Ultrasound kit developed for non-invasive moxibustion treatment
Kim G, Hwang YI, Ryu Y, Kim HJ, Bae YM, Kim KB. Ultrasonic device developed for non-invasive moxibustion therapy. Integr Med Res. 2021 Dec; 10(4):100729. doi: 10.1016/j.imr.2021.100729. Epub 2021 May 19. PMID: 34150497; PMCID: PMC8190483.
Recently, some adverse effects of moxibustion, such as burns, smoke, allergies, etc., have been reported. To overcome the adverse effects of traditional moxibustion, an ultrasonic moxibustion device (UMD) was designed, simulated, fabricated, and tested. The purpose of this study is to provide detailed information on the main design parameters, simulation results, and performance test results.
METHODS:The main components of UMD are a 1 MHz ultrasonic transducer (UT) with a concave lens and its applicator. Use the finite element method (FEM)-based COMSOL software to graphically model and describe the sound pressure and temperature distribution of a UT. The temperature distribution of pork rinds was experimentally verified. The temperature curve of pork was associated with an increase in treatment time and was obtained at the unfocused point (2 mm) and at a focal length of 13 mm. In the performance test, the abdominal skin of mice was subjected to moxibustion treatment for 120 min using the new UMD and histological images were acquired to analyze skin tissue damage.
Results: The finite element simulations of temperature distribution and sound pressure are in good agreement with the experimental results. Histological images showed no skin tissue lesions in the abdomen of the mice after treatment. The results showed that the newly developed UMD was able to overcome the shortcomings of traditional moxibustion therapy and achieve the proposed design parameters.
Conclusion: Finite element simulation and performance testing provide valuable information for the development of future UMDs. In addition, its performance can be compared with traditional moxibustion therapies for future research.
Moxibustion is gaining traction in the Western Pacific region for the treatment of a variety of ailments such as stroke and pain. There are two types of methods: direct moxibustion burns cone-shaped wormwood on acupuncture points, while indirect moxibustion leaves space between the skin and wormwood.
The temperature of moxibustion is 550-890°C, and direct moxibustion can heat the skin to 56°C and the external to 130°C; Indirect moxibustion is about 65°C for the skin and 45°C for the subcutaneous tissue. The safe hyperthermia temperature is 42-44°C. Moxibustion smoke contains harmful substances and is similar to tobacco smoke. Treatment is 20 to 30 minutes/time, several times a week for several weeks, and the treatment person is exposed to smoke damage.
In order to solve the shortcomings of traditional moxibustion, researchers have developed new technologies, such as near-infrared laser, electromoxibustion, etc. However, these studies did not detail the fabrication, sound field, activation system, or design parameters of ultrasound moxibustion (UMD). The purpose of the study is to provide UMD design, manufacturing and performance information. The COMSOL sound pressure was simulated to verify the temperature distribution in pork, and the mouse moxibustion treatment was performed and histological images were analyzed to assess the damage.
2. Method
2.1. Ultrasound systems for UMD
The supplementary material details an ultrasound system (UT) for safe moxibustion treatment, controlling UMD power and processing time within the safe range of 42-44°C.
The duration of the treatment is set at 30 minutes.
The main components include:
脉冲发生器、功率放大器、16位微处理器 (dsPIC33F, Microchip Technology, 美国) 和微型热敏电阻止 (Murata Electronics, Japan).
Use a burst signal to excite the UT with a high signal-to-noise efficiency.
The power amplifier has a maximum performance of 50W and an input voltage of 48V.
The tonal burst waveform parameters are controlled by a microprocessor, and the UT temperature change is monitored in real time by means of a thermistor.
Figure 1 illustrates the operation of an ultrasonic system.
Figure 1
Ultrasonic system operation process flow chart: (a) sonic burst wave control flow chart, (b) temperature feedback system flow chart. T is the real-time temperature of the specimen.
