Mechanical and clinical performance of pulse-inversion tissue harmonic imaging in the superficial region

To compare image quality between fundamental imaging (FI; transmitted and received frequencies 8.0 and 9.0 MHz, respectively) and pulse-inversion tissue harmonic imaging (PI-THI; transmitted frequencies 4.0 and 4.5 MHz, respectively) within 40 mm of the surface of the probe, we tested axial, lateral, and contrast resolution.

The axial and lateral resolution were tested by use of a tissue-mimicking test object. For contrast resolution, milk agar blocks of different concentration were used for the comparison test.

The lateral resolution was significantly improved by use of PI-THI at a depth of 20 to 40 mm from the surface of the phantom. Axial resolution was not reduced by use of PI-THI compared with FI. The value of the contrast index was higher in PI-THI than in FI. The researchers also evaluated the two modes clinically, by comparing the visibility of 170 cervical lymph nodes (identification of lymph node, echogenic hilus, parenchymal echogenicity). The results revealed significant advantages of PI-THI over FI for three features.

This study suggests that PI-THI might be mechanically and clinically useful in the superficial region.