Microvascular pressure drives perfusion in tissues but is difficult to measure. A method is proposed here to estimate relative pressures in microvessels using photoacoustic and ultrasound tracking of small vessels during calibrated tissue compression. A photoacoustic–ultrasound dual imaging transducer is used to directly compress on tissue in vivo. Photoacoustic signals from blood vessels diminish as an external load is applied and eventually reaches a minimum or vanishes when external pressure is sufficiently greater than the internal pressure. Two methods were proposed to estimate relative pressures. In the first approach, vessels were tracked during compression and when the vessel photoacoustic signals vanished below a set threshold, the internal pressures were assigned as the external loading pressure at the respective collapse point. In this approach pressures required to collapse vessel signatures completely were found to be much greater than physiological blood pressures. An alternative approach was to track the cross-sectional area of small vessels with changing external load and fitting the data to a known Shapiro model for thin-walled vessel compression. This approach produced estimates of internal pressures which were much more realistic. Both approaches produced the same rank-ordering of relative pressures of various vessels in vivo. Approaches thus far require future work to become fully quantitative but the present contributions represent steps towards this goal.

微血管压力驱动组织中的灌注，但难以测量。这里提出了一种在校准组织压缩期间使用小血管的光声和超声跟踪来估计微血管中的相对压力的方法。光声-超声双成像换能器用于直接压迫体内组织。来自血管的光声信号随着外部负载的施加而减弱，并且当外部压力充分大于内部压力时最终达到最小值或消失。提出了两种方法来估计相对压力。在第一种方法中，在压缩过程中跟踪血管，当血管光声信号消失到设定阈值以下时，内部压力被指定为相应塌陷点的外部加载压力。在这种方法中，发现完全塌陷血管特征所需的压力比生理血压大得多。另一种方法是跟踪外部载荷变化的小血管的横截面积，并将数据拟合到已知的薄壁血管压缩夏皮罗模型。这种方法产生了更加真实的内部压力估计。两种方法都产生了体内各种血管相对压力的相同排序。迄今为止的方法要求未来的工作完全量化，但目前的贡献代表了实现这一目标的步骤。