In Figure 1a, when an acoustic pulse excitation signal is generated after setting the waveform parameters, the temperature feedback logic is activated at the same time. In Figure 1b, T is the real-time temperature of UT. If the temperature of the UT exceeds the maximum temperature, the UT power supply will be cut off. Otherwise, if the skin temperature is lowered below the minimum temperature, the tonal burst waveform is activated again to excite the UT. Depending on the time of treatment chosen, this procedure lasts up to 30 minutes.
2.2. Finite element simulation
The sound pressure in vivo with the UT was simulated and compared using finite element software, the heat distribution was simulated for a 300-second treatment time, and an aluminum heat sink was designed and installed to prevent overheating. The thermal distribution involves piezoelectric elements (PZTs), water couplants, heat sinks, and concave lenses.
2.3. Performance Testing
UMD performance was experimentally validated, analyzed by measuring temperature changes in pork and performing moxibustion treatment on mouse skin.
Using a 1 MHz operating frequency and a 10 Hz PRF, pulse durations range from 10% to 100%.
Miniature thermistors with insertion depths of 2 and 13 mm measure the temperature for 1200 seconds.
It is carried out at laboratory temperature to ensure accurate control of pork temperature in real time.
Use UMD moxibustion on the abdomen of the mouse for 120 min with the same settings as in Supplementary Figure S1 but replaced with mice.
Traditional moxibustion for 30 minutes compared to UMD for 120 minutes for safety and durability.
Skin lesions were assessed by histological analysis using H&E (ab245880) and MT (ab150686) stains.
The staining operation is performed according to the method provided by the supplier.
3. Results
3.1. Finite Element Analysis
The finite element simulation results of the sound pressure of the human body and its measured sound pressure are shown in Figure 2 (a) and (b) below.
Figure 2
(a) Simulation results of sound pressure in vivo; (b) Experimental results of on-axis sound pressure and prepared UMD for finite element simulation; The results of finite element analysis and the newly developed ultrasonic moxibustion device: (c) the relationship between the temperature distribution of the ultrasonic transducer with the radiator and the increase of the excitation time; (d) Heating curves for two UTs with and without radiator; Temperature profiles obtained with increasing excitation time (10%, 30%, 50%, 75%, and 100% excitation pulse duration) in pork: (e) temperature curve at 2 mm depth and (f) temperature profile at 13 mm depth.
Figure 2 illustrates the following:
- (a) A 1 MHz plane wave is generated from 0 mm with a maximum sound pressure of 0.83×10^6 Pa and is focused at 13 mm FD.
- (b) The red/black lines represent the experimental results of sound pressure and UMD on the simulated axis, respectively;
The FDs for the three UMDs are 13 mm, 13 mm, and 12 mm, respectively.
- (c) PZT generates the highest temperature in the center during vibration.
The simulation results show the effect of increasing excitation time on temperature over 300 seconds:
Temperature profiles without radiator (black line) and with radiator (red line).
Both initially warmed up rapidly and linearly for 20 seconds, but the slope of the black line was 2.5 times that of the red line, resulting in a final 90°C vs 54°C.
- (d) Improved UMD image showing a UT with heat sink.
3.2. Performance Testing
Figures 2(e) and (f) of the UMD Therapy Performance Test show a maximum temperature change of 4°C over about 900 seconds at 100% pulse duration, after which the slope is close to zero. 75% pulse up to 4°C at 1200 sec; The slopes of 10%, 30%, and 50% are lower than 75% and 100%. In Figure 2(f), the 50%, 75%, and 100% pulses reach 7°C at about 1000 seconds, with little change in the slopes of 10% and 30%.
Figure 3 shows the results of histological analysis of traditional moxibustion treatment (30 min) and ultrasound moxibustion treatment time (0, 30, 60, and 120 min).
Figure 3
Images of abdominal skin of mice stained with hematoxylin and eosin (H&E) and Masson tricolor (MT) after moxibustion treatment: (a) traditional moxibustion therapy (30 min for direct and indirect methods) and (b) novel ultrasound moxibustion device (0, 30, 60 and 120 min).
