Diffusion-weighted imaging (DWI) is a technique that assesses the cellularity, tortuosity of the extracellular/extravascular space, and cell membrane density based on differences in water proton mobility in tissues. The strength of the diffusion weighting is reflected by the b value. DWI using several b values enables the quantification of the apparent diffusion coefficient. DWI is increasingly used in liver imaging for multiple reasons: it can add useful qualitative and quantitative information to conventional imaging sequences; it is acquired relatively quickly; it is easily incorporated into existing clinical protocols; and it is a noncontrast technique.
Key points
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Diffusion-weighted imaging (DWI) is based on differences in the mobility of water protons in tissues. Single-shot echo planar DWI sequences are most commonly used in liver imaging.
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DWI is generally more sensitive than fast-spin-echo fat-suppressed T2-weighted imaging for liver lesion detection. The combination of DWI and contrast-enhanced T1-weighted imaging is most sensitive for the detection of malignant liver lesions.
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Apparent diffusion coefficient (ADC) quantification can be used to characterize liver lesions as cystic/necrotic or solid. However, ADC alone is insufficient for lesion characterization.
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ADC has potential value in the evaluation of tumor treatment response, with changes in ADC preceding changes in lesion size.
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ADC quantification and intravoxel incoherent motion DWI have diagnostic value in the noninvasive detection of liver fibrosis and cirrhosis.
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