Peripheral artery disease is often asymptomatic, and various imaging and nonimaging techniques have been used for assessment and monitoring treatments. This study is designed to demonstrate the ability of photoacoustic imaging to noninvasively determine changes in tissue oxygenation that occur in mice’s hind limb skeletal muscle as they age. Mice from two age cohorts were scanned bilaterally with a pulsed laser. The photoacoustic signal was unmixed to generate a parametric map of estimated oxygen saturation and then overlaid on grayscale ultrasound images. Tissue oxygenation measured in young and old mice was compared. Photoacoustic imaging visually and quantitatively showed the decrease in skeletal muscle oxygenation that occurs with age. Percent tissue oxygenation decreased from 30.2% to 3.5% (p < 0.05). This reduction corresponded to reduced fractional area of oxygenation, which decreased from 60.6% to 6.0% (p < 0.05). The change in oxygenation capacity of the still active vascular regions was insignificant (p > 0.05). Intrasubject, intra-, and interobserver comparisons showed low variability in measurements, exhibited by high regression and intraclass correlations exceeding 0.81 for all ages. The decrease in oxygenation detected by photoacoustic imaging paralleled the known oxygenation decrease observed in aging tissues, demonstrating that photoacoustic imaging can assess age-related changes in a mouse calf muscle. These intramuscular changes could potentially act as a strong diagnostic marker for peripheral artery disease. This study thus opens the doors for a novel, affordable, noninvasive method of evaluation free of radiation or exogenous material.

中文翻译：

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通过光声成像评估与年龄相关的小腿骨骼肌氧合变化：外周动脉疾病的潜在工具

外周动脉疾病通常是无症状的，各种影像和非影像技术已被用于评估和监测治疗。这项研究旨在证明光声成像能够无创地确定随着年龄增长在小鼠后肢骨骼肌中发生的组织氧合变化。用脉冲激光对来自两个年龄组的小鼠进行双侧扫描。光声信号被分离以生成估计氧饱和度的参数图，然后叠加在灰度超声图像上。比较了在年轻和年老小鼠中测量的组织氧合。光声成像在视觉上和定量上显示随年龄增长而发生的骨骼肌氧合减少。组织氧合百分比从 30.2% 降至 3.5% (p < 0.05)。这种减少对应于氧合部分面积的减少，从 60.6% 减少到 6.0% (p < 0.05)。仍然活跃的血管区域的氧合能力的变化是微不足道的（p > 0.05）。受试者内部、内部和观察者间的比较显示测量值的低变异性，表现为所有年龄段的高回归和组内相关性超过 0.81。光声成像检测到的氧合减少与衰老组织中观察到的已知氧合减少平行，表明光声成像可以评估小鼠小腿肌肉中与年龄相关的变化。这些肌内变化有可能成为外周动脉疾病的有力诊断标志物。因此，这项研究为一种新颖的、负担得起的、