Axial resolution in elastography

Improvement of elastographic displacement estimation using a two-step cross-correlation method

“…Trade-offs between the SNR e and CNR e improvement and axial resolution have also been previously discussed (Srinivasan et al 2003;Srinivasan et al 2004). As mentioned earlier in this paper, Righetti et al (2002) have shown that the axial resolution in elastography is ultimately limited by the wavelength of the ultrasound system. In this paper, we demonstrate that strain estimation on the order of a single ultrasound wavelength can be achieved using the two-step algorithm.…”

“…The use of small processing windows with high overlap can significantly improve the axial resolution in the strain images for clinical diagnosis (Alam et al 2000;Righetti et al 2002). The algorithm proposed in this paper requires approximately twice the signal processing or computational load.…”

“…They also operate under the assumption or constraint that the displacement field would be continuous and along the direction of compression (generally axial), with expansion only along the lateral and elevational directions. The use of smaller kernels for 2D processing indicate the possibility of using smaller window lengths, thereby improving the axial resolution (Alam et al 2000;Righetti et al 2002) for 1D cross-correlation, if these gated windows could be accurately localized within the postcompression echo signals.…”

“…Axial resolution in elastography depends on two signal processing parameters, namely, the cross-correlation window length and the amount of overlap in the data segments between successive windows (Cespedes 1993;Bilgen and Insana 1997;Alam et al 2000;Righetti et al 2002). The cross-correlation window length at a fixed overlap was initially utilized as a measure of the axial resolution in elastography (Cespedes 1993).…”

“…This requirement on the window length precludes the use of smaller gated window lengths that would otherwise enable improvement in the axial resolution of the strain images. The use of smaller window lengths is important, since Righetti et al (2002), have demonstrated that the ultimate axial resolution in elastography is only limited by and directly proportional to the wavelength (i.e., inversely proportional to the fractional bandwidth) of the ultrasound system. To enable the use of smaller window lengths, we propose the use of a two-step cross-correlation method, where we demonstrate accurate and precise strain estimation with window lengths on the order of a single wavelength.…”