Monitoring of brain potassium with rubidium flame photometry and MRI.
An animal model was developed to monitor [K(+)] in the brain using partial K(+) replacement with Rb(+) and (87)Rb MRI. Fifty-one rats were given 0-80 mM of RbCl in the drinking water for up to 90 days. Focal cerebral ischemia was produced in 15 of the animals. Na, K, and Rb content in precision-guided submilligram samples of cortical brain were determined by emission flame photometry. Multinuclear (87)Rb/(23)Na/(1)H MRI was performed on phantoms and rats at 3T using a twisted projection imaging (TPI) scheme for (87)Rb/(23)Na, and custom-built surface or parallel cosine transmit/receive coils. Brain [Rb(+)] was safely brought up to 17-25 mEq/kg within 2-3 weeks of feeding. The characteristic patterns of [K(+)] decrease (with a sharp drop at 3-4 hr of ischemia) and [Na(+)] increase (at a rate of 31%/hr) observed previously in animals without Rb/K substitution were reproduced in ischemic cortex. The Rb/(Rb+K) ratio increased over time in ischemic areas (R = 0.91, P < 0.001), suggesting an additional index of ischemia progression. Preliminary (87)Rb MRI gave an estimate of 20-25 mEq Rb/kg brain weight (N = 2). In conclusion, brain Rb(+) is detectable by (87)Rb MRI and does not significantly interfere with ion dynamics in ischemic brain, which enables (87)Rb MRI studies of K(+) in ischemia.
Yushmanov
Victor E
VE
Department of Anesthesiology, Allegheny-Singer Research Institute, Pittsburgh, Pennsylvania 15212-4772, USA. vyushman@wpahs.org
Kharlamov
Alexander
A
Boada
Fernando E
FE
Jones
Stephen C
SC
D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D010783:Photometry / Q000379:methods; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012414:Rubidium Radioisotopes
D012414:Rubidium Radioisotopes; D011188:Potassium