Calibration techniques and datatype extraction for time-resolved optical tomography

This article describes the preprocessing and calibration methods currently applied to data acquired with the University College London multichannel ti me-resolved optical tomography system. We briefly outline the imaging syste m and describe the features of our experimentally collected data, sources o f stochastic noise, and systematic errors. We examine two methods of calibr ating data: "difference imaging" using two image data sets with and without the features of interest to produce an image, and "absolute imaging" using an independent calibration measurement. We describe the methods developed to apply each calibration to raw data. Although the difference imaging perf ormed is found to produce images with fewer artifacts, analysis indicates t hat it will not be directly applicable for clinical applications. Also exam ined are the effects of using a two dimensional (2D) reconstruction scheme to produce images from measured data. For absolute imaging, artifacts are s hown to dominate such images even in the case of a homogeneous third dimens ion. The feasibility of deriving an ad-hoc correction factor to allow the u se of a 2D reconstruction for measured data is examined, and is shown to re duce artifact. Difference imaging is demonstrated to be more robust to such effects. (C) 2000 American Institute of Physics. [S0034-6748(00)03609-1].