Abstract
PurposeTo determine if a new photoacoustic imaging (PAI) system successfully depicts (1) peripheral arteries and (2) microvascular circulatory changes in response to thermal stimuli.MethodsFollowing ethical permission, 8 consenting subjects underwent PAI of the dorsalis pedis (DP) artery, and 13 completed PAI of the index fingertip. Finger images were obtained after immersion in warm (30-35 °C) or cold (10-15 °C) water to promote vasodilation or vasoconstriction. The PAI instrument used a Fabry-Perot interferometeric ultrasound sensor and a 30-Hz 750-nm pulsed excitation laser. Volumetric images were acquired through a 14 × 14 × 14-mm volume over 90 s. Images were evaluated subjectively and quantitatively to determine if PAI could depict cold-induced vasoconstriction. The full width at half maximum (FWHM) of resolvable vessels was measured.ResultsFingertip vessels were visible in all participants, with mean FWHM of 125 μm. Two radiologists used PAI to correctly identify vasoconstricted fingertip capillary beds with 100% accuracy (95% CI 77.2-100.0%, p < 0.001). The number of voxels exhibiting vascular signal was significantly smaller after cold water immersion (cold: 5263 voxels; warm: 363,470 voxels, p < 0.001). The DP artery was visible in 7/8 participants (87.5%).ConclusionPAI achieves rapid, volumetric, high-resolution imaging of peripheral limb vessels and the microvasculature and is responsive to vasomotor changes induced by thermal stimuli.Key points• Fabry-Perot interferometer-based photoacoustic imaging (PAI) generates volumetric, high-resolution images of the peripheral vasculature.• The system reliably detects thermally induced peripheral vasoconstriction (100% correct identification rate, p < 0.001).• Vessels measuring less than 100 μm in diameter can be depicted in vivo.
Highlights
Peripheral arterial disease (PAD) is a common, important condition, affecting approximately 27 million individuals across the USA and Europe [1]
We have developed a PA system that uses a Fabry-Perot (FP) interferometer as the ultrasound sensor [8]
Average acquisition time was 90 s; the small vessels (SVs) experiment was completed in approximately 15 min and the large vessels (LVs) experiment was completed in approximately 5 min
Summary
There were no symptomatic side effects from PAI for any participant. No skin damage, irritation, or discomfort was reported either immediately following image acquisition or in the days thereafter. SVs were depicted successfully in all 13 volunteers Both readers judged there to be fewer visible vessels after cold water immersion vs warm in all cases for the direct stimulus (correct identification rate = 100%, 95% CI 77.2 to 100.0%, p < 0.001, Fig. 2 and Supplemental Material 1 and 2). Each individual volunteer showed less PAI signal after cold vs warm water immersion after the direct stimulus (Fig. 3a), mirroring the 100% discrimination recorded subjectively. The dorsalis pedis (DP) artery was visible (score of ≥ 2) for all eight participants except one (examples in Fig. 4 and Supplementary material 3) This participant had dark skin (Fitzpatrick scale = 6) and deeper vessels were obscured by strong laser absorption by melanin at the wavelength used. Several accompanying veins demonstrated internal fold-like structures, taken to be normal venous valves (Fig. 5)
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