Effect of apertures in ultrasound-modulated optical tomography with photomultiplier tube

Improving signal to noise ratio in ultrasound-modulated optical tomography (UOT) is a research topic. Laying apertures in front of a photomultiplier tube (PMT) can reduce the ambient noise collected by the PMT, and efficiently improve the signal to noise ratio of UOT. In addition, the effective area of detection and the off-axis position of the PMT would be varied by changing the aperture size and position in front of the PMT. Experimental results indicated that ultrasound-modulated signal is dependent on the area of detection. The greater the detector area, the smaller the ultrasound-modulated signal and its modulation depth. The modulated signal also depended on the off-axis position of the PMT from the optic axis. In particular, the modulated signal did not reach the biggest value when the PMT just placed on the optics axis. Choosing appropriate size, position of aperture, can improve the signal to noise ratio and image contrast.