Toward image quality assessment in optical coherence tomography (OCT) of rat kidney.

BACKGROUND: Optical coherence tomography (OCT) is a useful tool for the evaluation of structure and function of the kidney, but the image quality can be effected by many factors. OBJECTIVE: The objective of this study was to assess the image quality of different OCT systems in OCT imaging of the living kidney. METHODS: One swept-source OCT (SSOCT) of 1300 nm, one spectral domain OCT (SDOCT) of 1300 nm and another of 900 nm were used. A FeO phantom was used to establish the point spread function (PSF). Rat kidneys were imaged for image quality assessment. Light penetration in the kidney and the optical attenuation coefficient were also evaluated. The quantification of uriniferous tubules was carried out via the threshold segmentation of 3D OCT images. RESULTS: The quality of kidney images was resolution dependent. SDOCT of 900 nm showed higher peak signal-to noise ratio and dynamic range. The spatial resolution in the light field could be derived from the PSF distribution along three mutually orthogonal axes. In conjunction with the PSF, the Lucy-Richardson algorithm could improve image quality but could not reveal more microstructural information. The penetration depth of 1300 nm was deeper than that of 900 nm. The attenuation coefficient of the kidney was 29 cm-1 at 1300 nm and 50 cm-1 at 900 nm (P < 0.001). More accurate measurement of uriniferous tubules was achieved with the SDOCT-900 due to its higher resolution. CONCLUSIONS: Both SSOCT and SDOCT systems could be useful for imaging uriniferous tubules in the superficial layers of the cortex. The OCT image quality was highly correlated with the spatial resolution of OCT system.

Quantitative assessment of skin swelling using optical coherence tomography.

BACKGROUND: Preclinical and clinical studies suggest that optical coherence tomography (OCT) is a useful tool to visualize inflammatory conditions. OBJECTIVE: The objective of this study was to evaluate the usefulness of combining OCT and various image processing techniques for quantitative assessment of histamine-induced tissue swelling. METHODS: Both time-domain and frequency-domain OCT were used on a mouse ear model. The ear thickness and volume before and after histamine challenge were determined from pixel locations in 2D scans and voxel number counting in 3D scans. Swelling kinetics was analyzed on 3D contour mapping. Microvessel network was visualized using speckle decorrelation analysis. RESULTS: OCT images showed that the thickness and volume changes were histamine dose and contact time dependent. The 3D mapping showed that the histamine-induced swelling spread slowly and directionally. OCT data indicated that microvessel opening and vessel dilation occurred prior to tissue swelling. CONCLUSION: OCT is a robust and quantitative non-invasive imaging tool for assessing skin swelling.

In vitro assessment of effects of hyperglycemia on the optical properties of blood during coagulation using optical coherence tomography.

No published reports have demonstrated the capability of the optical coherence tomography technique for quantifying the optical coherence tomography signal slope, 1/e light penetration depth, and attenuation coefficient of hyperglycemic blood by an in vitro assessment. The purpose of this study was to investigate the effects of hyperglycemia on optical properties during in vitro blood coagulation by optical coherence tomography. Normal whole blood acted as the control group. After 1-h coagulation, the average optical coherence tomography signal slope decreased approximately 23.3 and 16.7%, and the 1/e light penetration depths increased approximately 21.5 and 19.2% for the control and hyperglycemic groups, respectively. It could be seen from the 1/e light penetration depth evolution curves that the blood coagulation time was about (425 ± 19) s for normal whole blood and (367 ± 15) s for the hyperglycemic blood. The coagulation time decreased 13.6% for the hyperglycemic blood compared with that for normal whole blood. There was statistically significant difference in blood coagulation time between the hyperglycemic and normal whole blood (p < 0.05). The results suggested that hyperglycemia has a procoagulant effect. Our experiment was the first reported study of monitoring hyperglycemic blood coagulation using OCT. We conclude that OCT is potential technique to quantify and follow the liquid-gel transition of hyperglycemic blood coagulation.

Assessment of the effects of ultrasound-mediated glucose on permeability of normal, benign, and cancerous human lung tissues with the Fourier-domain optical coherence tomography.

