Antagonistic role of noise and spatial resolution in the time-gated transillumination image quality: experiments in vitro on breast tissues

The resolution of transillumination images is improved by time gating. Theoretically, the point spread function can be made as small as desired by shortening sufficiently the time gate. This assertion does not imply that any small object can be made visible by shortening the time gate. Indeed the noise is a limiting factor to detect objects embedded in scattering medium. The noise has been measured experimentally as a function of the time gate. Experiments have been performed on formaldehyde fixed breast tissues (10 mm thick) with a pulsed Ti:sapphire source (200 fs pulses), detected by an ultrafast diode (the resolution of the measuring system is 40 ps). Any biological tissue, even without object such as tumors or haemorrhages, has heterogeneities, the contribution of which can be considered as a noise, called the anatomical noise. The results show that in our experimental conditions, this anatomical noise is predominant on the noise due to the measuring system, at the exception of very small time gate; and it decreases as the time gate increases. This noise will limit the spatial resolution achievable by time gated transillumination.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.