Resolution of time-resolved breast transillumination: in vitro measurements compared with theoretical predictions

The resolution of time-gated breast transillumination images has been investigated both theoretically and experimentally. The resolution limit is quantified as the size of the smallest object visible on an image (the image quality index), which depends on such image parameters as the transfer function, the contrast, and the noise. The smallest diameter of a detectable carcinoma located in the breast has been determined on the basis of Monte Carlo simulation results as well as in vitro time-of-flight measurements on breast samples. The comparison of the Monte Carlo simulation of light propagation within biological tissues with the experimental data has been able to confirm the validity of the simulation. The simulation results, compared with measurements, suggest that the formation of time-resolved transillumination images of biological tissues can be adequately modeled in the near infrared. The enhancement of the transfer function by the introduction of time-gated detection is verified, and the limiting contribution of the noise at short integration times has been investigated. The estimated diameter of the smallest detectable sphere embedded on the front surface of a 20-mm-thick breast slab is around 3 mm. Extrapolated for a full-size breast, the estimate is still better by a factor of 2 than the resolution of classical diaphanography, which is commonly taken to be worse than 20 mm.