Which component is crucial for calculating the scatter fraction in PET imaging?

The energy window is crucial for calculating the scatter fraction in PET imaging because it defines the range of detected photon energies that the system will consider for image reconstruction and analysis. In PET, scattered photon events can lead to inaccuracies in the resulting images, as they do not contribute useful information about the distribution of radiotracers in the body. By setting an appropriate energy window, which typically encompasses the full energy of the annihilation photons (511 keV) while filtering out lower-energy scatter events, the system can effectively differentiate true coincident events from scattered photons. This differentiation is essential for accurate estimation of scatter fraction, which is the ratio of scattered events to all detected events within the chosen energy window.

The other options, while important for various aspects of PET imaging, do not directly pertain to the calculation of scatter fraction. Time resolution affects how temporally separated events are recorded, attenuation coefficients relate to the reduction of signal strength as photons pass through tissues, and spatial resolution impacts the detail and clarity of the final images. Each of these is critical for optimizing image quality and interpretation, but they do not specifically influence the assessment of the scatter fraction.