In vivo imaging of extracellular pH using1H MRSI

TLDR

Tumor pH influences tumorigenesis and therapy, yet existing methods such as microelectrodes and 31P MRS are destructive, low‑resolution, and have poor SNR, limiting localized studies. The study aims to develop a non‑destructive method to map extracellular tumor pH with high spatial resolution. The technique uses an extrinsic chemical pHe probe with 1H MRSI to generate 1 × 1 × 4 mm³ pH maps, as demonstrated on a phantom. In vivo studies show the method produces accurate pH maps agreeing with prior values, with an accuracy better than 0.1 pH units. Published in Magn Reson Med 41:743–750 (1999); © 1999 Wiley‑Liss, Inc.

Abstract

Tumor pH is physiologically important since it influences a number of processes relevant to tumorigenesis and therapy. Hence, knowledge of localized pH within tumors would contribute to understanding these processes. The destructiveness, poor spatial resolution, and poor signal-to-noise ratio (SNR) of current technologies (e.g., microelectrodes, 31P magnetic resonance spectroscopy) have limited such studies. An extrinsic chemical extracellular pH (pHe) probe is described that is used in combination with 1H magnetic resonance spectroscopic imaging to yield pHe maps with a spatial resolution of 1 × 1 × 4 mm3. The principle of the technique is demonstrated on a phantom. Further data are shown to demonstrate its application in vivo, and results agree with previously reported pH values. The accuracy of the reported pH measurements is <0.1 pH units, as derived from a detailed analysis of the errors associated with the technique, the description of which is included. Magn Reson Med 41:743–750, 1999. © 1999 Wiley-Liss, Inc.