Ultrasound diagnostic apparatus

1. An ultrasound diagnostic apparatus comprising:

an ultrasound probe which has ultrasound transducers, wherein the ultrasound transducers are configured to transmit ultrasonic waves, receive an ultrasonic echo reflected by a subject, and output a reception signal according to the received ultrasonic echo;

a display;

an operating panel; and

a processor, wherein:

the processor is configured to produce a first B-mode image and a first M-mode image from the reception signal output from the ultrasound transducers,

the processor is configured to display on the display the first B-mode image and the first M-mode image,

the processor is configured to pause an image depending on an input instruction to the operation panel,

the processor is configured to detect a plurality of heartbeats in the first M-mode image,

the processor is configured to perform tracking of motion of a vascular wall in the first M-mode image which is displayed on the display, and

the processor is configured to calculate an elastic modulus of the vascular wall based on tracking results of the vascular wall,

wherein, in a case that image pausing is instructed with the first B-mode image and the first M-mode image being displayed on the display, the processor is further configured:

to cause a non-transitory storage device to store a second M-mode image comprising a portion of the first M-mode image representing an interval from the point of instructing the image pausing to a predetermined period before the instruction of image pausing;

to set boundaries of the plurality of detected heartbeats in the second M-mode image, wherein each pair of boundaries delimits a heartbeat region;

to discard from the delimited heartbeat regions in the second M-mode image both an entire first heartbeat region representing a heartbeat which occurred at the point in time when the image pausing was instructed and at least a part of a second heartbeat region adjacent to the first heartbeat region representing a heartbeat which occurred immediately before the point in time when the image pausing was instructed, on a side adjacent to the first heartbeat region, the entire first heartbeat region and the at least a part of the second heartbeat region being heartbeat regions possibly blurred by pressing a freeze button, to form a third M-mode image having at least one complete heartbeat from a start of the at least one heartbeat through an end of the at least one heartbeat;

to update the display by displaying the third M-mode image;

to select one of the at least one complete heartbeat in the displayed third M-mode image; and

to update the display by displaying both a second B-mode image which is captured at a time coincident with a start position of the selected complete heartbeat and a fourth M-mode image comprising the selected complete heartbeat side by side.

2. The ultrasound diagnostic apparatus according to claim 1 , wherein in the case that the image pausing is instructed, the processor is further configured to display the first M-mode image and the first B-mode image side by side on the display.

3. The ultrasound diagnostic apparatus according to claim 1 ,

wherein the processor is further configured to set a boundary of the vascular wall in the second B-mode image displayed on the display after image pausing is instructed, in the case that image pausing is instructed, in the case that image pausing is instructed.

4. The ultrasound diagnostic apparatus according to claim 1 ,

wherein the processor is further configured to set a region of interest in the first B-mode image at the point in time when the image pausing is instructed, and displaying the first region of interest on the display.

5. The ultrasound diagnostic apparatus according to claim 4 , wherein a frame rate of ultrasonic waves transmitted by the ultrasound transducers after the region of interest is set is higher than a frame rate of ultrasonic waves transmitted by the ultrasound transducers before the region of interest is set.

6. The ultrasound diagnostic apparatus according to claim 1 , wherein the processor is configured to set boundaries of the vascular walls in the second B-mode image with respect to the fourth M-mode image, and to perform tracking of motion of the vascular walls in the selected complete heartbeat in the fourth M-mode image, using information on the set boundaries of the vascular walls.

7. The ultrasound diagnostic apparatus according to claim 1 , wherein the processor is configured to set automatically the boundaries of the heartbeats in the second M-mode image, each boundary being an end of one heartbeat and a start of a next heartbeat for the entire second M-mode image, thereby performing automatic setting of the heartbeat regions.

8. The ultrasound diagnostic apparatus according to claim 7 , wherein the processor is configured to perform automatic setting of the heartbeat regions by analyzing the second M-mode image and using a moving velocity in a depth direction of a bright line extending in a horizontal direction in the second M-mode image, or pulsation of motion of the bright line in the depth direction.

9. The ultrasound diagnostic apparatus according to claim 8 , wherein the processor is configured to perform automatic setting of the heartbeat regions using a time point at which the moving velocity starts to increase.

10. The ultrasound diagnostic apparatus according to claim 1 , wherein the fourth M-mode image is an image of a remainder region which was not discarded in the second heartbeat region and a region of the selected complete heartbeat adjacent to the second heartbeat region.

11. The ultrasound diagnostic apparatus according to claim 1 , wherein the second B-mode image and the fourth M-mode image are displayed side by side in a horizontal direction or a vertical direction on the display.