Intravoxel incoherent motion analysis of abdominal organs: computation of reference parameters in a large cohort of C57Bl/6 mice and correlation to microvessel density

Abstract

Objective: Diffusion-weighted magnetic resonance imaging (DW-MRI) combined with intravoxel incoherent motion (IVIM) analysis may be applied for assessment of organ lesions, diffuse parenchymal pathologies, and therapy monitoring. The aim of this study was to determine IVIM reference parameters of abdominal organs for translational research in a large cohort of C57Bl/6 laboratory mice.

Materials and methods: Anesthetized mice (n = 29) were measured in a 4.7 T small-animal MR scanner with a diffusion-weighted echo-planar imaging sequence at the [Formula: see text]-values 0, 13, 24, 55, 107, 260, 514, 767, 1020 s/mm(2). IVIM analysis was conducted on the liver, spleen, renal medulla and cortex, pancreas, and small bowel with computation of the true tissue diffusion coefficient [Formula: see text], the perfusion fraction [Formula: see text], and the pseudodiffusion coefficient [Formula: see text]. Microvessel density (MVD) was assessed by immunohistochemistry (IHC) against panendothelial cell antigen CD31.

Results: Mean values of the different organs [[Formula: see text] (10(-3) mm(2)/s); [Formula: see text] (%); [Formula: see text] (10(-3) mm(2)/s); MVD (MV/mm(2))]: liver 1.15 ± 0.14; 14.77 ± 6.15; 50.28 ± 33.21, 2008.48 ± 419.43, spleen 0.55 ± 0.12; 9.89 ± 5.69; 24.46 ± 17.31; n.d., renal medulla 1.50 ± 0.20; 14.63 ± 4.07; 35.50 ± 18.01; 1231.88 ± 290.61, renal cortex 1.34 ± 0.18; 10.83 ± 3.70; 16.74 ± 6.74; 810.09 ± 193.50, pancreas 1.23 ± 0.22; 20.12 ± 7.46; 29.35 ± 17.82, 591.15 ± 86.25 and small bowel 1.06 ± 0.13; 16.48 ± 3.63; 15.31 ± 7.00; 420.50 ± 168.42. Unlike [Formula: see text] and [Formula: see text], [Formula: see text] correlates significantly with MVD (r = 0.90, p = 0.037).

Conclusion: This systematic evaluation of murine abdominal organs with IVIM and MVD analysis allowed to establish reference parameters for future DW-MRI translational research studies on small-animal disease models.

Keywords: Diffusion-weighted magnetic resonance imaging; Echo-planar imaging; IVIM; Intravoxel incoherent motion; Microvessel count; Microvessel density; Pseudodiffusion.