A depth-encoded PET detector

Radial blurring in high-resolution positron emission tomography (PET) can be reduced by measuring the PET photon´s depth of interaction within a detector crystal. Simulations show that dividing the crystal into two equiprobable regions of interaction almost eliminates this blurring. This has been done using a black band placed around a 3-cm bismuth germanate crystal, 1 cm from the front. A photomultiplier tube (PMT) collects light from the rear of the crystal for energy and timing measurement. Another PMT collects light through a light guide from the top front of the crystal to find the depth of interaction. Gamma rays interacting in the front of the crystal produce a strong signal in the depth-sensing PMT, while interactions behind the band produce a weaker (<10%) signal. The intensity of the light recorded by the energy PMT is almost constant (within ±3%) for interactions at any depth in the crystal