Single Integrating Sphere System Research Articles

Internal quality evaluation of ‘Fuji’ apples during storage based on bulk optical properties or diffuse reflection and transmission spectra

The purpose of this study is to compare the performance of prediction models based either on the bulk optical properties (BOP) or with models based on the diffuse reflection and transmission spectra to assess the soluble solids content (SSC) or fruit firmness (FF) of ‘Fuji’ apples. Diffuse reflection and transmission spectra of 240 apples in 500–1000 nm were acquired using a self-constructed single integrating sphere system, from which the absorption coefficient (μa) and reduced scattering coefficient (μ′s) were determined. The relationships of μa, μ′s, and the reflection and transmission spectra with the SSC and FF were analyzed, and detection models were established using partial least squares regression coupled with characteristic wavelength selection. Results showed that neither the SSC nor the FF changed obviously during 80-days storage, and the μa and μ′s showed no monotonic increase or decrease pattern. The SSC prediction model based on μa spectra combined with the baseline correction method performed the best (R2p = 0.79, RMSEP = 0.62), while the model based on μ′s spectra was the best for FF (R2p = 0.67, RMSEP = 0.35 N). Overall, the accuracy of the model based on BOP in predicting internal quality was better than that based on reflection and transmission spectra from the same measurement.

Detection of chlorophyll content based on optical properties of maize leaves

The chlorophyll content reflects plants’ photosynthetic capacity, growth stage, and nitrogen status. Maize is one of the three widely planted gain crops in the world. In order to offer useful information for the development of chlorophyll content detectors of maize leaves, a single integrating sphere system was used to measure the transmittance and reflectance spectra of maize leaves over the wavelength range of 500–950 nm. The linear relationships of transmittance and reflectance with chlorophyll content were investigated. The feature wavelengths (FWs) sensitive to chlorophyll content were extracted from the full transmittance and reflectance spectra using the successive projections algorithm (SPA). The partial least squares regression (PLSR) models for predicting the chlorophyll content were established using the full spectra and extracted FWs. The results showed that there were obvious linear relationships between transmittance and reflectance with chlorophyll content of maize leaves and the best linear relationships were found at 709 nm and 714 nm, respectively, with the linear correlation coefficients of 0.801 and 0.696, and the root-mean-squares error (RMSEP) of 0.321 mg·g−1 and 0.405 mg·g−1, respectively. Eight and 6 FWs were extracted from the transmittance and reflectance spectra, respectively. The PLSR model established using the selected FWs from transmittance spectra had better prediction performance with RMSEP of 0.208 mg·g−1 than using full transmittance spectra. The built PLSR models using the full reflectance spectra and extracted FWs had poor robustness. This research offers some theoretical basis for developing a maize leaf chlorophyll content detector based on transmittance or reflectance.

Detection of Alternaria alternata infection in winter jujubes based on optical properties and their correlation with internal quality parameters during storage

In this work, a single integrating sphere system was applied to characterize the optical absorption (μa) and reduced scattering (μs′) properties (550 – 1050 nm) in winter jujube flesh infected by Alternaria alternata during storage at 4 and 20 °C, respectively. Meanwhile, physical (L*, a*, weight loss) and biochemical characteristics (soluble solids content, titratable acids, chlorophyll, total phenolic, and ascorbic acid) of winter jujubes were measured. Among them, chlorophyll, weight loss and ascorbic acid were highly correlated with μa at 680 nm, 690 nm, while chlorophyll and a* had the best correlations with μs′ at 700 – 920 nm. These optimal optical properties were proved efficiently contributed to the disease detection of winter jujubes after 12 days at 4 °C and 3 days at 20 °C during storage, with satisfactory discrimination accuracies (acc > 93.75 %). Consequently, optical properties in Vis-NIR region were available to detect the postharvest disease in winter jujubes.

