A device images time-wise in parallel using transducer elements of a group. The elements are of a current group and imaging is time-wise sequential by group. The groups may be spatially disposed with respect to each other so as to mutually intermesh element-wise. The imaging may include volumetric imaging. The device may be configured for not collectively using any of the elements to focus, nor to steer, a beam used in the imaging. The device may further be operable to transition between spacing states at least one of which is characterized by a respective minimum, nonzero, degree of intra-group, element-to-element non-adjacency, or may be fixed at a selected spacing state. The transitioning may be automatic, in response to input indicative of blood vessel size and/or depth.