Photoacoustic imaging (PAI) is a biomedical imaging modality that can provide structural, functional, and molecular information. In PAI, laser pulses illuminate the tissue, and transient light absorption leads to instant thermal expansion and succeeding ultrasound emission. Since oxy- and deoxyhemoglobin are the major light-absorbing chromophores in biological tissue, PAI has very high contrast and is intrinsically suitable for the imaging of blood vessels. Meanwhile, superb microvascular imaging (SMI) is an emerging ultrasound imaging technique for angiography. In comparison to traditional color Doppler and power Doppler techniques which rely on the suppression of low-velocity components, SMI works by an intelligent algorithm that renders small vessels with low flow velocity visible. To date, there is no work to compare PAI and SMI in terms of vascular imaging capabilities. In this paper, we provide our recent evaluation results in imaging depths, speeds, sensitivities, and resolutions of these two modalities through phantom experiments and in-vivo studies. We used PAI and SMI to image the human forearm, and our preliminary data show that PAI is superior in imaging speeds, and sensitivities for superficial blood vessels. We acknowledge that more work needs to be done to compare the two techniques in diverse clinical applications more quantitatively, and we hope our work can pave the way for such systematic studies..
Photoacoustic imaging (PAI, also called optoacoustic imaging) combines light excitation and ultrasound detection for deep-tissue imaging with light absorption contrast. PAI can map the distribution of endogenous chromophores such as oxy-hemoglobin, deoxy-hemoglobin, lipids, water, and melanin. PAI performs especially well for structural and functional imaging of blood vessels. Its centimeter-deep imaging depth and ultrasound-defined resolution make it well suited for clinical application, where systems employing a linear array ultrasound probe are most commonly used due to simplicity, flexibility, and easy integration with standard ultrasonic imaging. The existing linear array based imaging systems typically employ optical fiber bundles for light delivery, such a scheme enjoys mechanical flexibility, optical stability, and simple light coupling. However, major drawbacks associated with fiber illumination include suboptimal transmission efficiency and a lack of control of the illumination pattern. Articulated arms provide an alternative light delivery option which potentially offer high transmission efficiency, stable and flexible operation, and low cost. Despite its wide applications in cosmetology, articulated arms for light delivery were understudied in the PAI community. In this paper, we reported the fabrication and experimental evaluation of an articulated arm specifically designed for linear-array-based PAI. Without losing the flexibility provided by the linear probe. Moreover, the articulated arm can be equipped with spatial positioning devices to perform three-dimensional reconstructions.
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