Measuring tissue pH heterogeneity by P NMR spectroscopy

Introduction Pathological processes are frequently induce variations in tissue pH. Thus, reliable measurement of intra and extracellullar pH (pHi, pHe) should be very useful for the characterization of tissue metabolism. Ideally, the pH measurement method of choice should be able to simultaneously determine pHi and pHe in vivo. P MRS-based methods have been introduced many years ago for pHi (chemical shift, δ, of endogenous Pi [1]), and for pHe (δ of exogenous 3-aminopropylphosphonate, APP [2]), notably for application in tumor animal models [3,4]. However, the consequences of pH heterogeneity have not been considered in these pH calculations. We suggest here three P MRS-based pH calculation methods that take into account the characteristics of the pH distribution under consideration.