Ultrasonic imaging apparatus or techniques can include obtaining at least an approximation of samples of reflected ultrasonic energy and constructing a representation of an imaging plane within the tissue region. Such apparatus or techniques can include separately determining, for respective focusing locations respective first sums of at least approximated complex samples of reflected ultrasonic energy obtained via respective first lines of transducers, and separately determining, for the specified focusing location, a second sum of at least some the respective first sums of at least approximated complex samples of reflected ultrasonic energy, the second sum corresponding to a second line of transducers in the ultrasonic transducer array. The separately determining the first or second sums of at least approximated complex samples can include phase-rotating at least some of the complex samples. The second line of transducers can be orthogonal to respective first lines in the transducer plane.