Development of an open microcavity optoacoustic sensor for photoacoustic tomography, microscopy, and spectroscopy

The purpose of this study was to develop a unique optical ultrasound detection system for the purpose of collecting photoacoustic signals obtained from photoacoustic microscopy, spectroscopy, and tomography. The unique characteristics of the open microcavity detection system exploited in this research included the ability to be reconfigured quickly and easily to increase its sensitivity to ultrasound, its ability to facilitate direct coupling of the sensor to the ultrasound source without any intervening material which would attenuate high frequency ultrasound signals, and the property of being optically transparent to any excitation laser used to generate a photoacoustic signal. This detection system was integrated into an automated scanning and acquisition control loop. When used for photoacoustic microscopy, images with clear contrast and 6 μm resolution were obtained of a phantom target. When used for photoacoustic spectroscopy, the ability to spectroscopically determine the percent concentration of dangerous methemoglobin in polymer encapsulated hemoglobin was demonstrated. This would be highly useful in determining if methemoglobin buildup has occurred in polymer encapsulated hemoglobin due to improper storage. Buildup up methemoglobin in polymer encapsulated hemoglobin may induce Methemoglobinemia if used as a blood substitute. This spectroscopic determination can only be determined using our optical absorption based methodology. Finally, when used for photoacoustic tomography, this system was able to provide a tomographic scan of melanoma developed using a unique and highly specialized mouse model. Our in-vivo melanoma model uses an approach different from the conventional B-16 cell injection methodology and produces melanoma lesions which more closely approximate human melanoma. We demonstrated the ability to noninvasively determine melanoma tumor depth using non-ionizing radiation.