One of the main technical challenges when integrating magnetic resonance imaging (MRI) systems with medical linear accelerator is the strong interference of fringe magnetic fields from the MRI system with the electron beams of linear accelerator, making the linear accelerator not to work properly. In order to minimize the interference of magnetic fields, a magnetic shielding cylinder with an open structure made of high permeability materials is designed. ANSYS Maxwell was used to simulate Helmholtz coil which generate uniform magnetic field instead of the fringe magnetic fields which affect accelerator gun. The parameters of shielding tube, such as permeability, radius, length, side thickness, bottom thickness and fringe magnetic fields strength are simulated, and the data is processed by MATLAB to compare the shielding performance. This article gives out a list of magnetic shielding effectiveness with different side thickness and bottom thickness under the optimal radius and length, which showes that this design can meet the shielding requirement for the MRI-linear accelerator system.
Studying effects of 50 Hz sinusoidal electromagnetic fields (SEMFs) with different intensities on peak bone mass (PBM) of rats may provide a theoretical basis for application of electromagnetic clinical field. 30 female SD rats, 6 weeks of age, were randomly divided into three groups: the control group, 0.1 mT electromagnetic field group (EMFs) and 0.6 mT EMFs. The EMFs groups were treated for 3 h/day. After 8 weeks, we examined their bone mineral densities (BMD), measured their bone biomechanical properties, and made serum levels of osteocalcin (OC), tartrate-resistant acid phosphatase 5b (TRACP 5b), and histomorphometry. It was found that the BMD (P < 0.01), maximum mechanical load (P < 0.01) in the 0.1 mT group were significantly higher than those in the control group, and Yield strength (P < 0.05), the analyses of serum bone turnover markers and histomorphometric parameters were better than those in the control group (P < 0.05). However, the 0.6 mT group did not have significantly difference comparing with that in the control group. This study proved that 50 Hz 0.1 mT SEMFs can increased BMD, bone strength, and bone tissue microstructure. Therefore, 50 Hz 0.1 mT SEMFs can improve peak bone mass of rats.
As drug carriers, magnetic nanoparticles can specifically bind to tumors and have the potential for targeted therapy. It is of great significance to explore non-invasive imaging methods that can detect the distribution of magnetic nanoparticles. Based on the mechanism that magnetic nanoparticles can generate ultrasonic waves through the pulsed magnetic field excitation, the sound pressure wave equation containing the concentration information of magnetic nanoparticles was derived. Using the finite element method and the analytical solution, the consistent transient pulsed magnetic field was obtained. A three-dimensional simulation model was constructed for the coupling calculation of electromagnetic field and sound field. The simulation results verified that the sound pressure waveform at the detection point reflected the position of magnetic nanoparticles in biological tissue. Using the sound pressure data detected by the ultrasonic transducer, the B-scan imaging of the magnetic nanoparticles was achieved. The maximum error of the target area position was 1.56%, and the magnetic nanoparticles regions with different concentrations were distinguished by comparing the amplitude of the boundary signals in the image. Studies in this paper indicate that B-scan imaging can quickly and accurately obtain the dimensional and positional information of the target region and is expected to be used for the detection of magnetic nanoparticles in targeted therapy.
With the acceleration of the aging in the world and our society, osteoarthritis has become a health concern for patients and health workers. At present, its treatment mainly relies on drug treatment, surgical treatment and rehabilitation. As a safe, non-invasive and simple treatment, pulsed electromagnetic field (PEMF) therapy has been used in clinical treatment of osteoporosis, promoting fracture healing and improving symptoms of osteoarthritis. However, the mechanism of PEMF in the treatment of knee osteoarthritis is still unclear. This paper reviews the effects of PEMF on apoptosis, cytokines, cartilage and subchondral bone in knee osteoarthritis in animal experiments, and the changes of chondrocyte morphology and extracellular matrix in cell experiments, aiming to enable medical workers to better understand the status and development of PEMF in the treatment of knee osteoarthritis in basic experimental researches.
