Patent ID: 7717851

Claim:
An ultrasonic observation apparatus for acquiring ultrasonic image information on an object to be inspected by scanning the object in a body cavity thereof according to one of a radial scan method and a convex scan method so as to generate an ultrasonic image based on the ultrasonic image information, said apparatus comprising: an ultrasonic endoscope including plural ultrasonic transducers, arranged on one of a circumference and a circular arc, configured to generate ultrasonic waves according to drive signals applied thereto and receive the reflected ultrasonic waves to output reception signals, respectively; transmission aperture setting means for setting, from among said plural ultrasonic transducers, plural ultrasonic transducer groups for respectively transmitting plural ultrasonic beams in directions different from one another as plural transmission apertures; transmission frequency setting means for setting frequencies of drive signal groups to be supplied to the plural ultrasonic transducer groups set as said plural transmission apertures; transmission timing setting means for changing pulse repetition frequencies of the drive signal groups according to the frequencies of the drive signal groups to be supplied to the plural ultrasonic transducer groups set as said plural transmission apertures; drive signal generating means for generating the drive signal groups having the frequencies set by said transmission frequency setting means and the pulse repetition frequencies set by said transmission timing setting means to supply the drive signal groups to the plural ultrasonic transducer groups set as said plural transmission apertures; reception aperture setting means for setting plural ultrasonic transducer groups as plural reception apertures corresponding to said plural transmission apertures; signal processing means for performing signal processing on reception signal groups respectively outputted from the plural ultrasonic transducer groups set as said plural reception apertures; and control means for controlling said transmission aperture setting means to sequentially change regions of the plural ultrasonic transducer groups to be set as said plural transmission apertures at a predetermined time interval, wherein: said transmission timing setting means lowers a pulse repetition frequency of a drive signal group having a lower frequency than that of a drive signal group having a higher frequency; and said control means controls said transmission aperture setting means such that scan density of an ultrasonic beam having the lower frequency becomes lower than that of an ultrasonic beam having the higher frequency so as to keep an angular interval between the ultrasonic beam having the lower frequency and the ultrasonic beam having the higher frequency within a predetermined range.