Different modes of cavitation zones in an immersion-type sonochemical reactor have been realized based on the concept of acoustic resonance fields. The reactor contains three main components, namely a Langevin-type piezoelectric transducer (20 kHz), a metal horn, and a circular cylindrical sonicated cell filled with tap water. In order to diminish the generation of cavitation bubbles near the horn-tip, an enlarged cone-shaped horn is designed to reduce the ultrasonic intensity at the irradiating surface and to get better distribution of energy in the sonicated cell. It is demonstrated both numerically and experimentally that the cell geometry and the horn position have prominent effects on the pressure distribution of the ultrasound in the cell. With appropriate choices of these parameters, the whole reactor works at a resonant state. Several acoustic resonance modes observed in the simulation are realized experimentally to generate a large volume of cavitation zones using a very low ultrasonic power.

Objective This study aimed to investigate the diagnostic value of doing a second ultrasound‐guided fine‐needle aspiration (US‐FNA) for thyroid nodules of different sizes that could not be diagnosed by the first US‐FNA. Methods One hundred and forty‐three patients (162 nodules) were diagnosed with suspected malignant thyroid nodules in a routine ultrasound examination, but since the diagnosis could not be confirmed by the cytology of the samples collected in the first US‐FNA, the patients underwent US‐FNA again 3 months later. The ultrasound results, cytology results, and postoperative pathology of these nodules were collected. The nodules were divided into three groups according to the largest diameter (L) of the thyroid nodules: Group 1, L < 0.5 cm, 26 nodules; Group 2, L = 0.5–1.0 cm, 76 nodules; and Group 3, L > 1.0 cm, 60 nodules. Results In the second US‐FNA, the overall diagnosis rate of the 162 thyroid nodules that could not be given a definitive diagnosis by the first US‐FNA was 51.8% (84/162). The definitive diagnosis rates of the nodules in Groups 1, 2, and 3 were 30.8% (8/26), 67.1% (51/76), and 41.7% (25/60), respectively. The diagnosis rate was the highest in Group 2, and the differences between this group and the other two groups were statistically significant (χ2 = 10.489, 8.801, p < 0.05 for both). The diagnostic accuracy rates of Groups 1, 2, and 3 were 100% (8/8), 96.1% (49/51), and 92% (23/25), respectively. Conclusion Second US‐FNA is highly recommended for such nodules.

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This work aims at analyzing and realizing a horn-type sonochemical reactor which can be operated in a very low ultrasonic power density but results in a large volume of cavitation zones. The sonoreactor contains three main components, namely a Langevin-type piezoelectric transducer (20 kHz), a metal horn, and a circular cylindrical sonicated cell filled with tap water. In order to diminish the generation of cavitation bubbles near the horn-tip, an enlarged cone-shaped horn is designed to reduce the ultrasonic intensity at the irradiating surface and to get better distribution of energy in the sonicated cell. It is demonstrated both numerically and experimentally that the cell geometry and the horn position have prominent effects on the pressure distribution of the ultrasound in the cell. With appropriate choices of these parameters, the whole reactor works at a resonant state. Several acoustic resonance modes observed in the simulation are realized experimentally and used for generating a large volume of cavitation field.