According to the coupling relationship of electromagnetic field and acoustic field when electromagnetic field irradiates low conductivity objects, we carried out a study on the magnetoacoustic effect and thermoacoustic effect in pulsed magnetic excitation. In this paper, we provide the pressure wave equation in pulsed magnetic excitation based on the theory of electromagnetic field and acoustic wave propagation. A 2-dimensional coil carrying current and a circular thin sheet model were constructed to simulate the physical imaging environment. The transient electromagnetic field was simulated using finite element method. Numerical studies were conducted to simulate the pressures excited by magnetoacoustic effect and thermoacoustic effect according to the result of electromagnetic simulation. It was shown that the thermoacoustic effect played a leading role in the low conductivity objects on the microsecond Gauss pulsed magnetic excitation, and thermoacoustic effect and magnetoacoustic effect coexisted on the microsecond Gauss pulsed magnetic field and 0.2 T static magnetic field excitation. This study lays the foundation for the further application of magnetoacoustic tomography with magnetic induction and magnetically mediated thermoacoustic imaging.
To observe the effect of pulsed electromagnetic fields (PEMFs) of different treatment time on bone mineral density of femur in ovariectomized rats, so as to find out the treatment time for the best therapeutic efficacy. Methods Fifty female SD rats were randomly divided into 5 groups: sham-ovariectomized (SHAM) group (no PEMFs treatment), ovariectomy (OVX) control group (no PEMFs treatment), OVX I, II and III groups (PEMFs treatment at 8 Hz frequency with 3. 8 ×10-10A/m intensity 20, 40, and 60 minutes daily for 30 days, respectively). All rats were given bilateral ovariectomy except those in the SHAM control group. Bone mineral density (BMD) of femur was assessed at 30 days after PEMFs treatment. Results In OVX control group, hypotrichosis, hypoactivity and l istlessness were observed after operation; and in SHAM group, OVX I group, OVX II group and OVX III group, pilus, psyche and activity were normal. The BMD values were (0.226 ± 0.011), (0.210 ± 0.011), (0.231 ± 0.013), (0.231 ± 0.017) and (0.229 ± 0.013) g/cm2 in SHAM group, OVX control group, OVX I group, OVX II group and OVX III group respectively, showing significant differences between OVX control group and other groups (P lt; 0.05), but showing no significant differences between other 4 groups (P gt; 0.05). Conclusion P EMFs of the three different treatment times can maintain the BMD in ovariectomized rats. It shows that PEMFs have the same effect of maintaining BMD with increasing of treatment time at the range of 20-60 minutes in ovariectomized rats.
We investigated the effects and optimal treatment frequency of pulsed electromagnetic fields (PEMFs) on postmenopausal osteoporosis (PMO). A comparison was performed with the cyclical alendronate and a course of PEMFs in the treatment for postmenopausal osteoporosis on bone mineral density (BMD), pain intensity and balance function. There was no significant difference between the two groups on mean percentage changes from baseline of BMD within 24 weeks after random treatments (P≥0.05). However, at the ends of 48 weeks and 72 weeks, the BMD of the PEMFs group were significantly lower than that of the alendronate group (P<0.05). No significant difference was detected between the two groups with regard to treatment effects on Visual Analogue Scale score, the Timed Up & Go Test and Berg Balance Scale score. Compared with cyclical alendronate, a course of PEMFs was as effective as alendronate in treating PMO for at least 24weeks. So its optimal treatment frequency for PMO may be one course per six months.
The gradient field, one of the core magnetic fields in magnetic resonance imaging (MRI) systems, is generated by gradient coils and plays a critical role in spatial encoding and the generation of echo signals. The uniformity or linearity of the gradient field directly impacts the quality and distortion level of MRI images. However, traditional point measurement methods lack accuracy in assessing the linearity of gradient fields, making it difficult to provide effective parameters for image distortion correction. This paper introduced a spherical measurement-based method that involved measuring the magnetic field distribution on a sphere, followed by detailed magnetic field calculations and linearity analysis. This study, applied to assess the nonlinearity of asymmetric head gradient coils, demonstrated more comprehensive and precise results compared to point measurement methods. This advancement not only strengthens the scientific basis for the design of gradient coils but also provides more reliable parameters and methods for the accurate correction of MRI image distortions.