Internal quality assessment of kiwifruit by bulk optical properties and online transmission spectra

The purpose of this study was to compare the accuracy and robustness of the detection models based on bulk optical properties (BOP) with that based on conventional spectroscopy in kiwifruit quality evaluation. 81 kiwifruit were selected as experimental samples in this study. A single integrating sphere system was built to estimate the bulk absorption coefficient (μa) and bulk reduced scattering coefficient (μs′) of samples and a self-designed online system was used to obtain transmission spectra. The relationship of μa and μs′ with SSC and flesh firmness was analyzed, and detection models were established using partial least squares regression (PLSR). Competitive adaptive reweighted sampling (CARS) was also used to eliminate the variables in the original spectra that do not contribute to the improvement of the model performance. Results showed that μa at 670 nm decreased with the increase of SSC, μa at 720–900 nm and 950–1000 nm increased with the increase of SSC, and spectra of μs′ decreased with the decreasing firmness. CARS-PLSR models were developed, based on μa, μs′, μa×μs′, μeff, μt′, and transmission spectra. The accuracy of the model based on BOP in predicting internal quality was better than that based on transmission spectra. The model based on μa was the best for SSC (Rp2 = 0.97, RMSEP = 0.25%), and the model based on μa×μs′ was the best for flesh firmness (Rp2 = 0.97, RMSEP = 0.02 N). 20 kiwifruit that differed from the experimental samples in planting orchard and harvest time were used to compare the robustness and portability of the models. Results showed that all SSC models and the firmness model based on μa×μs′ had good robustness and portability. However, the model based on transmission spectra had a poor performance in predicting the firmness of samples from the external validation set. This study provides an effective reference for the prediction of firmness and SSC based on BOP and transmission spectra of kiwifruit.

Optical characterization of liquid phantoms in 500–1000 nm using an improved single integrating sphere system

This paper reports on optical characterization (absorption coefficient μa and reduced scattering coefficient μs′) of liquid phantoms in the wavelength range of 500–1000 nm using an improved single integrating sphere system. 54 liquid optical phantoms (18 pure absorption, pure scattering and mixed samples each) with known optical properties were first prepared. The overall performance of a laboratory-established single integrating sphere system was then evaluated, and the results indicated that the system has perfect stability, repeatability, and accuracy in optical property measurement. After that, effect of cuvette size (i.e., optical path and wall thickness) on optical property measurement was investigated. The experimental results showed that the discrepancies of the measured optical properties for the pure absorption and scattering phantoms held by different cuvettes with varying optical paths and wall thicknesses were within 8.76 %. Finally, the effect of different concentrations of absorber and scatterer on optical property determination of mixed liquid phantoms were explored. It was found the measured optical properties of the mixed liquid phantoms had a considerable difference from those of the pure absorption and pure scattering phantoms. We guessed that the addition of the absorber (scatterer) would dilute the concentration level of scatterer (absorber), and also brought about interaction between the two particles, and thus resulting in an offset for the measured optical properties. Future work needs to test our conjecture from the micro level, like monitoring the dynamic change of the absorption and scattering particle distribution and interaction, when optically characterizing the mixed liquid phantoms.

Differences in optical properties and internal qualities of ‘Fuji’ apple produced in different areas of the Loess Plateau region

Present studies have shown that near-infrared spectroscopy (NIRS) could be used to identify the producing area of apple. However, we still do not know whether the producing area affects the optical properties of apple, whether it affects the relationship between optical properties and internal qualities, and whether the optical parameters could be used to predict the apple-producing area. To answer these questions, the apples produced in three areas with different temperatures, precipitations, and altitudes in the Loess Plateau region, China, were used as samples to obtain the optical properties of apple pulp by a single integrating sphere system, analyze the differences in optical properties of apples produced in different areas, analyze the correlations between optical properties (absorption coefficient (μa) and reduced scattering coefficient (μs')) and internal quality indices (soluble solids content (SSC), moisture content and firmness), and investigate the feasibility of discriminating the apples produced in different areas and predicting the internal qualities using NIRS. The results showed that the apples produced in Luochuan had the highest SSC while Yangling apples had the highest moisture content. The μa had three absorption peaks at around 985, 1200, and 1430 nm, and the μs' of apples from three areas showed a similar trend with wavelength. The best correlation of μa with SSC and moisture content was found in Yangling apples with a correlation coefficient of −0.90 and 0.79, respectively. The built linear discriminant analysis based on μa spectra performed better in discriminating producing area. The established partial least squares regression models based on μa spectra had the best prediction performance for SSC and moisture content, while the model built with μs' had the best prediction performance for firmness. This study is helpful to understand the differences in optical property of ‘Fuji’ apple produced in different areas and offers information for identifying the producing area of fruit using NIRS technology.

