Diffuse reflectance spectroscopy (DRS) is a minimally invasive optical technique used to analyze the composition of biological tissues and fluids. It delivers broadband light to tissue using a small probe and collects the diffusely reflected light using a spectrometer.1,2
Image Credit: Gorodenkoff/Shutterstock.com
DRS provides important clinical information, including tissue scattering properties, lipid and water content, tissue oxygen saturation, total hemoglobin content, and oxy- and deoxyhemoglobin. These capabilities make DRS useful for various diagnostic and disease-monitoring applications.1,2
Tissue Characterization
DRS is used to distinguish between healthy and diseased tissues by analyzing the spectral properties of light reflected from tissue surfaces.1,2 For instance, it is clinically applied to differentiate cancerous lesions from non-cancerous tissue.2
This technique uses a white light source with a defined spectral band to illuminate a sample through a fiber probe. The diffusely reflected light from various tissue layers—cancerous and non-cancerous—is collected by fibers positioned at different distances from the illumination fiber, and the resulting spectra are recorded.2
The spectra are different for cancerous and healthy tissue, providing crucial information for cancer screening. DRS can detect changes in spectral intensity caused by the absorption of oxygenated hemoglobin.2
This spectral information can be used to calculate parameters based on the amount of light scattered by tissue at different wavelengths. By analyzing the spectral profile, DRS can help identify specific characteristics of cancerous tissues, supporting the classification of hyperplastic, dysplastic, normal, and squamous cell carcinoma (SCC) categories.2
An advantage of DRS is its ability to perform in vivo tissue analysis, eliminating the need for tissue removal or biopsies. This reduces patient risk and discomfort while allowing real-time monitoring of tissue changes during treatment.2
DRS has been used in ex vivo studies of resected human colon tissue to accurately differentiate between tissue types. This approach could be adapted for in vivo use during colorectal cancer surgery to provide real-time guidance. Additionally, DRS has been incorporated into fiber-optic biopsy needles to evaluate functional tissue properties in vivo in lung cancer patients.1
Despite its potential in tissue characterization, the broader clinical adoption of DRS is limited by challenges such as inconsistent probe-tissue interface pressure, which affects reproducibility and introduces operator-dependent variability.
A paper published in Current Oncology evaluated and validated an automatic self-calibration and pressure-sensing DRS in individuals with suspected head and neck squamous cell carcinoma (HNSCC).3
Results showed that cancerous tissues possess a substantially lower hemoglobin saturation when compared to normal controls, which could be indicative of tumor hypoxia. Additionally, minimal changes were observed over time with probe placement and repeated measurements, indicating that pressure-induced effects were negligible and repeated measurements were consistent with the initial values.3
This study demonstrated the feasibility of performing optical spectroscopy measurements on intact lesions prior to their removal during HNSCC procedures. The probe also provided diagnostically relevant physiologic information that could impact future treatment.3
What is Diffuse Reflection?
Diagnostics and Disease Monitoring
DRS has emerged as a useful tool for non-invasive diagnostics and disease monitoring. By analyzing the spectral properties of reflected light, it can help detect and monitor various medical conditions, including diabetes and skin disorders. Advances in DRS technology have also facilitated early disease detection by evaluating tissue oxygenation and blood flow.4-7
Non-Invasive Blood Glucose Monitoring
Non-invasive blood glucose monitoring is important for managing diabetes and overall patient health. The sensitivity of glucose-induced optical signals within human tissue serves as a key reference for such measurements.4
A study published in Sensors assessed the sensitivity of glucose-induced diffuse reflectance in the 1000–1700 nm range. The rate of change in the scattering coefficient due to glucose is significantly higher in living tissue compared to non-living media, primarily influencing the diffuse light signal level.4
In this study, near-infrared DRS was applied for in vivo measurement of blood glucose signals. The researchers compared differential absorbance sensitivity results from human experiments with those calculated using the Monte Carlo method. This comparison validated the effect of glucose on the scattering coefficient within the 1000–1700 nm waveband.4
DRS in Skin Disease Diagnosis
DRS could be used for accurate, non-invasive, and fast diagnosis of skin disease. The diffuse reflection of light by skin involves the skin surface and the presence of scattering centers below the skin surface.