Objective To study major influential factors of the micturition alert device dedicated to neurogenic bladders for the product design and cl inical appl ication of the device. Methods One ferrite permanent magnet with thickness and diameter of 3 mm and 10 mm, respectively, and three NdFeB permanent magnets with the thickness of 3 mm and diameter of 10, 15 and 20 mm, respectively, were used. The effects of thickness of the abdominal wall as well as the position and type of permanent magnets on the micturition alert device dedicated to neurogenic bladders were measured in vitro simulated test, when the abdominal wall was set to 2, 3, 4, 5, 6, 7, 8 and 9 cm, respectively, and the position of permanent magnets was 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 cm, respectively. The effect of the geomagnetic field on the device was measured under the condition that the thickness of the simulated abdominal wall was set to 2, 3, 4 and 5 cm, respectively,and the position of permanent magnets was 2, 3, 4, 5, 6, 7, 8, 9 and 10 cm, respectively. Results The value showed inthe warning unit was positively correlated with the position of the ferrite permanent magnet only when the thickness ofthe simulated abdominal wall was 2 cm (r=0.632, P lt; 0.05). The correlation between the value of the warning unit andthe position of NdFeB permanent magnets was significant (r gt; 0.622, P lt; 0.05), which was intensified with the increasingdiameter of NdFeB permanent magnets, but weakened with the increasing thickness of the simulated abdominal wall. The effect of the geomagnetic field was correlated with the exposition of the body, the position of the permanent magnet and the thickness of the abdominal wall. Conclusion The major influential factors of the micturition alert device dedicated to neurogenic bladder include the magnetism and location of the permanent magnet, the thickness of the abdominal wall and the geomagnetic field. These factors are correlated with and affect each other. Reasonable allocation of these factors may optimize the device.
ObjectiveTo investigate whether signal molecule mitogen-activated protein kinases (MAPKs) involves in the process of the mineralization and maturation of rat calvarial osteoblasts promoted by 50 Hz, 0.6 mT pulsed electromagnetic fields. MethodsRat calvarial osteoblasts were obtained by enzyme digestion from the skull of 6 neonatal Wistar rats of SPF level. The primary osteoblasts were treated in 50 Hz and 0.6 mT pulsed electromagnetic fields for 0, 5, 10, 20, 40, 60, and 120 minutes; the protein expression of phosphorylated MAPKs was detected by Western blot. The osteoblasts were randomly divided into group A (control group), group B (low frequency pulse electromagnetic fields treatment group), group C (SB202190 group), and group D (SB202190+low frequency pulse electromagnetic fields treatment group); the alkaline phosphatase (ALP) activities were tested after corresponding treatment for 1, 4, and 7 days. The corresponding treated more than 90% confluenced osteoblasts were cultured under condition of osteogenic induction, then ALP staining and alizarin red staining were carried out at 9 and 12 days respectively. ResultsThe results of Western blot showed that there was no significant changes in the protein expressions of phosphorylated level of extracellular signal-related kinases 1/2 and c-Jun amino N-terminal kinases 1/2 in 50 Hz, 0.6 mT pulsed electromagnetic fields P>0.05), but the phosphorylated level of p38 began to increase at 5 minutes, peaked at 40 minutes, then gradually decreased, and it was significantly higher at 5-120 minutes than at 0 minute (P<0.05). After the activities of p-p38 was inhibited by inhibitor SB202190, the ALP activities, positive colonies and area of ALP and calcified nodules of group B were significantly higher than groups A, C, and D (P<0.05). Conclusionp38 is one of the signal molecules involved in the process of the mineralization and maturation of rat calvarial osteoblasts promoted by 50 Hz, 0.6 mT pulsed electromagnetic fields.