TURBULENT FLUCTUATION VELOCITY - THE MOST SIGNIFICANT DETERMINANT OF SIGNAL LOSS IN STENOTIC VESSELS

Studies of flow in a 90%-stenosis phantom were conducted to elucidate the parameters and mechanisms responsible for signal loss in MR angiog raphic images. The studies independently evaluated the effect of veloc ity, Reynolds number, turbulent fluctuation velocity, and turbulence i ntensity on the amount of post-stenotic signal loss. Results suggested that the magnitude of the turbulent fluctuation velocity, not merely the presenceof turbulence or the intensity of turbulence, was the para meter that determined the extent of the signal loss. The study suggest s that future flow phantom studies should be conducted with fluids hav ing physiologic velocities and viscosities to obtain accurate levels o f turbulent fluctuation velocities and hence reproduce results of in-v ivo signal-loss patterns. The mechanism for signal loss is that the te mporal and spatial variations of the turbulent fluctuation velocity ca use a range of phases to be present within a voxel. Examination of the theoretical aspects of fluid turbulence suggest that shortening gradi ent durations and imaging during diastole may help reduce signal loss.