Changes in Phosphorus-31 Magnetic Resonance Spectra Caused by Epidural Balloon in Cats

Changes in brain high energy phosphate metabolite and pH levels were studied using serial phosphorus (P)-31 magnetic resonance spectroscopy (MRS) in an epidural balloon cat model. The balloon was inflated with 1, 2, 3, or 4 ml of water at 1 ml/sec and deflated after obtaining a spectrum 4 minutes later. Serial spectra, intracranial pressure (ICP), physiological parameters, and the pupil sizes were observed for 1 hour. The mean ICP after balloon inflation increased to between 36 ± 3 and 130 ± 6 mmHg. Some animals showed oculomotor paralyses. Phosphocreatine, adenosine triphosphate, phosphodiester, and phosphomonoester levels suddenly decreased after inflation and gradually recovered after balloon deflation. Acidosis progressed with cerebral compression for 4 minutes and gradually recovered. All changes and recovery were volume related. This study demonstrates the potential of P-31 MRS for noninvasive, serial, in vivo measurements of critical high energy phosphate metabolites and intracellular pH after head injury.