Spatial-Temporal Oxygenation Mapping Using a Near-Infrared Optical Scanner: Towards Peripheral Vascular Imaging.

Near-infrared spectroscopy (NIRS)-based peripheral perfusion, or microcirculation, can be used to assess the severity of peripheral vascular dysfunction. A low-cost, portable non-contact near-infrared optical scanner (NIROS) was developed for spatio-temporal mapping of tissue oxygenation and perfusion in tissues. In vivo validation studies were carried out on control subjects (n = 3) to assess the ability of NIROS to measure real-time oxygenation changes in response to an occlusion paradigm on the dorsum of the hand. NIROS captured real-time tissue oxygenation changes with 95% correlation when compared to a commercial device. A feasibility peripheral imaging study was performed in a mouse model (n = 5) of chronic kidney disease (CKD) induced vascular calcification to assess differences in microcirculatory peripheral tissue oxygenation. The tissue oxygenation (in terms of oxy-, deoxy-, and total hemoglobin changes) due to the occlusion paradigm was distinctly different prior to (week-6) and after the onset of vascular calcification (week-12) in the murine tails. Future work will involve extensive studies to correlate these microcirculatory tissue oxygenation changes in the peripheral tail to the vascular calcification in the heart.

Assessment of Tissue Oxygenation and Radiation Dermatitis Pre-, During, and Post-Radiation Therapy in Breast Cancer Patients.

Over 95% of breast cancer patients treated with radiation therapy (RT) undergo an adverse skin reaction known as radiation dermatitis (RD). Assessment of severity or grading of RD is clinically visual and hence subjective. Our objective is to determine sub-clinical tissue oxygenation (oxygen saturation) changes in response to RT in breast cancer patients using near-infrared spectroscopic imaging and correlate these changes to RD grading. A 4-8 week longitudinal pilot imaging study was carried out on 10 RT-treated breast cancer patients. Non-contact near-infrared spectroscopic (NIRS) imaging was performed on the irradiated ipsilateral and the contralateral breast/chest wall, axilla and lower neck regions before RT, across the weeks of RT, and during follow-up after RT ended. Significant changes (p < 0.05) in oxygen saturation (StO2) of irradiated and contralateral breast/chest wall and axilla regions were observed across weeks of RT. The overall drop in StO2 was negatively correlated to RD scaling (in 7 out of 9 cases) and was higher in the irradiated regions when compared to its contralateral region. Differences in the pre-RT StO2 between ipsilateral and contralateral chest wall is a potential predictor of the severity of RD. The subclinical recovery of StO2 to its original state was longer than the visual recovery in RD grading scale, as observed from the post-RT assessment of tissue oxygenation.

Breath-Hold Paradigm to Assess Variations in Oxygen Flow in Diabetic Foot Ulcers Using a Noncontact Near-Infrared Optical Scanner.

Objective: Diabetic foot ulcers (DFUs) occur in almost 25% of all patients with diabetes in their lifetime, with oxygen being the key limiting factor in healing. Identifying regions of compromised oxygenated flow can help clinicians cater the wound treatment process, possibly reducing wound healing time. Herein, a handheld, noncontact near-infrared optical scanner (NIROS) was developed and used to measure temporal changes in hemoglobin concentrations in response to a breath-hold (BH) paradigm. Approach: Noncontact imaging studies were carried out on DFU subjects and control subjects in response to a 20-s BH paradigm. Continuous-wave-based multiwavelength diffused reflective signals were acquired to generate effective oxy-hemoglobin, deoxy-hemoglobin, total hemoglobin, and oxygen saturation concentration maps using modified Beer-Lambert's law. Pearson's correlation analysis was carried out to determine variations in oxygen flow from hemoglobin concentration maps and the extent of variation observed in controls versus DFU subjects. Results: Temporal changes in hemoglobin concentration maps were observed in controls and DFU subjects. However, the oxygen flow in response to BH varied within 10% in all controls but significantly varied between wound and background regions in subjects with DFUs. Innovation: A method to assess variations in oxygen supply in and around DFUs was demonstrated using NIROS. This approach has potential to better cater DFU treatment process. Conclusion: Changes in all hemoglobin parameters due to 20 s of BH was observed. Pearson's analysis indicates that oxy-hemoglobin, deoxy-hemoglobin, and oxygen saturation fluctuations are synchronous in controls. In DFUs, changes are asynchronous with blood flow between the wound region and background region being significantly different.

Tissue Oxygenation Changes to Assess Healing in Venous Leg Ulcers Using Near-Infrared Optical Imaging.

Objective: Venous leg ulcers (VLUs) comprise 80% of leg ulcers. One of the key parameters that can promote healing of VLUs is tissue oxygenation. To date, clinicians have employed visual inspection of the wound site to determine the healing progression of a wound. Clinicians measure the wound size and check for epithelialization. Imaging for tissue oxygenation changes surrounding the wounds can objectively complement the subjective visual inspection approach. Herein, a handheld noncontact near-infrared optical scanner (NIROS) was developed to measure tissue oxygenation of VLUs during weeks of treatment. Approach: Continuous-wave-based diffuse reflectance measurements were processed using Modified Beer-Lambert's law to obtain changes in tissue oxygenation (in terms of oxy-, deoxy-, total hemoglobin, and oxygen saturation). The tissue oxygenation contrast obtained between the wound and surrounding tissue was longitudinally mapped across weeks of treatment of four VLUs (healing and nonhealing cases). Results: It was observed that wound to background tissue oxygenation contrasts in healing wounds diminished and/or stabilized, whereas in the nonhealing wounds it did not. In addition, in a very slow-healing wound, wound to background tissue oxygenation contrasts fluctuated and did not converge. Innovation: Near-infrared imaging of wounds to assess healing or nonhealing of VLUs from tissue oxygenation changes using a noncontact, handheld, and low-cost imager has been demonstrated for the first time. Conclusion: The tissue oxygenation changes in wound with respect to the surrounding tissue can provide an objective subclinical physiological assessment of VLUs during their treatment, along with the gold-standard visual clinical assessment.