AVERAGE VALUE METHOD - A NEW APPROACH TO PRACTICAL OPTICAL COMPUTED-TOMOGRAPHY FOR A TURBID MEDIUM SUCH AS HUMAN TISSUE

We propose a new algorithm for optical computed tomography to determin e the concentrations of absorber in turbid media such as human tissue. Our method does not require the measurement of a reference phantom, s o that it is free from significant errors caused by geometric and stru ctural differences between the target and reference media. We use an i maginary reference medium for which the optical properties are specifi ed by the average or quasi-average values measured for the real target medium. Since we can calculate the weight function and re-emission fo r such an imaginary medium, tomographic images can be reconstructed ba sed on the difference in values measured for the target medium and det ermined for the imaginary reference. The validity of our method was co nfirmed by measuring an 80-mm-diameter cylindrical, tissue-like phanto m containing three different absorbers. The image quality such as imag e distortion and the capability for quantifying the concentrations of absorber are also discussed.