Relationship of the optical properties with soluble solids content and moisture content of strawberry during ripening

To understand the relationship of optical properties with soluble solids content (SSC) and moisture content of strawberry during ripening, a single integrating sphere system was built to estimate the absorption coefficient (μa) and reduced scattering coefficient (μs') of strawberry in white, color turning and red ripening stages over the wavelength range of 550−850 nm and 950−1650 nm. The relationship between optical properties and SSC and moisture content was analyzed, and the determination models for SSC and moisture content were established by using partial least squares regression and support vector machine methods based on the spectra of μa, μs', and μa together with μs'. The results showed that the absorption peaks of strawberry were at 675, 975, 1197 and 1411 nm, and the μs' generally decreased with increased maturity of strawberry. The μa was positively correlated with SSC and negatively correlated with moisture content, while the μs'was positively correlated with moisture content and negatively with SSC. The best correlations of μa with SSC and moisture content were found at 1411 nm with the correlation coefficients of 0.72 and -0.74, respectively. The established support vector machine models based on the μa spectra in 950−1650 nm and 550−850 nm had the smallest root-mean-squares error of calibration set of 0.98 % and 0.89 % for SSC and moisture content, respectively. This study indicates that SSC and moisture content mainly affect the absorption property of strawberry, and μa has greater potential than μs' and μa together with μs' in determining the internal quality of strawberry.

Determination of anthocyanin and moisture content of purple sweet potatoes during drying process by their optical properties in the 400–1050 nm range

This research investigated the potential of using optical properties to assess quality attributes of purple sweet potatoes (PSPs) during drying process. The absorption (μa) and scattering (μs') properties of PSPs during drying were determined at 400–1050 nm using a single integrating sphere system. The absorption spectra were marked by pronounced anthocyanin peaks around 545 nm, and very small water peaks around 980 nm. The average μs' was relatively flat in the 670–1000 nm range, which increased as drying time increased. Good prediction of anthocyanins (determined by pH-differential method) and moisture (determined by oven-drying method) contained in PSPs were obtained using their optical properties through SVM models, with determination coefficients of prediction (R2p) of 0.866–0.917, and residual predictive deviation (RPD) of 2.626–3.190. These results were consistent with correlation results between optical properties and the two quality parameters, suggesting the former can be used for predicting PSP quality during drying.

Optical investigation of bovine grey and white matters in visible and near-infrared ranges

Abstract Introduction: Due to enormous interests for laser in medicine and biology, optical properties characterization of different tissue have be affecting in development processes. In addition, the optical properties of biological tissues could be influenced by storage methods. Thus, optical properties of bovine white and grey tissues preserved by formalin have been characterized over a wide wavelength spectrum varied between 440 nm and 1000 nm. Materials and Methods: To that end, a single integrating sphere system was assembled for spectroscopic characterization and an inverse adding-doubling algorithm was used to retrieve optical coefficients, i.e. reduced scattering and absorption coefficients. Results: White matter has shown a strong scattering property in comparison to grey matter. On the other hand, the grey matter has absorbed light extensively. In comparison, the reduced scattering profile for both tissue types turned out to be consistent with prior works that characterized optical coefficients in vivo. On the contrary, absorption coefficient behavior has a different feature. Conclusion: Formalin could change the tissue’s optical properties because of the alteration of tissue’s structure and components. The absence of hemoglobin that seeps out due to the use of a formalin could reduce the absorption coefficient over the visible range. Both the water replacement by formalin could reduce the refractive index of a stored tissue and the absence of hemoglobin that scatters light over the presented wavelength range should diminish the reduced scattering coefficients over that wavelength range.

