The effects of image degradation on ultrasound-guided HIFU

High-intensity focused ultrasound (HIFU) has recently found a wide range of applications. In the case of ultrasound-guided HIFU, clutter and phase-aberration can degrade the image quality such that visualization of the target can be significantly diminished. In this case the quality of the HIFU intensity deposition can be unknown. We modeled an 8 cm, 1.5 MHz HIFU array and a 6 cm, 2.5 MHz imaging array with propagation of acoustic waves through a histological characterization of the human abdominal layer using a nonlinear, full-wave simulation method. Modifications were made to the simulated medium in order to assess the impact of the individual image degradation mechanisms on intensity. For small targets (5 mm diameter lesions), the addition of a 3 cm thick abdominal layer completely obscured the imaging target positioned at 5 cm depth, however, the deposition of HIFU intensity was not significantly degraded. An average elongation of 0.5 mm of the intensity distribution was produced with the abdominal layer, and the location of the peak focal intensity moved approximately 0.03 mm laterally and 0.9 mm axially. The average peak focal intensity dropped 0.6 dB compared to the homogeneous tissue case, despite the presence of strong phase aberration and reverberation clutter. The intensity distribution returned nearly to normal when the phase aberration effects were removed and remained relatively unchanged when reverberation clutter was removed.