Two-Photon Laser Scanning Stereomicroscopy for Fast Volumetric Imaging

Three-photon excited fluorescence imaging in neuroscience: From principles to applications

The development of three-photon microscopy (3PM) has greatly expanded the capability of imaging deep within biological tissues, enabling neuroscientists to visualize the structure and activity of neuronal populations with greater depth than two-photon imaging. In this review, we outline the history and physical principles of 3PM technology. We cover the current techniques for improving the performance of 3PM. Furthermore, we summarize the imaging applications of 3PM for various brain regions and species. Finally, we discuss the future of 3PM applications for neuroscience.

High speed two-photon laser scanning stereomicroscopy for three-dimension tracking multiple particles simultaneously in three-dimension

In this paper, we will describe a video rate two-photon laser scanning stereomicroscopy for imaging-based three-dimensional particle tracking. Using a resonant galvanometer, we have now achieved 30 volumes per second (frame size 512 × 512) in volumetric imaging. Owing to the pulse multiplexing and demultiplexing techniques, the system does not suffer the speed loss for taking two parallax views of a volume. The switching time between left and right views is reduced to several nanoseconds. The extremely fast view switching and high volumetric imaging speed allow us to track fast transport processes of nanoparticles in deep light-scattering media. For instance, in 1%-intralipid solution and fibrillar scaffolds, the tracking penetration depth can be around 400 μm.

Depth random-access two-photon Bessel light-sheet imaging in brain tissue

Two-photon light-sheet fluorescence microscopy enables high-resolution imaging of neural activity in brain tissue at a high frame rate. Traditionally, light-sheet microscopy builds up a 3D stack by multiple depth scans with uniform spatial intervals, which substantially limits the volumetric imaging speed. Here, we introduce the depth random-access light-sheet microscopy, allowing rapid switching scanning depth for light-sheet imaging. With a low-cost electrically tunable lens and minimum modification of an existing two-photon light-sheet imaging instrument, we demonstrated fast random depth hopping light-sheet imaging at 100 frames per second in the live brain slice. Through depth random-access, calcium activities for an astrocyte were recorded on four user-selected detection planes at a refreshing rate of 25 Hz.

Effect of postoperative radiotherapy in women with localized pure mucinous breast cancer after lumpectomy: a population-based study

Purpose

Pure mucinous breast cancer is a rare subtype of invasive breast cancer with favorable prognosis, in which the effect of postoperative radiotherapy remains unclear. We aimed to investigate the prognostic value of postoperative radiotherapy in women with localized pure mucinous breast cancer after lumpectomy.

Methods

We conducted a retrospective cohort study to compare the effectiveness of postoperative radiotherapy (RT) and omitting postoperative radiotherapy (non-RT) in patients with first primary T1-2N0M0 (T ≤ 3 cm) pure mucinous breast cancer who underwent lumpectomy between 1998 and 2015 using the Surveillance, Epidemiology, and End Results (SEER) database. Breast cancer-specific survival (BCSS) was compared between RT and non-RT groups using Kaplan–Meier method and Cox proportional hazards regression model. Propensity score matching (PSM) was carried out to balance cohort baselines. In addition, an exploratory analysis was performed to verify the effectiveness of RT in subgroup patients.

Results

Of 7832 eligible patients, 5352 (68.3%) underwent lumpectomy with postoperative RT, 2480 (31.7%) received lumpectomy without postoperative RT. The median follow-up duration was 92 months. The median age was 66 years in the RT group and 76 years in the non-RT group.The 15-year BCSS was 94.39% (95% CI, 93.08% to 95.35%) in the RT group versus 91.45%(95% CI, 88.93% to 93.42%) in the non-RT group (P < 0.001). The adjusted hazard ratio for BCSS was 0.64 (95% CI, 0.49 to 0.83; P = 0.001) for RT group versus non-RT group. After propensity score matching, similar results were yielded. Adjuvant RT reduced the 15-year risk of breast cancer death from 7.92% to 6.15% (P = 0.039). The adjusted hazard ratio for BCSS were 0.66 (95%CI, 0.47 to 0.92; P = 0.014) for RT group versus non-RT group. The benefit of RT was well consistent across subgroup patients.

Conclusion

Among women with T1-2N0M0 (tumor size ≤ 3 cm) pure mucinous breast cancer, the addition of RT after lumpectomy was significantly associated with a reduced incidence of breast cancer death compared with non-RT, and the magnitude of benefit may be modest. This suggests that postoperative RT is recommended in the treatment of localized pure mucinous breast cancer.

