Blind Localization of Heating in Neural Tissues Induced by a Train of the Infrared Pulse Laser

Ophthalmic surgeries on post mortem porcine eyes with picosecond ultrashort laser pulses

Purpose

This work demonstrates significant advantages in ophthalmic surgeries through the use of picosecond ultrashort laser pulses instead of state-of-the-art nanosecond laser pulses. These ultrashort lasers shall serve as universal tools more effectively combining advantages of high precision, low impact and economic advantages compared to existing instruments.

Methods

As samples, we used post-mortem porcine eyes on which we performed the experiments with both picosecond and nanosecond lasers. Performed surgeries were laser iridotomy, (post-) cataract treatment/capsulotomy and selective laser-trabeculoplasty. Pulse widths were between 12 ps and 220 ns with pulse energies between 30 μJ and 10 mJ at 532 nm and 1,064 nm. Additionally, we investigated accompanying shock waves, cavitation bubbles, and heat effects during the ablation processes.

Results

For all surgeries, significant differences were observed between picosecond and nanosecond pulses: It was possible to scale the pulse energy down to 10 of microjoules rather than requiring millijoules, and resulting tissue ablations are much more precise, more deterministic and less frayed. The shock wave and cavitation bubble investigation revealed major differences in pressure between picosecond pulses (0.25 MPa, 50 μJ) and nanosecond pulses (37 MPa, 5 mJ). The heat input during ablation could be lowered by two orders of magnitude.

Conclusion

Picosecond ultrashort laser pulses show substantial benefits for several ophthalmic surgeries, with regard to ablation precision, shock wave generation and heat input. They are better than state-of-the-art ophthalmic nanosecond lasers in all aspects tested.

Targeted Optical Neural Stimulation: A New Era for Personalized Medicine

Targeted optical neural stimulation comprises infrared neural stimulation and optogenetics, which affect the nervous system through induced thermal transients and activation of light-sensitive proteins, respectively. The main advantage of this pair of optical tools is high functional selectivity, which conventional electrical stimulation lacks. Over the past 15 years, the mechanism, safety, and feasibility of optical stimulation techniques have undergone continuous investigation and development. When combined with other methods like optical imaging and high-field functional magnetic resonance imaging, the translation of optical stimulation to clinical practice adds high value. We review the theoretical foundations and current state of optical stimulation, with a particular focus on infrared neural stimulation as a potential bridge linking optical stimulation to personalized medicine.

The Temporal Confounding Effects of Extra-cerebral Contamination Factors on the Hemodynamic Signal Measured by Functional Near-Infrared Spectroscopy

Introduction: Functional near-infrared spectroscopy (fNIRS) has been broadly applied for optical brain imaging. This method is hemodynamic-based functional brain imaging relying on the measurement of the neurovascular coupling to detect changes in cerebral neuronal activities. The extra-cerebral hemodynamic changes are important contaminating factors in fNIRS measurements. This error signal can be misinterpreted as cerebral activities during fNIRS studies. Recently, it was assumed that temporal changes in deoxygenated hemoglobin concentration [HHb] was hardly affected by superficial blood flow, and it was proposed that the activation maps could be determined from [HHb] at large source-detector separation. Methods: In the current study, we measured the temporal changes in [HHb] using a continueswave fNIRS device at large source-detector separation, while superficial blood flow was stimulated by infrared lasers. A mesh-based Monte Carlo code was applied to estimate fNIRS sensitivity to superficial hemodynamic changes in a realistic 3D MRI-based brain phantom. Results: First, we simulated photon migration in a four-layered human-head slab model to calculate PPLs and fNIRS sensitivity. Then, the localization of the infrared laser inside a realistic brain model was studied using the Monte Carlo method. Finally, the changes in [HHb] over the prefrontal cortex of six adult males were measured by fNIRS at a source-detector separation of 3 cm. The results demonstrated that the relation between fNIRS sensitivity and an increase in S-D separation was nonlinear and a correlation between shallow and deep signals was observed. Conclusion: The presented results demonstrated that the temporal changes in the superficial blood flow could strongly affect HHb measurement at large source-detector separation. Hence, the cerebral activity map extracted from the [HHb] signal was mainly contaminated by superficial blood flow.