Publications by authors named "Austin B McElroy"

9 Publications

  • Page 1 of 1

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

Lasers Surg Med 2021 Jun 15. Epub 2021 Jun 15.

Department of Biomedical Engineering, The University of Texas Austin, Austin, Texas, 78712, USA.

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.
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http://dx.doi.org/10.1002/lsm.23446DOI Listing
June 2021

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

Theranostics 2019 26;9(12):3555-3564. Epub 2019 May 26.

University of Texas at Austin.

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 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). 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. 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. 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.
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http://dx.doi.org/10.7150/thno.31811DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6587169PMC
June 2020

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

Opt Eng 2018 Apr 1;57(4). Epub 2018 Mar 1.

The University of Texas at Austin, Department of Biomedical Engineering, 107 W Dean Keeton St, Austin, TX, USA, 78712 Code.

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.
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http://dx.doi.org/10.1117/1.OE.57.4.041407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859933PMC
April 2018

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

Lasers Surg Med 2018 03 7;50(3):202-212. Epub 2017 Aug 7.

Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas.

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 mm /sec was achieved experimentally, in comparison to the model prediction of approximately 6 mm /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.
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http://dx.doi.org/10.1002/lsm.22705DOI Listing
March 2018

Conducting polymer-based multilayer films for instructive biomaterial coatings.

Future Sci OA 2015 Nov 2;1(4):FSO79. Epub 2015 Nov 2.

J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA; Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78712, USA; J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA; Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.

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.
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http://dx.doi.org/10.4155/fso.15.79DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5137882PMC
November 2015

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

J Biomed Opt 2013 May;18(5):56005

University of Texas at Austin, Departments of Electrical and Computer Engineering, Austin, TX 78712, USA.

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.
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http://dx.doi.org/10.1117/1.JBO.18.5.056005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3642243PMC
May 2013

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

Opt Express 2011 Nov;19(24):23831-44

Department of Ophthalmology, The University of Texas Health Science Center, San Antonio, Texas 78229, USA.

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.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3482904PMC
http://dx.doi.org/10.1364/OE.19.023831DOI Listing
November 2011

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

Opt Express 2011 May;19(11):10252-68

Department of Electrical and Computer Engineering, University of Texas at Austin, 1 University Station C0803, Austin, TX 78712, USA.

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.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3129618PMC
http://dx.doi.org/10.1364/OE.19.010252DOI Listing
May 2011

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

Biomed Opt Express 2011 Feb 3;2(3):491-504. Epub 2011 Feb 3.

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.
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http://dx.doi.org/10.1364/BOE.2.000491DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3047355PMC
February 2011