Effect of purification, dehydration, and coagulation processes on the optical parameters of biological tissues

In this study, the effects of purification, dehydration, and coagulation processes on the absorption and reduced scattering coefficients of chicken liver tissues have been investigated by using a single integrating sphere system. The purification process performed on the tissue samples to remove blood residue has been found to cause a slight change in the optical parameters. Although the dehydration process brings about an increase in the absorption coefficient due to the water loss, no direct relationship has been observed between the reduced scattering coefficient and the dehydration level of the tissue. In addition, it has been observed that there was a relatively small increase in the absorption coefficient and a significant increase in the reduced scattering coefficient after the coagulation process. Therefore, it can be said that the optical penetration depth decreased significantly after dehydration and coagulation processes unlike blood purification. Moreover, fluence rate distributions inside the fresh, blood purified, dehydrated, and coagulated tissue models have been investigated by using the Monte Carlo modeling of photon transport in multilayered tissues simulation code.

Optical properties in the visible range of two different India ink used as biological phantoms

The optical characteristics of two different brands of India ink, Parker Quink and Pelikan, as an absorber used in preparation a tissue-simulating phantom, have been investigated at visible wavelength range. For this purpose, a single integrating sphere system and a spectrophotometric transmission spectroscopy have been used to estimate the radiometric characteristics. Then, inverse adding-doubling algorithm was implemented to retrieve the optical coefficients of pure ink samples. Parker ink's absorption behavior turned out to incompatible with Pelikan over the present wavelength range. Furthermore, scattering property of both two brands has been exhibited and the albedo was calculated. Parker albedo showed a decremental behavior with wavelength and varied between 0.381 and 0.13. A structural profile of albedo was found for Pelikan, which varied between 0.366 and 0.03. This discrepancy might be explained by the variety of two brands composition besides experimental errors. Furthermore, Parker ink absorption variation turned out to be in correspondence to several tissues' absorption feature over broad wavelength ranges. Finally, Parker ink could be regarded as a better candidate to mimic absorption property for several tissues.

Effects of optical variables in a single integrating sphere system on estimation of scattering properties of turbid media

This research was aimed at determining the effect of optical variables for a single integrating sphere system, coupled with the inverse adding-doubling method, on estimating the reduced scattering coefficient ( μ s ′ ) of turbid media. Integrating sphere measurements were performed on a total of 36 liquid samples and two solid samples. The results demonstrated that the system had good accuracy, with average errors for estimating absorption coefficient μa (pure absorption) and μ s ′ (pure scattering) of liquid samples being 15.0% and 4.7% over 550–900 nm, compared with the collimated transmittance and empirical equation, respectively. The system also had good reproducibility for μa and μ s ′ , with the coefficients of variation lower than 4%. Sensitivity analysis revealed that the detectable values of μa and μ s ′ were around 0.02 cm−1 and 4.5 cm−1. Entrance and detector port diameters, standard reflectivity and anisotropy factor had a negligible effect on estimating μ s ′ ( μ s ′ (2.8%–35.3%). Hence these variables should be carefully chosen or accurately measured before optical property measurements are carried out. Application examples of the μ s ′ estimation for apple skin and flesh further validated the system performance, indicating that appropriate selection of optical variables could improve the estimation of μ s ′ .

