Detection of high-intensity focused ultrasound liver lesions using dynamicelastometry

A novel ultrasound technique was developed for detecting the distribution o f stiffness in biological tissue. The method, which we call 'dynamic elasto metry,' involves applying a low-frequency vibration (less than or equal to 5 Hz) to the tissue and measuring the resulting velocity pattern within the sample using Doppler spectral analysis. Based upon the velocity difference s, an elastically stiff region can be differentiated from surrounding soft tissue. Dynamic elastometry was used to both detect and quantify lesions pr oduced by high-intensity focused ultrasound (HIFU) in porcine livers. Measu rements of the lesion position and length agreed well with independent geom etric measurements. The mean and standard deviation of the differences betw een the two types of measurement were -0.01 cm and 0.10 cm for lesion posit ion, and -0.05 cm and 0.12 cm for lesion length, respectively. The relative stiffness between lesions and normal liver tissue was estimated by the vel ocity gradient ratio. Results were compared with the Young's modulus ratios between lesion and normal liver tissue obtained from mechanical measuremen t. The dynamic elastometric estimates had a strong linear correlation with the mechanical measurements (r = 0.93) but were smaller than the latter by 26%.