Handheld multispectral photoacoustic imaging for assessing myocardial metabolism.

Significance: Myocardial oxygen metabolism is a key focus of cardiac surgery. It serves as important evidence for surgeons to evaluate surgical quality and surgical plans. However, current clinical methods lack the capability to directly monitor dynamic changes in myocardial metabolism during surgery. Photoacoustic imaging (PAI), a biomedical optical imaging modality, offers real-time assessment of blood oxygen saturation. By visualizing oxygen saturation levels in both blood and muscle tissue, PAI provides a means to infer myocardial metabolic status intraoperatively.

Aim: We use PAI to observe the differences between infarcted myocardium and normal cardiac muscle and to explore the feasibility of using PAI to monitor myocardial metabolism levels during cardiac surgery.

Approach: Ten rabbits were randomly divided into experimental and control groups. The animals in the experimental group underwent thoracotomy followed by left anterior descending coronary artery ligation, whereas those in the control group received thoracotomy only. PAI was performed both at the beginning and before the end of the surgical procedure. The PAI results were compared between the two groups to analyze the relationship between myocardial PAI signal changes and oxygen metabolism levels.

Results: Following coronary ligation, the experimental group exhibited significant ST-segment elevation on electrocardiography, whereas no notable changes were observed in controls. PAI demonstrated: baseline myocardial oxygen saturation ( ${\mathrm{SmO}}_2$ ) ranged from 45% to 72% across all rabbits. Ligation-induced ischemia sharply reduced ${\mathrm{SmO}}_2$ to 1% to 19% in experimental animals. Control animals maintained stable ${\mathrm{SmO}}_2$ levels throughout the procedure. Histopathological examination confirmed extensive myocardial necrosis in the apical region of ligated rabbits, consistent with the observed functional and metabolic alterations.

Conclusions: PAI can detect myocardial oxygen saturation in real-time during surgery and determine the occurrence of myocardial ischemia and changes in oxygen metabolism levels based on differences in oxygen saturation.