I am trying to understand how the PM tubes and NaI(TI) crystals are used for the energy and spatial resolution.

I understand the principle behind how the crystals and PMT work, but very confused to how they relate to the different resolutions.

In one book I am reading it talk about the intrinsic and extrinsic resolution which the in simply terms, with and without a collimator.

I am quite new to this type of technology and if possible could someone explain it in laymen’s terms, every book I have tried to read so far seem to jump straight in the deep end, and I cant seem to build a visualise of what is actually happening.

  • $\begingroup$ Is this a question about PET (Positron Emission Tomography)? One likes to distinguish the 511 keV photons from the other gamma rays. And ordinary PMTs are bulky and expensive, difficult to make a high-resolution camera. $\endgroup$
    – user137289
    Jul 23, 2018 at 8:20

1 Answer 1


For nuclear medicine imaging, a good scintillator will produce flashes of light that are proportional to the energy deposited in the scintillator. A gamma ray that deposits more energy will produce a brighter flash of light. This is where the energy resolution of the detector comes from.

Spatial resolution is determined by how much the light flash spreads out before being detected by the photomultipliers. In a gamma camera, this is largely determined by the thickness of the scintillator layer. A thinner detector layer will have slightly better resolution than a thicker layer, but lower detection efficiency.


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