Measuring extracellular pH in a lung fibrosis model with acidoCEST MRI.

Abstract

PURPOSE: A feed-forward loop involving lactic acid production may potentially occur during the formation of idiopathic pulmonary fibrosis. To provide evidence for this feed-forward loop, we used acidoCEST MRI to measure the extracellular pH (pHe), while also measuring percent uptake of the contrast agent, lesion size, and the apparent diffusion coefficient (ADC). PROCEDURES: We developed a respiration-gated version of acidoCEST MRI to improve the measurement of pHe and percent uptake in lesions. We also used T2-weighted MRI to measure lesion volumes and diffusion-weighted MRI to measure ADC. RESULTS: The longitudinal changes in average pHe and % uptake of the contrast agent were inversely related to reduction in lung lesion volume. The average ADC did not change during the time frame of the study. CONCLUSIONS: The increase in pHe during the reduction in lesion volume indicates a role for lactic acid in the proposed feed-forward loop of IPF.