Optical characterization of tissue-simulating phantom components at 405nm

Optical properties of India ink (1950375, Parker, Quink, England) and 1-µm polystyrene microsphere (07310-15, Polysciences, USA) have been predicted at 405nm. For this purpose, a single integrating sphere system and spectrophotometric transmission spectroscopy have been used to estimate the radiometric characteristics. Radiometric measurements utilized to retrieve optical coefficients based on two different methods. Extinction coefficient has been estimated using collimated transmittance. To reconstruct absorption and scattering coefficients, total transmittance, diffuse reflectance and transmittance were measured. Polystyrene albedo was 0.9925 and was 0.1044 for ink. The agreement of PS scattering coefficient in comparison to Mie theory was obvious. Full Text: PDF ReferencesB.W. Pogue, and M.S. Patterson, "Review of tissue simulating phantoms for optical spectroscopy, imaging and dosimetry", J. Biomed. Opt. 11, 4(2006). CrossRef D. Coluccia, J. Fandino, M. Fujioka, S. Cordovi, C. Muroi, and H. Landolt, "Intraoperative 5-aminolevulinic-acid-induced fluorescence in meningiomas", Acta. Neurochir. 152 (2010). CrossRef P. Valdes et al. "https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8928/892809/Quantitative-spectrally-resolved-intraoperative-fluorescence-imaging-for-neurosurgical-guidance-in/10.1117/12.2039090.short", Congress. Neuro. Surg. 10, 1(2014). CrossRef S. J. Madeson, M. S. Patterson, and B. C. Wilson, "The use of India ink as an optical absorber in tissue-simulating phantoms", Phys. Med. Bio. 37, 5(1997). CrossRef P. Ninni, F. Martelli, and G. Zaccanti, "The use of India ink in tissue-simulating phantoms", Opt. Express. 18, 26(2010). CrossRef F. Martelli, and G. Zaccanti, "Calibration of scattering and absorption properties of a liquid diffusive medium at NIR wavelengths. CW method", Opt. Express.15, 2(2007). CrossRef L. Spinelli et al. "Determination of reference values for optical properties of liquid phantoms based on Intralipid and India ink", Biomed. Opt. Express. 5, 7(2014). CrossRef Y. Liu, Y. Kim, and V. Beckman, "Development of a bioengineered tissue model and its application in the investigation of the depth selectivity of polarization gating", App.Opt. 44, 12 (2005). CrossRef B. Wilson, M. Patterson, and S. Flock, "INDIRECT VERSUS DIRECT TECHNIQUES FOR THE MEASUREMENT OF THE OPTICAL PROPERTIES OF TISSUES", Photochem. Photobiol. 46, 5(1987). CrossRef L. L. Sandell, and T. C. Zhu, "A review of in‐vivo optical properties of human tissues and its impact on PDT", J. Biophotonics. 4,(2011). CrossRef A. Shahin, M. Sayem El-Daher, and W. Bachir, "Determination of the optical properties of Intralipid 20% over a broadband spectrum", Phot. Lett. Poland. 10, 4(2018). CrossRef A. Karinov, A. Mokeeva, E. Segeeva, P. Agrba, and M. Kirillin, "Optical properties of mouse biotissues and their optical phantoms", Opt. Spec. 115, 2(2013). CrossRef C. Matzler, Matlab Functions for Mie Scattering and Absorption, version 2 (Bern, Bern university 2002). DirectLink D. Roysten, R. Poston, and S. Prahl, "Optical properties of scattering and absorbing materials used in the development of optical phantoms at 1064 nm", JBO. 1, 1(1996). CrossRef A. Shahin, and W. Bachir, "Broadband spectroscopy for characterization of tissue-like phantom optical properties", Pol. J. Med. Phys. Eng. 21, 4(2017). CrossRef

Polystyrene Microsphere Optical Properties by Kubelka–Munk and Diffusion Approximation with a Single Integrating Sphere System: A Comparative Study

The optical properties of 1 μm polystyrene in the wavelength range of 500–750 nm were estimated by using a white light spectrophotometric transmittance spectroscopy and a single integrating sphere system. To retrieve the optical characteristics, two analytical methods, namely, diffusion approximation and Kubelka–Munk were used, and then their results were compared with Mie theory calculations. The correspondence of the Kubelka–Munk scattering coefficient with Mie was obvious, and relative errors varied between 6.73% and 2.66% whereas errors varied between 6.87% and 3.62% for diffusion theory. Both analytical methods demonstrated the absorption property of polystyrene over the abovementioned wavelength range. Although absorption coefficient turned out to be much lower than scattering, constructing a realistic optical phantom requires taking into account absorption property of polystyrene. Complex refractive index of polystyrene based on these two methods was determined. Inverse Mie algorithm with scattering coefficient was also used to retrieve the real part of refractive index and absorption coefficient for calculating the imaginary part of refractive index. The relative errors of the real part did not exceed 2.6%, and the imaginary part was in consistence with the prior works. Finally, the presented results confirm the validity of diffusion theory with a single integrating sphere system.

