Ultrasound imaging pickup apparatus

1. An ultrasound image pickup apparatus comprising:

an ultrasound element array in which a plurality of ultrasound elements are arranged in a predefined direction;

a transmission beamformer configured to transmit a focusing-type transmission beam from a transmission aperture of the ultrasound element array to an imaged area of a test object; and

a reception beamformer configured to delay reception signals output by the plurality of ultrasound elements, upon receiving ultrasound waves from the test object, by delay times to phase the reception signals, and outputs phased signals after adding the delayed and phased reception signals,

wherein the reception beamformer includes at least one processor which is programmed to:

calculate an irradiation area in the imaged area of the focusing-type transmission beam transmitted by the transmission beamformer;

set a plurality of reception scanning lines, each of which includes a plurality of reception phasing points, in the imaged area, and divide each of the reception scanning lines into a plurality of segments and a plurality of nodes;

calculate a plurality of first delay times at positions of the nodes of the segments using a predefined calculation method;

calculate one or more second delay times at one or more of the reception phasing points included in each of the segments using the first delay times at the nodes of the segments; and

delay the reception signals at the reception phasing points by the calculated second delay times

wherein respective lengths of the plurality of segments are set in accordance with positional relationships between a shape of the calculated irradiation area and the scanning lines.

2. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

calculate an outer area located outside of the irradiation area and an inner area located inside of the irradiation area among the reception scanning lines, and set the length of at least one segment among the segments in the outer area to be shorter than the length of at least one segment among the segments in the inner area.

3. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

set the plurality of segments by equally dividing an outer area located outside of the irradiation area among the reception scanning lines into segments each of which has a predefined length, and setting the plurality of segments, having lengths longer than the predefined length of the segments in the outer area, in an inner area located inside of the irradiation area among the reception scanning lines.

4. The ultrasound image pickup apparatus according to claim 1 , wherein a total number of the segments set on the reception scanning lines are within a predefined range.

5. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

calculate the second delay times at the respective reception phasing points located in an outer area located outside of the irradiation area among the reception scanning lines,

calculate a curve representing a relationship between the second delay times and positions of the reception phasing points, set the lengths of segments in first areas, in which a change of the curve is larger to be shorter than the lengths of segments in second areas in which the change of the curve is smaller.

6. The ultrasound image pickup apparatus according to claim 5 , wherein a number of the segments set in the outer area is within a predefined range.

7. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

calculate the second delay times at the respective reception phasing points located in an outer area located outside of the irradiation area among the reception scanning lines,

calculate a curve representing a relationship between the second delay times and positions of the reception phasing points,

set the plurality of nodes of the segments on the curve,

calculate a plurality of line segments that connect the nodes of the segments with straight lines,

calculate dimensions of areas bounded by the curve and the line segments, and

adjust the lengths of the segments so that the dimensions are reduced.

8. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

calculate an outer area located outside of the irradiation area and an inner area located inside of the irradiation area among the reception scanning lines, and

set the nodes of the segments on boundaries between the outer area and the inner area.

9. The ultrasound image pickup apparatus according to claim 1 , wherein the second delay times at the reception phasing points are calculated using linear interpolation calculation with reference to the first delay times at the nodes of the segments.

10. The ultrasound image pickup apparatus according to claim 1 , wherein the reception beamformer includes the at least one processor which is further programmed to:

calculate the first delay times at the nodes of the segments located inside of the irradiation area among the reception scanning lines using a virtual source method, and calculates the first delay times at the nodes of the segments located outside of the irradiation area under an assumption that spherical waves are irradiated from the ultrasound elements at both ends of the transmission aperture.

11. The ultrasound image pickup apparatus according to claim 1 ,

wherein the reception beamformer includes a memory configured to store the the phased signals at each of the reception phasing points for each of the transmissions by the transmission beamformer and the at least one processor which is further programmed to:

select the phased signals regarding the same reception phasing point from the phased signals stored for the respective transmissions in the memory, and

synthesize the selected phased signals.

12. The ultrasound image pickup apparatus according to claim 1 , wherein the shape of the irradiation area is calculated based on a result of a sound wave propagation calculation in an interior of a test object and a transmission condition of the transmission beam of the transmission beamformer.

13. The ultrasound image pickup apparatus according to claim 1 ,

wherein the reception beamformer includes at least one processor which is programmed to:

execute reception beamforming using nonlinear components of an acoustic wave; and

calculate an irradiation area for the frequencies of the nonlinear components used for the reception beamforming within a frequency band of the transmission beam.