Optimizing acoustical velocity in photoacoustic imaging

An image generating apparatus, comprising a processing unit of generating an acoustic image based on signal data of acoustic waves obtained by measuring a predetermined test part,

• the processing unit executing the following processing:
• reconstructing a temporary measurement image including an acoustic image, based on the signal data;
• accepting a partial designation of a region of interest in the temporary measurement image;
• while changing an acoustic velocity parameter, sequentially reconstructing a region of interest image including an acoustic image, based on the changed acoustic velocity parameter, in the region of interest;
• determining an appropriate value of the acoustic velocity parameter based on the region of interest image;
• and
• reconstructing an acoustic image in a region larger than the region of interest, based on the appropriate value of the acoustic velocity parameter,
• wherein in the reconstruction of the temporary measurement image, by making a picture element size of the temporary measurement image larger than a picture element size of the region of interest image, a calculation amount per unit area for reconstructing the temporary measurement image is made smaller than a calculation amount per unit area for reconstructing the region of interest image.