a very good signal to work with that allows you to form a bright image so this transiting allows us to generate ultrasonic emission is going to generate Christic wave through the photo acoustic effect okay so this is the bells effect and because of the acoustic transparency we can detect all the acoustic signals and form a very sharp image outside however the contrast comes from optical absorption so we're combining optical contrast without drisana krez Ellucian these one common question is why don't we use ultrasound tomography why do you