Tunable depth of focus with modified complex amplitude modulation of an optical field

Bessel beams have nondiffraction and self-healing properties in the propagation direction and are widely used in particle optical manipulation and optical microscopy. Bessel beams can be generated by axicons or spatial light modulators, which can produce a zero-order or high-order Bessel beam with different parameters depending on the specific application. The modulation of Bessel beams achieved in the spatial spectrum domain by optimization algorithms has a low light energy utilization rate due to the small effective modulation region. We propose a Bessel-like beam phase generation algorithm based on an improved iterative optimization algorithm directly in the spatial domain to achieve a tunable modulation of the beam's length and the axial center position. The optimization time is reduced from minutes to seconds relative to the genetic algorithm, providing a new means of modulation for different applications in various fields.

Binocular stereo-microscopy for deforming intact amoeba

A powerful and convenient method for measuring three-dimensional (3D) deformation of moving amoeboid cells will assist the progress of environmental and cytological studies as protists amoebae play a role in the fundamental environmental ecosystem. Here we develop an inexpensive and useful method for measuring 3D deformation of single protists amoeba through binocular microscopy and a newly proposed algorithm of stereo-scopy. From the movies taken from the left and right optical tubes of the binocular microscope, we detect the 3D positions of many intrinsic intracellular vesicles and reconstruct cellular surfaces of amoeboid cells in 3D space. Some observations of sampled behaviors are shown in a single-celled organism of Amoeba proteus. The resultant surface time series is then analyzed to obtain surface velocity, curvature and volume increasing rates of pseudo-pods for characterizing the movements of amoeboid cells. The limitations and errors of this method are also discussed.

High-speed volumetric two-photon fluorescence imaging of neurovascular dynamics

Understanding the structure and function of vasculature in the brain requires us to monitor distributed hemodynamics at high spatial and temporal resolution in three-dimensional (3D) volumes in vivo. Currently, a volumetric vasculature imaging method with sub-capillary spatial resolution and blood flow-resolving speed is lacking. Here, using two-photon laser scanning microscopy (TPLSM) with an axially extended Bessel focus, we capture volumetric hemodynamics in the awake mouse brain at a spatiotemporal resolution sufficient for measuring capillary size and blood flow. With Bessel TPLSM, the fluorescence signal of a vessel becomes proportional to its size, which enables convenient intensity-based analysis of vessel dilation and constriction dynamics in large volumes. We observe entrainment of vasodilation and vasoconstriction with pupil diameter and measure 3D blood flow at 99 volumes/second. Demonstrating high-throughput monitoring of hemodynamics in the awake brain, we expect Bessel TPLSM to make broad impacts on neurovasculature research.

Direct observation and characterization of optical guiding of microparticles by tightly focused non-diffracting beams

Due to the propagation-invariant and self-healing properties, nondiffracting beams are highly attractive in optical trapping. However, little attention has been paid to investigating optical guiding of microparticles in nondiffracting beams generated by high-numerical-aperture (NA) optics with direct visualization. In this letter, we report a technique for direct observation and characterization of optical guiding of microparticles in a tight focusing system. With this technique, we observed a parabolic particle guiding trajectory with a longitudinal distance of more than 100µm and a maximal lateral deviation of 20 µm when using Airy beams. We also realized the tilted-path transport of microparticles with controllable guiding direction using tilted zeroth-order quasi-Bessel beams. For an NA of the focusing lens equal to 0.95, we achieved the optical guiding of microparticles along a straight path with a tilt angle of up to 18.8° with respect to the optical axis over a distance of 300 µm. Importantly, quantitative measurement of particle's motion was readily accessed by measuring the particle's position and velocity during the transport process. The reported technique for direct visualization and characterization of the guided particles will find its potential applications in optical trapping and guiding with novel nondiffracting beams or accelerating beams.

Two-photon Bessel beam tomography for fast volume imaging

Light microscopy on dynamic samples, for example neural activity in the brain, often requires imaging volumes that extend over several 100 µm in axial direction at a rate of at least several tens of Hertz. Here, we develop a tomography approach for scanning fluorescence microscopy which allows recording a volume image in a single frame scan. Volumes are imaged by simultaneously recording four independent projections at different angles using temporally multiplexed, tilted Bessel beams. From the resulting projections, three-dimensional images are reconstructed using inverse Radon transforms combined with convolutional neural networks (U-net).