Rapid Quantitative Imaging of Heterogeneous Tissue Hemoglobin Dynamics Using Spatial Frequency Domain Imaging

Introduction: Arterial insufficiency is a key factor in chronic wounds, diabetes, and peripheral arterial disease, all of which impair vascular function. Accurate monitoring of tissue-level oxygenation and hemodynamics is critical for assessing outcomes in cases of vascular compromise. However, many existing tools only measure small, localized regions of tissue. This study evaluates spatial variation in oxygenation during a vascular occlusion test (VOT) using wide-field spatial frequency domain imaging (SFDI).

Tissue oxygenation and perfusion dynamics were assessed using SFDI to map oxygen saturation (StO₂) and total hemoglobin in the papillary dermis (HbT1) and deeper tissue (HbT2) during a VOT in 13 subjects. Measurements were taken immediately before induction of the occlusion, after 4 min of occlusion, and immediately after occlusion release. Two regions of interest (ROIs) were analyzed: (1) areas with larger subsurface vessels (macrovasculature) and (2) areas dominated by capillary networks (microvasculature).

StO₂ values differed significantly between microvascular-only and macrovascular ROIs at all time points. Microvascular ROIs showed greater StO₂ changes during occlusion, indicating higher oxygen extraction. HbT1 concentrations did not differ significantly between ROIs at any time point.

Spatial variation is critical when comparing tissue hemodynamics across time and subjects. Noncontact wide-field imaging enables assessment of heterogeneous tissue regions that are difficult to evaluate with probe-based methods.