Research on sinusoidal alternating magnetic field therapy system based on inverter technology / 医疗卫生装备

Objective To develop a sinusoidal alternating magnetic field therapy system in order to overcome the disadvantages of the single output frequency and the low effective value of the output magnetic field strength of the alternating magnetic field therapy system in the market,of which the frequency and magnetic density both were continuously adjustable. Methods Multi winding Helmholtz coil was used as the magnetic field generator.On the basis of inverter technology,bipolar equivalent area method considering dead zone and variable speed integral incremental PID control algorithm were used to achieve the accuracy control of magnetic frequency and density in the coil.The accuracy of the resulting waveform and the accuracy of the magnetic field strength was verified by simulation calculation and system current and magnetic field strength test.Results The magnetic field treatment system gained high performance,total harmonic distortion (THD)of sine wave met the requirements of international standards.The obtained magnetic density was as expected of the simulation and calculation. Conclusion The device provides continuously adjustable magnetic field,which has a positive effect on the research for the medical staff, and technical references are provided to the research of magnetic field therapy system.

Introduction to high field strength magnetic resonance imaging

Recently 3 tesla (T) magnetic resonance imaging (MRI) has been increasingly used in the clinical field. 3T MRI has many advantages, such as a better signal-to-noise ratio, increased chemical shift, and increased susceptibility, whereas it has several disadvantages such as increased relaxation time, radiofrequency field inhomogeneity, and increased specific absorption rate. The awareness of these advantages and disadvantages of 3T MRI will lead to better outcomes in clinical and research applications.

High field strength magnetic resonance imaging of cardiovascular diseases

Given the continuous advances in the hardware and software of magnetic resonance imaging (MRI), cardiac MRI has come to be a routine imaging modality in clinical settings for evaluating both cardiac function and anatomy in various cardiovascular diseases. Recently, 3 tesla (T) MRI has become available and has demonstrated advantages over 1.5T in a broad range of clinical applications although some technical challenges still remain. This review will focus on the potential advantages and limitations of 3T cardiac MRI and its current clinical applications.

High field strength magnetic resonance imaging of abdominal diseases

Due to the development of dedicated receiver coils for 3 tesla (T) magnetic resonance (MR) imaging and increased gradient performance, 3T MR imaging of the abdomen is rapidly becoming a part of routine clinical practice. The most important advantage of 3T MR imaging is a higher signal-to-noise ratio and contrast-to-noise ratio compared with 1.5T systems, which can be used to improve spatial resolution and shorten image acquisition time. In the abdomen, the improved image quality of non-enhanced and enhanced solid organ imaging, MR angiography, MR cholangiopancreatography, and MR spectroscopy can be obtained at 3T due to the increased signal-to-noise ratio and contrast-to-noise ratio. However, 3T abdominal MR imaging also presents several technical challenges, such as increased energy deposition within the patient's body, standing wave artifacts, and increased susceptibility artifacts. Therefore, abdominal MR imaging at 3T requires adjustments in the sequence parameters of pulse sequences designed for 1.5T to optimize image quality. At present, 3T abdominal MR imaging is feasible with high image quality in an acceptable scan time, but 3T imaging is not significantly superior to 1.5T imaging in terms of cost-effectiveness. Future improvements in coil technology and new sequences suitable for 3T may enable wider clinical use of 3T for abdominal MR imaging.

High field strength magnetic resonance imaging of musculoskeletal diseases

Musculskeletal magnetic resonance imaging (MRI) applications are making the transition rapidly from 1.5 tesla (T) to 3T. The higher signal-to-noise ratio (SNR) that is available with a 3T MRI system allows for greater spatial resolution and provides the potential to improve the diagnostic capability of musculoskeletal MRI. With the use of 3T systems, one can enhance the SNR, spatial resolution, and contrast-to-noise ratio of intrinsic joint structures such as osseous, tendinous, cartilaginous, and ligamentous structures, which makes them more discernable and amenable to proper radiologic assessment. The SNR gain and coil technology advances allow for a smaller voxel-size and parallel imaging, reducing the acquisition time without significant signal loss. Three-dimensional (3D) fast spin echo sequences with isotropic resolution reduce partial volume artifacts through the acquisition of thin continuous sections and enable free 3D-multiplanar-reformatting without loss of image quality. This technique may be a promising method to replace currently used 2D sequences in clinical practice. In addition to current clinical applications, 3T MRI will contribute to the development of new molecular and functional MRI techniques.

