Rapid volumetric photoacoustic tomographic imaging with a Fabry-Perot ultrasound sensor depicts peripheral arteries and microvascular vasomotor responses to thermal stimuli.

PURPOSE: To determine if a new photoacoustic imaging (PAI) system successfully depicts (1) peripheral arteries and (2) microvascular circulatory changes in response to thermal stimuli. METHODS: Following 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. RESULTS: Fingertip 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%). CONCLUSION: PAI 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.

Image vector histogram approach to nanoparticle sizing.

A novel approach to measuring the size distribution of particles in the range of a few nanometers to a few micrometers is described. The method is based on processing multiple images of a sample of particles suspended in a liquid and undergoing Brownian motion. From each image, the centers of the particle positions are measured, then a histogram of the vectors connecting the centers in each image with all the centers in the next image is formed. This vector histogram contains information about the particle size distribution. A maximum-likelihood data inversion procedure to invert the data to yield a particle size distribution is described. Both computer simulation and experimental results are presented to demonstrate the effectiveness of the approach.