EFFECT OF MAGNETIZATION-TRANSFER ON THE MEASUREMENT OF CEREBRAL BLOOD-FLOW USING STEADY-STATE ARTERIAL SPIN TAGGING APPROACHES - A THEORETICAL INVESTIGATION

A simple four-compartment model for magnetization transfer was used to obtain theoretical expressions for the relationship between regional cerebral blood flow and Delta M, the change in longitudinal magnetizat ion of brain water spins when arterial water spins are perturbed, The theoretical relationship can be written in two forms, depending on the approach used to normalize Delta M. Using the first approach, the cal culation of cerebral blood flow requires a knowledge of R(1)(omega(1), Delta omega), the longitudinal relaxation rate observed in the presen ce of continuous off-resonance RF irradiation, Using the second approa ch, the calculation of cerebral blood flow requires a knowledge of R(1 )(omega(1), Delta omega), where R(1)(omega(1), Delta omega) is given b y the product of R(1)(omega(1), Delta omega) and the fractional steady -state longitudinal water magnetization in the presence of off-resonan ce RF irradiation, If the off-resonance RF irradiation used for arteri al tagging does not produce appreciable magnetization transfer effects , R(1)(omega(1), Delta omega) can be approximated by the longitudinal relaxation rate measured in the absence of off resonance RF irradiatio n, R(1obs). Theoretical expressions obtained by using the four-compone nt model for magnetization transfer are compared with equivalent expre ssions obtained by using two-compartment models.