title: Extended T2-IVIM model for correction of TE dependence of pseudo-diffusion volume fraction in clinical diffusion-weighted magnetic resonance imaging.
abstract: The bi-exponential intravoxel-incoherent-motion (IVIM) model for diffusion-weighted MRI (DWI) fails to account for differential T2s in the model compartments, resulting in overestimation of pseudodiffusion fraction f. An extended model, T2-IVIM, allows removal of the confounding echo-time (TE) dependence of f, and provides direct compartment T2estimates. Two consented healthy volunteer cohorts (n  =  5, 6) underwent DWI comprising multiple TE/b-value combinations (Protocol 1: TE  =  62-102 ms, b  =  0-250 mm-2s, 30 combinations. Protocol 2: 8 b-values 0-800 mm-2s at TE  =  62 ms, with 3 additional b-values 0-50 mm-2s at TE  =  80, 100 ms; scanned twice). Data from liver ROIs were fitted with IVIM at individual TEs, and with the T2-IVIM model using all data. Repeat-measures coefficients of variation were assessed for Protocol 2. Conventional IVIM modelling at individual TEs (Protocol 1) demonstrated apparent f increasing with longer TE: 22.4  ±  7% (TE  =  62 ms) to 30.7  ±  11% (TE  =  102 ms); T2-IVIM model fitting accounted for all data variation. Fitting of Protocol 2 data using T2-IVIM yielded reduced f estimates (IVIM: 27.9  ±  6%, T2-IVIM: 18.3  ±  7%), as well as T2=  42.1  ±  7 ms, 77.6  ±  30 ms for true and pseudodiffusion compartments, respectively. A reduced Protocol 2 dataset yielded comparable results in a clinical time frame (11 min). The confounding dependence of IVIM f on TE can be accounted for using additional b/TE images and the extended T2-IVIM model.
authors.affiliation: Cancer Research UK Cancer Imaging Centre, Division of Radiotherapy & Imaging, The Institute of Cancer Research, London, SM2 5NG, UK.
authors.forename: N P
authors.initials: NP
authors.lastname: Jerome
authors.forename: J A
authors.initials: JA
authors.lastname: d'Arcy
authors.forename: T
authors.initials: T
authors.lastname: Feiweier
authors.forename: D-M
authors.initials: DM
authors.lastname: Koh
authors.forename: M O
authors.initials: MO
authors.lastname: Leach
authors.forename: D J
authors.initials: DJ
authors.lastname: Collins
authors.forename: M R
authors.initials: MR
authors.lastname: Orton
mesh_terms: D000328:Adult; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008099:Liver / Q000033:anatomy & histology*; D008875:Middle Aged; D008962:Models, Theoretical; D011446:Prospective Studies; D015203:Reproducibility of Results