A Multi-dimensional TCSPC Design Of Time-domain DOT/DFT System

Diffuse optical tomography (DOT), as an endogenous-contrast-based imagingmodality, has been widely applied to breast tumor diagnosis. Compared withtraditional breast imaging techniques, DOT has the advantage of better sensitivity,specificity and safety. However, due in part to the moderate tumor-to-normalhemoglobin contrast, DOT does not have satisfactory sensitivity for early breasttumor detection and is vulnerable to breast and its periphery structures. Diffusefluorescence tomography (DFT), with the introduction of exogenous near-infrareddyes, is able to significantly improve detection sensitivity. However, as the onlyfluorescent agent approved by the FDA for human use, Indocyanine Green (ICG)suffers from low quantum yield which leads to longer measuring time andsusceptibility to the auto-fluorescence of tissues. To compensate the limitations ofDOT in sensitivity and DFT in specificity, a combination of both methods, in whichthe DOT and DFT are conducted on breast tissue respectively, has been demonstratedof improving the quantitative accuracy of DOT by using the a priori informationprovided by DFT.According to the type of signal, diffuse optical imaging is usually classified intothree modes: continuous wave (CW), frequency domain (FD) and time domain (TD).Among the three modes, TD offers the richest optical information but suffers fromlonger detecting period and the TD system is much more expensive. However, withthe introduction of the state-of-the-art time-correlated single photon counting (TCSPC)technique, a multichannel system can reduce the detecting periods and costs largely.A primary time-domain DOT-DFT system had been constructed based on theprinciples of the TCSPC technique. However, the capacity of the single photoncounting (SPC) module was not fully exploited, leading to a structural redundancyand uneconomic configuration.In this thesis, an advanced time-domain DOT/DFT system based on amulti-dimensional TCSPC design is presented. The advanced system takes fully useof the multi-dimensional capacity of a SPC module with the application of a routerwhich directs signals from different channels into separate memory banks in the SPCmodule. Correspondently, a series of optimization strategies and adjustments of measurement procedure are originally proposed to improve signal-noise-ratio (SNR)and reduce measurement period. Moreover, a truncated singular value decomposition(tSVD) method and a conjugated gradient (CG) method is investigated for offeringbetter resolution in the image reconstruction of fluorescent parameters. Numericalsimulations are then employed to validate the efficiency of the methods. Furthermore,the performances of the advanced system and the methods are experimentallyassessed on breast-mimicking phantoms for time-domain DOT and DFT respectively.The results demonstrate the feasibility of the application of the system on bothtime-domain DOT and DFT, and the efficacy of improving the accuracy oftime-domain DFT based on both the tSVD method and the CG method.