Burn depth assessment in clinics is still inaccurate because of the lack of feasible and practical testing devices and methods. Therefore, this process often depends on subjective judgment of burn surgeons. In this study, a new unilateral magnetic resonance imaging (UMRI) sensor equipped with a 2D gradient coil system was established, and we attempted to assess burns using unilateral nuclear magnetic resonance devices. A reduced Halbach magnet was utilized to generate a magnetic field that was relatively homogeneous on a target plane with a suitable field of view for 2D spatial localization. A uniplanar gradient coil system was designed by utilizing the mainstream target field method, and a uniplanar RF (radio frequency) coil was designed by using a timeharmonic inverse method for the UMRI sensor. A 2D image of the cross sections of a simple burn model was obtained by a fast 2D pure-phase encoding imaging method. The design details of the novel single-sided MRI probe and imaging tests are also presented.

The improvement of water management in agriculture by exactly detecting moisture parameters of soil is crucial. To investigate this problem, a mini inside-out nuclear magnetic resonance sensor (NMR) was proposed to measure moisture parameters of model soils. This sensor combines three cylindrical magnets that are magnetized in the axial direction and three arc spiral coils of the same size in series. We calculated and optimized the magnet structure by equivalent magnetization to current density. By adjusting the radius and height between the cylinders, a circumferential symmetric constant gradient field (2.28 T/m) was obtained. The NMR sensor was set at 2.424 MHz to measure the water content of sandy soil with small particle diameter and silica sand with large particle diameter. The complete decaying, an NMR signal was analyzed through inverse Laplace transformation and averaged on a T₂ space. According to the results, moisture content of the sample is positively correlated with the integral area of T₂ spectrum peak (A_peak); T₂ of the water in small pores is shorter than that in large pores, because the movement of water molecules are limited by the inner wall of the pores. In the same volume, water in large pore sample is more than that in small pore sample, so A_peak of silica sand is larger than A_peak of sandy soil. Therefore, the sensor is capable of detecting moisture both content and pore size of the sample. This mini sensor (4.0 cm in diameter and 10 cm in length) is portable, and the lowest measurable humidity is 0.38%. Thus, this sensor will allow easy soil moisture measurements on-field in the future.

ferromagnetic structures, particularly the anti-eddy plate, in a bi-planar permanent-magnet-type low-field (0.05 T) magnetic resonance imaging (MRI) brain scanner can distort the gradient field in the target region. This study aims to provide a new gradient coil design method that reduces ferromagnetic influences on gradient field linearity. Thus, a simplified model of electromagnetic (EM) structures of the permanent-magnet-type MRI scanners was established. By using precise analytical proof, the anti-eddy plate was reduced to a homogeneous magnetic plate. The overall effects of the EM structures, which can be represented by bi-planar magnetic plates, were evaluated. In sequence, the image magnetic dipole was first introduced to show the effects of anti-eddy plates were added to the conventional equivalent magnetic dipole (EMD) approach. A novel equivalent image magnetic dipole (EIMD) method was proposed to build the gradient coil pattern. The effect of ferromagnetic materials was predicted throughout the gradient coil design phase using the proposed method, and a high-linear gradient field was generated under real working conditions. The computational and experimental results showed that the gradient coil was linear when ferromagnetic structures were present. The effectiveness of the proposed method was demonstrated by comparing T1-weighted images of the conventional method to those of the proposed method. The proposed method reduced image distortion caused by nearby EM structures in bi-planar permanent-magnet-type low-field MRI systems and provided an effective and concise solution for gradient coil designs.

In an ultra-low-field magnetic resonance imaging (ULF-MRI) system, the uniformity of static magnetic field B ₀ is essential for maintaining good imaging quality. However, achieving high B ₀ homogeneity is difficult due to the low magnitude. This paper proposes a flexible active shimming approach for ULF B ₀ optimization, where an original geometry-based method is presented for first- and second-order shim coil designs. Different types of shim coils are approximated by combinatorial geometric curves, where no additional wire is needed for overall connection. An optimization problem is established to ensure that each shim coil generates a high-purity harmonic magnetic field, which is comparable to the optimization results obtained using the conventional stream function method. A computer-controlled multichannel current source is designed to drive the second-order shim coils, where the current output reaches an accuracy of 1 mA. The performance of optimized coils is verified by imaging experiments. It is demonstrated that B ₀ homogeneity is improved from 157 ppm to 111 ppm following the implementation of second-order shimming. The in vivo experiment shows that imaging quality is improved after shimming with the local signal-to-noise ratio increasing 1.16 to 1.92 folds.

Magnetic resonance imaging (MRI) has proven excellent performance in dental imaging, especially for temporomandibular joint (TMJ), teeth, and periodontal apparatus. However, the high price and strict installation environment of the conventional high-field MRI has prevented its widespread use in dental clinics or developing regions. The introduction of low-cost and portable MRI scanners will help increase the easy accessibility of MRI examination and reduce the patients’ waiting time. This work introduces a low-cost portable 50 mT MRI scanner for dental imaging. First, the overall structure including permanent magnets, gradient coils, and radio-frequency (RF) coils is introduced. The cooling system is removed because the static field is maintained by the permanent magnets. The system stands 90 cm wide, 110 cm high and weighs 600 kg, which makes it possible to install in an average-sized room. Then, the design processes of specialized RF receiving coils for TMJ, teeth are illustrated. In order to improve patient comfort, an intraoral wireless coil for boosting the signal-to-noise ratio (SNR) inside the oral cavity is proposed. Furthermore, the T1-weighted images of TMJ and teeth are given to show the dental imaging performance of the proposed device.