Er:YAG laser brain surgery with vascular specific coagulation.

BACKGROUND AND OBJECTIVE: Erbium:yttrium-aluminum-garnet (Er:YAG) laser ablation can effectively resect water-bearing tissues. Application of Er:YAG resection in neurosurgery is complicated by unpredictable bleeding in surgical field. Recently, an integrated theranostic system combining a dual-wavelength laser surgery system using a thulium (Tm) fiber-laser for coagulation and Er:YAG for resection, combined with optical coherence tomography (OCT) guidance was demonstrated for the in vivo resection of tumor tissue. However, lateral thermal spread in the range of 100s of micrometers is common due to lack of vascular specificity using a Tm fiber-laser for coagulation. In this study, a vascular specific ytterbium (Yb) fiber-laser is utilized for enhanced photocoagulation during in vivo neurosurgery improving the precision of Er:YAG tissue resection with minimal lateral thermal spread. METHODS: Mice underwent stereotactic laser surgery with the proposed Yb/Er:YAG dual wavelength vascular specific neurosurgery in vivo. An OCT system (wavelength range 1310 ± 70 nm) and OCT derived angiography  images were used to record cortical images to confirm the coagulation of blood vessels and guide subsequent Er:YAG resection steps. After the laser surgery, mice were killed, and histological analysis was carried out using hematoxylin and eosin staining and Nissl staining to compare the lateral thermal spread with our previously reported Tm/Er:YAG neurosurgery where a continuous wave  Tm fiber-laser was used for coagulation. RESULTS: Coagulation scheme using a Yb fiber-laser allowed stoppage of blood flow in disparately sized blood vessels encountered in the mice brain. Histological analysis of murine brain slices post Yb/Er:YAG laser surgery yielded lower thermal spread compared with Tm/Er:YAG laser surgery, maximizing the efficiency in both hemostasis (blood flow stoppage) and maximizing tissue ablation efficiency with minimal residual thermal damage zone. CONCLUSION: In this study, a vascular specific coagulation scheme with Yb/Er:YAG dual-wavelength surgery is presented for neurosurgery. Additionally, Yb/Er:YAG study results are compared with that of a tissue coagulation approach in Tm/Er:YAG surgery previously reported to highlight improved coagulation, reduced nonspecific thermal damage and limited lateral thermal spread. Experimental results suggest that the developed dual-wavelength laser system can effectively resect neural tissues with high localization, minimal lateral thermal spread at the micrometer level while maintaining a bloodless surgical field.

Differentiation of Brain Tumor Microvasculature From Normal Vessels Using Optical Coherence Angiography.

BACKGROUND AND OBJECTIVES: Despite rapid advances and discoveries in medical imaging, monitoring therapeutic efficacy for malignant gliomas and monitoring tumor vasculature remains problematic. The purpose of this study is to utilize optical coherence angiography for vasculature characterization inside and surrounding brain tumors in a murine xenograft brain tumor model. Features included in our analysis include fractional blood volume, vessel tortuosity, diameter, orientation, and directionality. STUDY DESIGN/MATERIALS AND METHODS: In this study, five tumorous mice models at 4 weeks of age were imaged. Human glioblastoma cells were injected into the brain and allowed to grow for 4 weeks and then imaged using optical coherence tomography. RESULTS: Results suggest that blood vessels outside the tumor contain a greater fractional blood volume as compared with vessels inside the tumor. Vessels inside the tumor are more tortuous as compared with those outside the tumor. Results indicate that vessels near the tumor margin are directed inward towards the tumor while normal vessels show a more random orientation. CONCLUSION: Quantification of vascular microenvironments in brain gliomas can provide functional vascular parameters to aid various diagnostic and therapeutic studies. © 2021 Wiley Periodicals LLC.

Optical coherence tomography image-guided smart laser knife for surgery.