DRS can characterize the structural properties of skin tissue, with sensitivity and specificity values ranging from 64–92 % and 72–92 %, respectively.5
Tissue Oxygenation and Diabetic Foot Monitoring
Tissue oxygenation is an important indicator of health, particularly for diabetic patients, as it reflects microcirculatory complications in the extremities. A study published in the Journal of Biomedical Optics demonstrated the use of DRS to obtain tissue oxygen saturation through diffuse reflectance measurements.6
The proposed DRS-based method demonstrated feasibility as an effective approach for measuring tissue oxygen saturation. It can be applied non-invasively and in vivo without requiring high computational resources, allowing for rapid, quantifiable, and objective evaluations.6
In another recent work published in Optical Diagnostics and Sensing XXI: Toward Point-of-Care Diagnostics, DRS was utilized for non-invasive and real-time monitoring of localized blood volume parameters like oxygen saturation, oxyhemoglobin, and reduced hemoglobin. Measurements were taken from the great toe, calcaneum, 5th metatarsal, and ball of the great joint.7
The results suggest that DRS could be an effective diagnostic tool for monitoring blood oxygenation in ulcerated diabetic feet, supporting early diagnosis and intervention. This application could help reduce healthcare costs and improve the quality of life for patients with diabetic foot.7
Research Applications
DRS is a valuable tool for studying drug pharmacokinetics. It provides insights into drug absorption, distribution within tissues, and the effects of treatments on tissue properties, aiding in the development of new therapeutic strategies.8,1
For instance, reflectance spectroscopy, which encompasses several modalities like DRS, hyperspectral imaging, and Raman spectroscopy, has emerged as a powerful analytical technique in dermatology. This technique offers a non-invasive strategy to assess skin response to topical products.8
Specifically, this analytical technique allows the monitoring of changes in skin physiology to study drug absorption and facilitate the assessment of long-term effects of topical products.8
Similarly, the DRS system has been used to monitor tumor response to chemotherapy within a murine subcutaneous colonic tumor model. By monitoring the response, this technique could enable researchers to understand how a tumor responds to treatment at a biological level, which is crucial for personalized cancer therapies and optimizing therapeutic strategies.1
Conclusion
DRS is an important tool for medical diagnostics and research. It offers noninvasive, real-time insights into tissue properties, tumor responses, and disease progression. Its applications include monitoring drug absorption, tissue oxygenation, and skin conditions, with potential uses in personalized medicine and early disease detection.
The future of DRS lies in refining non-invasive techniques to enable more accurate and cost-effective disease monitoring in clinical practice. Continued advancements in this technology could enhance patient care and support therapeutic decision-making across various medical fields.
More from AZoOptics: Elevating Healthcare with Cutting-Edge XR Technology: Ensuring Quality in Medical AR/VR Systems
References and Further Reading
- Bess, SN., Greening, GJ., Muldoon, TJ. (2019). Efficacy and clinical monitoring strategies for immune checkpoint inhibitors and targeted cytokine immunotherapy for locally advanced and metastatic colorectal cancer. Cytokine & Growth Factor Reviews. DOI: 10.1016/j.cytogfr.2019.10.002, https://www.sciencedirect.com/science/article/abs/pii/S1359610119301108
- Singh Mehta, D., et al. (2023). Multimodal and multispectral diagnostic devices for oral and breast cancer screening in low resource settings. Current Opinion in Biomedical Engineering. DOI: 10.1016/j.cobme.2023.100485, https://www.sciencedirect.com/science/article/abs/pii/S2468451123000417
- Rickard, AG., et al. (2023). A Clinical Study to Assess Diffuse Reflectance Spectroscopy with an Auto-Calibrated, Pressure-Sensing Optical Probe in Head and Neck Cancer. Current Oncology. DOI: 10.3390/curroncol30030208, https://www.mdpi.com/1718-7729/30/3/208
- Ge, Q., et al. (2024). Evaluation and Validation on Sensitivity of Near-Infrared Diffuse Reflectance in Non-Invasive Human Blood Glucose Measurement. Sensors. DOI: 10.3390/s24185879, https://www.mdpi.com/1424-8220/24/18/5879
- Akter, S., et al. (2018). Medical applications of reflectance spectroscopy in the diffusive and sub-diffusive regimes. Journal of Near Infrared Spectroscopy. DOI: 10.1177/0967033518806637, https://www.researchgate.net/publication/328382795_Medical_applications_of_reflectance_spectroscopy_in_the_diffusive_and_sub-diffusive_regimes
- Sánchez-Ramos, LL., Morales-Cruzado, B., Pérez-Gutiérrez, FG. (2023). Determination of tissue oxygen saturation by diffuse reflectance spectroscopy. Journal of Biomedical Optics. DOI: 10.1117/1.JBO.28.9.095002, https://pmc.ncbi.nlm.nih.gov/articles/PMC10534074/
- Kumar, A., Chellappan, K., Nasution, A., Kanawade, R. (2021). Diffuse reflectance spectroscopy based blood oxygenation monitoring: a prospective study for early diagnosis of diabetic foot. Optical Diagnostics and Sensing XXI: Toward Point-of-Care Diagnostics. DOI: 10.1117/12.2583022, https://ui.adsabs.harvard.edu/abs/2021SPIE11651E..0TK/abstract
- Mancuso, A., Cristiano, MC., Paolino, D. (2024). Reflectance spectroscopy: A non-invasive strategy to explore skin reactions to topical products. Frontiers in Chemistry. DOI: 10.3389/fchem.2024.1422616, https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1422616/full
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.