Rongsheng Lu

Optimization and experimental test of a miniature permanent magnet structure for a microfluidic magnetic resonance chip

We propose a general global optimal algorithm to optimize the miniature permanent magnet structure of a micro magnetic resonance chip (μNMR-chip). For this purpose, we analyze the sensitivity of the permanent magnet structure to the design variables and determine the optimization variables. After this, radial basis function neural networks (RBFNNs) are constructed to model the objective functions, and the nondominated sorting genetic algorithm II (NSGA II) is improved by in- troducing a different weighting factor for each objective function in calculating the crowding distance. Combining the RBFNN with the improved NSGA II optimizes the miniature permanent magnet structure. Through comparison, the optimization solu- tions are proven effective. Finally, the optimized permanent magnet structure is manufactured and tested experimentally. After optimization, the volume of the permanent magnet block is reduced by 39%, and the permanent magnet becomes easier to manufacture.

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

Effect of flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip

ABSTRACT The detection of samples in a microfluidic nuclear magnetic resonance chip is generally performed under flow condition. To study the effect of sample flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip, theoretical calculations were performed on three microfluidic samples (including deionized water, absolute ethanol, and copper sulfate pentahydrate) for flow velocities in the range 1.7–25 mm/s. A microfluidic nuclear magnetic resonance device with a low cost microfluidic solenoid coil was fabricated to verify the theoretical calculations by experiments. The results show that the apparent transverse relaxation time of the sample is a monoexponential decay with respect to flow velocity. In addition, it was found that the experimental values and the theoretical values of the apparent transverse relaxation time are identical when the samples are prepolarized completely; but for the samples that are not prepolarized completely, all the experimental values are smaller than the theoretical values and their difference increases with the flow velocity of the sample. After further study, it was discovered that the relative error between the experimental values and the theoretical values is a monoexponential decay to the level of the sample to be prepolarized. This discovery is very useful, because it can be used to modify the theoretical calculation model of the apparent transverse relaxation time for the samples that are prepolarized incompletely, as well as improve the application of microfluidics on nuclear magnetic resonance.

Miniature nuclear magnetic resonance spectrometer using a partially enclosed permanent magnet

ABSTRACT Conventional nuclear magnetic resonance (NMR) instruments are limited by their large volume volume. A miniature NMR spectrometer is reported using a partially enclosed miniature permanent magnet and a low-cost solenoid microcoil probe. The miniature NMR spectrometer uses a sample volume smaller than conventional NMR spectrometers by a factor of 1000. Transverse relaxation times were obtained by the miniature spectrometer using 150 nL of 40 mM copper sulfate, 1 M aqueous sucrose, absolute ethanol, and deionized water. The results demonstrate that high signal-to-noise ratios were obtained. The results were also compared with a commercial NMR spectrometer and suitable accuracy of the laboratory-constructed device was obtained. The miniature NMR spectrometer was employed for the characterization of heated soybean oil. The reported miniature NMR spectrometer is anticipated to have applications for onsite detection.ABSTRACTConventional nuclear magnetic resonance (NMR) instruments are limited by their large volume volume. A miniature NMR spectrometer is reported using a partially enclosed miniature permanent magnet and a low-cost solenoid microcoil probe. The miniature NMR spectrometer uses a sample volume smaller than conventional NMR spectrometers by a factor of 1000. Transverse relaxation times were obtained by the miniature spectrometer using 150 nL of 40 mM copper sulfate, 1 M aqueous sucrose, absolute ethanol, and deionized water. The results demonstrate that high signal-to-noise ratios were obtained. The results were also compared with a commercial NMR spectrometer and suitable accuracy of the laboratory-constructed device was obtained. The miniature NMR spectrometer was employed for the characterization of heated soybean oil. The reported miniature NMR spectrometer is anticipated to have applications for onsite detection.

Development of Permanent Magnet Probe for Intravascular Magnetic Resonance Imaging Device

Intravascular magnetic resonance imaging is a new approach for the diagnosis of cardiovascular diseases (CVDs). This paper shows the design of a permanent magnet probe, including the structure configuration, the design parameters and the selected materials of the probe assembly. The effect of magnetization angles on the static magnetic field distribution is computed using Maxwell finite element (Ansoft) simulation, and the optimal magnetization angle of the permanent magnet is chosen for the probe design. Then equations of the static magnetic field distribution and the gradient distribution produced by the permanent magnet are given using data fitting method under the optimal angle. In conclusion, calculations and fitting results demonstrate the validity of the static magnetic field produced by the permanent magnet probe which could be used in the intravascular magnetic resonance imaging for detecting the CVDS accurately as well as operating easily

Low-field nuclear magnetic resonance spectrometer for non-invasive monitoring of fluctuations in blood glucose in the human finger

Abstract A low-field nuclear magnetic resonance spectrometer for non-invasive monitoring of human finger blood glucose fluctuations was developed. Saline solution and blood serum samples with different glucose concentrations were first detected by the spectrometer and it has been found that there was a high-linear correlation between the glucose concentration and the transverse relaxation time. Then, the spectrometer was employed to noninvasively measure a finger from each of the several volunteers. The experiment results showed that the transverse relaxation time of the human finger increases with human blood glucose concentration. In conclusion, the human finger nuclear magnetic resonance spectrometer could be a potential tool to noninvasive monitoring of human body’s blood glucose fluctuations in the future.