The objective of this study was to evaluate the effects of ultrasound-mediated analyte diffusion on permeability of normal, benign, and cancerous human lung tissue in vitro and to find more effective sonophoretic (SP) delivery in combination with the optical clearing agents (OCAs) method to distinguish normal and diseased lung tissues. The permeability coefficients of SP in combination with OCAs diffusion in lung tissue were measured with Fourier-domain optical coherence tomography (FD-OCT). 30% glucose and SP with a frequency of 1 MHz and an intensity of 0.80 W/cm2 over a 3 cm probe was simultaneously applied for 15 min. Experimental results show that the mean permeability coefficients of 30% glucose/SP were found to be (2.01±0.21)×10(-5) cm/s from normal lung (NL) tissue, (2.75±0.28)×10(-5) cm/s from lung benign granulomatosis (LBG) tissue, (4.53±0.49)×10(-5) cm/s from lung adenocarcinoma tumor (LAT) tissue, and (5.81±0.62)×10(-5) cm/s from lung squamous cell carcinoma (LSCC) tissue, respectively. The permeability coefficients of 30% glucose/SP increase approximately 36.8%, 125.4%, and 189.1% for the LBG, LAT, and LSCC tissue compared with that for the NL tissue, respectively. There were statistically significant differences in permeability coefficients of 30% glucose/SP between LBG and NL tissue (p<0.05), between LAT and NL tissue (p<0.05), and between LSCC and NL tissue (p<0.05). The results suggest that the OCT functional imaging technique to combine an ultrasound-OCAs combination method could become a powerful tool in early diagnosis and monitoring of changed microstructure of pathologic human lung tissue.

[Spectral characteristics of normal breast samples in the 350-850 nm wavelength range].

Spectral characteristics of normal female breast samples in the 350-850 nm wavelength range were measured using a UV/Vis/NIR spectrophotometer system with integrating sphere attachment for measuring the diffuse reflectance and transmittance. The optical properties of normal breast tissue in vitro were obtained by the inverse adding doubling method. And then the optical penetration depths in this spectral range were analyzed based on the principle of tissue optics. The results show that the reduced scattering coefficient of normal female breast tissue is significantly higher than the absorption coefficient in the 350-850 nm wavelength range. The reduced scattering coefficient decreases with the wavelength increment. It reaches maximum at shorter wavelengths with a decrease at longer wavelengths and ranges from 9.731 mm(-1) at 350 nm to 1.476 mm(-1) at 850 nm. The absorption coefficient of normal breast tissue is about from 0.798 mm(-1) at 350 nm to 0.102 mm(-1) at 850 nm. The maximal and minimal values are at 350 nm and 850 nm respectively. An absorption peak for the normal breast tissue is at 410 nm of wavelength with the value of 0.506 mm(-1), which belongs to hemoglobin. The absorption coefficient remains relatively constant when the wavelength is longer than 600 nm. The optical penetration depth increases with the wavelength increment and ranges about from 0.199 mm at 350 nm to 1.439 mm at 850 nm. Deep penetration depth noted in normal breast samples, especially at longer wavelengths, reflects the weak absorption and reduced scattering at these wavelengths. The calculated optical parameters of normal breast samples by the inverse adding doubling method agree well with the Monte Carlo simulations. This study may be useful for breast optical biopsy or the optical diagnosis of breast diseases.

[The impact of blood content in skin tissue on skin spectra].

Based on the analysis of skin structure, and the production mechanism of fluorescence and reflectance spectra, six-layer optical models for skin of different blood content in both upper blood plexus and deep blood plexus were developed, and Monte Carlo simulation was made. The result shows that (1) Both fluorescence and reflectance spectra could reflect the change of blood content in skin tissue; (2) The impact of blood content in upper blood plexus on skin spectra intensity is large, while the impact of blood content in deep blood plexus on skin spectra intensity is small; (3) Fluorescence and reflectance spectra could be used to detect or analyze change of blood content in skin tissue, especially to test the treatment and tune of dermatosis with plexus or blood pathological changes in upper dermis.

Monte Carlo simulation of cutaneous reflectance and fluorescence measurements--the effect of melanin contents and localization.

Melanin content and distribution in skin were studied by examining a patient with white, brown and blue skin tones expressed on skin affected by vitiligo. Both diffuse reflectance and autofluorescence spectra of the three distinction skin sites were measured and compared. Monte Carlo simulations were then performed to help explain the measured spectral differences. The modeling is based on a six-layer skin optical model established from published skin optical parameters and by adding melanin content into different locations in the model skin. Both the reflectance and fluorescence spectra calculated by Monte Carlo (MC) simulation were approximately in agreement with experimental results. The study suggests that: (1) trichrome vitiligo skin may be an ideal in vivo model for studying the effect of skin melanin content and distribution on skin spectroscopy properties. (2) Based on the skin optical model and MC simulation, the content and distribution of melanin in skin, or other component of skin could be simulated and predicted. (3) Both reflectance and fluorescence spectra provided information about superficial skin structures but fluorescence spectra are capable of providing information from deeper cutaneous structures. (4) The research method, including the spectral ratio method, the method of adding and modifying the melanin content in skin optical models, and MC simulation could be applied in other non-invasive optical studies of the skin.