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TH‐AB‐209‐05: Validating Hemoglobin Saturation and Dissolved Oxygen in Tumors Using Photoacoustic Computed Tomographic Spectroscopic Imaging
Author(s) -
Burnett J,
Sick J,
Cao N,
Liu B,
Nakshatri H,
Mendonca M,
Stantz K
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4958096
Subject(s) - imaging phantom , nuclear medicine , pulse oximetry , oxygenation , in vivo , medicine , photoacoustic spectroscopy , oxygen , hemoglobin , pulse (music) , photoacoustic imaging in biomedicine , biomedical engineering , materials science , nuclear magnetic resonance , chemistry , optics , anesthesia , physics , microbiology and biotechnology , detector , biology , organic chemistry
Purpose: Photoacoustic computed tomographic spectroscopy (PCT‐S) provides intra‐tumor measurements of oxygenation with high spatial resolution (0.2mm) and temporal fidelity (1–2 minutes) without the need for exogenous agents or ionizing radiation, thus providing a unique in vivo assay to measure SaO 2 and investigate acute and chronic forms of hypoxia. The goal of this study is to validate in vivo SaO 2 levels within tail artery of mice and the relationship between SaO 2 and pO 2 within subcutaneous breast tumors using PCT‐S imaging, pulse oximetry and an OxyLite probe. Methods: A closed circuit phantom was fabricated to control blood oxygenation levels, where SaO 2 was measured using a co‐oximeter and pO 2 using an Oxylite probe. Next, SaO 2 levels within the tail arteries of mice (n=3) were measured using PCT‐S and pulse oximetry while breathing high‐to‐low oxygen levels (6‐cycles). Finally, PCT‐S was used to measure SaO 2 levels in MCF‐7, MCF‐7‐VEGF165, and MDA‐MB‐231 xenograft breast tumors and compared to Oxylite pO 2 levels values. Results: SaO 2 and pO 2 data obtained from the calibration phantom was fit to Hill's equation: aO 2 levels between 88 and 52% demonstrated a linear relationship (r2=0.96) and a 3.2% uncertainty between PCT‐S values relative to pulse oximetry. Scatter plots of localized PCT‐S measured SaO2 and Oxylite pO 2 levels in MCF‐7/MCF‐7‐VEGF165 and MDA‐MD‐231 breast tumors were fit to Hill's equation: P50=17.2 and 20.7mmHg, and n=1.76 and 1.63. These results are consistent with sigmoidal form of Hill's equation, where the lower P 50 value is indicative of an acidic tumor microenvironment. Conclusion: The results demonstrate photoacoustic imaging can be used to measure SaO 2 cycling and intra‐tumor oxygenation, and provides a powerful in vivo assay to investigate the role of hypoxia in radiation, anti‐angiogenic, and immunotherapies.