Fluorescence excitation analysis by two-photon confocal laser scanning microscopy: a new method to identify fluorescent nanoparticles on histological tissue sections

Internal-illumination photoacoustic computed tomography

We report a photoacoustic computed tomography (PACT) system using a customized optical fiber with a cylindrical diffuser to internally illuminate deep targets. The traditional external light illumination in PACT usually limits the penetration depth to a few centimeters from the tissue surface, mainly due to strong optical attenuation along the light propagation path from the outside in. By contrast, internal light illumination, with external ultrasound detection, can potentially detect much deeper targets. Different from previous internal illumination PACT implementations using forward-looking optical fibers, our internal-illumination PACT system uses a customized optical fiber with a 3-cm-long conoid needle diffuser attached to the fiber tip, which can homogeneously illuminate the surrounding space and substantially enlarge the field of view. We characterized the internal illumination distribution and PACT system performance. We performed tissue phantom and in vivo animal studies to further demonstrate the superior imaging depth using internal illumination over external illumination. We imaged a 7.5-cm-deep leaf target embedded in optically scattering medium and the beating heart of a mouse overlaid with 3.7-cm-thick chicken tissue. Our results have collectively demonstrated that the internal light illumination combined with external ultrasound detection might be a useful strategy to improve the penetration depth of PACT in imaging deep organs of large animals and humans.

The effects of low-frequency ultrasound and microbubbles on rabbit hepatic tumors

High-intensity focused ultrasound in combination with microbubbles (MBs) is able to inhibit the growth of VX2 rabbit liver tumors in vivo and prolong the survival time of the animals. In this study, we attempt to investigate the feasibility of VX2 tumor growth inhibition using low-frequency ultrasound (US)-mediated MB disruption. Forty-eight New Zealand rabbits with hepatic VX2 tumors were divided into four groups: control, MBs group, low-frequency US group, and US + MB group. The parameters of the US were 20 kHz, 2 W/cm², 40% duty cycle, 5 min, and once every other day for 2 weeks. At the end of the therapy experiment, 24 rabbits were euthanized, and the cancers were collected and cut into five sections for histological examination, immunohistochemistry, laser confocal microscopy, western blotting assays, and transmission electron microscopy (TEM). Another 24 rabbits were saved, and overall survival time was recorded. The tumor volumes in control, MB, US, and US + MB groups were 6.36 ± 0.58, 5.68 ± 0.42, 5.29 ± 0.26, and 2.04 ± 0.14 cm³, respectively (US + MB versus the other three groups, P < 0.01). Tumor cells manifested coagulation necrosis with internal calcification. Hematoxylin and eosin (H–E) staining revealed interstitial hemorrhage and intravascular thrombosis. The intensity of cyclooxygenase-2 (COX-2), and vascular endothelial growth factor (VEGF) in the US + MB group in the immunohistochemical staining, laser confocal microscopy, and western blotting assays was lower than that of the other three groups (P < 0.05). TEM of the US + MB group revealed vascular endothelial cell wall rupture, widened endothelial cell gaps, interstitial erythrocyte leakage, and microvascular thrombosis, while intact vascular endothelial cells and normal erythrocytes in the tumor vessels were observed in control, MB, and US groups. Rabbits treated with US + MB had a significantly longer overall survival than those in the other three groups (χ2 = 9.328, P = 0.0242). VX2 tumor growth could be inhibited by cavitation induced using low-frequency US and MB.