Clinical Implications of Non-Steatotic Hepatic Fat Fractions on Quantitative Diffusion-Weighted Imaging of the Liver

Abstract

Diffusion-weighted imaging (DWI) is an important diagnostic tool in the assessment of focal liver lesions and diffuse liver diseases such as cirrhosis and fibrosis. Quantitative DWI parameters such as molecular diffusion, microperfusion and their fractions, are known to be affected when hepatic fat fractions (HFF) are higher than 5.5% (steatosis). However, less is known about the effect on DWI for HFF in the normal non-steatotic range below 5.5%, which can be found in a large part of the population. The aim of this study was therefore to evaluate the diagnostic implications of non-steatotic HFF on quantitative DWI parameters in eight liver segments. For this purpose, eleven healthy volunteers (2 men, mean-age 31.0) were prospectively examined with DWI and three series of in-/out-of-phase dual-echo spoiled gradient-recalled MRI sequences to obtain the HFF and T2*. DWI data were analyzed using the intravoxel incoherent motion (IVIM) model. Four circular regions (ø22.3 mm) were drawn in each of eight liver segments and averaged. Measurements were divided in group 1 (HFF≤2.75%), group 2 (2.75< HFF ≤5.5%) and group 3 (HFF>5.5%). DWI parameters and T2* were compared between the three groups and between the segments. It was observed that the molecular diffusion (0.85, 0.72 and 0.49 ×10−3 mm2/s) and T2* (32.2, 27.2 and 21.0 ms) differed significantly between the three groups of increasing HFF (2.18, 3.50 and 19.91%). Microperfusion and its fraction remained similar for different HFF. Correlations with HFF were observed for the molecular diffusion (r = −0.514, p<0.001) and T2* (−0.714, p<0.001). Similar results were obtained for the majority of individual liver segments. It was concluded that fat significantly decreases molecular diffusion in the liver, also in absence of steatosis (HFF≤5.5%). Also, it was confirmed that fat influences T2*. Determination of HFF prior to quantitative DWI is therefore crucial.

Renal Adiposity Confounds Quantitative Assessment of Markers of Renal Diffusion With MRI

“…In contrast to a previously reported study in a fat-water mixed phantom (12), our simulations and in vivo observations suggested that underestimation of renal diffusion coefficients may be significant even at low fractions of the fat signal, and the rate of underestimation decreases until the curve nearly plateaus. Dijkstra et al showed that the correlation of pure-diffusivity and FRF is stronger using a log-linear compared to linear correlation (14), concordant with our observed correlation of this marker and Oil-Red-O. Taken together, these findings support a non-linear relationship between the FRF and pure-diffusivity (28).…”

“…The confounding effect of fat on hepatic DWI parameters has been suggested by several recent studies, demonstrating an inverse correlation of ADC and pure-diffusivity with fat content (13, 15), and its significance emphasized even in non-steatotic livers (14). In contrast to a previously reported study in a fat-water mixed phantom (12), our simulations and in vivo observations suggested that underestimation of renal diffusion coefficients may be significant even at low fractions of the fat signal, and the rate of underestimation decreases until the curve nearly plateaus.…”

“…However, recent studies on hepatic DWI identified fat as a potential third compartment with a significant confounding effect (12, 13), even in non-steatotic livers (14, 15). Similar outcomes were also observed in other organs (16, 17).…”

Inter-observer reproducibility of quantitative dynamic susceptibility contrast and diffusion MRI parameters in histogram analysis of gliomas

“…However, when taking the minimal ADC value of the ROI, they observed significant differentiation between glioma grades by the ADC, which is in accordance with our results. In addition, other compounds, such as fatty acids and calcifications, potentially present in oligodendroglioma, can affect the minimal ADC of a tumor which can be avoided by a manually selected area of low diffusion with a circle ROI (17,18).…”

Mutual constraining of slow component and fast component measures: some observations in liver IVIM imaging

“…We reviewed the published results on IVIM-derived PF of steatotic livers. Most of papers reported elevated PF (9), a small portion of papers(17) reported PF similar to normal liver which also indicate PF was artificially elevated since steatotic livers should have reduced true PF.…”