Ultrasonic imaging device, ultrasonic imaging method and program for ultrasonic imaging

1. An ultrasonic imaging apparatus comprising:

a transmitter confiqured to transmit ultrasonic waves directed to an object;

a receiver configured to receive ultrasonic waves coming from the object, and to output signals representing the received ultrasonic waves to the processor; and

a processor configured to process signals received from the receiver, and to generate an image a including plurality of frames;

wherein the processor is configured to:

assume one frame as a reference frame, in the image including a plurality of frames being generated,

set a region of interest at either of a predetermined position and a position accepted from an operator,

assume another one frame as a comparative frame,

set a search area wider than the region of interest, at either of a predetermined position and a position accepted from an operator,

set multiple candidate regions in the search area, which are destination candidates of the region of interest,

calculate a degree of similarity between an image characteristic value in the region of interest and an image characteristic value in the candidate region, with respect to each of the candidate regions, so as to obtain a similarity distribution of the degrees of similarity across the search area; and

obtain statistics that compare a minimum value of the degree of similarity with an overall value of the degree of similarity in the similarity distribution, by using the minimum value of the degree of similarity, a mean value of the degree of similarity, and a standard deviation of the degree of similarity, and compares the obtained statistics with a threshold value, thereby determining the confidence of the region of interest.

2. The ultrasonic imaging apparatus according to claim 1 ,

wherein the processor is configured to generate a vector which connects a position associated with the region of interest in the comparative frame, to a position of the candidate region with the minimum degree of similarity, and to substitute zero or a predetermined vector for the vector with regard to the region of interest determined as having low confidence.

3. The ultrasonic imaging apparatus according to claim 1 ,

wherein the processor is configured to calculate a mean value, the minimum value, and a standard deviation of the degree of similarity, with regard to the similarity distribution, and to obtain as the statistics, a degree of separation obtained by dividing a difference between the mean value and the minimum value, by the standard deviation.

4. The ultrasonic imaging apparatus according to claim 1 ,

wherein the processor is configured to calculate a mean value and a standard deviation of the degree of similarity, with regard to the similarity distribution, and to obtain as the statistics, a coefficient of variation obtained by dividing the standard deviation by the mean value.

5. The ultrasonic imaging apparatus according to claim 1

wherein the processor is configured to set multiple regions of interest, to obtain statistics with respect to each of the regions of interest, to obtain a histogram distribution representing a frequency of values of the statistics obtained, and to use, as the threshold value, a median value or a mean value of the histogram distribution, or if the histogram distribution shows multiple peaks, a minimum value of the statistics associated with a trough between the peaks.

6. The ultrasonic imaging apparatus according to claim 1 ,

wherein the processor is configured to perform a smoothing process on the similarity distribution, and to subtract the resulting similarity distribution after the smoothing process from the similarity distribution prior to the smoothing process, thereby obtaining a differential similarity distribution.

7. The ultrasonic imaging apparatus according to claim 6 ,

wherein the smoothing process is configured to set a filter of a predetermined size on the similarity distribution, and to repeat a process for smoothing the distribution within the filter, while moving the filter by a predetermined distance; and

wherein the processor is configured to generate a vector with respect to each of multiple regions of interest, a vector connecting a position associated with the region of interest in the comparative frame, to the position of the candidate region with the minimum degree of similarity in the similarity distribution prior to the smoothing process, and to assume a maximum length of the vector, out of the vectors generated, as the size of the filter.

8. The ultrasonic imaging apparatus according to claim 1 , wherein the processor is configured to subject the similarity distribution to a filtering process using a Laplacian filter, therebv creating a distribution of edge enhancement, and to extract a continuous edge from the distribution of edge enhancement, thereby obtaining a boundary of the object.

9. The ultrasonic imaging apparatus according to claim 1 , wherein, the processor comprises,

a first processing means for obtaining the similarity distribution as to the region of interest set near a boundary of a tumor in a living body, generating a similarity distribution image assuming the degree of similarity as an image characteristic value, and setting an one-dimensional area with a predetermined length in each of multiple different directions with a central focus on a position associated with the region of interest on the similarity distribution image;

a second processing means for calculating a total sum of the degrees of similarity within the one-dimensional area, with respect to each of the directions set;

a third processing means for calculating a ratio of a total sum of the degrees of similarity in the direction in which the total sum of the degrees of similarity becomes the minimum, to a total sum of the degrees of similarity of the one-dimensional area in the direction orthogonal to the direction in which the total sum of the degrees of similarity becomes the minimum; and

a fourth processing means for determining a degree of invasiveness of the tumor based on the ratio.

10. The ultrasonic imaging apparatus according to claim 9 ,

wherein when the ratio calculated in the third processing means is smaller than a predetermined certain value, the processor is configured to determine that the region of interest corresponds to a point constituting the boundary.