High field strength magnetic resonance imaging of brain lesion

The primary merit of a 3 tesla (T) magnetic resonance (MR) scanner is the increase in the signal-to-noise ratio (SNR). It can offer high spatial and temporal image resolution and its diagnostic potential for brain lesions can be improved at the magnetic strength of 3T. In addition to the increased SNR, strong prolongation of T1 relaxation time at high field MR leads to overall improvements in enhancing lesions versus non-enhancing tissue on contrast-enhanced T1-weighted images and blood versus tissue contrast on time-of-flight MR angiography. Increased chemical shift and susceptibility can improve the spectral resolution in MR spectroscopy and the sensitivities in the micro-hemorrhage detection of gradient echo image, the perfusion change of perfusion MRI, and the blood oxygen level-dependent effect of functional magnetic resonance imaging (MRI). The short acquisition time of diffusion MRI at 3T can decrease motion artifacts in irritable stroke patients and it can be easier to estimate anisotrophy and to increase the efficiency of tractography in diffusion tensor imaging with high numbers of gradient directions. On the other hand, the regulation of the specific absorption rate due to increased radio-frequency energy deposition and the controls for signal loss and increased artifacts at 3T are the main clinical problems. If the drawbacks can be addressed by parallel imaging or pulse sequence changes, 3T MRI can be a useful diagnostic tool and increase the diagnostic accuracy in various brain lesions, such as stroke, trauma, epilepsy, multiple sclerosis, dementia, and brain tumors.

High field strength magnetic resonance imaging in children

Thanks to the benefits of 3 tesla (T) magnetic resonance imaging (MRI), its clinical use is increasing in pediatric patients. However, technical considerations and clinical applications of 3T MRI have not been comprehensively reviewed. Potential advantages of 3T imaging over 1.5T imaging include a higher signal-to-noise ratio, higher contrast-to-noise ratio, higher spatial resolution, and shorter scan time. These merits are easily achieved in neuroimaging, musculoskeletal imaging, and pelvic imaging, while body imaging is substantially limited by dielectric shading and an increased specific absorption rate (SAR) owing to B1 inhomogeneity and increased susceptibility artifacts. T1 and T2 relaxation times as well as chemical shifts are influenced by the higher magnetic field strength. SAR issues and dielectric shading of 3T body MRI are less problematic in pediatric patients having a smaller body size. Improved image quality can be achieved by using parallel imaging, the shortest echo time or echo train length, the highest receiver bandwidth, and improved local shimming. Potential reduction of scan time at 3T should be emphasized for pediatric patients. Three-dimensional MRI with post-processing can improve the image quality in a short acquisition time and, therefore, has become a clinical reality at 3T. A dual-source parallel radiofrequency excitation system can reduce dielectric shading, SAR, and scan time by increasing B1 homogeneity, which eventually improves the image quality of 3T body MRI. The usefulness of 3T MRI in pediatric patients can be maximized by further technical developments and optimization.

Effects of repetition time and field strength on diffusion indices of brain white matter / 中国医学影像技术

Objective To observe whether repetition time (TR) and field strengths have effects on diffusion indices of brain white matter. Methods Seven rhesuses underwent diffusion tensor MR imaging (DT-MRI) with a series of TRs (from 500 to 6000 ms) at 1.5T and 3.0T MR scanners, respectively. The mean diffusivity (MD), fractional anisotropy (FA), primary (λ1) and transverse eigenvalues (λ2, 3) were measured in region of interest (ROI) at the posterior limb of internal capsule. Pearson correlation analysis and two-way ANOVA were performed. Results None of the diffusion indices was correlated with TR (P＞0.05) when SNR was high enough (SNR>35). FA was significantly higher and the MD and λ2, 3 were significantly lower at 3.0T than those at 1.5T (P＜0.001). No significant difference of λ1 was found between the two field strengths (P＞0.05). Conclusion Field strength may influence diffusion quantification, but not for TR, which should be considered in multi-center studies.

MR Imaging of the Internal Auditory Canal and Inner Ear at 3T: Comparison between 3D Driven Equilibrium and 3D Balanced Fast Field Echo Sequences

OBJECTIVE: To compare the use of 3D driven equilibrium (DRIVE) imaging with 3D balanced fast field echo (bFFE) imaging in the assessment of the anatomic structures of the internal auditory canal (IAC) and inner ear at 3 Tesla (T). MATERIALS AND METHODS: Thirty ears of 15 subjects (7 men and 8 women; age range, 22-71 years; average age, 50 years) without evidence of ear problems were examined on a whole-body 3T MR scanner with both 3D DRIVE and 3D bFFE sequences by using an 8-channel sensitivity encoding (SENSE) head coil. Two neuroradiologists reviewed both MR images with particular attention to the visibility of the anatomic structures, including four branches of the cranial nerves within the IAC, anatomic structures of the cochlea, vestibule, and three semicircular canals. RESULTS: Although both techniques provided images of relatively good quality, the 3D DRIVE sequence was somewhat superior to the 3D bFFE sequence. The discrepancies were more prominent for the basal turn of the cochlea, vestibule, and all semicircular canals, and were thought to be attributed to the presence of greater magnetic susceptibility artifacts inherent to gradient-echo techniques such as bFFE. CONCLUSION: Because of higher image quality and less susceptibility artifacts, we highly recommend the employment of 3D DRIVE imaging as the MR imaging choice for the IAC and inner ear.

