pH Dependence of for Hyperpolarizable C-Labelled Small Molecules Enables Spatially Resolved pH Measurement by Magnetic Resonance Imaging.

Hyperpolarized C magnetic resonance imaging often uses spin-echo-based pulse sequences that are sensitive to the transverse relaxation time . In this context, local -changes might introduce a quantification bias to imaging biomarkers. Here, we investigated the pH dependence of the apparent transverse relaxation time constant (denoted here as ) of six C-labelled molecules. We obtained minimum and maximum values within pH 1-13 at 14.1 T: [1-C]acetate ( = 2.1 s; = 27.7 s), [1-C]alanine ( = 0.6 s; = 10.6 s), [1,4-C]fumarate ( = 3.0 s; = 18.9 s), [1-C]lactate ( = 0.7 s; = 12.6 s), [1-C]pyruvate ( = 0.1 s; = 18.7 s) and C-urea ( = 0.1 s; = 0.1 s). At 7 T, -variation in the physiological pH range (pH 6.8-7.8) was highest for [1-C]pyruvate (Δ = 0.95 s/0.1pH) and [1-C]acetate (Δ = 0.44 s/0.1pH). Concentration, salt concentration, and temperature alterations caused variations of up to 45.4% for [1-C]acetate and 23.6% for [1-C]pyruvate. For [1-C]acetate, spatially resolved pH measurements using -mapping were demonstrated with 1.6 pH units accuracy in vitro. A strong proton exchange-based pH dependence of suggests that pH alterations potentially influence signal strength for hyperpolarized C-acquisitions.