اندازه گیری غیریکنواختی امواج رادیوئی در ام آر آی

Introduction: Non-uniformity is one of the most important parameters affecting MRI images which can lead to harmful effects in the diagnosis and analysis of qualitative and quantitative methods. The present study introduced a method for measuring RF non-homogeneity in MRI systems. Methods and Materials: To verify the uniformity of B0 and B1 fields, a cylindrical phantom with a diameter of 24 cm and a height of 25.5 cm was made of plexiglass and filled with vegetable oil. In this method, a single slice of a uniform phantom was imaged with different flip angles using a standard spin echo protocol. The signal intensity in these images were fitted to a mathematical model which describes the relationship between signal intensity and flip angle in spin echo images. Multi-angled echo spin and three dimensional echo gradient protocols were used to assess the uniformity of B0 and B1 magnetic fields respectively. Two different echo times were used for multi-angled echo including spin and three dimensional echo gradient protocol using an MRI Siments Prisma 3 Tesla in the National Brain Laboratory. Results: RF waves were sent uniformly; however, there was no uniformity in the received waves by the lumbar coil. The uniformity has been observed in the waves received by the head coil. Moreover, the non-uniformity of B0 field was equal to 0.3125 ppm over a 24 cm DSVC (diameter of spherical volume). Discussion and Conclusion: The accuracy of coils and the plan of B0 and B1 magnetic fields can be evaluated and prepared using this phantom. In addition, artifacts caused by nonuniformity of these two fields on functional images such as diffusion and magnetic spectroscopy eliminate by using this phantom. Furthermore, this phantom can be used for assessing the uniformity of magnetic fields in devices with various powers.