Fabrication of New 3D Phantom for Measuring Geometric Distortion in Magnetic Resonance Imaging System

  Introduction: Geometric distortion is a major shortcoming of magnetic resonance imaging (MRI), which has an important influence on the accuracy of volumetric measurements, an important parameter in neurology and oncology. Our goal is to design and construct a new three- dimensional phantom using a 3D printer in order to measure geometric distortion and its reproducibility in three dimensions. Materials and Methods: In this study, we designed a new phantom containing 13,824 reference features (control points) with AutoCAD software, fabricated it with a 3D printer, and filled it with vegetable oil. This phantom was tested on the Siemens 3 Tesla Prisma MRI model using a 64-channel head coil. We used imaging from a six-slice CT scan (Siemens) as a reference and matched the reference features in the MRI images with the CT-scan images. To achieve this, we used a three-dimensional reference feature model. Reproducibility on the phantom was investigated with three different imaging sessions per day for three different days. Results: The geometric distortion in the 3D results was found to be due to field non-uniformity and nonlinearity of the gradients and its reproducibility. The mean Euclidean distance error for MRI volume was less than 1 mm. The maximum Euclidean error was 1.5 mm. Distortion in the whole volume is pronounced exclusively at the edges of the magnetic field. Conclusion: As with other investigations carried out in our work, the amount of distortion in the middle of the field was less than at its sides. This phantom can be used to check the distortion filters on the device. Also, this phantom can be used to study geometric distortion in scenarios that require a small study volume, such as prostate studies.