Isometric multimodal photoacoustic microscopy based on optically transparent micro-ring ultrasonic detection

Abstract

Photoacoustic microscopy (PAM) is an attractive imaging tool complementary to established optical microscopic modalities by providing additional molecular specificities through imaging optical absorption contrast. While the development of optical resolution photoacoustic microscopy (ORPAM) offers high lateral resolution, the acoustically-determined axial resolution is limited due to the constraint in ultrasonic detection bandwidth. ORPAM with isometric spatial resolution along both axial and lateral direction is yet to be developed. Although recently developed sophisticated optical illumination and reconstruction methods offer improved axial resolution in ORPAM, the image acquisition procedures are rather complicated, limiting their capabilities for high-speed imaging and being easily integrated with established optical microscopic modalities. Here we report an isometric ORPAM based on an optically transparent micro-ring resonator ultrasonic detector and a commercial inverted microscope platform. Owing to the superior spatial resolution and the ease of integrating our ORPAM with established microscopic modalities, single cell imaging with extrinsic fluorescence staining, intrinsic autofluorescence, and optical absorption can be achieved simultaneously. This technique holds promise to greatly improve the accessibility of PAM to the broader biomedical researchers.

Quantifying melanin concentration in retinal pigment epithelium using broadband photoacoustic microscopy

“…In addition, the measurement system setup can be easily integrated with other parallel microscopic studies for comprehensive RPE investigation. For example, the RPE melanin concentration for each single cell can be easily extracted and correlated with its susceptibility to lethal photic stress [40]; a dual-modality system combining PAM and autofluorescence imaging can be developed to monitor the real-time variation of RPE intracellular melanin and lipofuscin, the two major indicators of RPE aging, in response to various physical and chemical stimulations [26,39,41]. Detection of broadband acoustic signal is critical for quantification of RPE melanin concentration by PAM.…”

“…We experimentally demonstrated accurate quantification of RPE melanin concentration on a broadband PAM system [26]. The schematic of the experimental setup is shown in Fig.…”

“…Recently, we developed a broadband 3D isometric optical resolution PAM using an optically transparent micro-ring resonator (MRR) based ultrasonic detector on a commercial inverted microscope platform [26]. The MRR ultrasonic detector was fabricated on a microscope coverslip with the total device thickness of 225 μm.…”

“…Such a miniaturized ultrasonic detector could be seamlessly integrated into microscopic modalities while providing a large ultrasonic detection bandwidth (280 MHz at −6 dB) for PA imaging. We demonstrated single cell 3D PA imaging with an axial resolution of 2.12 μm, which could potentially resolve the RPE layer from choroid [26].…”

Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

“…[29][30][31][32][33][34][35] The spatial resolution and sensitivity of the imaging systems depend on the laser excitation and acoustic detection con¯gurations. Like PAM, PAE is emerging as a novel technology for imaging internal organs with longer depth.…”