A SEGMENTED K-SPACE VELOCITY MAPPING PROTOCOL FOR QUANTIFICATION OF RENAL-ARTERY BLOOD-FLOW DURING BREATH-HOLDING

Two important prerequisites for MR velocity mapping of pulsatile motio n are synchronization of the sequence execution to the time course of the flow pattern and robustness toward loss of signal in complex flow fields, Synchronization is normally accomplished by using either prosp ective ECG triggering or so-called retrospective gating. However, if t he studied vessel moves periodically in space as a result of respirato ry motion, as in the case of renal arteries, a second synchronization with respect to the vessel motion in space may be necessary, One metho d to overcome this problem is to use the segmented k-space technique, in which the entire data acquisition can be made within a breath-hold by the sampling of several phase-encoding lines within a small time wi ndow during each heart cycle. The aim of this study was to investigate the performance of a segmented k-space velocity mapping protocol for renal artery flow determination. The protocol uses 16 phase-encoding l ines per heart beat during 16 heart cycles and gives a temporal veloci ty resolution of 160 msec, Comparison with a conventional EGG-triggere d velocity mapping protocol was made in phantoms as well as in volunte ers. In our study, both methods showed sufficient robustness toward co mplex flow in a phantom model, In comparison with the EGG technique, t he segmentation technique reduced vessel blurring and pulsatility arti facts caused by respiratory motion, and average flow values obtained i n vivo In the left renal artery agreed between the two methods studied . Although presently hampered by a relatively low temporal resolution, velocity mapping with k-space segmentation in combination with breath -holding will benefit from future increased gradient quality, and we a ssume that in the future the method will become an attractive choice f or noninvasive renal artery flow determination.