Magnetic Resonance in Medicine

The effect of irreproducible bulk tissue motions upon quantification of tissue perfusion and diffusion was studied via computer simulation of random phase error in conventional phase-encoded perfusion /diffusion MRI. Simulations using acquisition parameters typical for human brain studies demonstrate that bulk motion irreproducibility of -60 pm/s can produce phase instability on the order of 20" which overwhelms estimates of perfusion fraction and produces significant errors in diffusion values. Bulk tissue motion control of the human brain via cardiac gating and substantial head restraint was studied by direct measurement of voxel phase stability. Phase instability of 10" to 20" was observed from right-to-left and anterior-to-posterior motions and significantly greater phase variability from superior-to-inferior motion. The spatial pattern of phase variability indicates the source is likely a mixture of cardiac pulsation and respiration.