BACKGROUND AND OBJECTIVE: Surgical oncology can benefit from specialized tools that enhance imaging and enable precise cutting and removal of tissue without damage to adjacent structures. The combination of high-resolution, fast optical coherence tomography (OCT) co-aligned with a nanosecond pulsed thulium (Tm) laser offers advantages over conventional surgical laser systems. Tm lasers provide superior beam quality, high volumetric tissue removal rates with minimal residual thermal footprint in tissue, enabling a reduction in unwanted damage to delicate adjacent sub-surface structures such as nerves or micro-vessels. We investigated such a combined Tm/OCT system with co-aligned imaging and cutting beams-a configuration we call a "smart laser knife." METHODS: A blow-off model that considers absorption coefficients and beam delivery systems was utilized to predict Tm cut depth, tissue removal rate and spatial distribution of residual thermal injury. Experiments were performed to verify the volumetric removal rate predicted by the model as a function of average power. A bench-top, combined Tm/OCT system was constructed using a 15W 1940 nm nanosecond pulsed Tm fiber laser (500 µJ pulse energy, 100 ns pulse duration, 30 kHz repetition rate) for removing tissue and a swept source laser (1310 ± 70 nm, 100 kHz sweep rate) for OCT imaging. Tissue phantoms were used to demonstrate precise surgery with blood vessel avoidance. Depth imaging informed cutting/removal of targeted tissue structures by the Tm laser was performed. RESULTS: Laser cutting was accomplished around and above phantom blood vessels while avoiding damage to vessel walls. A tissue removal rate of 5.5 mm3 /sec was achieved experimentally, in comparison to the model prediction of approximately 6 mm3 /sec. CONCLUSION: We describe a system that combines OCT and laser tissue modification with a Tm laser. Simulation results of the tissue removal rate using a simple model, as a function of average power, are in good agreement with experimental results using tissue phantoms. Lasers Surg. Med. 50:202-212, 2018. © 2017 Wiley Periodicals, Inc.

In situ process monitoring in selective laser sintering using optical coherence tomography.

Selective laser sintering (SLS) is an efficient process in additive manufacturing that enables rapid part production from computer-based designs. However, SLS is limited by its notable lack of in-situ process monitoring when compared to other manufacturing processes. We report the incorporation of optical coherence tomography into an SLS system in detail and demonstrate access to surface and sub-surface features. Video frame rate cross-sectional imaging reveals areas of sintering uniformity and areas of excessive heat error with high temporal resolution. We propose a set of image processing techniques for SLS process monitoring with OCT and report the limitations and obstacles for further OCT integration with SLS systems.

Detection of plaque structure and composition using OCT combined with two-photon luminescence (TPL) imaging.

BACKGROUND AND OBJECTIVES: Atherosclerosis and plaque rupture leads to myocardial infarction and stroke. A novel hybrid optical coherence tomography (OCT) and two-photon luminescence (TPL) fiber-based imaging system was developed to characterize tissue constituents in the context of plaque morphology. STUDY DESIGN/MATERIALS AND METHODS: Ex vivo coronary arteries (34 regions of interest) from three human hearts with atherosclerotic plaques were examined by OCT-TPL imaging. Histological sections (4 µm in thickness) were stained with Oil Red O for lipid, Von Kossa for calcium, and Verhoeff-Masson Tri-Elastic for collagen/elastin fibers and compared with imaging results. RESULTS: Biochemical components in plaques including lipid, oxidized-LDL, and calcium, as well as a non-tissue component (metal) are distinguished by multi-channel TPL images with statistical significance (P < 0.001). TPL imaging provides complementary optical contrast to OCT (two-photon absorption/emission vs scattering). Merged OCT-TPL images demonstrate the distribution of lipid deposits in registration with detailed plaque surface profile. CONCLUSIONS: Results suggest that multi-channel TPL imaging can effectively identify lipid sub-types and different plaque components. Furthermore, fiber-based hybrid OCT-TPL imaging simultaneously detects plaque structure and composition, improving the efficacy of vulnerable plaque detection and characterization.

Laser coagulation and hemostasis of large diameter blood vessels: effect of shear stress and flow velocity.

Photocoagulation of blood vessels offers unambiguous advantages to current radiofrequency approaches considering the high specificity of blood absorption at available laser wavelengths (e.g., 532 nm and 1.064 µm). Successful treatment of pediatric vascular lesions, such as port-wine stains requiring microvascular hemostasis, has been documented. Although laser treatments have been successful in smaller diameter blood vessels, photocoagulation of larger sized vessels is less effective. The hypothesis for this study is that a primary limitation in laser coagulation of large diameter blood vessels (500-1000 µm) originates from shear stress gradients associated with higher flow velocities along with temperature-dependent viscosity changes. Laser (1.07 µm) coagulation of blood vessels was tested in the chicken chorio-allantoic membrane (CAM). A finite element model is developed that includes hypothetical limitations in laser coagulation during irradiation. A protocol to specify laser dosimetry is derived from OCT imaging and angiography observations as well as finite element model results. Laser dosimetry is applied in the CAM model to test the experimental hypothesis that blood shear stress and flow velocity are important parameters for laser coagulation and hemostasis of large diameter blood vessels (500-1000 µm). Our experimental results suggest that shear stress and flow velocity are fundamental in the coagulation of large diameter blood vessels (500-1000 µm). Laser dosimetry is proposed and demonstrated for successful coagulation and hemostasis of large diameter CAM blood vessels.

