Iron oxide nanoparticle, named synthetic magnetite, as contrast agent has been widely used in clinical MRI. Recently, a new magnetite nanocrystal, called magnetosome, has been found in magnetotactic bacteria. Physicochemical and magnetorelaxo-metric characterization of bacteria magnetosomes and iron oxide nanoparticles are investigated. Bacterial magnetosomes have the larger mean aggregate size, better dispersion and obviously stronger ferromagnetism compared to synthetic magnetites. The samples of several concentrations of magnetic nanoparticles were analyzed using a clinical 3.0 T MR-scanner. The signal decay in the Magnetic Resonance images is found to change proportionally to the nanoparticles concentration. Two kinds of nanoparticles can be though as a negative contrast agent and show slight effects on T 1 , but strong effects on T 2 weighted images. Notice that at the same concentration the signal attenuation of bacterial magnetite samples is more obvious than that of synthetic magnetite samples.Index Terms-Bacterial magnetosome, molecular probe, MR molecular imaging, synthetic iron oxide nanoparticle.

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This paper presents an approach of designing biplanar shim coils for a 1.5 T permanent magnet of in vivo animal MRI. The 1.5 T permanent magnet used in the system has two confronting circular poles, the diameter of which is only 200 mm. Active shimming method is applied to improve the magnetic field generated by the magnet. A series of biplanar shim coils are designed which degenerate magnetic field in the form of certain spherical harmonic terms.In this approach, to restrict the current distribution on the coil plane within a finite radius, the current density is described by a summation of trigonometric functions which are similar to the Fourier series. The undetermined coefficients of these trigonometric functions can be obtained through a regularization approach based on the target-field method. Then the current density distribution is transformed to the winding pattern of the coils using the stream function method. The magnetic fields generated by the shim coils are verified via Biot-Savart law which shows that this approach of designing shim coils is practical.