Author: Jiayi Chen, Shaolei Li, Fuhua Yan, Yingli Yang, Jie Zhang 👨🔬
Affiliation: Department of Radiology, Ruijin Hospital, Institute for Medical Imaging Technology, Ruijin Hospital, Department of Radiology, Ruijin Hospital Shanghai Jiaotong University School of Medicine, Shanghai United imaging Healthcare Advanced Technology Research Institute, Department of Radiation Oncology, Ruijin Hospital 🌍
Purpose: The aim of this exploratory study is to investigate the feasibility of establishing a model to explore tissue component heterogeneity using multidimensional diffusion magnetic resonance imaging (MDD MRI) at 5T. Different tissue components within tumors (such as hypoxic, necrotic, and normoxic tissues) exhibit varying diffusion characteristics. MDD can facilitate the quantitative analysis of the heterogeneity of these different tissue components, thereby assisting in the development of personalized radiotherapy plans.
Methods: A healthy volunteer’s brain (male, 39 years old) was scanned. Imaging was conducted on a 5T MRI system (uMR® Jupiter, United Imaging Healthcare Co. Ltd.) which features a maximum gradient amplitude of 120 mT/m, a slew rate of 200 T/m/s, and is equipped with a 48-channel head coil array. We customized a pulse sequence based on diffusion-weighted echo-planar imaging to achieve spherical, linear, and planar diffusion waveform encoding. Processing was performed using an algorithm that estimates the non-parametric diffusion tensor distribution (DTD) space. By dividing the distribution space into smaller subspaces ("bins"), a color-coded image of intra-pixel heterogeneity can be generated. Three bins were defined to separate signals from specific cell types: elongated cells (bin1), isotropic cells (bin2), and free water (bin3) and are color-coded as Red, Green and Blue correspondingly. For every pixel, the fractions from different bins were represented by intensities of RGB.
Results: The DTD was divided into three bins, named elongated cells (bin1, R), isotropic cells (bin2, G), and free water (bin3, B), which accurately captured the diffusion characteristics of white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF), respectively.
Conclusion: This exploratory study indicates that MDD MRI provides intra-pixel information regarding microscopic heterogeneity. With the high field strength of 5T, MDD MRI has the potential to accurately representing tumor heterogeneity and differentiating different types of tumor cells.