Asymmetry index (AI)

In many brain PET studies a reference tissue is not available. It may still be possible to use the contralateral side as reference, and calculate asymmetry index:

${AI} = \frac{C_{dx}(T) - C_{sin}(T)}{(C_{dx}(T) + C_{sin}(T)) / 2 }$

This is a very robust semiquantitative method, not affected by calibration issues or decay correction. Note, however, that side differences may also be caused by movement artefacts, possibly related to attenuation correction.

AI can also be computed from parametric images, or from regional results using resai.

asymmetry — Asymmetry index is often used in epilepsy studies, since seizure focus is usually unilateral.

References

McGinnity CJ, Hammers A, Barros DAR, Luthra SK, Jones PA, Trigg W, Micallef C, Symms MR, Brooks DJ, Koepp MJ, Duncan JS. Initial evaluation of ¹⁸F-GE-179, a putative PET tracer for activated N-methyl D-aspartate receptors. J Nucl Med. 2014; 55(3): 423-430. doi: 10.2967/jnumed.113.130641.

Tags: Asymmetry index, Ratio

Updated at: 2020-12-09
Created at: 2013-12-18
Written by: Vesa Oikonen

Asymmetry index (AI)

See also:

References