Re: Role of diffusion-weighted MRI in differentiation of hepatic abscesses from non-infected fluid collections

Sir d We read the recent article by Schmid-Tannwald et al., 1 published in the Journal with a great interest. In this article, the authors discussed the role of quantitative and qualitative assessment of diffusion-weighted (DW) images and apparent diffusion coefficient (ADC) maps in infected and non-infected collections in the liver. As we have a special interest in DW imaging in the characterization of liver lesions, 2e6 we would like to contribute regarding the efficacy of DW imaging and ADC measurement in the evaluation of the hepatic abscess and noninfected fluid collection. As the authors mentioned in the article, ADC values of each lesion were measured by drawing a circular region of interest (ROI), encompassing the entire lesion, on the image in which the lesion was largest. We think that ADC measurement must be performed several times with using small ROIs in different regions and the lowest ADC value must be take into consideration. 2e6 In our clinical practice, we noticed that ROIs encompassing the entire lesion can lead to misinterpretation of the ADC value of the lesion, particularly in those with different components such as necrotic, cystic, infected, or neoplastic tissue. Those areas with high ADC values can increase the mean ADC value of the lesion and can lead to misinterpretation. Another issue is the visual assessment of the DW images and ADC maps, which provides easy and confident evaluation of the solidecystic and simpleecomplicated focal liver lesions. Particularly, in hepatic abscess, central diffusion restriction and peripherally relative increased diffusion in DW images and ADC maps are unique findings and these features can be easily evaluated by visual assessment without time-consuming ADC measurements. Visual assessment is also useful for overcoming the reproducibility problems associated with DW imaging in the liver due different magnetic resonance imaging (MRI) machines, sequence parameters, and differences in ADC values in different parts of the liver.2,4e6