Le volume effectif de distribution de l'indicateur : Le "second paramètre" dans les méthodes d'évaluation du débit sanguin)

This paper discusses the different interpretations of the distribution parameter (Vi) involved in the determination of cerebral blood flow with inert radioactive tracers. A general equation for Vi is proposed: depending on the used indicator, Vi is more accurately estimated either by its tissue-to-blood partition coefficient, or by its volume of distribution. Single photon detection, with or without tomography, allows only a one-parameter estimation of blood flow, with a systematic error linked to the necessity of alloting a predetermined value to Vi. Positron emission tomography performed at equilibrium during the continuous administration of short-lived radiotracers shares that shortcoming. Sequential PET date are the basis of a two-parameter computation of blood flow and Vi. When H2 15O is used as an indicator, V1 is an estimate of local volume of exchangeable water. Normal values for the human brain are reported