"Moxibustion can cause skin damage. Ultrasonic moxibustion was non-damaging, and the temperature was raised to 6.5°C for 120 minutes. This abbreviation retains the core message of the original text: moxibustion treatment may cause skin deformation and burns, but ultrasound moxibustion does not cause damage during treatment, and clarifies the time and temperature changes of treatment.
4. Discussion
4.1. Finite Element Analysis and Performance Testing
Figures 2(a) and (b) show that the FD of the third UT is shorter due to machining errors, but the measurement radius is still within the error range (±0.5 mm).
UMD's UT design parameters can simulate its focal point, making it an alternative to traditional moxibustion.
Compared to less expensive and simpler EMDs, UMDs can limit mechanical vibrations to specific points and areas, allowing precise stimulation of acupuncture points in three-dimensional space.
4.2. Performance Testing
Experiments have shown that focused ultrasound can heat up rapidly in FD (focal area), which is better than that in non-focused areas.
Derived design parameters were used to control thermal stimulation points for more than 50% of the pulse time in moxibustion treatment (see Supplementary Figure S3).
Tests on mice showed no skin lesions for 120 minutes within a safe temperature range.
Compared with the typical moxibustion treatment time (20-30 minutes), the design of UMD and its sonothermal characterization analysis are effective.
"Although the ultrasound moxibustion treatment takes a long time, it avoids skin damage. UMD can accurately monitor temperature changes to ensure effective treatment within a safe range without side effects. "
4.3. Clinical and Research Implications
The mechanism of moxibustion includes thermal radiation and pharmacological effects, with thermophysical effects as the core. Burning herbal ingredients can cause painful burns, produce an unpleasant odor, and may cause dizziness, nausea, and throat irritation. Ultrasound moxibustion aims to solve these problems, providing detailed design and manufacturing parameters.
4.4. Restrictions
Medical ultrasound equipment requires expensive materials for high-precision control, so it is necessary to study low-cost UMD. UMD should study the effective resonance frequency for different medicinal materials. 1 MHz was used in this study, but UMDs for low-cost, drug-profiling should be further developed.
4.5. Conclusion
A new type of UMD alternative to traditional moxibustion therapy has been developed, which has the following characteristics:1. Integrated 1MHz ultrasonic transducer (UT). 2. Excitation parameters are controlled using a concave lens and an ultrasonic system. 3. Real-time temperature feedback system ensures safe heat treatment (42-44°C). 4. Simulation and experimental results have proved that it is safer and more stable than traditional methods in the range of effective hyperthermia. 5. Forge promising paths for future research.
Table 1 Components and material properties of UT components
| Components | Properties (unit) | Values |
| Piezo-electric material (Lead zirconate titanate) | Radius (mm) | 6.35 |
| Thickness (mm) | 1.96 | |
| Dielectric constant ( ) | 5500 | |
| Sound speed (m/s) | 3920 | |
| Acoustic impedance (106 kg/m2 s) | 30 | |
| Resonance frequency in thickness mode (MHz) | 1 | |
| Piezo-electric charge constant (10-12 N/m2) | 65 | |
| Curie point (℃) | 165 | |
| Near-field length of PZT, f1 | 11.86 | |
| Wavelength of the lens at the operating frequency, (mm) | 3.4 | |
| Concave lens (polymethyl methacrylate) | Curvature of the lens, R (mm) | 5.8 |
| Focal distance of the lens, F (mm) | 6.2 | |
| Center thickness of the lens, d (mm) | 0.85 | |
| Acoustic impedance (106 kg/m2 s) | 3.5 | |
| Sound speed (m/s) | 2800 | |
| Medium (human skin water) | Acoustic impedance (106 kg/m2 s) | 1.55 |
| Sound speed (m/s) | 1550 | |
| Backing material (Epoxy resin) | Acoustic impedance (106 kg/m2 s) | 3 |
| Sound speed (m/s) | 2600 |
Figure 1 Schematic diagram for the FD of UT with concave lens
Figure 2 Experimental setup for measuring the on-axis acoustic pressure: (a) Conceptual diagram and (b) Photograph