Pre-clinical experiment of pH-weighted magnetic resonance imaging in human brain tumor at 1.5 tesla

Acid-base balance is the very important part of human homeostasis. Alteration in tissue pH can be an indicator of many diseases, such as tumor. Amide proton transfer imaging, a novel technique based on magnetization transfer and chemical exchange, was proved to be relying on pH to a great extent, in which proton transfer between endogenous proteins and peptides and tissue water. To the present APT imaging technology, a steady state of chemical exchange is needed, hence the specific absorption rate limit precludes its use. In order to minimize the SAR and extend the pH-weighted imaging in clinical practice, we establish a new algorithm in the unsteady state. Our earlier experiments with pH phantom prove that we can detect the pH value at 1.5 Tesla. And now we are carrying out pioneering work at 1.5 Tesla. We use a new sequence with 3.5 ppm. and -3.5 ppm. radiofrequency offset to obtain pH-weighted magnetic resonance imaging of volunteers with brain tumor at 1.5 Tesla. We find that this imaging technology can delineate the heterogeneous areas of brain tumor at 1.5 Tesla, such as separating the mass of solid tumor and infiltration from the surrounding edema without gadolinium enhanced. Artifact caused by field inhomogeneity is the weakness of this technology, which need to be optimized in post processing. This finding may provide metabolic imaging marker as a complement for conventional imaging, and has its potential advantages in predicting the nature of tumor.