In ultrasound imaging, fully-developed speckle arises from the spatiotemporal superposition of pressure waves backscattered by randomly distributed scatterers. Speckle appearance is affected by the imaging system characteristics (lateral and axial resolution) and the random-like nature of the underlying tissue structure. In this work, we examine speckle formation in acoustic-resolution photoacoustic (PA) imaging using simulations and experiments. Numerical and physical phantoms were constructed to demonstrate that PA speckle carries information related to unresolved absorber structure in a manner similar to ultrasound speckle and unresolved scattering structures. A fractal-based model of the tumor vasculature was used to study PA speckle from unresolved cylindrical vessels. We show that speckle characteristics and the frequency content of PA signals can be used to monitor changes in average vessel size, linked to tumor growth. Experimental validation on murine tumors demonstrates that PA speckle can be utilized to characterize the unresolved vasculature in acoustic-resolution photoacoustic imaging.

在超声成像中，完全散发的斑点是由随机分布的散射体反向散射的压力波的时空叠加引起的。散斑外观受成像系统特征（横向和轴向分辨率）和基础组织结构的类似随机性质的影响。在这项工作中，我们使用模拟和实验研究了声分辨光声（PA）成像中的斑点形成。构造了数字和物理模型，以证明PA散斑以类似于超声散斑和未解散的散射结构的方式携带与未解散的吸收体结构有关的信息。基于分形的肿瘤脉管系统模型用于研究未分辨圆柱血管的PA斑点。我们显示散斑特征和PA信号的频率含量可用于监测与肿瘤生长相关的平均血管大小的变化。对鼠类肿瘤的实验验证表明，PA散斑可用于表征声分辨光声成像中未解决的脉管系统。