Application of single integrating sphere system to obtain the optical properties of turbid media

In this study, a simple method to determine the reflectance and transmittance of turbid media is proposed. The method is based on a single integrating sphere system. The integrating sphere theory is used to calculate the reflectance and transmittance under diffuse and directional illumination, and an experimental setup is proposed to measure these quantities. This method was used to determine the reflectance and transmittance of poly(vinyl alcohol) (PVA) hydrogels. Monte Carlo calculations were also implemented to validate our results. The comparison shows that the optical properties obtained through this method propagate low values of uncertainty, and a setup simpler than that of the double integrating sphere system can be realized. However, our system is limited to the diffuse–diffuse transmittance. The results suggest that the single sphere system and Monte Carlo method can be a strong combination to calculate the inherent optical properties of PVA samples.

Determination of the optical properties of Intralipid 20% over a broadband spectrum

The aim of this study is to characterize the optical properties of Intralipid20% using two methods modified Kubelka-Munk model and Mie theory and to test the applicability of a modified Kubelka-Munk model with a single integrating sphere system over a wide wavelength range 470 – 725nm. Scattering coefficients which estimated by these two methods were matched and the absorption effect was observed and quantified. Finally, the imaginary part of the refractive index was estimated besides scattering, absorption and anisotropy coefficients. Full Text: PDF ReferencesB.W. Pogue, and M.S. Patterson, "Review of tissue simulating phantoms for optical spectroscopy, imaging and dosimetry", J. Biomed. Opt. 11, 4(2006). CrossRef J. Hwang, C. Ramella-Roman, and R. Nordstrom, "Introduction: Feature Issue on Phantoms for the Performance Evaluation and Validation of Optical Medical Imaging Devices", Biomed. Opt. Express. 3, 6(2012). CrossRef P. Ninni, F. Martelli, and G. Zaccanti, "Intralipid: towards a diffusive reference standard for optical tissue phantoms", Phys. Med. Biol 56, 2(2011). CrossRef S. Flock, S. Jacques, B. Wilson, W. Star, and J.C. van Gemert, "Optical properties of intralipid: A phantom medium for light propagation studies", Lasers. Surg. Med 4, 12(1992). CrossRef R. Michels, F. Foschum, and A. Kienle, "Optical properties of fat emulsions", Opt. Express. 16, 8(2008). CrossRef L. Spinelli et al. "Calibration of scattering and absorption properties of a liquid diffusive medium at NIR wavelengths. Time-resolved method", Opt. Express. 15, 11(2007). CrossRef L. Spinelli et al. "Determination of reference values for optical properties of liquid phantoms based on Intralipid and India ink", Biomed. Opt. Express. 5, 7(2014). CrossRef H. van Staveren, C. Moes, J. van Marle, S. Prahl, and J. van Gemert, "Light scattering in lntralipid-10% in the wavelength range of 400–1100 nm", Appl. Opt. 30, 31(1991). CrossRef B. Wilson, M. Patterson, and S. Flock, "Indirect versus direct techniques for the measurement of the optical properties of tissues", Photochem. Photobiol. 46, 5(1987). CrossRef H. Soleimanzad, H. Gurden, and F. Pain, "Optical properties of mice skull bone in the 455- to 705-nm range", J. Biomed. Opt. 22, 1(2017). CrossRef C. Holmer et al. "Optical properties of adenocarcinoma and squamous cell carcinoma of the gastroesophageal junction", J. Biomed. Opt. 12, 1(2007). CrossRef S. Thennadil, "Relationship between the Kubelka–Munk scattering and radiative transfer coefficients", OSA. 25, 7(2008). CrossRef L. Yang, and B. Kruse, "Qualifying the arguments used in the derivation of the revised Kubelka–Munk theory: reply", OSA. 21, 10(2004). CrossRef W. Vargas, and G. Niklasson, "Applicability conditions of the Kubelka–Munk theory", Appl. Opt. 36, 22(1997). CrossRef A. Krainov, A. Mokeeva, E. Segeeva, P. Agrba, and M. Kirillin, "Optical properties of mouse biotissues and their optical phantoms", Opt. Spec. 115, 2(2013). CrossRef H.C. van de Hulst, Light Scattering by Small Particles. (New York, Dover Publication 1981). CrossRef C. Matzler, Matlab Functions for Mie Scattering and Absorption. (Bern, Bern university 2002). DirectLink C. Matzler, Matlab Functions for Mie Scattering and Absorption, version 2 (Bern, Bern university 2002). DirectLink G. Segelstein, The complex refractive index of water [dissertation]. (Kansas, university of Missouri-Kansas city 1981). DirectLink A. Shahin, and W. Bachir, Pol. J. Med. Phys. Eng. 21, 4(2017). CrossRef

