Reflection-mode in vivo photoacoustic microscopy with subwavelength lateral resolution

Abstract

Abstract:We developed a reflection-mode subwavelength-resolution photoacoustic microscopy system capable of imaging optical absorption contrast in vivo. The simultaneous high-resolution and reflection-mode imaging capacity of the system was enabled by delicately configuring a miniature high-frequency ultrasonic transducer tightly under a water-immersion objective with numerical aperture of 1.0. At 532-nm laser illumination, the lateral resolution of the system was measured to be ~320 nm. With this system, subcellular structures of red blood cells and B16 melanoma cells were resolved ex vivo; microvessels, including individual capillaries, in a mouse ear were clearly imaged label-freely in vivo, using the intrinsic optical absorption from hemoglobin. The current study suggests that, the optical-absorption contrast, subwavelength resolution, and reflection-mode ability of the developed photoacoustic microscopy may empower a wide range of biomedical studies for visualizing cellular and/or subcellular structures.

Advances in Imaging Techniques and Genetically Encoded Probes for Photoacoustic Imaging

“…We have reported the development of blind-deconvolution OR-PAM to achieve both fine spatial resolution and extended depth of focus, and further utilized the system to visualize the mouse ear microvasculature in vivo (Figure 2) 24. By applying an optical objective lens with a much higher numerical aperture and a novel design for PA signal detection, a reflection-mode in vivo PA microscope with sub-wavelength lateral resolution was developed that is capable of imaging sub-cellular structure of red blood cells and melanoma cells (Figure 3) 17. Because OR-PAM typically uses a single-element ultrasonic transducer combined with mechanical or optical scanning to acquire the signal, its imaging speed is relatively slow (Table 1).…”

“…(B) Photograph of the PA signal detection probe (left); sub-wavelength resolution PA image of red blood cells (middle) and melanoma cells (right). Figure adapted with permission from 17.…”

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.…”

Toward in vivo biopsy of melanoma based on photoacoustic and ultrasound dual imaging with an integrated detector

“…However, the examination accuracy rate is low in the detection of early-stage melanoma because of the poor definition at shallow levels [16,17]. PAI was a hybrid imaging modality [18][19][20][21], the image can be reconstructed by detecting the acoustic pressure irradiated by a short pulsed laser beam [22][23][24]. Previous works demonstrated that PAI could be used in the detection of melanoma [25,26], but melanin in most melanomas has a broad and strong absorption spectrum, which causes a high light attenuation.…”