An intraluminal ultrasound imaging system, comprising: an intraluminal catheter or guidewire, comprising: a flexible elongate member configured to be positioned within a body lumen of a patient; an annular array of acoustic elements configured to transmit ultrasonic energy into an anatomy and receive echoes corresponding to the transmitted ultrasonic energy, wherein the annular array is positioned around a circumference of the flexible elongate member; and a processor in communication with the annular array and configured to: activate a first subaperture of the annular array at a first time, wherein the first subaperture comprises a subset of the acoustic elements associated with a portion of the circumference; thereafter, activate a second subaperture of the annular array, wherein the second subaperture comprises a different subset of the acoustic elements associated with a different portion of the circumference; activate the first subaperture at a different, second time only after activating the second subaperture such that each activation in a sequence of the first and second subapertures moves around the circumference; receive ultrasound signals obtained by activating the first and second subapertures; characterized in that the processor is further configured to: determine temporal differences between the received ultrasound signals obtained from the first subaperture at the first and second times; and detect motion in the body lumen based on the determined temporal differences. an intraluminal catheter or guidewire, comprising: a flexible elongate member configured to be positioned within a body lumen of a patient; an annular array of acoustic elements configured to transmit ultrasonic energy into an anatomy and receive echoes corresponding to the transmitted ultrasonic energy, wherein the annular array is positioned around a circumference of the flexible elongate member; and a flexible elongate member configured to be positioned within a body lumen of a patient; an annular array of acoustic elements configured to transmit ultrasonic energy into an anatomy and receive echoes corresponding to the transmitted ultrasonic energy, wherein the annular array is positioned around a circumference of the flexible elongate member; and a processor in communication with the annular array and configured to: activate a first subaperture of the annular array at a first time, wherein the first subaperture comprises a subset of the acoustic elements associated with a portion of the circumference; thereafter, activate a second subaperture of the annular array, wherein the second subaperture comprises a different subset of the acoustic elements associated with a different portion of the circumference; activate the first subaperture at a different, second time only after activating the second subaperture such that each activation in a sequence of the first and second subapertures moves around the circumference; receive ultrasound signals obtained by activating the first and second subapertures; characterized in that the processor is further configured to: determine temporal differences between the received ultrasound signals obtained from the first subaperture at the first and second times; and detect motion in the body lumen based on the determined temporal differences. activate a first subaperture of the annular array at a first time, wherein the first subaperture comprises a subset of the acoustic elements associated with a portion of the circumference; thereafter, activate a second subaperture of the annular array, wherein the second subaperture comprises a different subset of the acoustic elements associated with a different portion of the circumference; activate the first subaperture at a different, second time only after activating the second subaperture such that each activation in a sequence of the first and second subapertures moves around the circumference; receive ultrasound signals obtained by activating the first and second subapertures; characterized in that the processor is further configured to: determine temporal differences between the received ultrasound signals obtained from the first subaperture at the first and second times; and detect motion in the body lumen based on the determined temporal differences. determine temporal differences between the received ultrasound signals obtained from the first subaperture at the first and second times; and detect motion in the body lumen based on the determined temporal differences.