Microfluidic Test Target for Photoacoustic Imaging

P. Schneider, N. Eadie, L. Christie, Y. Zhan, T. Siskar, D. Koh, J. Xia, K.W. Oh
University at Buffalo's Sensors & MicroActuators Learning Lab (SMALL),
United States

Keywords: microfluidics, photoacoustic imaging, test target, ultrasonic imaging


Photoacoustic imaging involves the use of optics (typically a high power pulsed laser) and acoustics (ultrasonics frequency ranges >1MHz) to image a targeted object. Individually, these modalities, being optical and ultrasonic imaging, can be quantified in terms of their system performance taking into factors such as image quality, lateral resolution, signal to noise ratio, etc. Traditionally, this is done by imaging a test target pattern or structure. Test targets contain an array of lines, dots, or other patterns in which the imaging system views in order to allow for determination of system’s imaging characteristics such as resolution, distortion, and/or color/grayscale. For optical imaging a simple paper colored pattern is sufficient. For acoustical imaging the test target must have micro features that have a different acoustic impedance for imaging. This can be a simple air/material interface similar to that of a mold. Examples of optical and acoustical imaging of a test target can be seen in [1]. However, for photoacoustic imaging, the test target must have an optical absorption material (i.e. a colored dye) and thus must have a depth dimension aspect to it. Through microfabrication techniques a microfluidic test target has been created for the calibration and baselining of a photoacoustic system. The design stemmed from an Appendix F test target (figure 1) design used to certify a biometric fingerprint imaging system with US FBI. This pattern was then converted to a fluidic design. Fabricated by means of photolithography, the process of which shown in figure 2, a 3D microfluidic test target device was fabricated and implanted into a silicone based block.This test target as shown in figure 3, is a series of line pairs ranging from 5 mm spacing down to 40μm spacing. Current experimentation involves the photoacoustic imaging of this target at different depths, then performing image analysis to baseline the photoacoustic system. The innovations behind this research is that this target will be the first time a photoacoustic system has been able to be characterized using a test target opening up quantifiable metrics for system performance under different testing conditions. In addition, resolution for imaging is typically only lateral, whereas with this test target, axial resolution will now be a consideration when imaging.