Permanent Magnetic Resonance Imaging System Research Articles

Fluid-Attenuated Inversion Recovery Sequence in MRI in Distinguishing Fluid Cyst from Tumor in the Brain

Nuclear magnetic resonance (NMR) is a physical phenomenon used to investigate the characteristics of atomic nuclei. It is the absorption and emission of energy by nuclei in a magnetic field, which can offer extensive information on the structure, dynamics, reaction state, and chemical environment of molecules. Magnetic Resonance Imaging (MRI) is the safest imaging method. It gives a visual representation of human tissue without surgical intervention for clinical diagnosis. In this research, Fast Spin Echo (SE), Multi-Slice Spin Echo (MSSE), and Fluid Attenuated Inversion Recovery (FLAIR) sequences were used. The case under study is placed in an i-open permanent MRI system type in order to image a brain lesion. The obtained signals are encoded to fill k-space through the three stages, i.e., slice selection, phase encoding and frequency. The MRI-processed brain image is reconstructed by inverse Fourier transform in order to find the location of the cyst, and T1 weighted, T2 weighted, and FLAIR tests were performed to obtain three types of images. The images were compared with normal images in each type of applied sequence. Subsequently, the fluid signal was specifically attenuated in the targeted location to help distinguish between a tumor and fluid in the transverse relaxation time-weighted image. The signal was attenuated in the designated location, turned black, and appeared the color of free water, like cerebrospinal fluid, indicating that it was a fluid rather than a tumor. Consequently, a cyst fluid lesion is detected. Our study establishes a foundation for utilizing free fluid signal attenuation to differentiate between cyst fluid and tumors when other sequences fail to do the same.

Design of Shimming Rings for Small Permanent MRI Magnet Using Sensitivity-Analysis-Based Particle Swarm Optimization Algorithm

The main magnet in a magnetic resonance imaging (MRI) system creates a static magnetic field that determines the final imaging quality. In a permanent MRI system, shimming rings are commonly used to improve field homogeneity. However, the optimization of the ring structure is challenging owing to the nonlinear properties of the ferromagnetic material. To design a small permanent magnet system, this study explores the application of sensitivity analysis (SA) and particle swarm optimization (PSO) algorithm for the optimization of shimming rings. SA is used to identify the most important parameter of the shimming rings that affects the quality of the magnetic field to simplify the optimization process and improve optimization accuracy and efficiency. PSO is used to solve the complex and nonlinear optimizations of the magnetic field. To illustrate the effectiveness of the proposed method, a specific permanent MRI magnet was modeled. The results show that the inner radius of the shimming ring crucially affects magnetic field quality, with ring height having relatively smaller impact. Compared with the PSO-only optimization procedure, the combined SA-PSO optimization more rapidly converges to a better solution. The optimized shimming rings significantly improve the magnetic field uniformity (~10 fold) compared with that of the initial magnet without shimming rings.

Simulation and Correction of the Slice Profile Based on SLR Theory in a 0.35 T Permanent MRI System

To locate the imaging slice, the hydrogen protons within the selected slice are excited by the coaction of radio-frequency pulse (RF pulse) and slice-selection gradient during the process of magnetic resonance imaging (MRI). However, the absolute consistency of the time between the RF transmitting system and gradient system can’t be guaranteed in an actual magnetic resonance system, which makes the slice profile not ideal enough. Imperfect slice profile will lead to poor imaging quality. In this paper, Shinnar-Le Roux (SLR) theory is used to simulate the slice profile with different relative delays between RF and slice-selection gradient to solve this problem. By matching the actual slice profile with the simulation results, the relative delay is measured in an actual 0.35T permanent magnet MRI system. The practicability of the method is verified for the improvement of image quality after applying the measured delay to correct the actual MRI system.

The use of a permanent magnetic resonance imaging system for radiotherapy treatment planning of bone metastases

Purpose: To evaluate the usefulness of magnetic resonance (MR) imaging–based radiotherapy treatment planning (RTTP) for bone metastases in clinical applications. Methods and Materials: MR imaging–based RTTP was carried out for 28 patients with bone metastases using a permanent magnetic MR unit. Twenty-three patients received MR imaging–assisted X-ray simulation, and five underwent MR simulation. In MR imaging–assisted X-ray simulation, the radiation fields defined by an X-ray simulator were modified based on MR information scanned in the exact treatment position using MR skin markers. In MR simulation, both isocenter position and field size were determined on MR images and projected onto the patient’s skin. Results: All lesions unclear on other imaging modalities could be clearly identified on MR imaging. Of the 23 patients receiving MR imaging–assisted X-ray simulation, modification of the original radiation field was necessary in 14 patients (extended in 9, reduced in 4, and completely changed in 1). In MR simulation, appropriate radiation fields could be easily and quickly determined using MR imaging. Conclusion: Methods for MR imaging–based RTTP were developed and clinically implemented for patients with bone metastases, and they were shown to be useful for improving the accuracy of the tumor location. They would provide better therapeutic/palliative benefit to particular patients with bone metastases and could also be applied to other lesions in the future.