DIAMondback Atherectomy With OCT Visualization for Calcified PAD Lesions (DIAMOCT-PAD Study).

OBJECTIVE: In this study, we aimed to describe the immediate and long-term vascular effects of OAS in patients with peripheral arterial disease (PAD) and moderate to severely calcified lesions. BACKGROUND: Debulking the calcified atherosclerotic plaque with the orbital atherectomy system (OAS) can potentially enhance vessel compliance and increase the chance of reaching a desirable angioplasty result. METHODS: A total of 7 patients were evaluated both at baseline and at 6-month follow-up. Following a diagnostic peripheral angiogram, patients with significant SFA disease had a baseline intravascular optical coherence tomography (IV-OCT) and the lesion was treated with OAS. Repeat IV-OCT was performed after atherectomy and after drug-coated balloon, if used. Patients were also evaluated with angiography and IV-OCT imaging at their 6-month follow-up. RESULTS: The majority of tissue removed was fibrous tissue. During follow-up, luminal volume increased for 4 of the 7 patients from baseline to 6-month follow-up and decreased in 3 patients. On average there was a 6% increase of luminal volume (P<.01 compared with baseline). A recent virtual histology algorithm was used for automatic classification of IV-OCT images unaided by any reader. The algorithm used convolutional neural networks to identify regions as either calcium, fibrous, or lipid plaque, and it agreed with an expert reader 82% of the time. CONCLUSION: To the best of our knowledge, the current report is the first to describe vascular effects of OAS in medial calcified lesions immediately after and at follow-up using IV-OCT in patients with severe PAD.

Birefringence measurement of the retinal nerve fiber layer by swept source polarization sensitive optical coherence tomography.

A Swept Source Polarization-Sensitive Optical Coherence Tomography (SS-PS-OCT) instrument has been designed, constructed, and verified to provide high sensitivity depth-resolved birefringence and phase retardation measurements of the retinal nerve fiber layer. The swept-source laser had a center wavelength of 1059 nm, a full-width-half-max spectral bandwidth of 58 nm and an A-line scan rate of 34 KHz. Power incident on the cornea was 440 µW and measured axial resolution was 17 µm in air. A multiple polarization state nonlinear fitting algorithm was used to measure retinal birefringence with low uncertainty. Maps of RNFL phase retardation in a subject measured with SS-PS-OCT compare well with those generated using a commercial scanning laser polarimetry instrument. Peak-to-valley variation of RNFL birefringence given here is less than values previously reported at 840nm.

In vivo depth-resolved oxygen saturation by Dual-Wavelength Photothermal (DWP) OCT.

Microvasculature hemoglobin oxygen saturation (SaO2) is important in the progression of various pathologies. Non-invasive depth-resolved measurement of SaO2 levels in tissue microvasculature has the potential to provide early biomarkers and a better understanding of the pathophysiological processes allowing improved diagnostics and prediction of disease progression. We report proof-of-concept in vivo depth-resolved measurement of SaO(2) levels in selected 30 µm diameter arterioles in the murine brain using Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) with 800 nm and 770 nm photothermal excitation wavelengths. Depth location of back-reflected light from a target arteriole was confirmed using Doppler and speckle contrast OCT images. SaO(2) measured in a murine arteriole with DWP-OCT is linearly correlated (R(2)=0.98) with systemic SaO(2) values recorded by a pulse-oximeter. DWP-OCT are steadily lower (10.1%) than systemic SaO(2) values except during pure oxygen breathing. DWP-OCT is insensitive to OCT intensity variations and is a candidate approach for in vivo depth-resolved quantitative imaging of microvascular SaO(2) levels.

Data automated bag breathing unit for COVID-19 ventilator shortages.

