A method for aligning spatially different subvolumes of ultrasonic data of a blood vessel comprising: acquiring temporally discrete signals of a blood vessel in a first subvolume with independently operated elements of a two dimensional array of ultrasonic transducer elements from spatially different depths of scanning opposed by each transducer element, said array being located in a first position with respect to the blood vessel during the acquiring; Doppler processing the temporally discrete signals received from each transducer element to produce spectral Doppler data of the scanning depth in the first subvolume opposed by each transducer element; producing a first three dimensional map of the spectral Doppler data in spatial relationship to the position of the array with respect to the blood vessel in the first subvolume; acquiring temporally discrete signals of the blood vessel in a second subvolume with independently operated elements of the two dimensional array of ultrasonic transducer elements from spatially different depths of scanning opposed by each transducer element, said array being located in a second position with respect to the blood vessel during the acquiring, wherein the second subvolume has at least one partially overlapping region with the first subvolume; Doppler processing the temporally discrete signals received from each transducer element to produce spectral Doppler data of the scanning depth in the second subvolume opposed by each transducer element; producing a second three dimensional map of the spectral Doppler data in spatial relationship to the position of the array with respect to the blood vessel in the second subvolume; aligning the first three dimensional map with the second three dimensional map on the basis of one or more identified regions of matching spectral Doppler data of the two three dimensional maps corresponding to the partially overlapping regions; and producing a combined three dimensional map of the blood flow of the vessel from the aligned first and second three dimensional maps. acquiring temporally discrete signals of a blood vessel in a first subvolume with independently operated elements of a two dimensional array of ultrasonic transducer elements from spatially different depths of scanning opposed by each transducer element, said array being located in a first position with respect to the blood vessel during the acquiring; Doppler processing the temporally discrete signals received from each transducer element to produce spectral Doppler data of the scanning depth in the first subvolume opposed by each transducer element; producing a first three dimensional map of the spectral Doppler data in spatial relationship to the position of the array with respect to the blood vessel in the first subvolume; acquiring temporally discrete signals of the blood vessel in a second subvolume with independently operated elements of the two dimensional array of ultrasonic transducer elements from spatially different depths of scanning opposed by each transducer element, said array being located in a second position with respect to the blood vessel during the acquiring, wherein the second subvolume has at least one partially overlapping region with the first subvolume; Doppler processing the temporally discrete signals received from each transducer element to produce spectral Doppler data of the scanning depth in the second subvolume opposed by each transducer element; producing a second three dimensional map of the spectral Doppler data in spatial relationship to the position of the array with respect to the blood vessel in the second subvolume; aligning the first three dimensional map with the second three dimensional map on the basis of one or more identified regions of matching spectral Doppler data of the two three dimensional maps corresponding to the partially overlapping regions; and producing a combined three dimensional map of the blood flow of the vessel from the aligned first and second three dimensional maps.