The heartbeat induces microvascular blood volume pulsations and subsequent tissue deformations in the brain. Although subtle (typically <1%), these deformations are highly relevant as they accelerate clearance of brain waste products. Moreover, they enable non-invasive assessment of mechanical tissue properties. We developed a sensitive MRI technique with full brain coverage for voxelwise quantification of the cardiac-induced brain tissue strain tensor with 3mm isotropic resolution, based on displacement encoding with stimulated echoes (DENSE). We visualize the strain tensor similar to diffusion tensor imaging. Strain tensor imaging opens a window on brain tissue mechanics and physiological blood volume dynamics in the brain.