Proof-of-Principle to Measure Potassium in the Human Brain: A Feasibility Study.

We describe the results of a proof-of-principle to measure the potassium content in the human brain using the natural radioisotope (40)K that is in equilibrium with the stable isotopes of potassium, (39)K and (41)K. A fixed relationship exists between radioactive potassium and the total potassium in the brain, which in turn reflects the brain's cell mass and intracellular water compartment. Accordingly, we explored whether measurements of brain potassium could serve as possible indicators of intracellular cerebral edema. We designed, built, and then calibrated our system using a spherical phantom containing KCl salt dissolved in water at levels comparable to those in the human brain. Emitted radiation was detected using sodium iodide (Nal) and high-purity germanium (HP-Ge) detectors. Our results with phantoms and with five volunteers demonstrate the feasibility of measuring potassium at the levels normally present in human brain tissue. We plan to extend the system to detect the onset of brain edema in patients with multiple sclerosis.