Abstract
Once the functional MRI has been developed in 1990's, it has promptly prevailed as a vital tool for investigation of the human brain function as well as for clinical diagnosis. Although it is 1.5 T in currently prevailing MRI system, the strength of magnetic filed is planning to be elevated up to 7T in order to achieve a higher spatiotemporal resolution and a higher signal to noise ratio of MR images. However, biological effects of the intense magnetic filed are still unclear, and the guide line currently applied for MRI as a safety criteria in the world is based on the experimental results accumulated before dozen years. The following factors should be reconsidered as the biological effects of magnetic field: 1) strength of magnetic field, 2) area and duration exposed to the magnetic field, and 3) dynamic property of the magnetic field. Here, we show changes in the distribution of flowing erythrocytes in a model branched vessels under an inhomogeneous magnetic field as follows: 1) attraction of paramagnetic erythrocytes induced by a gradient magnetic field was demonstrated by an increase in the concentration of erythrocytes, 2) the degree of attraction was proportional to the "magnetic susceptibility" of the erythrocytes and also proportional to "magnetic flux density" x "magnetic field gradient" as long as it was up to 10 T^2/m. Further, we discuss effects of gradient magnetic fields on the in vivo observation from the viewpoint of imaging artifacts and safety criteria on human brain mapping. [Jpn J Physiol 54 Suppl:S216 (2004)]
