Application of missing pulse steady state free precession to the study of renal microcirculation.

Missing pulse steady state free precession (MP-SSFP), an extension of steady state free precession (SSFP), was evaluated for its ability to measure slow fluid flows. In experiments using flow phantoms, the MP-SSFP signal was sensitive to fluid velocities in the millimeters per second range. Isolated perfused rabbit kidneys were then used to determine if MP-SSFP could measure perfusion in a biological tissue. The signal intensities in the different anatomical regions of the kidney were observed to be related to the total flow to the organ. Furthermore, increasing the flow sensitivity of the pulse sequence by increasing the gradient strength resulted in decreases in the image signal intensity. The MP-SSFP signal was more sensitive to flow in the medulla than in the cortex. This can be related to slow flow sensitivity of MP-SSFP and the known differences in velocity profiles between these two regions. These results suggest that MP-SSFP may be a powerful tool for the noninvasive measurement of slow fluid flows in different regions of the kidney.