Publications & Presentations

A 2-D imaging dosimeter for photodynamic therapy

Y. Zhao, M. Hinds, J. Gunn, B. W. Pogue, and S. J. Davis
SPIE Photonics West 2019, SPIE Paper No. 10860-23, 2-7 February, 2019, San Francisco, CA

Photodynamic Therapy (PDT) is a promising modality for cancer treatment. Typically, a laser is used to photo-excite a photosensitizer (PS) that subsequently collides with oxygen molecules promoting them to the metastable singlet delta state O2. Singlet oxygen molecules are believed to be the species that destroys cancerous cells during PDT.

In this paper we describe a novel 2D imaging sensor for photosensitizer fluorescence and singlet oxygen luminescence. We describe our instrument and initial results from both in-vitro and in-vivo studies that indicate that this system may be a valuable dosimeter for both PDT researchers and eventually for clinical application.

Applications of the Tunable Diode Laser Absorption Spectroscopy: In-Process Estimation of Primary Drying Heterogeneity and Product Temperature During Lyophilization

Applications of the Tunable Diode Laser Absorption Spectroscopy In-Process Estimation of Primary Drying Heterogeneity and Product Temperature During Lyophilization
Puneet Sharma, William J. Kessler, Robin Bogner, Meena Thakur, and Michael J. Pikal
Journal of Pharmaceutical Sciences 108 (2019) 416-430

The aim of this research was to evaluate the impact of variability in ice sublimation rate (dm/dt) measurement and vial heat transfer coefficient (Kv) on product temperature prediction during the primary drying phase of lyophilization. The mathematical model used for primary drying uses dm/dt and Kv as inputs to predict product temperature.

A second-generation tunable diode laser absorption spectroscopy (TDLAS)ebased sensor was used to measure dm/dt. In addition, a new approach to calculate drying heterogeneity in a batch during primary drying is described. The TDLAS dm/dt measurements were found to be within 5%-10% of gravimetric measurement for laboratory- and pilot-scale lyophilizers. Intersupplier variability in Kv was high for the same “type” of vials, which can lead to erroneous product temperature prediction if “one value” of vial heat transfer coefficient is used for “all vial types” from different suppliers. Studies conducted in both a laboratory- and a pilot-scale lyophilizer showed TDLAS product temperature to be within ±1 C of average thermocouple temperature during primary drying. Using TDLAS data and calculations to estimate drying heterogeneity (number of vials undergoing primary drying), good agreement was obtained between theoretical and experimental results, demonstrating usefulness of the new approach.

The full article is available at:

Monitoring Fugitive Methane Emissions Utilizing Advanced Small Unmanned Aerial Sensor Technology

Michael B. Frish, Nicholas F. Aubut, Shuting Yang, Robert W. Talbot, Levi M. Golston, Mark A. Zondlo, Paul D. Wehnert, and James Rutherford
FLAIR 2018 - field Laser applications in Industry and Research, September 10-14, 2018, S. Maria degli Angeli (Assisi), Italy

Methane, the primary component of natural gas, is a potent greenhouse gas (GHG) when vented to the atmosphere. Unburned emissions of natural gas from infrastructure can undermine the environmental benefits of using this low carbon fuel for power generation. Detecting and quantifying these emissions where and when they occur is essential for mitigating them.

To provide an affordable sensing system enabling more effective methane mitigation programs, we have adapted the backscatter-TDLAS technology embedded in the Remote Methane Leak Detector (RMLD) for mounting on PSI’s two-foot-wide quadrotor Unmanned Aerial Vehicle (UAV) featuring highly advanced autonomy.

Quantitative Gas Imager and Leak Rate Estimator

Nicholas F. Aubut, Richard T. Wainner, Shin-Juh Chen, and Michael B. Frish
FLAIR 2018 - Field Laser Applications in Industry and Research, September 10-14, 2018, S. Maria degli Angeli (Assisi), Italy

Natural gas pipeline leakage poses safety hazards, contributes to greenhouse gas loads, and costs customers the price of lost gas.

The principal purpose of developing rapid and remote leak rate measurement techniques is to rank leaks based not only on the current practice of measuring local concentration (which can be very high for a small leak in a no wind condition), but also on measuring leak rate. No current leak survey tool directly images gas leak plumes quantitatively, much less quantifies emission rate, a technology gap that this sensor development addresses. The technology under development, which we call “RMLD-QGI” (Quantitative Gas Imager), combines low-cost laser scanner, visible camera, and near-IR tunable diode laser absorption spectroscopy (TDLAS) gas detection to answer this need.

Natural Gas Fugitive Leak Detection Using an Unmanned Aerial Vehicle: Localization and Quantification of Emission Rate

Levi M. Golston, Nicholas F. Aubut, Michael B. Frish, Shuting Yang, RobertW. Talbot, Christopher Gretencord, James McSpiritt, and Mark A. Zondlo
Atmosphere 2018, 9(9), 333

We describe a set of methods for locating and quantifying natural gas leaks using a small unmanned aerial system equipped with a path-integrated methane sensor. The algorithms are developed as part of a system to enable the continuous monitoring of methane, supported by a series of over 200 methane release trials covering 51 release location and flow rate combinations.

The system was found throughout the trials to reliably distinguish between cases with and without a methane release down to 2 standard cubic feet per hour (0.011 g/s). Among several methods evaluated for horizontal localization, the location corresponding to the maximum path-integrated methane reading performed best with a mean absolute error of 1.2 m if the results from several flights are spatially averaged. Additionally, a method of rotating the data around the estimated leak location according to the wind is developed, with the leak magnitude calculated from the average crosswind integrated flux in the region near the source location. The system is initially applied at the well pad scale (100–1000 m2 area). Validation of these methods is presented including tests with unknown leak locations. Sources of error, including GPS uncertainty, meteorological variables, data averaging, and flight pattern coverage, are discussed. The techniques described here are important for surveys of small facilities where the scales for dispersion-based approaches are not readily applicable.