The diffusion properties of the liver parenchima are important in many applications, even if many methodological points (diffusion wheigthings, sampling methods) are still open. Given this background, the aim of this study is to evaluate mean and dispersion of liver ADC measurements, at two different b values, varying: the size of the region of interest (ROI); the age of the subjects. Results are compared with phantom measurements (Fig. 1).

Subjects Two observers evaluated 40 healthy subjects, divided in 4 age classes (18-30, 31-45, 46-65, >65), comparing the results with phantom measurements. MR-DwI DWI breath-old echo-planar acquisitions (b=0-300-1000 s/mm²) were executed on a 1.5 T MR scanner. Sampling methods Liver sampling methods: total volume (TV), one ROI per slice (OR), comprising, respectively, the 70% and the 4% of the entire liver volume. Similar sampling methods, with ROIs including about the 70% and the 4% of the phantom volume, were applied on phantom measurements.

In vivo Absence of significative ADC (10 -6 mm2/s) correlation with age. A wide dispersion of data, more pronounced at b=300 s/mm2, was observed, with a results variation with ROI size: the larger the ROI, the higher the ADC mean 2563±572 vs 1558±247 (TV), 2412±512 vs 1375±261 (OR), respectively b=300 s/mm2 vs b=1000 s/mm2. In vitro No ADC variation was osberved at different b values and varying ROI size.

Absence of ADC correlation with age. ADC increment with ROI size can be explained by the greater perfusion contribution when enlarging the ROI [1,2]. This hypothesis is confirmed by the absence of ADC increment, varying the ROI size, in phantom measurements (monoexponential signal behaviour) [1,2,3].

1. Le Bihan D, Breton E, Lallemand D et al (1988) Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging. Radiology 168:497–505. 2. Le Bihan D (2008) Intravoxel Incoherent Motion Perfusion MR Imaging: A Wake-Up Call. Radiology 249:748–752. 3. Colagrande S, Pasquinelli F, Mazzoni LN et al (2010) MR-diffusion weighted imaging of healthy liver parenchyma: repeatability and reproducibility of apparent diffusion coefficient measurement. J Magn Reson Imaging 31:912-920.

Lorenzo Nicola Mazzoni C.I.R.M. University of Florence, AOU-Careggi, Largo Brambilla, 3 - 50134, Florence. [email protected]