Application Cases

Experimental Name: Focused Ultrasound Ablation Experiments Based on Bovine Serum Gelatin Phantoms, Ex Vivo Porcine Muscle, and In Vivo Guinea Pigs

Research Direction:
Investigating the influence mechanism of superficial tissue layer thickness on the efficacy of high-frequency focused ultrasound ablation and optimizing transducer design. Quantifying the effects of tissue thickness variations on acoustic and thermal fields through multiphysics simulation models; further optimizing the transducer F-number parameter based on ethnic skin thickness differences and validating efficacy in ex vivo and in vivo guinea pig experiments: the F=0.67 transducer increased lesion area by 40% in Caucasian models and extended safe irradiation time to 600 ms. Revealing the quantitative relationship between tissue thickness differences, energy deposition, and epidermal damage, providing design guidelines for reducing adverse reactions such as redness, swelling, and scarring in clinical applications.

Experimental Objective:
First, theoretical simulations were used to explore the effects of different epidermal, dermal, and fat thicknesses in superficial tissues on focal acoustic pressure, pressure ratios, and lesion area. Subsequently, based on skin thickness data from different ethnic groups, focused ultrasound aesthetic transducers with different F-numbers were designed according to ethnic skin thickness characteristics. Their effectiveness was investigated through ex vivo and in vivo experiments.

Test Equipment:
Focused ultrasound transducer, ATA-8202 radio frequency power amplifier, signal generator, fiber-optic hydrophone, 3D motion system, impedance analyzer, acoustic radiation force balance, oscilloscope, high-speed microscopic imaging system, constant-temperature water bath, depth adjuster.

Experimental Procedure:
First, computer simulations were used to model the focusing effects of ultrasound probes of different sizes in multi-layered skin. It was found that Asians, with thinner dermis and thicker fat layers, are better suited for F=0.57 probes that focus deeper. In contrast, Caucasians, with thicker dermis and thinner fat layers, require F=0.67 probes to avoid energy dispersion. Based on these findings, two types of probes were fabricated, with tests confirming that the F=0.57 probe achieved an electro-acoustic efficiency of 94% and a focal field error of <0.05 mm.

Subsequently, in ex vivo experiments using bovine serum gelatin phantoms and porcine muscle, the lesion patterns were validated: at a fixed depth of 3.0 mm and power of 10 W, the F=0.67 probe achieved a lesion area of 0.66 mm² with a 200 ms irradiation time, and no surface damage occurred at irradiation times ≤200 ms. Finally, in in vivo experiments on guinea pigs, the dorsal skin was irradiated at a depth of 2.0 mm. It was found that the F=0.57 probe required 300–700 ms to effectively heat deep tissues, while exceeding 700 ms caused epidermal burns. In contrast, the F=0.67 probe, with its shallower focus, had a safe time window shortened to 200–600 ms.

The final experimental results indicate that ultrasound aesthetics requires customized probe parameters based on ethnic skin thickness: Asians are better suited for F=0.57 probes with irradiation times exceeding 300 ms, while Caucasians require F=0.67 probes with irradiation times of 200 ms to mitigate treatment risks and enhance efficacy.

Figure 1: Block Diagram of Transducer Electro-Acoustic Conversion Efficiency Testing

Figure 2: Block Diagram of Transducer Acoustic Field Testing

Figure 3: Block Diagram of Transducer Irradiation on Skin Tissue Testing

Experimental Results:
When ultrasound power increased from daily vibration levels (0.5 W) to therapeutic levels (10 W), nonlinear effects repeatedly叠加 (superimposed), causing focal acoustic pressure to surge from 5.01 MPa to 26.55 MPa—releasing 23.3% more energy than traditional models. This explains why high-power ultrasound can deeply heat tissues. More importantly, the layered structure of skin acts as a filter: a 0.1 mm increase in epidermal thickness reduces focal acoustic pressure by 20%, while thickening the fat layer triples energy accumulation on the skin surface.

To address these differences, it is recommended that transducers be tailored to different ethnic skin types: Asians, with thinner epidermis and thicker fat layers, benefit from F=0.57 transducers to minimize surface thermal damage risks. Caucasians, with thicker epidermis and thinner fat layers, require F=0.67 transducers for precise focusing. In vivo guinea pig experiments further validated these findings: using the Asian-adapted protocol (F=0.57 + 300–700 ms irradiation), lesion area expanded controllably from 0.53 mm² to 2.65 mm², while the Caucasian protocol (F=0.67 + 200–600 ms) remained safe and effective. However, excessive irradiation times (>700 ms) led to abrupt increases in lesion area (e.g., 3.14 mm²), highlighting the critical importance of "millisecond-level safety" to avoid burns.

Figure 4: Linear Fitting Curves of Electro-Acoustic Conversion Efficiency for F=0.57 (a) and F=0.67 (b) Transducers

Figure 5: Axial (a) and Radial (b) Acoustic Field Distributions of F=0.57 Transducer in Simulation and Experiment; Axial (c) and Radial (d) Acoustic Field Distributions of F=0.67 Transducer in Simulation and Experiment

Figure 6: Statistical Results of Lesion Area vs. Irradiation Time for F=0.57 and F=0.67 Transducers Ablating Bovine Serum Gelatin Phantoms (a) and Porcine Muscle Tissue (b) (n=6)

Figure 7: Statistical Results of Lesion Area vs. Irradiation Time for F=0.57 and F=0.67 Transducers Ablating Guinea Pig Skin Tissue (n=6)

Amplifier Performance in the Experiment:
The power amplifier ATA-8202 employs a two-stage gain amplification mechanism to boost the milliwatt-level control signal from the function generator to the hundred-volt level, thereby driving the piezoelectric transducer to produce 10 W-level acoustic power output.

Recommended Power Amplifier: ATA-8000 Series Radio Frequency Power Amplifier

Figure: ATA-8000 Series Radio Frequency Power Amplifier Specifications and Parameters