Selection of voxel size and photon number in voxel-based Monte Carlo method: criteria and applications.

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.

Digital surgical templates for managing high-energy zygomaticomaxillary complex injuries associated with orbital volume change: a quantitative assessment.

PURPOSE: This study sought to introduce 3-dimensional (3D) virtual surgical planning and digital rapid-prototyping templates for zygomaticomaxillary complex (ZMC) injuries associated with orbital volume change and to evaluate the surgical outcomes quantitatively. PATIENTS AND METHODS: Eight patients who underwent open reduction and fixation for a ZMC injury with orbital volume change were studied. Computed tomographic (CT) scan of the zygomaticomaxillary area was performed before the operation in each case. Scanned data were converted into 3D models using Mimics software (Materialise, Brussels, Belgium) for surgical designs. Virtual surgical reductions and correlated guiding templates were designed using Mimics and Magics software (Materialise). The operations were performed with the help of prefabricated templates to reduce the fractures. A postoperative CT scan of each patient was obtained within 2 weeks after surgery, and quantitative measurements were made to assess the surgical outcomes. Preoperative volumes of the bilateral orbits were compared, and concordance with postoperative volumes of the bilateral orbits was assessed. Twenty-one pairs of distances from 7 marker points to 3 reference planes were measured to assess postoperative facial symmetry. RESULTS: Volumes of the injured orbits were significantly different from volumes of the uninjured orbits preoperatively (P < .05), whereas bilateral orbital volumes showed no statistically significant difference postoperatively (P > .05). In addition, 19 of the 21 pairs of bilateral distances showed no significant difference postoperatively (P > .05). CONCLUSIONS: Quantitative assessment showed that digitally designed, rapid-prototyping templates for ZMC fractures have a positive impact on restoring facial symmetry and concordance of bilateral orbital volumes.

Fluorescence excitation-emission spectroscopy with regional integration analysis for assessment of compost maturity.

Composting of animal manures is believed as an alternative way for directly recycling them in farms, and therefore assessment of compost maturity is crucial for achieving high quality compost. Fluorescence excitation-emission matrices (EEMs) combined with regional integration analysis is presented to assess compost maturity. The results showed that the EEM contours of water-extract organic matter (WEOM) from immature composts exhibited four peaks at excitation/emission (Ex/Em) of 220/340nm, 280/340nm, 220/410nm, and 330/410nm, whereas EEM contour of WEOM from mature composts had only two peaks at Ex/Em of 230/420nm and 330/420nm. Pearson correlation demonstrated that peaks intensity rather than their ratios had a significantly correlation with the common indices assessing compost maturity, whereas the normalized excitation-emission area volumes (Φ(i,n)s) from regional integration analysis had a stronger correlation with the common indices assessing compost maturity than peaks intensity. It is concluded that the Φ(i,n)s from regional integration analysis are more suitable to assess the maturity of compost than the intensities of peaks. Therefore, the fluorescence spectroscopy combined with regional integration analysis can be used as a valuable industrial and research tool for assessing compost maturity, given its high sensitivity and selectivity.