Chemical shift ratio (CSR)

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Calculating the chemical shift ratio (CSR) is one way of differentiating benign thymic tissue from thymic neoplasms :

  • CSR = (tSIopp / mSIopp) / (tSIin / mSIin)

in = in phase, m = muscle, opp = opposed phase, SI = signal intensity, and t = thymus

Using a cut-off if 0.849, CSR is 100% specific and ~97% sensitive for the diagnosis of residual thymus / thymic hyperplasia .