Pascal's of pressure rice which is already detectable so if you generate hundreds of million degrees temperature rise then you get a very bright signal to detect and that allows us to form a image so this is called a photo acoustic effect so basically it's a photo thermal and thermal acoustic in the end that we just call that photo acoustic affect the standard detectors has to be coupled acoustically to the tissue you can direct it touch it just like when you perform ultrasound imaging in the hospital they typically apply some gel