Model robustness improvement by absorption and reduced scattering spectra in short wave near infrared spectral region

Model robustness has always been the research focus for near infrared spectroscopy technique. In this study, we compared the model performance of four different kinds of spectra (transmittance, reflectance, absorption (μa) and reduced scattering (μ′s)) for the prediction of fat and protein of milk. The protein content of milk in prediction set was totally out of range of fat calibration set. The same happens in the case of the fat content of milk in prediction set and protein calibration set. The aim of this present study was to investigate the effect of the difference of protein content on the robustness of four fat calibration models, and of the difference of fat content on the robustness of four protein calibration models. The single integrating sphere system was first calibrated by using 90 liquid phantoms. The detection accuracy of the calibrated system was externally validated by another 80 phantoms. It turned out that the system can measure the absorption and reduced scattering coefficients with relatively high precision in the range of 780–1073 nm, which gave mean relative errors less than 12% and 5% for μa and μ′s respectively. Partial least squares regression (PLSR) and stepwise multiple linear regression (SMLR) models were established, and the results showed that calibration model based on reduced scattering spectra could predict fat with the highest robustness for both regression methods, while the absorption spectra could predict protein content with the highest robustness by using SMLR. The separation of absorption and reduced scattering has great potential in improving the robustness of calibration models.

Investigation of absorption and scattering characteristics of kiwifruit tissue using a single integrating sphere system

For a quantitative understanding of light interaction with fruit tissue, it is critical to obtain two fundamental parameters: the absorption coefficient and the scattering coefficient of the tissue. This study was to investigate the optical properties of kiwifruit tissue at the wavelength of 632.8 nm. The total reflectance and total transmittance of kiwifruit tissue from three parts (including the flesh part, the seed part, and the seed-base part) were measured using a single integrating sphere system. Based on the measured spectral signals, the absorption coefficient μa and the reduced scattering coefficient μs' of kiwifruit tissue were calculated using the inverse adding-doubling (IAD) method. Phantoms made from Intralipid 20% and India ink as well as a Biomimic solid phantom were used for system validation. The mean values of μa and μs' of different parts of the kiwifruit were 0.031-0.308 mm(-1) and 0.120-0.946 mm(-1), respectively. The results showed significant differences among the μa and μs' of the three parts of the kiwifruit. The results of this study confirmed the importance of studying the optical properties for a quantitative understanding of light interaction with fruit tissue. Further investigation of fruit optical properties will be extended to a broader spectral region and different kinds of fruits.

A SIMPLE METHOD FOR PREDICTION OF THE REDUCED SCATTERING COEFFICIENT IN TISSUE-SIMULATING PHANTOMS

This paper proposes a method for predicting the reduced scattering coefficients of tissue-simulating phantoms or the desired amount of scatters for producing phantoms according to Mie scattering theory without measurements with other instruments. The concentration of the scatters TiO 2 particles is determined according to Mie theory calculation and added to transparent host epoxy resin to produce phantoms with different reduced scattering coefficients. Black India Ink is added to alter the absorption coefficients of the phantoms. The reduced scattering coefficients of phantoms are measured with single integrating sphere system. The results show that the measurements are in direct proportion to the concentration of TiO 2 and have identical with Mie theory calculation at multiple wavelengths. The method proposed can accurately determine the concentration of scatters in the phantoms to ensure the phantoms are qualified with desired reduced scattering coefficients at specified wavelength. This investigation should be possible to manufacture the phantom simply in reasonably accurate for evaluation of biomedical optical imaging systems.