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23 February 2010 Off-axis photoacoustic microscopy
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Photoacoustic microscopy (PAM) is a high-contrast, high-resolution imaging modality used primarily for imaging hemoglobin and melanin. Important applications include mapping of the microvasculature and melanoma tumor margins. We have developed a novel photoacoustic microscope design, which substantially simplifies construction by enabling the use of unmodified commercial optics and ultrasonic transducers. Moreover, the simple design may be readily incorporated into a standard light microscope, thus providing a familiar imaging platform for clinical researchers. A proof-of-concept Off-Axis PAM system with a lateral resolution of 26 μm and a modest axial resolution of 410 μm has been assembled and characterized using tissue samples. We have derived the appropriate equations to describe the relevant design parameters and verified the equations via measurements made on our prototype Off-Axis PAM system. A consequence of the simple design is a reduction in axial resolution compared to coaxial designs. The reduction is inversely proportional to the cosine of the angle between excitation and detection and equal to 15% and 41% for angles of 30º and 45º, respectively. While resolution is negatively affected by off-axis detection, the ability to measure weak signals at depth is enhanced. Off-axis detection has an inherent dark-field quality; chromophores excited outside the numerical aperture of the ultrasonic detector will not be detected. The physical geometry of Off-Axis PAM enables the placement of the ultrasonic transducer at the minimum distance from the sample with no obstructions between the sample and transducer. This may prove to be an additional advantage of Off-Axis PAM over designs that incorporate long working distance ultrasonic transducers and/or require the propagation of the acoustic wave through the laser excitation optics to achieve co-axial detection.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ryan Shelton and Brian E. Applegate "Off-axis photoacoustic microscopy", Proc. SPIE 7564, Photons Plus Ultrasound: Imaging and Sensing 2010, 756410 (23 February 2010);

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