Half acceptance angle, determination

Figure 2.5. The transverse field of view determined by the acceptance angles of individual detectors in a PET scanner. Each detector is connected in coincidence with as many as half the total number of detectors in a ring and the data for each detector are acquired in a fan beam projection. All possible fan beam acquisitions are made for all detectors, which define the FOV as shown in the figure. (Reprinted with the permission of The Cleveland Clinic Center for Medical Art Photography 2009. All Rights Reserved).

The spatial resolution of the microscope is determined by the wavelength of the radiation, X, and the numerical aperture (NA) of the Cassegrain. Less fundamentally, spatial resolution is also limited by the SNR that can be achieved when the size of the aperture is very small. The NA is the sine of the acceptance half-angle at the sample. At the beginning of this chapter it was stated that the diffraction-limited spatial resolution is approximately equal to the wavelength, X. More accurately, it is given by... 

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