In vivo photoacoustic tomography of total blood flow and Doppler angle
As two hallmarks of cancer, angiogenesis and hypermetabolism are closely related to increased blood flow. Volumetric blood flow measurement is important to understanding the tumor microenvironment and developing new means to treat cancer. Current photoacoustic blood flow estimation methods focus on either the axial or transverse component of the flow vector. Here, we propose a method to compute the total flow speed and Doppler angle by combining the axial and transverse flow measurements. Both the components are measured in M-mode. Collating the A-lines side by side yields a 2D matrix. The columns are Hilbert transformed to compare the phases for the computation of the axial flow. The rows are Fourier transformed to quantify the bandwidth for the computation of the transverse flow. From the axial and transverse flow components, the total flow speed and Doppler angle can be derived. The method has been verified by flowing bovine blood in a plastic tube at various speeds from 0 to 7.5 mm/s and at Doppler angles from 30 to 330°. The measurement error for total flow speed was experimentally determined to be less than 0.3 mm/s; for the Doppler angle, it was less than 15°. In addition, the method was tested in vivo on a mouse ear. The advantage of this method is simplicity: No system modification or additional data acquisition is required to use our existing system. We believe that the proposed method has the potential to be used for cancer angiogenesis and hypermetabolism imaging.
Additional Information© 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). The authors thank Christopher Favazza, Lidai Wang, and Arie Krumholz for helpful discussions, Zijian Guo for data processing. This research was supported by the National Institutes of Health Grants R01 EB000712, R01 EB008085, R01 CA134539, U54 CA136398, R01 EB010049, R01 CA157277, and 5P60 DK02057933. L.V.W. has a financial interest in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work.
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