Final answer:
T2 weighting in MRI is determined by differences in the T2 relaxation times of different tissues. The question regarding a specific percentage amplitude for the definition of T2 weighting is not standard as T2 weighting is more about the contrast arising from timing parameters in an MRI sequence that accentuate the differences in tissues with different T2 relaxation times.
Step-by-step explanation:
The subject of this question is related to magnetic resonance imaging (MRI), specifically T2 weighting in imaging sequences. When discussing T2 weighting in MRI, the term refers to imaging where the contrast is determined primarily by differences in the T2 relaxation times of tissue. An imaging sequence is considered T2 weighted when the interactions between the magnetic spins of water and fat tissue, also known as spin-spin interactions, cause the signal from different tissues to dephase to an extent where the image contrast shows these differences effectively. While T2 weighting is inherently relative and can vary by pulse sequence and system, there is not a standard percentage amplitude of dephasing that defines T2 weighting as it is more about the timing parameters in the MRI pulse sequence that maximize the contrast between tissues with different T2 relaxation times.