Acoustic Radiation Force Impulse Imaging

Acoustic Radiation Force Impulse (ARFI) Imaging is a type of ultrasound elastography used in medicine, particularly for the diagnosis and monitoring of cancers. ARFI imaging uses acoustic radiation force to generate images of the mechanical properties of soft tissue.

Acoustic radiation force is a phenomenon associated with the propagation of acoustic waves in attenuating media. Attenuation includes both scattering and absorption of the acoustic wave. Attenuation is a frequency dependent phenomenon, and in soft tissues it is dominated by absorption. With increasing acoustic frequencies, the tissue does not respond fast enough to the transitions between positive and negative pressures, thus its motion becomes out of phase with the acoustic wave, and energy is deposited into the tissue. This energy results in a momentum transfer in the direction of wave propagation and tissue heating. The momentum transfer generates a force that causes displacement of the tissue, and the time scale of this response is much slower than that of the ultrasonic wave propagation. This displacement (typically a few micrometers), which is typically detected by computing the correlation of ultrasonic RF signal, can be used to derive additional information about the tissue beyond what is normally provided in an ultrasonic image. The magnitude, location, spatial extent, and duration of acoustic radiation force can be controlled to interrogate the mechanical properties of the tissue.

Clinical applications of ARFI imaging include:

The speed at which shear waves propagate in tissue can be used to quantify the shear modulus of the tissue. Acoustic radiation force-based imaging modalities, including SWEI, are being studied to non-invasively characterize the liver without the need for liver biopsy.

Liver Fibrosis Quantification efforts at Duke University

Acoustic Radiation Force Impulse Imaging (ARFI): a New Technique to Assess Liver Elasticity

Yoneda et al. also recently compared ARFI shear wave imaging as implemented on the Siemens Acuson S2000 with transient elastography using the FibroScan system (EchoSens, Paris, France) in the context of evaluating patients with Non-alcoholic Fatty Liver Disease (NAFLD).

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