Navigator‐based slice tracking for kidney pCASL using spin‐echo EPI acquisition

Purpose To apply a navigator‐based slice‐tracking method to prospectively compensate respiratory motion for kidney pseudo‐continuous arterial spin labeling (pCASL), using spin‐echo (SE) EPI acquisition. Methods A single gradient‐echo slice selection and projection readout at the location of the diaphragm along the inferior–superior direction was applied as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice of the readouts of a 2D‐SE‐EPI‐based pCASL sequence. Motion information was calculated after exclusion of the signal saturation in the navigator signal caused by EPI excitations. The motion information was then used to directly adjust the slice positioning in real time. Results The respiratory motion from the navigator signal was calculated, and slice positioning was changed in real time based on the motion information. We could show that motion compensation reduces kidney movement, and that the coefficients of variation across renal perfusion values were significantly reduced when motion correction was applied. The average reduction of coefficients of variation was approximately 20%, resulting in a more accurate and detailed structure of the respective perfusion maps. Conclusions This study demonstrates the feasibility of a navigator‐based slice‐tracking technique in kidney imaging with a SE‐EPI readout pCASL sequence to reduce kidney motion.