Technical Aspects of TCSPC-Based DOT

8 Technical Aspects of TCSPC-Based DOT Multiplexing of Lasers 

Routing Signal Channel 1 Routing Signal Channel 2 

The required IRF width, stability, and spectral range put some constraints on the selection of detectors for DOT. 

The typical width of the time-of-flight distributions recorded in DOT is of the order of a few ns see Fig. 5.51 and Fig. 5.52, page 109. Therefore a detector IRF width of 150 to 300 ps is normally sufficient. Even longer detector IRFs are sometimes tolerated, especially if the pulse dispersion in long fibre bundles dominates 

Currently available single photon avalanche photodiodes (SPADs) are not applicable to optical tomography. Although the efficiency in the NIR can be up to 80%, the detector area is only of the order of 0.01 mm. Diffusely emitted light cannot be concentrated on such a small area. A simple calculation shows that SPADs carmot compete with PMTs unless their active area is increased considerably. Another obstacle is the large IRF count-rate dependence sometimes found in single-photon APDs. 

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