Abstract
Venous thromboembolism (VTE) is a condition in which blood clots form within the deep veins of the leg or pelvis to cause deep vein thrombosis. The optimal treatment of VTE is determined by thrombus properties such as the age, size, and chemical composition of the blood clots. The thrombus properties can be readily evaluated by using photoacoustic computed tomography (PACT), a hybrid imaging modality that combines the rich contrast of optical imaging and deep penetration of ultrasound imaging. With inherent sensitivity to endogenous chromophores such as hemoglobin, multispectral PACT can provide composition information and oxygenation level in the clots. However, conventional PACT of clots relies on external light illumination, which provides limited penetration depth due to strong optical scattering of intervening tissue. In our study, this depth limitation is overcome by using intravascular light delivery with a thin optical fiber. To demonstrate in vitro blood clot characterization, clots with different acuteness and oxygenation levels were placed underneath ten-centimeter-thick chicken breast tissue and imaged using multiple wavelengths. Acoustic frequency analysis was performed on the received PA channel signals, and oxygenation level was estimated using multispectral linear spectral unmixing. The results show that, with intravascular light delivery, clot oxygenation level can be accurately measured, and the clot age can thus be estimated. In addition, we found that retracted and unretracted clots had different acoustic frequency spectrum. While unretracted clots had stronger high frequency components, retracted clots had much higher low frequency components due to densely packed red blood cells. The PACT characterization of the clots was consistent with the histology results and mechanical tests.
Highlights
Venous thromboembolism (VTE) is one of the leading causes of death worldwide and accounts for significant morbidity and mortality [1]
We found that an occupation percentage of >90% corresponded to low frequency components of
We found that the red blood cells (RBCs) were more densely packed near the clot edges, which were in close contact with the Pasteur pipets
Summary
Venous thromboembolism (VTE) is one of the leading causes of death worldwide and accounts for significant morbidity and mortality [1]. Deep vein thrombosis (DVT) may cause life-threatening pulmonary embolism (PE) when clots can break free and the debris enters lung arteries, resulting in sudden death [2]. VTE has affected 300,000–600,000 patients every year and one-third of DVT cases have turned into PE [3]. The age of the clot affects the level of pulmonary embolism risk and DVT treatment method. It is hypothesized that the mechanical properties of the clots result in different resistance of clots to the thrombolytic treatment: the retracted or fibrin-rich clots are stiffer and denser than the unretracted or erythrocytes-rich clots, and has lower thrombolysis efficiency [6], [9]
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