BACKGROUND: The COVID-19 pandemic has caused a global mechanical ventilator shortage for treatment of severe acute respiratory failure. Development of novel breathing devices has been proposed as a low cost, rapid solution when full-featured ventilators are unavailable. Here we report the design, bench testing and preclinical results for an 'Automated Bag Breathing Unit' (ABBU). Output parameters were validated with mechanical test lungs followed by animal model testing. RESULTS: The ABBU design uses a programmable motor-driven wheel assembled for adult resuscitation bag-valve compression. ABBU can control tidal volume (200-800 ml), respiratory rate (10-40 bpm), inspiratory time (0.5-1.5 s), assist pressure sensing (- 1 to - 20 cm H2O), manual PEEP valve (0-20 cm H2O). All set values are displayed on an LCD screen. Bench testing with lung simulators (Michigan 1600, SmartLung 2000) yielded consistent tidal volume delivery at compliances of 20, 40 and 70 (mL/cm H2O). The delivered fraction of inspired oxygen (FiO2) decreased with increasing minute ventilation (VE), from 98 to 47% when VE was increased from 4 to 16 L/min using a fixed oxygen flow source of 5 L/min. ABBU was tested in Berkshire pigs (n = 6, weight of 50.8 ± 2.6 kg) utilizing normal lung model and saline lavage induced lung injury. Arterial blood gases were measured following changes in tidal volume (200-800 ml), respiratory rate (10-40 bpm), and PEEP (5-20 cm H2O) at baseline and after lung lavage. Physiological levels of PaCO2 (≤ 40 mm Hg [5.3 kPa]) were achieved in all animals at baseline and following lavage injury. PaO2 increased in lavage injured lungs in response to incremental PEEP (5-20 cm H2O) (p < 0.01). At fixed low oxygen flow rates (5 L/min), delivered FiO2 decreased with increased VE. CONCLUSIONS: ABBU provides oxygenation and ventilation across a range of parameter settings that may potentially provide a low-cost solution to ventilator shortages. A clinical trial is necessary to establish safety and efficacy in adult patients with diverse etiologies of respiratory failure.

Assessment of Vascular Patency and Inflammation with Intravascular Optical Coherence Tomography in Patients with Superficial Femoral Artery Disease Treated with Zilver PTX Stents.

PURPOSE: Zilver PTX nitinol self-expanding drug-eluting stent with paclitaxel coating is effective for treatment of superficial femoral artery (SFA) disease. However, as with any stent, it induces a measure of vascular inflammatory response. The current clinical trial (NCT02734836) aimed to assess vascular patency, remodeling, and inflammatory markers with intravascular optical coherence tomography (OCT) in patients with SFA disease treated with Zilver PTX stents. METHODS: Serial OCT examinations were performed in 13 patients at baseline and 12-month follow-up. Variables evaluated included neointimal area, luminal narrowing, thrombus area, stent expansion as well as measures of inflammation including, peri-strut low-intensity area (PLIA), macrophage arc, neovascularization, stent strut apposition and coverage. RESULTS: Percentage of malapposed struts decreased from 10.3 ±â€¯7.9% post-intervention to 1.1 ±â€¯2.2% at 12-month follow-up, but one patient showed late-acquired stent malapposition (LASM). The percent of uncovered struts at follow-up was 3.0 ±â€¯4.5%. Average expansion of stent cross-sectional area from baseline to follow-up was 35 ±â€¯19%. The average neointimal area was 7.8 ±â€¯3.8 mm2. Maximal luminal narrowing was 61.1 ±â€¯25.0%, and average luminal narrowing was 35.4 ±â€¯18.2%. Average peri-strut low-intensity area (PLIA) per strut was 0.017 ±â€¯0.018 mm2. Average number of neovessels per mm of stent was 0.138 ±â€¯0.181. Average macrophage angle per frame at follow-up was 7 ±â€¯11°. Average thrombus area at follow-up was 0.0093 ±â€¯0.0184 mm2. CONCLUSION: At 12-month follow-up, OCT analysis of Zilver PTX stent shows outward remodeling and minimal neointimal growth, but evidence of inflammation including PLIA, neovessels, thrombus and macrophages. SUMMARY: Thirteen patients with PAD had paclitaxel-coated stents implanted in their SFAs and were then imaged with OCT at baseline and 12-month follow-up. OCT proxy metrics of inflammation were quantified.

Laser brain cancer surgery in a xenograft model guided by optical coherence tomography.

