The aim of the study was to evaluate the visualization of the rabbit common calcanean tendon and adjacent structures in the high-field magnetic resonance imaging (MRI) of 1.5 T field strength and to compare the results with those previously obtained for the low-field MRI (0.25 T). Eight New Zealand rabbits were used in the post-mortem study and the results indicate that the high-field MRI provides more detailed images only in transverse scans, where the outer outline of the tendon was visualized more accurately. Other analysed structures were imaged with a resolution comparable to the low-field MRI.
The spin-lattice (T1) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T1 dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing-field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing-field strength and duration can optimize the contrast between two types of tissue having different T1 relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields