An investigation of 11-methane, 13N-nitrous oxide and 13C-acetylene as regional cerebral blood flow agents

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Abstract
Radioisotopes of xenon or krypton are generally used as the inert diffusible indicators in regional cerebral blood flow (rCBF) studies. These gases have disadvantages when introduced into the body by inhalation because of their low solubility in body tissues. The use of 11C-methane, 13N-nitrous oxide and 11C-acetylene as inhalation rCBF agents has been investigated. These gases span a wide range of solubilities: methane is four times less soluble than xenon in body tissues while nitrous oxide and acetylene are respectively 3 and 6 times more soluble. Cerebral blood flow measurements were performed on normal volunteers using the three labelled gases as well as 133Xe. All tracers were administered by inhalation and the cerebral clearance of the gases was monitored by coincidence detection. Uptake in the body was found to be dependent on solubility. The computed blood flow values found using the various indicators were in excellent agreement and were within the normal cerebral blood flow range. The high solubilities of acetylene and nitrous oxide result in a more efficient transfer of tracer from lung to brain that the conventionally used agents. The positron emission is also advantageous for tomographic rCBF measurements.