USE OF SCATTERING OF ULTRASOUND PULSES AND SHOCK WAVES BY KIDNEY STONES FOR IMAGING IN LITHOTRIPSY

摘要

Shock wave lithotripsy, as a procedure for kidney stones fragmentation, would be more efficient if the kidney stone position and size are estimated, and if the progress of the stone fragmentation by shock waves is assessed. These two challenges can be addressed using scattering of ultrasound waves on stones. Although the acoustic impedance of stones often differs by more than a factor of 2 from surrounding tissue, stones are not always readily visible on B-mode ultrasound, for example because a small stone can be lost in the speckle of the kidney tissue. However, we and others have found stones can be made to light up on Doppler imaging in what is called a "twinkling artifact", that may be in part due to stone displacement by acoustic radiation force and partly due to multiple scattering at rough edges. As for fragmentation feedback, fractures in the stone push the frequency of resonance scattering of lithotripter shock wave to bands related to the reverberation period of the pieces. Acoustic scattering of the diagnostic pulses and shock waves by the stones was calculated numerically using a linear elastic model, initialized with known elastic constants. Based on this data, acoustic radiation force and scattered field in the farfield were calculated using integral representation of the corresponding parameters. These methods provide new ways to locate kidney stone stones and to monitor the fragmentation process.