Higher precision surgical devices are needed for tumor resections near critical brain structures. The goal of this study is to demonstrate feasibility of a system capable of precise and bloodless tumor ablation. An image-guided laser surgical system is presented for excision of brain tumors in vivo in a murine xenograft model. The system combines optical coherence tomography (OCT) guidance with surgical lasers for high-precision tumor ablation (Er:YAG) and microcirculation coagulation (Thulium (Tm) fiber laser). Methods: A fluorescent human glioblastoma cell line was injected into mice and allowed to grow four weeks. Craniotomies were performed and tumors were imaged with confocal fluorescence microscopy. The mice were subsequently OCT imaged prior, during and after laser coagulation and/or ablation. The prior OCT images were used to compute three-dimensional tumor margin and angiography images, which guided the coagulation and ablation steps. Histology of the treated regions was then compared to post-treatment OCT images. Results: Tumor sizing based on OCT margin detection matched histology to within experimental error. Although fluorescence microscopy imaging showed the tumors were collocated with OCT imaging, margin assessment using confocal microscopy failed to see the extent of the tumor beyond ~ 250 µm in depth, as verified by OCT and histology. The two-laser approach to surgery utilizing Tm wavelength for coagulation and Er:YAG for ablation yielded bloodless resection of tumor regions with minimal residual damage as seen in histology. Conclusion: Precise and bloodless tumor resection under OCT image guidance is demonstrated in the murine xenograft brain cancer model. Tumor margins and vasculature are accurately made visible without need for exogenous contrast agents.

Impact of ticagrelor and aspirin versus clopidogrel and aspirin in symptomatic patients with peripheral arterial disease: Thrombus burden assessed by optical coherence tomography.

PURPOSE: To compare OCT identified white thrombus decline, neointimal hyperplasia and clinical outcomes of patients treated with ticagrelor plus aspirin with those patients treated with clopidogrel plus aspirin after peripheral interventions. BACKGROUND: Ticagrelor is a potent platelet inhibitor. In patients with coronary artery disease, ticagrelor and aspirin demonstrated reduced rates of stent thrombosis, compared to aspirin and clopidogrel. The clinical importance of potent antiplatelet inhibition after peripheral endovascular interventions is unknown. METHODS: We enrolled 18 patients with superficial femoral artery disease and the presence of OCT-detected clot post-stent placement. Patients were randomized to 75 mg clopidogrel once daily for 1 month vs. 90 mg ticagrelor twice daily for 6 months, both in addition to 81 mg aspirin for 6 months. Clot volumes, ankle-brachial index (ABI), 6-minute walk test, and Rutherford classification were measured at baseline and 6-month follow-up. Neointimal hyperplasia and neovascularization were calculated at 6-month follow-up. RESULTS: N = 11 patients were enrolled in the clopidogrel group and N = 7 in the ticagrelor group. There was a significantly greater decrease in white thrombus in the ticagrelor group (median volume/stent length (0.067 vs 0.014 mm3/mm, p = 0.05)). No differences were found in % neointima (0.412 vs 0.536 mm3/mm, p = 0.44) and neovascularization (28 vs 44, p = 0.16). ABI and Rutherford classification were improved significantly after 6 months in the clopidogrel group, with no difference between groups at 6 months in ABI or Rutherford. CONCLUSION: In symptomatic patients with PAD, ticagrelor showed significant improvement relative to clopidogrel with respect to white thrombus burden decline.

Conducting polymer-based multilayer films for instructive biomaterial coatings.

AIM: To demonstrate the design, fabrication and testing of conformable conducting biomaterials that encourage cell alignment. MATERIALS & METHODS: Thin conducting composite biomaterials based on multilayer films of poly(3.4-ethylenedioxythiophene) derivatives, chitosan and gelatin were prepared in a layer-by-layer fashion. Fibroblasts were observed with fluorescence microscopy and their alignment (relative to the dipping direction and direction of electrical current passed through the films) was determined using ImageJ. RESULTS: Fibroblasts adhered to and proliferated on the films. Fibroblasts aligned with the dipping direction used during film preparation and this was enhanced by a DC current. CONCLUSION: We report the preparation of conducting polymer-based films that enhance the alignment of fibroblasts on their surface which is an important feature of a variety of tissues.

Dual-modality fiber-based OCT-TPL imaging system for simultaneous microstructural and molecular analysis of atherosclerotic plaques.

