Transverse flow measurement using photoacoustic Doppler bandwidth broadening: phantom and in vivo studies
In photoacoustic (PA) imaging of microvascular networks, the transverse component of the blood flow that is perpendicular to the acoustic probing beam is usually dominant. We propose a new method to measure the transverse flow, based on the Doppler bandwidth broadening. The bandwidth broadening is inversely proportional to the transit time spent by the absorbers passing through the focus. Because the photoacoustic signal in one A-scan has a wide band, multiple successive A-scans are used to estimate the relatively small signal variance. Then the bandwidth broadening can be calculated from the standard derivation of the Doppler spectrum. By exploiting the pulse excitation and bidirectional raster motor scanning, threedimensional structural and flow information can be obtained simultaneously. From a flow of a suspension of carbon particles (diameter: 6 μm), transverse flow speeds from 0 to 2.5 mm/s were measured using optical-resolution photoacoustic microscopy. The bandwidth broadening at each speed was in good agreement with the theoretical prediction. The blood flow in a mouse brain was also imaged.
Additional Information© 2010 Society of Photo-Optical Instrumentation Engineers (SPIE). The authors thank Christopher Favazza, Song Hu, and Arie Krumholz for helpful discussion. This research was supported by the National Institutes of Health Grants R01 EB000712, R01 NS46214, R01 EB008085, R01 CA113453901, U54 CA136398, and 5P60 DK02057933. LW has a financial interest in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work.
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