Neodymium:yttrium aluminum garnet (Nd:YAG) lasers exhibit considerable potential for treating deeply buried port-wine stains. However, the application of Nd:YAG laser is limited by its weak absorption to blood. This in vivo study tested the efficacy and safety of utilizing thiol-terminated methoxypolyethylene glycol-modified gold nanorods (PEG-GNRs) to enhance the absorption of Nd:YAG laser to blood. Mouse mesentery and dorsal skinfold chamber (DSC) model were prepared to analyze the thermal responses of a single venule without anatomic structures, as well as blood vessels in the complex structure of the skin, to laser light. After the injection of 0.44 mg of PEG-GNRs, the required threshold density of laser energy for blood coagulation and complete vasoconstriction decreased from 24 to 18 J/cm2 in the mesentery model and from 36 to 31 J/cm2 in the DSC model. The laser pulse required for blood coagulation and complete vasoconstriction decreased by 67.75% and 62.25% on average in the mesentery model and by 67.55% and 54.45% on average in the DSC model. Histological and histochemical results confirmed that PEG-GNRs are nontoxic in the entire mouse life span. Therefore, combining PEG-GNRs with Nd:YAG laser may be effective and safe for inducing an obvious thermal response of blood vessels under low energy density and minimal pulse conditions.
Laser scanning is widely used in on-line industrial 3D inspection, cultural heritage conservation and reverse engineering.
However, in the traditional laser scanning, the most widely-used approach is based on the projection of a single directional
laser stripe over an object. Because the width of the laser stripe is physically difficult to compress enough to be fine at the
edge of the object, the traditional measurement method is not accurate for edge measurements. This paper proposes an
edge sensitive 3D measurement system which is fast and accurate, using two directional laser stripes scanning with a laser
projector. Scanning metal edge steps and complex surface edge with this system only require a single scanning to perform
3D reconstruction. So this scanning method has the advantages of high efficiency, high speed and edges with high precision.
Line structure light measurement needs accurate mechanical movement device and high -frame-rate camera, which is
difficult to realize. We propose a high-speed full-field profilometry to solve these difficult ies, using coded laser strips
projected by a MEMS scanning mirror. The mirror could take place of the mechanical movement device with its high
speed and accurate. Besides, a method with gray code and color code is used to decrease the frames number of projection,
retaining the advantage of line structure light measurement. In the experiment, we use a laser MEMS scanner and two
color cameras. The laser MEMS scanner projects coded stripes, with two color cameras collecting the modulated pattern
on the measured object. The color cameras compose a stereo vision system so that the three-dimensional data is
reconstructed according to triangulation.
The Fringe Projection System (FPS) and the Laser Stripe Projection System (LSPS) both have the limitations in 3D
measurements. For a shiny and diffusive surface with complex shape, neither of the systems could manage it individually
at a low cost. To overcome these difficulties, we propose a method combining these two ways of projections together
using a laser projector, which could project fringe patterns and scanning-laser-stripes both. In this method, we obtain two
disparity maps and two quality maps by FPS and LSPS, respectively. Then combine two disparity maps together by
quality maps and reconstruct the surface of the object with the combined disparity map. Real experiments are carried out
to verify the proposed method and to evaluate the system performance. The plain, the colored and the metal plastic
mixed objects are all reconstructed successfully in the proposed method.
The voxel-based Monte Carlo method (VMC) is now a gold standard in the simulation of light propagation in turbid media. For complex tissue structures, however, the computational cost will be higher when small voxels are used to improve smoothness of tissue interface and a large number of photons are used to obtain accurate results. To reduce computational cost, criteria were proposed to determine the voxel size and photon number in 3-dimensional VMC simulations with acceptable accuracy and computation time. The selection of the voxel size can be expressed as a function of tissue geometry and optical properties. The photon number should be at least 5 times the total voxel number. These criteria are further applied in developing a photon ray splitting scheme of local grid refinement technique to reduce computational cost of a nonuniform tissue structure with significantly varying optical properties. In the proposed technique, a nonuniform refined grid system is used, where fine grids are used for the tissue with high absorption and complex geometry, and coarse grids are used for the other part. In this technique, the total photon number is selected based on the voxel size of the coarse grid. Furthermore, the photon-splitting scheme is developed to satisfy the statistical accuracy requirement for the dense grid area. Result shows that local grid refinement technique photon ray splitting scheme can accelerate the computation by 7.6 times (reduce time consumption from 17.5 to 2.3 h) in the simulation of laser light energy deposition in skin tissue that contains port wine stain lesions.
To adapt the complex tissue structure, laser propagation in a two-layered skin model is simulated to compare voxel-based Monte Carlo (VMC) and tetrahedron-based MC (TMC) methods with a geometry-based MC (GMC) method. In GMC, the interface is mathematically defined without any discretization. GMC is the most accurate but is not applicable to complicated domains. The implementation of VMC is simple because of its structured voxels. However, unavoidable errors are expected because of the zigzag polygonal interface. Compared with GMC and VMC, TMC provides a balance between accuracy and flexibility by the tetrahedron cells. In the present TMC, the body-fitted tetrahedra are generated in different tissues. No interface tetrahedral cells exist, thereby avoiding the photon reflection error in the interface cells in VMC. By introducing a distance threshold, the error caused by confused optical parameters between neighboring cells when photons are incident along the cell boundary can be avoided. The results show that the energy deposition error by TMC in the interfacial region is one-tenth to one-fourth of that by VMC, yielding more accurate computations of photon reflection, refraction, and energy deposition. The results of multilayered and n-shaped vessels indicate that a laser with a 1064-nm wavelength should be introduced to clean deep-buried vessels.
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