组织
成分折射率 吸收系数
(cm‒1)散射系数
(cm‒1)各向异
性因子声速
(m/s)密度
(kg/L)心脏 肌肉组织 1.37 0.78 132 0.96 1580 1.060 肺 肌肉组织 1.37 0.72 114 0.95 1561 1.043 肾 结缔组织 1.36 0.76 205 0.90 1560 1.050 肝脏 肌肉组织 1.37 0.75 103 0.91 1595 1.060 胸骨 钙质 1.37 0.05 150 0.96 1580 1.050 
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