Optical coherence tomography (OCT) is a useful non-invasive optical tool for imaging various biological tissues. As OCT imaging is based on interferometry, speckle noises are inherent and can degrade the quality of OCT image. The objective of this study was to evaluate the effectiveness of conventional denoising algorithms for OCT image denoising and for improving image quality. OCT images of human skin were obtained from a swept source OCT of 1300 nm. Three image denoising algorithms, including median filtering, mean filtering and Gaussian bilateral filtering, were applied for denoising OCT images of different quality. Five quality evaluation criteria, including signal to noise ratio (SNR), equivalent number of looks (ENL), contrast-to-noise ratio (CNR), cross correlation (XCOR), and peak signal to noise ratio (PSNR) were used for comparing the effectiveness of each denoising process. In terms of improving local contrast, three denoising algorithms showed similar effect. In terms of the equivalent views, Gaussian bilateral filtering algorithm showed the most significant increase and therefore caused certain degrees of blurry. For signal to noise ratio, all three denoising algorithms showed improvement while Gaussian bilateral filtering algorithm had better protection effect of the effective information and edge of the original image. Gaussian bilateral filtering algorithm provides better denoising outcomes for OCT image processing.
In situ quantification of photosensitizer is critical in photodynamic therapy (PDT) and photodiagnosis (PD). Fluorescence detection is a feasible approach for the quantification of fluorescent photosensitizer. However, due to the interference of tissue absorption and scattering on the fluorescence spectrum of photosensitizer, it is still challenging to perform in situ fluorescence quantification. In this preliminary study, a Monte Carlo (MC)-based method was used to simulate the fluorescence spectrum and diffuse reflection spectrum of different biological tissues. A calibration algorithm was developed for the correction of the influence of tissue absorption and scattering on protoporphyrin IX (PpIX) fluorescence. Under the excitation of blue light of 405 nm the dispersion coefficient of the original PpIX fluorescence spectrum of the soft tissue phantoms was 28%, which was reduced to 3% after the correction using the calibration algorithm. Under the excitation of red light of 635 nm, the dispersion coefficient of the original PpIX fluorescence spectrum of the soft tissue phantoms was 25%, which was reduced to 1.5% after the correction using the calibration algorithm. The results show that the MC-based method can effectively improve the accuracy of PpIX fluorescence measurement.
Early studies suggest that some PDT photosensitizers can be used as sonosensitizer for sonodynamic therapy (SDT). In this study, sonodynamic effects of a novel water soluble chlorin YLG-1 were evaluated. SDT of YLG-1 solution was carried out using an ultrasound transducer of 450 KHz at 2.0 W/cm2 for 0 – 600 s. Comparison of spectroscopic profiles of YLG-1 before and after SDT demonstrated that sonification could cause the reduction of YLG-1 absorbance and fluorescence emission but did not cause obvious change of the Raman spectrum. No significant by-products were identified from spectroscopic study. Nevertheless, this study demonstrated that the sonification mediated sensitizer fluorescence bleaching effect could be partially blocked by the addition of NaN3, which suggests a possible involvement of singlet oxygen in the process of sonification of YLG-1 compound.
Photodynamic therapy (PDT) utilizes the combined action of photosensitizer, light, and molecular oxygen to generate reactive singlet oxygen (1O2) to treat various diseases. Photosensitizer is a key component in PDT and its singlet oxygen quantum yield determines the effectiveness of its photodynamic reaction. This study evaluated the singlet oxygen production of a novel water soluble chlorin photosensitizer (YLG-I) using a 1O2-specificfluorescence probe - Singlet Oxygen Sensor Green reagent (SOSG). The spectra and singlet oxygen luminescence in different solvents were evaluated using mTHPC as a reference. It was estimated and verified that the singlet oxygen quantum yield of the new photosensitizer YLG-I was at the same level of the potent chlorin sensitizer mTHPC. Preliminary evaluation suggested that YLG-I was a promising photosensitizer for PDT.
Photodynamic therapy (PDT) utilizes the combined action of photosensitizer, light and molecular oxygen to generate singlet oxygen to treat various diseases. Photosensitizer is a key component and its optical properties and singlet oxygen quantum yield determine the effectiveness of its photodynamic reaction. This study evaluated the singlet oxygen production of a novel water solubility chlorin photosensitizer - namely YLG-I, which was developed in China. The absorption spectra and singlet oxygen luminescence different solvents were evaluated. It was estimated that the singlet oxygen quantum yield of the new photosensitizer YLG-I was at the same level of the potent chlorin sensitizer mTHPC. Preliminary evaluation suggested that YLG-I was a promising photosensitizer for PDT. This presentation will report the detection of singlet oxygen luminescence of the newly developed PDT sensitizer.
Some of the key optical properties of a new water soluble chlorine (YLG-1) were evaluated. The sensitizer has a strong absorption at 398 nm and 655 nm in DMSO. A strong red fluorescence is detected under the excitation of 398 nm. The fluorescence life time is approximately 5 ns and fluorescence quantum yield 20%. The sensitizer does not accumulate in normal skin after topical use or IV injection. Preliminary in vivo results suggest that this novel chlorine causes little cutaneous phototoxicity. Its potentials in photodynamic therapy (PDT) deserve further study.
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