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Abstract #3578

Vasodynamic changes significantly impact the interpretation of TOLD MRI

Manabu Horikawa1, Shun Kishimoto1, Kazumasa Horie1, Nallathamby Devasahayam1, Norikazu Koyasu1, Kazutoshi Yamamoto1, Jeffrey R Brender1, and Murali C Krishna1
1NCI, Bethesda, MD, United States

Synopsis

Keywords: fMRI Analysis, Oxygenation, TOLD MRI tumor hypoxia

Motivation: Although TOLD MRI shows potential in evaluating tumor hypoxia by identifying hypoxic regions through T1 or R1 changes after a hyperoxic gas challenge, studies have shown inconsistent correlations between TOLD MRI results and hypoxia markers or radiosensitivity.

Goal(s): This study used EPR oximetry to measure pO₂ distribution in MC38 murine colon tumors, examining the correlation between pO₂ changes and ΔR1 in TOLD MRI.

Approach: A pixel-by-pixel comparison between the pO₂ map from EPR oximetry and the ΔR1 map was conducted.

Results: The effects of 100% oxygen and carbogen on tumor oxygenation differed, and both hyperoxic challenges triggered significant vasodynamic responses, complicating data interpretation.

Impact: In this study, hypoxic regions showed improved pO₂ without a corresponding R1 increase, indicating that factors beyond pO₂—such as blood perfusion, volume, and interstitial exchanges—also influence R1 values and may obscure isolated pO₂ effects.

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