Exhaustive review of acceleration strategies for Monte Carlo simulations in photon transit

Monte Carlo simulation techniques have become the quintessence and a pivotal nexus of inquiry in the realm of simulating photon movement within biological fabrics.Through the stochastic sampling of tissue archetypes delineated by explicit optical characteristics,Monte Carlo simulations possess the theoretical capacity to render unparalleled accuracy in the depiction of exceedingly intricate phenomena.Nonetheless,the quintessential challenge associated with Monte Carlo simulation methodologies resides in their extended computational duration,which significantly impedes the refinement of their precision.Consequently,this discourse is specifically dedicated to exploring innovations in strategies and technologies aimed at expediting Monte Carlo simulations.It delves into the foundational concepts of various acceleration tactics,evaluates these strategies concerning their speed,accuracy,and practicality,and amalgamates a comprehensive overview and critique of acceleration methodologies for Monte Carlo simulations.Ultimately,the discourse envisages prospective trajectories for the employment of Monte Carlo techniques within the domain of tissue optics.

DEVELOPMENT OF HIGH-SPEED SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY SYSTEM AT 1320 nm

A swept-source optical coherence tomography(SSOCT)system based on a high-speed scanning laser source at center wavelength of 1320 nm and scanning rate of 20 kHz is developed.The axial resolution is enhanced to 8.3μm by reshaping the spectrum in frequency domain using a window function and a wave number calibration method based on a Mach-Zender Interferometer(MZI)integrated in the SSOCT system.The imaging speed and depth range are 0.04 s per frame and 3.9 mm,respectively.The peak sensitivity of the SSOCT system is calibrated to be 112 dB.With the developed SSOCT system,optical coherence tomography(OCT)images of human finger tissue are obtained which enable us to view the sweat duct(SD),stratum corneum(SC)and epidermis(ED),demonstrating the feasibility of the SSOCT system for in vivo biomedical imaging.

NEAR-INFRARED IMAGING SENSOR WITH IMPROVED HANDLING AND DIRECT LOCALIZATION IN SIMULTANEOUS MAGNETIC RESONANCE IMAGING MEASUREMENTS

We present a novel optical sensor to acquire simultaneously functional near-infrared imaging(fNIRI)and functional magnetic resonance imaging(fMRI)data with an improved handling and direct localization in the MRI compared to available sensors.Quantitative phantom and interference measurements showed that both methods can be combined without reciprocal adverse effects.The direct localization of the optical sensor on MR images acquired with a T1-weighted echo sequence simplifies the co-registration of NIRI and MRI data.In addition,the optical sensor is simple to attach,which is crucial for measurements on vulnerable subjects.The fNIRI and T2^(*)-weighted fMRI data of a cerebral activation were simultaneously acquired proving the practicability of the setup.

Photon-Measurement Density Function of Fluorescence Molecular Tomography Based on Direct Method

Photon-measurement density function （PMDF）, which is the kernel of fluorescence molecular tomography （FMT）, largely determines the accuracy of reconstruction result of FMT. Based on the direct method, we propose an expression of PMDF in FMT, which is derived from the finite element method （FEM） solution of the diffusion equation. Compared with the traditional expression based on the perturbation method, the accuracy of expression based on the direct method is shown in theory. Lastly the reconstruction results of phantoms prove this accuracy in experiment.

Tomography-assisted Doppler photoacoustic microscopy:proof of concept

The previous methods to measure flow speed by photoacoustic microscopy solely focused on either the transverse or the axial flow component, which did not reflect absolute flow speed. Here, we present absolute flow speed maps by combining Doppler bandwidth broadening with volumetric photoacoustic microscopy. Photoacoustic Doppler bandwidth broadening and photoacoustic tomographic images were applied to measure the transverse flow component and the Doppler angle, respectively. Phantom experiments quantitatively demonstrated that ranges of 55° to 90° Doppler angle and 0.5 to 10 mm/s flow speed can be measured. This tomography-assisted method provides the foundation for further measurement in vivo.

Laser Immunotherapy:Novel Modality to Treat Cancer through Specific Antitumor Immune Response

Treatment of metastatic cancer remains a great challenge and needs novel approaches.Combining a selective photothermal therapy with an active immunological stimulation,laser immunotherapy(LIT) was developed to induce systemic immune responses through local intervention.LIT consists of three major components: a near-infrared laser,a light-absorbing agent,and an immunological stimulant.Its effect relies on two major interactions: a selective photothermal interaction and an active immunological stimulation.The selective photothermal interaction can reduce the tumor burden and at the same time release the tumor antigens,which can induce specific antitumor immune response.The expression of heat shock protein and the application of immunoadjuvant further enhance the host immunity.It has been proved in pre-clinical studies that LIT could not only eradicate treated local tumors but also regress and eliminate untreated metastases at distant sites.Moreover,LIT is well tolerated and has shown to have many advantages for cancer treatment compared with other traditional modalities.

Hydration of Fingernail Investigated by Optical Coherence Tomography

Optical coherence tomography(OCT) is used to investigate the microstructure changes of human fingernail induced by hydration.Images of nail plate are obtained to display the morphology of fingernail and to disclose the keratinization of basal cells of nail plate.Combined with digital vernier caliper,this imaging technology is used to evaluate thicknesses and changes of nail in vitro after immersion with time.OCT images of nails show that the dorsal and ventral layers of nails have similar thicknesses which are much thinner than intermediate layer.The total thickness of fingernail exponentially increases with immersion time,and the saturating phenomenon appears at about 12 min.Three layers show different contributions to the total increase of the thickness of 17.4%.Microstructure changes in vivo are similar to the results in vitro.The changes of optical path length also could be evaluated by this method.OCT is capable of reflecting precise microstructure changes,and it has the potential to provide physician with a modern and objective diagnostic standard for nail inspection(NI) and to monitor disorders in Chinese traditional medicine(CTM) clinical practice and research.