Evaluation of the SLAP Lesion Using a Low-field (0.2T) Magnetic Resonance System

PURPOSE: To evaluate the diagnostic capabilities of the low-field (0.2T) magnetic resonance (MR) system in the detection of the superior labrum anterior to posterior (SLAP) lesion. MATERIALS AND METHODS: One hundred fifty patients underwent magnetic resonance imaging of the shoulder over a 7-month period. Forty-six patients underwent arthroscopic surgery, and the surgical results were correlated with the findings of the MR imaging. Arthroscopic procedures were performed within a mean of 8 days after MR imaging. MR imaging of the shoulder was conducted as follows: shoulder coil; T1-weighted spin echo, coronal-oblique images; T2-weighted gradient echo, coronal-oblique and axial images; and T2-weighted spin echo, coronal-oblique and sagittal-oblique images. Prospectively, one radiologist interpreted the MR images. RESULTS: The results of surgery were as follows: SLAP II in 26 shoulders, SLAP III in 1 shoulder, SLAP IV in 1 shoulder, normal labrum in 6 shoulders. For SLAP lesions with a higher grade than type 2, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the low-field MRI were 85.7%, 55.5%, 75%, 71%, and 74%, respectively. CONCLUSION: There was relatively good agreement for the comparison of the MR results obtained using a low-field MR system with the surgical findings for identifying SLAP lesions.

Comparison of MRI artifacts caused by Ni-Cr alloy fixed prostheses on different field-strength magnets / 上海第二医科大学学报

Objective To evaluate the influence of different field-strength magnets(1.5 T and 3.0 T)on MRI artifacts caused by Ni-Cr alloy fixed prostheses.Methods The crown,bridge and upper denture fixed prostheses with different thickness were produced by Ni-Cr alloy as test samples,and were one by one put on the centre of water phantom for MR scanning with different field-strength magnets(1.5 T and 3.0 T).The artifact areas on these two field-strength magnets were measured and statistically compared.The plastic prostheses with the same shape and thickness as the test samples were served as controls.Results Ni-Cr alloy fixed prostheses could cause MRI artifacts,and the artifact areas increased with the mass of prostheses.However,no artifact area was found in controls.Compared with those on 1.5 T magnet,the MRI artifact areas significantly increased on 3.0 T magnet(P

Evaluation between 3.0 T vs 1.5 T MRI in Detection of Brain Metastasis using Double Dose Gd-DTPA

PURPOSE: Early detection of small brain metastases is important. The purpose of this study was to compare the detectability of brain metastases according to the size between 1.5 T and 3.0 T MRI. MATERIALS AND METHODS: We reviewed 162 patients with primary lung cancer who were examined for TNM staging. After administration of double dose of Gd-DTPA, MR imaging was performed with SPGR by 3.0 T MRI and then with T1 SE sequence by 1.5 T MRI. In each patient, three readers performed qualitative assessment. Sensitivity, positive predictive value, and diagnostic accuracy were calculated in 3.0 T and 1.5 T MRI according to size. Using the signal intensity (SI) measurements between the metastatic nodules and adjacent tissue, nodule-to-adjacent tissue SI ratio was calculated. RESULTS: Thirty-one of 162 patients had apparent metastatic nodules in the brain at either 1.5 T or 3.0 T MR imaging. 143 nodules were detected in 3.0 T MRI, whereas 137 nodules were detected at 1.5 T MRI. Six nodules, only detected in 3.0 T MRI, were smaller than 3.0 mm in dimension. Sensitivity, positive predictive value, and diagnostic accuracy in 3.0 T MRI were 100 %, 100 %, and 100 % respectively, and in 1.5 T MRI were 95.8 %, 88.3 %, and 85.1 % respectively. SI ratio was significantly higher in the 3.0 T MRI than 1.5 T MRI (p=0.025). CONCLUSION: True positive rate of 3.0 T MRI with Gd-DTPA was superior to 1.5 T MRI with Gd-DTPA in detection of metastatic nodules smaller than 3.0 mm.

DEVELOPMENT OF AN HIGH-EFFICIENT IMMUNOMAGNETIC ISOLATOR FOR THE PURIFICATION OF CD34~+ HEMATOPOIETIC CELLS / 解放军医学杂志

According to the principle of immunomagnetic separation, a novel high-efficient immunomagnetic isolator termed as CMSI 100 for the purification of human CD34 + hematopoietic cells was designed and successfully developed. To do this , neodymium iron boron having magnetic properties superior to any other permanent magnet materials was selected as the key parts of CMSI 100 isolator. The core of the magnet assembly was constructed by sandwiching mild steel bars between 4 pieces of magnet bars of neodymium iron boron. Each piece of magnet bars must be limited to the specifications of 3.5cm?2.0cm?0.3cm so that 2 700 gauss magnetic attractive force could be exerted at the magnet surface. Otherwise magnetic field above the surface of the magnet assembly is either very stronger or weaker, both of which are not beneficial to the enrichment of CD34 + hematopoietic cells. With CMSI 100 immunomagnetic isolator, more than 90% purity and over 95% viability of CD34 + hematopoietic cells could be obtained. These data indicate that CMSI 100 immunomagnetic isolator is as good as the internationally used Isolex TM 50 made by Baxter Company in USA.