Light imaging in a scattering medium, using ultrasonic probing and speckle image differencing

Apparatus for imaging portions of a scattering medium disposed between first and second opposed surfaces thereof, said scattering medium being transmissive of ultrasound pulses, said apparatus comprising:

• ultrasound transducer apparatus for propagating ultrasound pulses through said scattering medium in a direction substantially parallel to each of said first and second surfaces;
• apparatus for irridiating the first surface of said scattering medium with a coherent beam of radiant energy which said scattering medium at least partially disperses;
• optics for projecting onto a focal plane the radiant energy exiting the second surface of said scattering medium, thereby to form speckle patterns of radiant energy;
• a two-dimensional detector array located for detecting the speckle patterns projected on said focal plane, said detector array having detector elements spaced so as to resolve individual elements of said speckle patterns;
• means for sensing the difference in levels of detected energy in the corresponding individual elements of pairs of successive said speckle patterns to generate electrical signal representations of those differences;
• and
• means for integrating the electrical signal representations of the differences in levels of detected energy in the corresponding individual elements of pairs of successive said speckle patterns to generate electrical signal representations of respective images of the portions of said scattering medium through which an ultrasonic pulse travels.