Suppose a PET scanner has 1,000 detectors packed tightly around a circle of diameter of 1.5 m.

(a) What is the approximate size (width) of each detector? Explain the tradeoff between using deep (long) and shallow (short) detectors.

(b) What is the purpose of coincidence detection in PET? What is a nominal time interval defining a coincidence ‘‘event window’’ for PET? Explain why is it undesirable to make the event window (1) smaller or (2) longer.

(c) Assume there is no ‘‘wobbling’’ or ‘‘dichotomic’’ motion of the PET gantry. What is the line integral sampling interval (which has the symbol T in CT) in the center of the scanner? Assuming the usual sampling ‘‘rule of thumb’’ from CT, how many pixels would be in a typical PET image. Explain why motion of the PET gantry is desirable.

(d) Explain why resolution of the PET scanner is typically worse away from the center of the scanner