INSTITUTE OF PHYSICS PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 50 (2005) 2503–2517 doi:10.1088/0031-9155/50/11/005 Optical tomography of the breast using a multi-channel time-resolved imager Tara Yates 1 , Jeremy C Hebden 1 , Adam Gibson 1 , Nick Everdell 1 , Simon R Arridge 2 and Michael Douek 3 1 Department of Medical Physics and Bioengineering, University College London, Gower Street, London WC1E 6BT, UK 2 Department of Computer Science, University College London, Gower Street, London WC1E 6BT, UK 3 Department of Surgery, Royal Free and University College Medical School, 67-73 Riding House Street, London W1P 7LD, UK Received 29 October 2004 Published 18 May 2005 Online at stacks.iop.org/PMB/50/2503 Abstract A time-resolved optical tomography system has been used to generate cross- sectional images of the human breast. Images are reconstructed using an iterative, nonlinear algorithm and measurements of mean photon flight time relative to those acquired on a homogeneous reference phantom. Thirty-eight studies have been performed on three healthy volunteers and 21 patients with a variety of breast lesions including cancer. We have successfully detected 17 out of 19 lesions, and shown that optical images of the healthy breast of the same volunteer display a heterogeneity which is repeatable over a period of months. However, results also indicate that the lack of accurate quantitation of optical parameters and limited morphological information limits the ability to characterize different types of lesions and distinguish benign from malignant tissues. Drawbacks of our current methodology and plans for overcoming them are discussed. 1. Introduction The incidence of breast cancer in the UK alone is around 41 000 new cases each year, of whom about one-third die of the disease (Cancer Research UK 2004). It is recognized that mortality rate can be reduced by early detection and appropriate treatment. In symptomatic women, breast cancer often presents as a painless breast lump, and diagnosis is made by triple assessment (clinical examination, cytology/histology and imaging by x-ray mammography or ultrasound). X-ray mammography is the imaging modality of choice in women over 35–40 years of age, but breast ultrasound is used in younger women with denser breasts, due to the reduced effectiveness of x-ray mammography. In the UK, x-ray mammography 0031-9155/05/112503+15$30.00 © 2005 IOP Publishing Ltd Printed in the UK 2503