Negative Contrast Enhancement in T2*-Weighted Images of the Human Brain During Hyperoxia

David Thomas Pilkinton¹, Santosh Gaddam¹, Mark A. Elliott¹, Ravinder Reddy¹

Hyperoxia is known to provide positive contrast enhancement (CE) on T2*-weighted images based on the BOLD effect. We have shown here that hyperoxic contrast, despite producing positive CE across most of the brain, generates significant negative CE in T2*-weighted images in inferior regions of the brain located near large arteries, even at lower FiO2 levels (<0.6). We believe this effect is due to the shortening of T2* in arterial blood from excess paramagnetic molecular oxygen dissolved in the plasma. Hyperoxic contrast on T2*-weighted images may therefore produce negative or positive CE depending on the characteristics of the local blood volume.