Multispectral photoacoustic imaging for detection of ischemia in skeletal muscle

In clinical practice, failure to promptly diagnose acute limb ischemia(ALI) can result in muscle necrosis and severe impairment of limb function, significantly impacting the patient’s life and health. The objective of this study is to investigate methods for non-invasive real-time monitoring of muscle ischemia severity to aid clinicians in diag- nostic decision-making. This study employed multispectral photoacoustic imaging to assess a rabbit model of lower limb ischemia. Initially, ischemia was induced in one limb of New Zealand white rabbits by applying a tourniquet for 2 hours to occlude the arterial blood flow. Subsequently, the tibialis anterior muscle was subjected to multispectral photoacoustic measurements using a photoacoustic imaging system at 0, 1, and 2 hours of compression. The acquired photoacoustic spectral data were then analyzed to determine the muscle oxygen saturation(SmO₂). Photoacoustic functional imaging quantified muscle oxygenation by evaluating the percentage of oxygenated hemoglobin and myo- globin relative to the total hemoglobin and myoglobin content. Finally, venous blood gas analysis was performed at corresponding time points to ascertain intravascular oxygen saturation levels. The results of blood gas analysis re- vealed venous oxygen saturation in the lower limbs to be 73.1%, 62.7%, and 38.8%, respectively, indicating localized ischemia and hypoxia in the lower limbs of the animal model. Photoacoustic imaging yielded skeletal muscle oxygen saturation values of 78%, 46%, and 38% at the respective time points. As ischemia duration increased, skeletal muscle hypoxia intensified, leading to a reduction in muscle oxygen saturation values, consistent with physiological expecta- tions. When the tourniquet is released and blood supply is restored, SmO₂ rapidly returns to baseline levels, indicating that photoacoustic imaging is sensitive to changes in muscle oxygenation. Consequently, multispectral photoacoustic imaging enables real-time measurement of SmO₂ during acute limb ischemia. This validates the capability of this non-invasive technique to provide localized, real-time assessment of skeletal muscle ischemia, which holds significant importance for investigating numerous clinical conditions.