Dr. Alec B. Walter Profile

Dr. Alec B. Walter

Post-Doctoral Researcher

SPIE Involvement:

Author

Publications (10)

SPIE Journal Paper | 6 September 2024 Open Access

Impact of scattering phase function and polarization on the accuracy of diffuse and sub-diffuse spatial frequency domain imaging

Alec Walter, E. Duco Jansen

JBO, Vol. 29, Issue 09, 095001, (September 2024) https://doi.org/10.1117/12.10.1117/1.JBO.29.9.095001

KEYWORDS: Scattering, Reflectivity, Optical properties, Polarization, Absorption, Spatial frequencies, Zinc oxide, Backscatter, Photons, Monte Carlo methods

Read Abstract +

SignificanceAlthough spatial frequency domain imaging (SFDI) has been well characterized under diffuse optical conditions, tissue measurements made outside the diffuse regime can provide new diagnostic information. Before such measurements can become clinically relevant, however, the behavior of sub-diffuse SFDI and its effect on the accuracy of derived tissue parameters must be assessed.AimWe aim to characterize the impact that both the assumed scattering phase function (SPF) and the polarization state of the illumination light source have on the accuracy of SFDI-derived optical properties when operating under diffuse or sub-diffuse conditions, respectively.ApproachThrough the use of a set of well-characterized optical phantoms, SFDI accuracy was assessed at four wavelengths (395, 545, 625, and 850 nm) and two different spatial frequencies (0.3 and 1.0 mm−1), which provided a broad range of diffuse and sub-diffuse conditions, using three different SPFs. To determine the effects of polarization, the SFDI accuracy was assessed using both unpolarized and cross-polarized illumination.ResultsIt was found that the assumed SPF has a direct and significant impact on the accuracy of the SFDI-derived optical properties, with the best choice of SPF being dictated by the polarization state. As unpolarized SFDI retains the sub-diffuse portion of the signal, optical properties were found to be more accurate when using the full SPF that includes forward and backscattering components. By contrast, cross-polarized SFDI yielded accurate optical properties when using a forward-scattering SPF, matching the behavior of cross-polarization to attenuate the immediate backscattering of sub-diffuse reflectance. Using the correct pairings of SPF and polarization enabled using a reflectance standard, instead of a more subjective phantom, as the reference measurement.ConclusionsThese results provide the foundation for a more thorough understanding of SFDI and enable new applications of this technology in which sub-diffuse conditions dominate (e.g., μa≮μs′) or high spatial frequencies are required.

DOWNLOAD PAPER

Proceedings Article | 6 March 2023 Presentation

Epoxy resin tissue phantoms with spectra-fitted optical properties for broadband and multiband applications

Alec Walter, E. Duco Jansen

Proceedings Volume PC12370, PC1237004 (2023) https://doi.org/10.1117/12.2667146

KEYWORDS: Optical properties, Tissues, Epoxies, Pigments, Skin, Reflectance spectroscopy, Process modeling, Spectroscopy, Spectrophotometry, Scattering

Read Abstract +

SPIE Journal Paper | 20 February 2023 Open Access

Development of a platform for broadband, spectra-fitted, tissue optical phantoms

Alec Walter, E. Duco Jansen

JBO, Vol. 28, Issue 02, 025001, (February 2023) https://doi.org/10.1117/12.10.1117/1.JBO.28.2.025001

KEYWORDS: Pigments, Absorption, Tissues, Optical properties, Scattering, Diffuse reflectance spectroscopy, Skin, Optical phantoms, Light absorption, Epoxies

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 12 May 2022 Presentation

A novel paper-based substrate for coffee ring augmented surface-enhanced Raman spectroscopy

Anna Rourke, Alec Walter, Braden Carroll, Anita Mahadevan-Jansen, Andrea Locke

Proceedings Volume PC11968, PC1196802 (2022) https://doi.org/10.1117/12.2609871

KEYWORDS: Surface enhanced Raman spectroscopy, Raman spectroscopy, Nanoparticles, Bacteria, Scanning electron microscopy, Point-of-care devices, Modulation, Gold, Biological research

Read Abstract +

Proceedings Article | 9 March 2022 Presentation

Ex vivo determination of nerve and surrounding tissue optical properties in rats and human cadavers for nerve-sparing surgical applications

Ezekiel Haugen, Graham Throckmorton, Alec Walter, Zaiyang Guo, Justin Baba, Anita Mahadevan-Jansen

Proceedings Volume PC11949, PC119490D (2022) https://doi.org/10.1117/12.2608860

KEYWORDS: Nerve, Optical properties, Tissue optics, Tissues, Scattering, Absorption, Laser scattering, Injuries, Visualization, Transmittance

Read Abstract +

Proceedings Article | 7 March 2022 Presentation

Combined fluorescence and spatial frequency domain imaging to monitor photodynamic therapy dosimetry throughout treatment

Alec Walter, Ezekiel Haugen, E. Duco Jansen

Proceedings Volume PC11958, PC1195804 (2022) https://doi.org/10.1117/12.2613608

KEYWORDS: Photodynamic therapy, Luminescence, Optical properties, Imaging systems, Tissues, Tissue optics, Temporal resolution, Oxygen, Measurement devices, Calibration

Read Abstract +

Proceedings Article | 10 March 2020 Presentation

Effects of 690nm light on the response of Staphylococcus aureus to oxidative stress (Conference Presentation)

Alec Walter, Eric Skaar, E. Duco Jansen

Proceedings Volume 11221, 1122108 (2020) https://doi.org/10.1117/12.2544401

KEYWORDS: Modulation, Oxygen, Bacteria, In vitro testing, Photodynamic therapy, Hydrogen

Read Abstract +

Proceedings Article | 4 March 2019 Presentation

Increasing the efficacy of antimicrobial photodynamic therapy through the simultaneous activation of multiple coproporphyrin III absorption peaks (Conference Presentation)

Alec Walter, Jocelyn Simpson, J. Logan Jenkins, Dennis Hovarth, Eric Skaar, E. Duco Jansen

Proceedings Volume 10863, 108630R (2019) https://doi.org/10.1117/12.2508678

KEYWORDS: Photodynamic therapy, Absorption, In vivo imaging, In vitro testing, Oxygen, Bacteria, Resistance, Skin, Light sources

Read Abstract +

Proceedings Article | 18 March 2016 Presentation + Paper

Margin assessment of three-dimensional breast cancer phantoms using terahertz imaging

Tyler Bowman, Alec Walter, Magda El-Shenawee

Proceedings Volume 9700, 97000J (2016) https://doi.org/10.1117/12.2212671

KEYWORDS: Breast cancer, Tissues, Millimeter wave imaging, Cancer, 3D image processing, Optical phantoms, Terahertz radiation, Reflection, Tumors, Tumor growth modeling

Read Abstract +

Proceedings Article | 18 March 2016 Presentation + Paper

Development of breast cancer tissue phantoms for terahertz imaging

Alec Walter, Tyler Bowman, Magda El-Shenawee

Proceedings Volume 9700, 970003 (2016) https://doi.org/10.1117/12.2211176

KEYWORDS: Tissues, Breast, Breast cancer, Refractive index, Absorption, Spectroscopy, Terahertz spectroscopy, Cancer, Water, Terahertz radiation, Optical properties, Tissue optics, Tumors, Solids

Read Abstract +

Showing 5 of 10 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years