New optical imaging techniques that provide contrast to study both the anatomy and composition of atherosclerotic plaques can be utilized to better understand the formation, progression and clinical complications of human coronary artery disease. We present a dual-modality fiber-based optical imaging system for simultaneous microstructural and molecular analysis of atherosclerotic plaques that combines optical coherence tomography (OCT) and two-photon luminescence (TPL) imaging. Experimental results from ex vivo human coronary arteries show that OCT and TPL optical contrast in recorded OCT-TPL images is complimentary and in agreement with histological analysis. Molecular composition (e.g., lipid and oxidized-LDL) detected by TPL imaging can be overlaid onto plaque microstructure depicted by OCT, providing new opportunities for atherosclerotic plaque identification and characterization.

Dual-wavelength photothermal optical coherence tomography for imaging microvasculature blood oxygen saturation.

A swept-source dual-wavelength photothermal (DWP) optical coherence tomography (OCT) system is demonstrated for quantitative imaging of microvasculature oxygen saturation. DWP-OCT is capable of recording three-dimensional images of tissue and depth-resolved phase variation in response to photothermal excitation. A 1,064-nm OCT probe and 770-nm and 800-nm photothermal excitation beams are combined in a single-mode optical fiber to measure microvasculature hemoglobin oxygen saturation (SO(2)) levels in phantom blood vessels with a range of blood flow speeds (0 to 17 mm/s). A 50-µm-diameter blood vessel phantom is imaged, and SO(2) levels are measured using DWP-OCT and compared with values provided by a commercial oximeter at various blood oxygen concentrations. The influences of blood flow speed and mechanisms of SNR phase degradation on the accuracy of SO(2) measurement are identified and investigated.

Thickness, phase retardation, birefringence, and reflectance of the retinal nerve fiber layer in normal and glaucomatous non-human primates.

PURPOSE: We identified candidate optical coherence tomography (OCT) markers for early glaucoma diagnosis. Time variation of retinal nerve fiber layer (RNFL) thickness, phase retardation, birefringence, and reflectance using polarization sensitive optical coherence tomography (PS-OCT) were measured in three non-human primates with induced glaucoma in one eye. We characterized time variation of RNFL thickness, phase retardation, birefringence, and reflectance with elevated intraocular pressure (IOP). METHODS: One eye of each of three non-human primates was laser treated to increase IOP. Each primate was followed for a 30-week period. PS-OCT measurements were recorded at weekly intervals. Reflectance index (RI) is introduced to characterize RNFL reflectance. Associations between elevated IOP and RNFL thickness, phase retardation, birefringence, and reflectance were characterized in seven regions (entire retina, inner and outer rings, and nasal, temporal, superior and inferior quadrants) by linear and non-linear mixed-effects models. RESULTS: Elevated IOP was achieved in three non-human primate eyes with an average increase of 13 mm Hg over the study period. Elevated IOP was associated with decreased RNFL thickness in the nasal region (P = 0.0002), decreased RNFL phase retardation in the superior (P = 0.046) and inferior (P = 0.021) regions, decreased RNFL birefringence in the nasal (P = 0.002) and inferior (P = 0.029) regions, and loss of RNFL reflectance in the outer rings (P = 0.018). When averaged over the entire retinal area, only RNFL reflectance showed a significant decrease (P = 0.028). CONCLUSIONS: Of the measured parameters, decreased RNFL reflectance was the most robust correlate with glaucomatous damage. Candidate cellular mechanisms are considered for decreased RNFL reflectance, including mitochondrial dysfunction and retinal ganglion cell apoptosis.

Depth-resolved blood oxygen saturation measurement by dual-wavelength photothermal (DWP) optical coherence tomography.

Non-invasive depth-resolved measurement of hemoglobin oxygen saturation (SaO(2)) levels in discrete blood vessels may have implications for diagnosis and treatment of various pathologies. We introduce a novel Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) for non-invasive depth-resolved measurement of SaO(2) levels in a blood vessel phantom. DWP OCT SaO(2) is linearly correlated with blood-gas SaO(2) measurements. We demonstrate 6.3% precision in SaO(2) levels measured a phantom blood vessel using DWP-OCT with 800 and 765 nm excitation wavelengths. Sources of uncertainty in SaO(2) levels measured with DWP-OCT are identified and characterized.