Statistical assessment of a model combining IVIM and T2 decay for multi-b-value, multi-echo-time DW-MRI in abdominal organs

Matthew R Orton^{1}, Neil P Jerome^{1}, Thorsten Feiweier^{2}, Dow-Mu Koh^{3}, Martin O Leach^{4}, and David J Collins^{4}

**Model:** Two models were used to fit the data. An IVIM model including simple T_{2} dependency $${\sf{}Standard\;Model:}\quad{}S(b,\mathrm{TE})=S_0\mathrm{e}^{-\mathrm{TE}/T_2}\!\left(\,f\mathrm{e}^{-bD_p}+(1-f\,)\mathrm{e}^{-bD_t}\!\right),$$ and an extended IVIM model [3] that includes distinct T_{2} terms in each compartment $${\sf{}Extended\;Model:}\quad{}\;S(b,\mathrm{TE})=S_0\!\left(\,f\mathrm{e}^{-\mathrm{TE}/T_{2p}}\mathrm{e}^{-bD_p}+(1-f\,) \mathrm{e}^{-\mathrm{TE}/T_{2t}}\mathrm{e}^{-bD_t}\!\right),$$ where the subscripts $$$\small{}p$$$ and $$$\small{}t$$$ refer to the pseudo-diffusion and tissue compartments. These equations were fitted using a non-linear least-squares algorithm, from which the Akaike information criterion (AIC) was computed to guide model comparison. By considering the T_{2} scaling of the two diffusion terms in the extended model, an apparent $$$\small{}f$$$ can be defined as $$f_\mathrm{app}(\mathrm{TE}) = \frac{f \mathrm{e}^{-\mathrm{TE}/T_{2p}}}{f \mathrm{e}^{-\mathrm{TE}/T_{2p}} + (1-f\,) \mathrm{e}^{-\mathrm{TE}/T_{2t}}}$$ which is equal to the $$$\small{}f$$$ that would be estimated using the standard model. Thus,$$$\small{}\;f$$$ for the standard model is dependent on TE, but $$$\small{}f$$$ for the extended model is independent of TE.

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Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

2014