Characterization Of Pasteurized Milk In The Near-Infrared Range For Construction Of Tissue-Mimicking Optical Phantoms

INTRODUCTION

In the ever-evolving landscape of biomedical optics, the development and refinement of optical devices have revolutionized medical diagnostics, imaging, and therapeutic interventions. Central to the advancement of these technologies is the critical need for validation and quality assurance, ensuring the accuracy, reliability, and safety of biomedical optical devices in clinical practice.

Optical phantoms play a crucial role in biomedical imaging, aiding in the calibration and validation of photonic instruments. These phantoms, engineered to mimic the optical properties of biological tissues, provide a controlled testing environment where the performance of optical devices can be rigorously evaluated and optimized. Intralipid, a well-calibrated lipid emulsion, is commonly used. However, it is relatively expensive, motivating scientists to search for more affordable options.

Figure 1: Photo of a phantom made to match to the optical reflectance of a hand.

Pasteurized milk is a promising material for creating tissue-mimicking phantoms, especially in the near-infrared (NIR) spectral range. After heat treatment to kill bacteria and prolong the product's shelf life, it can be used as a potential material to mimic biological tissues since pasteurization alters its optical characteristics. In addition, pasteurized milk is inexpensive, easily accessible, and highly biocompatible, which makes it ideal for research and development as well as guaranteeing safety throughout testing.

By measuring the absorption and scattering properties of pasteurized milk at different wavelengths in the NIR spectrum, we can evaluate its suitability for tissue simulation applications.

METHODS

In order to characterize the pasteurized milk optically, optical phantoms were built, and optical measurements were conducted to ascertain the optical properties of the pasteurized milk samples, primarily attenuation, and scattering coefficients. Two optical setups were used to determine the attenuation and scattering coefficients of the pasteurized milk: collimated transmission spectroscopy, and diffuse reflectance spectroscopy.

Figure 2: Flowchart of the procedure for the determination of optical properties of pasteurized milk.

In collimated transmission spectroscopy, the attenuation coefficient describes the reduction in intensity of electromagnetic radiation passing through a material. It depends on material properties and radiation wavelength. This coefficient quantifies how much incident radiation is absorbed or scattered by the sample.

Diffuse reflectance spectroscopy uses the scattering coefficient to describe how light or electromagnetic radiation scatters when interacting with a material. This coefficient indicates the likelihood of scattering events within the material and is important in determining the material's reflectance properties.

RESULTS

As the milk concentration increases, there is a change in the extinction coefficient at the observed wavelengths. All fitting results according to the Rsquare value can be accepted (~0.9), especially the low-fat pasteurized milk sample because the absorption capacity of full-fat samples was higher than that of full-fat samples. (Fig. 5a).

The albedo of the milk samples was also estimated given the values of the scattering and absorption coefficients. It can be observed that albedo values for both low- and full-fat samples can be as high as 0.9 (Fig. 5b). This indicates that pasteurized milk as a scattering material can be used for optical phantom development that has albedo similar to corresponding values of biological tissue, which is nearly around 0.9 on average for most scattering tissues. One can also notice the low values of albedo for low-fat milk samples, especially for low concentrations of milk in comparison with other samples. This can be explained by the lower scattering coefficient for low-fat milk due to the larger distance between scattering particles in low-fat milk samples resulting from a low concentration of milk.

Figure 5: (a) Extinction coefficient of low and full-fat milk at 690 nm 830 nm as a function of concentration (b) Albedo of low and full-fat milk at 690 nm and 830 nm for different milk concentrations.

A comparison between the standard scattering coefficient value and the scattering coefficient value of two pasteurized milk samples leads to a large error of up to 40%. Meanwhile, the error of interlipid (a type of material commonly used in optical phantom) is only about 2%. Furthermore, whole milk samples show a higher degree of uncertainty than low-fat milk samples (Fig. 6). This can be explained by the imperfect linearity between the full-fat concentration and the extinction coefficient. At the same time, the commercial pasteurized milk used lacks uniformity in production, leading to large batch-to-batch variations in the dispersion coefficient of pasteurized milk.

Figure 6: Uncertainty levels in recovered scattering coefficient of (a) full and (b) low-fat milk at 690 nm 830 nm as a function of concentration and for three different tissue types.

BUILD SYSTEM

INTINS can provide a complete system for this application. The Ocean Optics USB4000+ spectrometer (Ocean Insight) is a high-performance, low-cost system that is easily configured for thousands of different applications in the NIR range. The spectrometer's long wavelength range of 200–1100 nm is suitable for both transmittance and reflection measurement applications in the NIR wavelength range of the application, which can be used in the laboratory or on industrial lines.

Figure 7: The USB4000+ spectrometer of the Ocean Insight.

For transmittance measurements, the Square One Cuvette Holder offers a smooth solution for transmittance measurements, guaranteeing ideal alignment and stability. The procedure is streamlined by robust construction and user-friendly design, allowing for analysis without sacrificing dependability. With its versatile platform that may be used for both diffuse and specular reflection, the Fiber Optic Reflection Probe Holder facilitates effective light collection and distribution for reflection measurements. Its precise and versatile design enables users to measure a range of samples with ease and accuracy.

Figure 8:  Square One Cuvette Holder (left) for the collimating transmission system and Fiber Optic Reflection Probe Holders (right) for the diffuse reflectance system.

CONCLUSION

Characterizing pasteurized milk in the NIR range offers a promising approach for constructing tissue-mimicking optical phantoms. Its similar optical properties to biological tissues, coupled with its availability, cost-effectiveness, and biocompatibility, make it an attractive option for researchers in the field of biomedical optics. By leveraging pasteurized milk as a phantom material, advancements in medical imaging and therapeutic techniques can be accelerated, ultimately contributing to improved healthcare outcomes.